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Answers to STEM Song
Study Questions

SongAnswers
29 Reasons(1) 50.

(2) Glycolysis, which is extremely limited at rest but can rise to very high rates during intense exercise.

(3) Answers will vary. For example, one can track improvements in a function such as the amount of weight lifted or the time taken to run a mile (although these changes may not be attributable solely to changes within the muscles). One can also notice histological changes such as increased mitochondrial density and increased capillary density resulting from endurance training. Finally, strength training may simply increase the size of muscles.
A&P(1) Simple columnar epithelium.

(2) Synovial joints are relatively mobile joints in which the articulating bones are separated by a fluid-filled cavity.

(3) The prefrontal cortex is the most anterior part of the cerebral cortex, directly in front of the premotor cortex.

(4) Proprioceptors are located in joints, muscles, and tendons.

(5) Rods and cones are located in the retina of the eye, the retina being deep to the sclera and choroid.

(6) Hair cells are mechanoreceptors that sense physical perturbations in the cell membrane.

(7) The hippocampus consolidates short-term memories into long-term memories.
A is for ALANINE(1) Histidine has a pKa close to the normal pH of the cytosol and therefore is an effective intracellular buffer; the R group of isoleucine is hydrophobic; and many protein kinases add a phosphate at the -OH site of tyrosine.

(2) Aspartate and glutamate are technically the names of the deprotonated amino acids, so, having already lost their protons, neither is a "good proton source" any longer.
Adjusting the Lens of the Eye(1) The ciliary muscles circle around the outside of the lens. They are connected to the lens by suspensory ligaments.

(2) Nearsighted people see nearby objects well, but distant objects more poorly. Their ability to see nearby objects, which requires high focusing power, suggests that their lenses are plenty fat -- perhaps too fat for optimal distance vision.

(3) As we have seen, the ciliary muscle adjust the thickness of the lens. In contrast, the pupillary muscles adjust the diameter of the pupil, thus adjusting the amount of light that enters the eye.
Adrenal Cortex(1) Aldosterone promotes the retention of Na+ and the excretion of K+, while cortisol regulates fuel metabolism, especially promoting the release of gluose and amino acids into the blood.

(2) These hormones are "awfully low" in Addison's Disease (think A <=> A) and "crazy high" in Cushing's Syndrome (think C <=> C).

(3) No -- the adrenal medulla produces different hormones (epinephrine and norepinephrine).
Amino Acid Alphabet Song(1) Twenty.

(2) A naturally occurring amino acid. A = alanine, C = cysteine, D = aspartate, E = glutamate, F = phenylalanine, G = glycine, H = histidine, I = isoleucine, K = lysine, L = leucine, M = methionine, N = asparagine, P = proline, Q = glutamine, R = , S = serine, T = threonine, V = valine, W = tryptophan, Y = tyrosine.

(3) The 3-letter abbreviations. They are simply the first 3 letters of the full names, with a few exceptions (Asn, Gln, Ile, Trp).
Antibodies(1) Answers will vary; confirm your drawing with your instructor, your textbook, or a reputable website.

(2) B cells, which often differentiate into plasma cells, which are highly specialized for secreting antibodies.

(3) A single type.

(4) Invading pathogens such as viruses or bacteria, whose antigens are bound by antibodies.
A Blaze of Glory(1) Yes! In fact, viruses generally go through cycles of invading host cells and then bursting out of them.

(2) Antibodies are Y-shaped proteins that bind to foreign antigens. They are made by the B lymphocytes (B cells) of the immune system.

(3) Neutralization consists of blocking a virus's proteins so that the virus cannot reproduce or otherwise hurt the host. Opsonization is the coating of a virus (or other object) with proteins in a way that enhances phagocytosis. Precipitation is when a substances crashes out of solution.

(4) Antibodies are relatively ineffective against intracellular viruses.

(5) Cells with viral antigens displayed by MHC I are targeted by cytotoxic T cells. Infected cells not meeting this criterion may need to be targeted by NK cells.

(6) Yes, inflammation is a normal part of the process. Inflammation, from its root "flamm," means "fire," and includes fever, redness, and swelling. These fire-like properties of inflammation are implied by the use of the phrase "blaze of glory."
Bones of the Human Limbs(1) There are 30 bones in each.

(2) Relative to the ulna, the radius is "thicker toward the wrist." Relative to the fibula, the tibia is larger. Other methods of distinction are possible too. For example, one can use the thumb to trace a circle in the air, and the concept of a circle may remind you of the geometry term radius, which is the bone that connects to the wrist on the side of the thumb.

(3) Strictly speaking, anatomists use the term "arm" only for the region from the shoulder to the elbow, and the term "leg" only for the region from the knee to the ankle. Thus a song that covers whole limbs (arms, forearms, and hands; thighs, legs, and feet) should refer to the limbs as such, and not as arms and legs.
Calcium Homeostasis(1) The words "high" and "low" are sung as high and low pitches, respectively, to emphasize the situations being sung about (high and low plasma calcium levels, respectively).

(2) Parathyroid hormone, which stimulates osteoclasts to break down existing bone tissue and release calcium into the blood.

(3) Calcitriol (not mentioned by name in this song).
(4) Reabsorption.

(5) Since the song says that calcitonin helps remove excess calcium from the blood, you might think that this hormone is important in building new bone tissue, as was previously thought to be the case. However, it now appears that physiological levels of calcitonin are not especially important for this process.
Cardiac Conduction Hoedown(1) SA = sinoatrial; AV = atrioventricular.

(2) The conduction delay allows the atria to pump blood into the ventricles without much resistance from the ventricles. If the atria and ventricles contracted simultaneously, the atria would not be able to pump blood through the closed AV valves.

(3) Gap junctions (which are part of intercalated discs).

(4) "Apex" means "point." The apex of the heart is the pointy part -- the most inferior part of the human heart.

(5) Here we are talking about the flow of ions from cell to cell via gap junctions. Calcium, potassium, sodium, etc. all can pass between cells, but since potassium is the most abundant intracellular ion, it is the main ion passing through these gap junctions.

(6) The interventricular septum, between the two ventricles.

(7) Answers will vary. For example, "SA to AV, node to node" is possibly a confusing way of saying that signals pass from the SA node to the AV node. Likewise, "AV bundle of His" is a possibly confusing way of combining two names (bundle of His, AV bundle) for the same structure.
Cardiac Output & Pulmonary Ventilation(1) “Volume of blood per minute” is cardiac output. “Volume moved per beat” is stroke volume. “Number of beats per minute” is heart rate. “Volume of air per minute” is pulmonary ventilation. “Volume moved per breath” is tidal volume. “Number of breaths per minute” is respiration rate.

(2) The respiratory equivalent of stroke volume is tidal volume. The respiratory equivalent of heart rate is respiration rate.

(3) All of these values (heart rate, stroke volume, cardiac output, respiration rate, tidal volume, and pulmonary ventilation) increase during aerobic exercise.

(4) In thinking about how CO and PV change with body size and with activity level, they should certainly be correlated -- i.e., if one goes up, the other goes up as well. However, there is no reason why the number of millilters of blood passing through the heart per minute should numerically match the number of milliliters of air passing through the lungs per minute.

(5) Systole is the contraction of the heart -- usually the ventricles in particular -- while systole is the relaxiation of the heart.

(6) 12 to 20 breaths per minute -- one breath every three to five seconds -- is considered normal.

(7) Answers will vary. For example, some students may lament that the individual components of each equation are not explicitly named and defined within the lyrics (see question #1).
Carpal-Tarsal Sing-Drome(1) The carpals.

(2) Carpals: scaphoid, lunate, triquetrum, pisiform; trapezium, trapezoid, capitate, hamate. Tarsals: talus, calcaneus, navicular, medial cuneiform, intermediate cuneiform, lateral cuneiform, cuboid.

(3) The proximal row is listed first.

(4) Lateral to distal (the same as the ordering of the metacarpals, with the thumb being I).

(5) This order of tarsals goes superior to inferior (talus to calcaneus), then posterior to anterior (calcaneus to navicular to medial cuneiform), then media to lateral (medial cuneiform, intermediate cuneiform, lateral cuneiform, cuboid).
Cations(1) Electrons are negatively charged.

(2) The overall charge of an atom is equal to the number of protons minus the number of electrons.

(3) Anion.

(4) Cations (positively charged ions) are a subset of ions (all charged particles, whether positive or negative).

(5) Answers will vary. Biologically important cations include Ca2+, Mg2+, Na+, NH4+,K+, etc.
Cauda Equina(1) Since the spinal cord is a compact, neatly arranged bundle of fibers, whereas the cauda equina consists of looser, less tightly bundled fibers, the relationship between the two could be considered similar to that of a road branching into a less tidy trail (or set of trails).

(2) Cranial (toward the head) or rostral (toward the beak).
CDs and MHCs(1) Activate the T cells.

(2) T cells.

(3) Possible CDs are CD4 and CD8. Possible MHCs are MHCI and MHCII.
Cell Division(1) This is the equatorial plane in the middle of the cell.

(2) No. Cytokinesis is the division of cellular materials into two daughter cells, whereas mitosis is technically defined as the division of genetic material into two daughter nuclei. While mitosis is generally accompanied by cytokinesis, this does not have to be the case.

(3) Answers may vary. Interphase is indeed "calm" in the sense that the chromosomes don't condense or separate from each other; however, since organelles, proteins, and DNA are all synthesized during Interphase, it can be argued that Interphase is not calm at all!
Chemical Synapses(1) These ends, specialized for releasing neurotransmitter, are called axon terminals or synyptic boutons.

(2) "Synapse" is the term used to refer to the connection between the two cells. "Synaptic cleft" refers specifically to the gap between the cells that is traversed by neurotransmitter.

(3) Ionotropic receptors double as ion channels, i.e., they themselves let ions into or out of the cell. Metabotropic receptors are not ion channels, but they alter the levels of signaling molecules that cause ion channels to open or close.

(4) EPSP = Excitatory Post-Synaptic Potential, i.e., depolarization of the membrane of the post-synaptic cell. IPSP = Inhibitory Post-Synaptic Potential, i.e., hyperpolarization of the post-synaptic cell.

(5) No. At electrical synapses, ions like Na+ simply diffuse from one cell into the next cell via gap junctions.
Circular Smooth Muscles(1) Chyme is the mixture of partially digested food that is in the stomach and then passes into the intestine.

(2) Yes. Although the word "fluid" usually makes us think of liquids, gases like air and semi-solid mixtures like can also be considered fluids. Most broadly, a fluid is anything that flows.

(3) No, smooth muscles are not under voluntary control.

(4) Many answers are possible here; examples include bronchodilators, which open up the bronchioles, and ACE (angiotensin converting enzyme) inhibitors, which dilate blood vessels.
Comparative Animal Physiology(1) The main function of the lungs is exchange of the gases oxygen and carbon dioxide, which happens by diffusion (hence "diffusive flux"). Since diffusion rate is directly proportional to surface area, the lungs' high surface area enable high diffusion rates.

(2) The concentration of solutes in freshwater is very, very low -- far below the solute concentration of any animal's body fluids. Thus, all freshwater dwellers except some degree of osmoregulation.

(3) The pancreas -- specifically the beta cells of the islets of Langerhans.
Countercurrent Flow(1) Two adjacent flows going in opposite directions.

(2) Concurrent flow (both flows go in the same direction).

(3) The gills of a fish transfer oxygen; the tongue of a whale transfers heat; and the nose of a camel transfers moisture (water). The loop of Henle of a mammal is less straightforward in that there is an osmolarity gradient maintained by the transfer of NaCl out of the ascending limb and the transfer of water out of the descending limb.

(4) With a countercurrent flow, exchange can occur along the entire length of the two side-by-side streams, as there is a (small) gradient between the two streams along this entire length.

(5) In birds, air and respiratory blood move at right angles to each other, an arrangement known as cross-current flow, which has at least some of the advantages of countercurrent flow.

(6) The loop of Henle is now often referred to as the nephron loop.

(7) Answers will vary. For example, it could be argued that the song does not clearly define what a countercurrent flow is. Also, mammals are not the only animals with loops of Henle; birds have them as well.
Cranial Nerve Functions(1) The song MOSTLY covers the cranial nerves in descending numerical order, starting at XII and ending at I, but there are exceptions to this progression.

(2) In the order mentioned in the song.... XII: moving your tongue. XI: your back and your neck. X: parasympathetic stuff. IX: saliva and taste (also covered by nerve VII -- hence the melody's quick dip to the 7th note of the 12 pitches). VIII: balance and hearing. V: facial senses and chewing. VII: adjusting your face. VI, IV, and III: steering your gaze. II: vision. I: smell.

(3) II (sensory), III (motor), IV (motor), and VI (motor).

(4) Mostly VII and IX, with a small contribution from X (not mentioned in the song).

(5) Nerves IX (glossopharyngeal) and XII (hypoglossal).

(6) The parasympathetic nervous system has effects consistent with a "rest-and-digest" state: slowing of heart rate, bronchoconstriction, salivation, contraction of smooth muscles lining the digestive tract, etc.

(7) Answers will vary. The descriptions of each nerve's function are terse by design, and thus incomplete. For example, the song mentions that nerves VI, IV, and III are for "steering your gaze," but does not specify that nerve VI controls the lateral rectus muscle, nerve IV controls the superior oblique muscle, and nerve III controls the other four extraocular muscles.
Dizygotic Twins(1) Polyovulation is the release of more than one oocyte at the same time. If two simultaneously released oocytes are both fertilized, the result is dizygotic twins.

(2) With mothers. Some women are genetically predisposed to release more than one oocyte at a time (polyovulation), which makes dizygotic twins more likely.

(3) Speaking genetically, full siblings have the same mother and father; half siblings share one parent but not both. If a woman has dizygotic twins, that is usually because two oocytes were both fertilized with sperm from the same man. However, it is possible that each oocyte could be fertilized by sperm from a different source.

(4) Not really. In the context of reproduction, most people use the word "egg" interchangeably with "oocyte."
Don't Attack Yourself(1) The myelin sheath of neurons' axons is attacked and destroyed. Without this insulation, the axons cannot conduct electrical signals as well.

(2) In myasthenia gravis, antibodies bind to acetylcholine receptors on skeletal muscle cells, thus reducing acetylcholine's access to these receptors, thus limiting the ability of motor neurons to activate the muscle cells.

(3) In type 1 diabetes mellitus, the insulin-producing beta cells of the islets of Langerhans of the pancreas are destroyed, thus preventing the body from making insulin to regulate blood glucose levels.

(4) In Graves' disease, antibodies stimulate the thyroid-stimulating hormone (TSH) receptors in the thyroid gland, causing this gland to overproduce thyroid hormones triiodothyronine (T3) and thyroxine (T4).
Do You Smell What I Smell?(1) MSUD is Maple Syrup Urine Disease. It is genetically inherited.

(2) BCAAs are branched-chain amino acids (isoleucine, leucine, and valine).

(3) In MSUD, there is a defect in an enzyme that breaks down the BCAAs, which build up to toxic levels. Reducing protein intake reduces the production of these amino acids via digestion.
Electrocardiogram Basics(1) Not exactly. They reflect electrical activity of cardiac muscle cells, but they represent a comparison of two surface electrodes rather than a comparison of intracellular and extracellular charge.

(2) Atrial repolarization is obscured by the depolarization of the ventricles (QRS complex), which are much bigger than the atria and thus generate much larger electrical signals.

(3) From the QRS complex to the T wave.

(4) Answers will vary. For example, the first verse lists the order in which electrical depolarization and repolarization events occur, and the chorus then lists the names of these events (P, QRS, T), but it is left to the listener to match up which events go with which labels. Also, the second verse's attempt to distinguish between electrical changes and mechanical changes will not necessarily be clear to a typical undergraduate student.
EMCN(1) Many epithelial cells along the respiratory airway contain cilia (as do cells along the uterine tubes). Epithelial cells with microvilli can be found along the digestive tract (as well as in the proximal convoluted tubule of kidney nephrons). However, many epithelial cells do not have either cilia or microvilli.

(2) The signals are electrical and chemical in nature. The movement of ions causes changes in membrane potential to sweep through neurons, which then pass the signal to other cells via chemical neurotransmitters (or pass ions directly into other cells via gap junctions).

(3) Processes that receive signals from other cells are called dendrites, while the process that carries a signal away from the cell body is called the axon.
Endochondral Ossification(1) "Endo" means "inside," "chondr" means "cartilage," and "oss" means "bone." Therefore, endochondral ossification is the replacement of interior cartilage with bony (osseus) tissue.

(2) The clavicles are exceptions to this rule.

(3) At the end of puberty, when the epiphyseal plates close.
Endocrine Friends(1) Autocrine, paracrine, endocrine, and synaptic.

(2) In general, signals are eliminated via breakdown by enzymes. Hormones travel all over the body through the bloodstream, so they are only broken down slowly, as various cells gradually take them up and process them. In contrast, most other signals are quickly eliminated by enzymes concentrated near the areas where the signals are produced and released.

(3) Many answers are possible. For example, a letter could be analogous to a hormone and the postal service could be analogous to the blood, or an email could be analogous to a hormone and the Internet could be analogous to the blood.

(4) Many answers are possible. Examples of hormones that have anabolic and proliferative effects include growth hormone (GH), insulin, testosterone, and the EGF family of proteins.

(5) The most obvious answer here is thyroid hormone, which increases the metabolic rate of most cells and thus increases heat production.

(6) Endocrine function is defined as releasing hormones into the blood, while exocrine function is defined as releasing anything other than hormones into ducts (generally bound for the outside of the body).

(7) Answers will vary. For example, in trying to cover both the basics of the endocrine system and their analogs in human relationships, the song is vague on the specifics of how hormones work, not specifically mentioning that hormones travel through the blood.
Erythropoietin(1) Epo is a peptide hormone, released from the kidney, that stimulates production of red blood cell (erythrocyte) precursors in the bone marrow.

(2) Red blood cells.

(3) Mostly oxygen (O2) and carbon dioxide (CO2).

(4) Oxygen binds to the iron (Fe) ion of the porphyrin ring of hemoglobin, the most abundant protein in erythrocytes. Some carbon dioxide binds to the N-terminal amino groups of hemoglobin subunits, and some dissolves in the cytoplasm.

(5) A low density of red blood cells (i.e., low hematocrit) leads to anemia, but an elevated density results in highly viscous, sludge-like blood, as experienced by certain cyclists in the early days of blood doping. Thus, as with many physiological variables, it is dangerous for erythrocyte density (and thus epo levels) to be either too high or too low.
Fick's Law of Diffusion(1) Pressure difference (delta P) refers to a difference in the partial pressures of a gas, and thus reflects a concentration gradient.

(2) “Constant” k depends on the temperature, the size of the molecule that is diffusing, the specific medium through which it is diffusing (water? air?), etc.

(3) D is a linear distance, so its units would be something like micrometers or millimeters. Surface area is two-dimensional, so units should be something like mm2, cm2, or m2.

(4) If D increases, diffusion rate decreases.

(5) Mammalian lungs have a high A but a low D.

(6) Not exactly. Blood flow is governed by a HYDROSTATIC pressure gradient, while the pressures in the Fick equation are partial pressures that indicate concentrations of gases.

(7) Answers will vary. For example, the fact that concentration gradient is included as a pressure difference is confusing to many students, and is worth explaining.
Follow the Sound!(1) The outer ear includes everything as far in as the tympanic membrane. The middle ear includes the auditory ossicles. The inner ear includes the cochlea (perilymph, endolymph, etc.)

(2) Sensorineural hearing loss is due to a problem with the hair cells in the cochlea or any structure downstream of the hair cells.

(3) The vestibulocochlear nerve.

(4) We have two of each of structure -- one on the left side of our brain and one set on the right side.

(5) At the superior olivary nucleus. Within this nucleus, the lateral superior olive (LSO) and medial superior olive (MSO) compare sounds from both ears to determine whether sounds are coming from the left or the right.

(6) The superior colliculus processes visual information, especially related to visual reflexes.
Gap Junctions(1) A connexin is an individual polypeptide; a connexon is a complex of connexin subunits.

(2) A connexon is a "hemi-channel" in the membrane of one cell; two connexons from adjacent cells come together to form a gap junction.

(3) Gap junctions have larger pores that can accommodate larger species such as amino acids.

(4) At electrical synapses, ions move directly from one neuron to the next, immediately altering the membrane potential of the postsynaptic neuron. At chemical synapses, these changes in postsynaptic membrane potential are achieved more indirectly: neurotransmitters bind to receptors on the postsynaptic cell, which then leads to the opening or closing of ion channels.
Gas Exchange Medley(1) The body's intake of oxygen and its release of carbon dioxide at the lungs need to keep up with the rest of the body's rates of oxygen consumption and carbon dioxide production. That is, the body needs to promptly replace all of the oxygen that is getting used and promptly get rid of all of the carbon dioxide that is getting made.

(2) Central chemoreceptors are located in the medulla; peripheral chemoreceptors are located in the carotid bodies of the common carotid arteries and the aortic body of the aorta.

(3) If breathing is inadequate, the levels of carbon dioxide and protons will both rise.

(4) Levels of carbon dioxide, protons, and oxygen are the regulated variables. If these things stray too far from their respective setpoints, ventilation increases or decreases to bring them back toward their setpoints. This counteracting of changes away from setpoint is negative feedback. For example, if carbon dioxide gets unusually low, the respiratory drive will decrease so that the person will breathe less and carbon dioxide will accumulate to more normal levels.

(5) PCO2.

(6) The curve of hemoglobin saturation (on the Y axis) versus PO2 (on the X axis) is S-shaped.

(7) To the right.

(8) Exercise by the muscles increases temperature, increases PCO2, and decreases pH, resulting in a modest right shift of the hemoglobin saturation curve. The curve is such that this shift does not greatly change hemoglobin saturation at arterial PO2's but DOES reduce hemoglobin saturation at capillary PO2's, enabling more unloading of oxygen at the capillaries.
Genotype Versus Phenotype(1) Mutations generally arise from incorrect copying or repair of DNA bases, such that the usual complementarity (A goes with T, and C goes with G) is violated. Mutations can happen spontaneously, but their frequency can be increased by radiation, chemicals, pieces of mobile DNA (viral or otherwise) that jump around the genome, mutations in DNA-checking enzymes, etc.

(2) Single-nucleotide polymorphisms often have no effect on phenotype, as they usually change only one amino acid in the protein or none at all. Frameshift mutations, in which bases are added or deleted, usually lead to premature stop codons and truncated proteins with altered functions, and thus altered phenotypes.
Glucose, Glucose(1) Glucose is a sugar whose chemical formula is C6H12O6. It is a naturally occurring energy-rich molecule that cells can break down to generate ATP.

(2) Answers will vary, but one general theme of the song is that glucose is a double-edged sword; it is a great source of energy, but one that can be exhausted relatively quickly, and also one that can generate lactic acid, which, as an acid, can inhibit cellular processes if it builds up too much.

(3) GLUT4 is a glucose transporter in muscle cells (among others) that increases glucose uptake by these cells in response to insulin secretion by the beta cells of the pancreas.

(4) Cardiac muscle and adipose tissue also express lots of GLUT4. Interestingly, the liver does NOT rely heavily on GLUT4, instead expressing GLUT2 (which is not insulin-sensitive).

(5) Glyogen is a glucose polymer or polysaccharide -- a storage form of glucose.

(6) Rigor mortis literally means "rigid death." It refers to the stiffening of muscles upon running out of ATP; the myosin heads can no longer detach from actin.

(7) Glucose, a sugar, tastes sweet; its breakdown product lactic acid, being an acid, tastes sour.

(8) When carbohydrate reserves are depleted, the body must switch to using fat as its primary fuel.

(9) This line is another way of saying that the liver and muscles are running out of carbohydrates. "Honeymoon" includes the word honey, which is basically sugar, so "the honeymoon is over" means that there is little sugar left. Get it?

(10) Answers will vary. For example, the singer's claim, "A few more seconds and I'll be rigor-mortis-bound" is whimsical and not meant seriously; people don't die from running out of glycogen!
Glucose Homeostasis(1) These phrases refer to increasing and decreasing the concentration of glucose in the blood, respectively.

(2) Plasma is the fraction of the blood that doesn't contain cells. Since glucose levels are measured in the plasma, "plasma glucose" is a more precise term than "blood glucose."

(3) There are no strict cutoffs on normal glucose levels. Plasma glucose after an overnight fast is often 70-80 milligrams per deciliter (mg/dL), which is definitely low enough to trigger a glucagon response. Plasma glucose after a meal often reaches twice that concentration, which sends insulin levels soaring.

(4) Glucagon's main target cells are in the liver, where glucagon causes liver cells to break down glycogen into glucose monomers and release it into the blood. Insulin promotes glycogen synthesis in the liver and also promotes glucose uptake by muscle and adipose cells.

(5) Epinephrine and cortisol also help raise plasma glucose levels, as glucagon does.

(6) Glucagon and insulin are both peptide hormones, i.e., relatively short chains of amino acids. In humans, glucagon is 29 amino acids long, while insulin is a dimer whose subunits are 30 amino acids and 21 amino acids, respectively.

(7) Answers may vary, but the songwriter's intention was that the "angry" lines would represent the concerning deviations from typical plasma glucose levels, while the "happy" lines would represent the successful resolution of the glucose-level problem via release of the appropriate hormone (glucagon or insulin).

(8) Answers will vary. For example, the lyrics focus on glucagon and insulin but do not cover how these hormones affect targets that actually do the work of changing blood glucose levels.
The Goldman-Hodgkin-Katz Equation(1) There are many differences. For example, the Nernst equation calculates the equilibrium potential for a single ion, while the GHK equation calculates a cell's membrane potential according to the contributions of multiple ions; the Nernst equation does not depend on ion permeances, but the GHK equation does. Among the similarities are that both equations (in their full, unsimplified forms) incorporate ion charges and concentrations as well as absolute temperature.

(2) At rest, PK+ is much higher than PNa+, so the cell's mebrane potential is much closer to EK+ than ENa+.

(3) During the rising phase, PNa+ is much higher than PK+, so the membrane potential moves toward ENa+.

(4) The two words are sometimes used interchangeably, but permeance is a property of the substance doing the permeating (e.g., an ion), while permeability is a property of the thing being permeated (e.g., a membrane).

(5) It depends on how the equation is written and the specific ions that are included. The form that I usually show (e.g., in the music video) has extracellular concentrations of Na+ and K+ in the numerator and the corresponding intracellular concentrations in the denominator. However, the numerator and the denominator could be flipped if the sign of the coefficient (61 mV) were flipped as well. Furthermore, if anions like Cl- are included, the positions of the intracellular and extracellular concentrations of those is the opposite of those of the cations. For example, a numerator might include extracellular Na+, extraceullar K+, and intracellular Cl-.

(6) Answers will vary. For example, the song lyrics only comment on the equation rather than spelling it out, which some students may find confusing.
Good Bacteria(1) Microbes are microscopic organisms, such as bacteria and other single-celled organisms like protozoa. Some people define the group to include microscopic multicellular organisms as well.

(2) Among the many bacteria that can live in our guts, some lead to diarrhea. There is evidence that Lactobacillus may reduce colonization of the gut by these other diarrhea-promoting bacteria.

(3) These are additional benefits that bacteria bestow upon humans: promoting tolerance of normal bacteria by the immune system, digesting otherwise indigestible materials such as dietary fiber, and outcompeting pathogens for niches on and within humans.
Good Form(1) Answers will vary, but should somehow convey the idea that structure and function go hand in hand.

(2) Yes, both are reasonable statements. Since structure and function are so interdependent, there is no need to think of one preceding the other.

(3) In this case, the nexus is the convergence of structure(anatomy) and function (physiology).

(4) Answers will vary. For the heart, the heart as a whole has hollow chambers whose walls are made of muscle, which is perfect for pumping blood. Cardiac muscle tissue features intercalated discs with gap junctions between cells, allowing electrical signals to spread from one cell to the next. Individual cardiac muscle cells have lots of mitochondria for robust continuous production of ATP. And at the protein level, myosin contains "heads" that can pivot, bind to actin, and break down ATP, allowing the myosin to slide past actin and thus bring about muscle contraction.

(5) Answers will vary. For example, a building might be really tall to serve the function of having a great view, really well-insulated to serve the function of conserving heat, etc.

(6) Answers will vary. For example, some listeners may not quite know what to make of the line "form follows function follows form," which is attempting to express that form can be said to follow function, but function can also be said to follow form.
Have Yourself a Healthy Little Kidney(1) Patients with kidney failure must receive dialysis, in which their blood is filtered by machines. Receiving a new, healthy kidney allows them to stop dialysis.

(2) GFR stands for glomerular filtration rate. 90,000 milliliters per day is equivalent to 62.5 milliliters per minute.

(3) The old kidneys are often left in place, so the new kidney is inserted lower down in the abdomen. The renal artery and vein will the connected to the external iliac artery and vein, respectively.

(4) Glucocorticoids such as prednisone.
Heart Valves(1) "Lub" is the sound associated with the closure of the atrioventricular valves, while "dub" is the sound associated with the closure of the semiliunar valves.

(2) Four (two atrioventricular valves plus two semilunar valves).

(3) The pulmonary valve and the aortic valve.

(4) Many students can remember that the atrioventricular valves are the bicuspid valve and the tricuspid valve, but have trouble remembering which one is on the left side and which one is one the right side. "Try to be right" is a reminder that the TRIcuspid valve is on the right.

(5) No -- "toward the moon" applies only to bipeds standing or walking upright on two feet.

(6) The line "Blood flows up toward the moon" is sung as ascending melody (the notes go higher and higher). The line "blood flowing down" is sung as a descending melody (the notes go lower and lower).
Hemostasis(1) Vascular spasm, platelet plug, coagulation/clotting, clot retraction, thrombolysis.

(2) People with hemophilia generally have a genetic mutation that disrupts the pathway that activates fibrin, so clots form slowly or not at all.

(3) "Thromb" means "clot" and "lysis" means "split," so thrombolysis is the dissolving of a clot.

(4) A cascade is a sort of chain reaction in which the movement or activation of one component leads to the movement or activation of another component, which then alters yet another component, and so on. In this case, the activation of one protease (e.g., factor XII) allows that protease to cleave and activate another protease (e.g., factor XI), which can then activate another.

(5) The intrinsic pathway (which is activated by conditions within the blood vessels), and the extrinsic pathway (which is activated by tissue factor, also known as factor III, a cell-surface protein that interacts with factor VII).

(6) Fibrin is created from its inactive form, fibrinogen, by the action of the protease thrombin, which itself is activated from its inactive form, prothrombin, by another protease.
Henle's Water Music(1) These processes all occur simultaneously, but are not quite the same. "Blood-cleaning" refers to the removal of wastes (e.g., urea) from the blood; "water-saving" refers to the reabsorption of water from the pre-urine back into the blood; and "urine-making" is the net result of filtering, secreting, and reabsorbing

(2) Glomeruli are the balls of capillaries where fluid is filtered into the Bowman's capsules, which begins the process of urine formation. The contents of this filtrate are then further adjusted as it flows through the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct, after which point the urine has been finalized. Thus, the glomeruli and collecting ducts are mentioned because they span the range of structures over which urine is created out of components of blood.

(3) Red is blood (due to red blood cells), urine is yellow (due to the pigment urochrome). Urine is created out of components of blood, so, in a way, red has been made into gold.

(4) The hypothalamus is heavily involved in fluid balance. It senses the osmolarity of extracellular fluid, is responsible for our sense of thirst, and synthesizes the hormone ADH (which is released by the posterior pituitary). A disruption to any of these functions could lead to excessive urination.

(5) If aquaporins are not installed in the membranes of the epithelial cells in the collecting duct -- either because of inadequate ADH release or an inadequate response to that release -- lots of water will not be able to escape the collecting duct, and will instead be released in the urine.

(6) Furosemide is a loop diuretic that inhibits sodium transport out of the ascending limb, thus reducing the size of the medullary osmotic gradient and reducing the osmotic pressure that drives water's exit from collecting ducts.

(7) The most likely reason is that the narrator is using a diuretic (furosemide)!
Hey, Urethra!(1) The sperm's path starts at the seminiferous tubules; the urine's path starts at Bowman's capsule.

(2) Urine.

(3) The renal tubule includes the proximal convoluted tubule (PCT), the loop of Henle (nephron loop), and distal convoluted tubule (DCT).

(4) From the collecting duct, urine passes through the minor calyces and major calyces before entering the renal pelvis.

(5) The efferent ductules are also called the vasa efferentia. The vas deferens is also called the ductus deferens.

(6) Bowman's capsule is also called the glomerular capsule.
Hooray for NMR Spectroscopy!(1) Based on the context of the song, the narrator is referring to a clinical NMR magnet that is capable of whole-body scanning. These kinds of magnets are cylindrical, with a large bore in the center where the subject can lie.

(2) NMRS and MRI are not exactly the same thing but are very closely related. The "I" in MRI stands for imaging, so MRI typically results in a series of 2D images that collectively can be used to form a 3D image. In spectroscopy, no images are generated; instead, spectroscopy measures the concentrations of specific types of nuclei over a defined anatomical region, so the output is a set of peaks, with larger peaks representing higher concentrations.

(3) For water, the target nucleus would be 1H. For ATP, the target nucleus would be 31P.

(4) Spectroscopy is sometimes used to measure changes in concentration over time. "Time resolution is several seconds" means that a new data point could be generated every few seconds.

(5) NMR spectroscopy signals can be detected from spinning nuclei that generate their own magnetic field (magnetic moment), but not all nuclei do this. It turns out that nuclei with an odd number of protons (e.g., 1H, 13C, 19F, and 31P) are easiest to detect.

(6) If [B] = 5 mM, then [A] = 10 mM.

(7) Shimming is adjusting the magnetic field over the region of interest to make it as homogeneous as possible in order to maximize the signal-to-noise of the data.

(8) Movement by the subject will take the region of interest out of the specific area where the magnetic field has been homogenized by shimming.

(9) Answers will vary. For example, the song does not explain the difference between magnetic resonance spectroscopy and magnetic resonance imaging (MRI), which is more commonly used clinically.
Hot Hot Hot(1) The neck is bulging because the thyroid gland is enlarged.

(2) TSH is thyroid-stimulating hormone, which is produced by the anterior pituitary in response to TRH from the hypothalamus and which acts on the thyroid gland. High levels of thyroid hormone (T3 and T4) exert negative feedback on TSH release, so TSH levels are low.

(3) Hyper means elevated and thermic refers to temperature, so hyperthermic is a synonym for hot hot hot!

(4) Metabolic rate should be elevated.

(5) Yes. The symptoms (elevated body temperature and metabolism, high heart rate, etc.) all point to hyperthyroidism, as if the patient has a tumor of the thyroid gland.

(6) The thyroid gland's overproduction of thyroid hormone needs to be slowed down, so this can be done with various drugs, or via the surgical removal of some or all of the thyroid gland.

(7) Answers will vary. For example, the line "How, in middle age, can I be low in TSH, but hyperthermic?" suggests that the patient is both curious and knowledgeable about thyroid endocrinology in general and their own case in particular, to an extent that they should probably be able to make a diagnosis.
How Do You Heal a Wound?(1) Mast cells.

(2) Fibrinogen, which gets converted to fibrin.

(3) Epithial cells, phagocytes, and fibroblasts.

(4) Fibroblasts.

(5) The dermis may not be as well vascularized or as well innervated as it was before.
How Muscles Contract(1) Tropomyosin rolls away from myosin's binding site on actin so that myosin may bind there.

(2) SR is the sarcoplasmic reticulum.

(3) Sodium moves into the cell.

(4) ACh is the neurotransmitter acetylcholine.
Hypersensitivity(1) Hypersensitivity and immune deficiency are sort of opposites. Hypersensitivity may be thought of as an overly robust immune response, whereas immune deficiency involves an inadequate immune response.

(2) Type II hypersensitivity is NOT the only antibody-related type of hypersensitivity. Type I hypersensivity involves IgE, which is an antibody. (Ig is short for immunoglobulin, a synonym for antibody.) Type III hypersensitivity involves immune complexes, which consist of antibodies bound to soluble antigens.

(3) Autoimmune problems can cause hypersensitivity of types II, III, and IV. Rheumatic heart disease is an example of type II; systemic lupus erythematosus is an example of type III; multiple sclerosis is an example of type IV. (Graves' disease and myasthenia gravis are usually considered type II but sometimes are put in their own category: type V.)
Hypohypothalamus(1) "Hypo" means "under," so just as the hypothalamus is located underneath the thalamus, the pituitary is located underneath the hypothalamus and thus could be dubbed the "hypohypothalamus."

(2) By "master gland," it is meant that the pituitary is a gland that controls many other glands (e.g., the adrenal gland, thyroid gland, ovaries, and testes).

(3) The anterior pituitary.

(4) No -- the anterior pituitary has different cells specialized for making the different hormones (corticotropes for ACTH, gonadotropes for FSH and LH, thyrotropes for TSH).

(5) The short answer is "through the blood." By definition, endocrine signals travel through the blood to their target cells.

(6) The adrenal gland secretes mineralocorticoids like aldosterone and glucocorticoids like cortisol, and androgens like dehydroepiandrosterone (DHEA). The thyroid gland secretes the thyroid hormones triiodothyronine (T3) and thyroxine (T4). The gonads secrete estrogen, progesterone, testosterone, and inhibin.

(7) Antidiuretic hormone (ADH), growth hormone (GH), melanocyte stimulating hormone (MSH), oxytocin (OXT), and prolactin (PRL).

(8) Answers will vary. For example, while the pituitary gland takes center stage in this song, and is presented as the "master gland," the key role of the hypothalamus in controlling the pituitary is not acknowledged. That is, in some ways the hypothalamus is the master gland's master!
I'm Clotting Factor VIII, I Am(1) Protein.

(2) The song is most likely referring to Factor IX, a fellow protein. Calcium ions and the phospholipid membranes of platelets are also involved.

(3) The intrinsic and extrinsic pathways, both of which lead to the activation of factor X.

(4) An enzyme that cleaves another protein.

(5) Answers will vary.
Iliac Crest(1) The ilium is the bone with an iliac crest.

(2) The lips are the inner and outer edges of the crest.

(3) Answers will vary. Examples include the abdominal external oblique, abdominal internal oblique, iliacus, iliocostalis (part of the erector spinae), latissimus dorsi, quadratus lumborum, tensor fascia latae, and transverse abdominal muscles.

(4) For bone grafts and bone marrow transplants, the iliac crest is often used as a source.

(5) L4 is the 4th lumbar vertebra. Its level corresponds approximately to the top of the iliac crest. Thus, the iliac crest can be used to help identify a place to do a lumbar puncture (which is usually done between L3 and L4 or between L4 and L5.
In-Lever, Out-Lever(1) MA is unitless; the units of the numerator and denominator cancel.

(2) In theory, mechanical advantage can be anywhere from just above 0 to far above 1.

(3) MA is also equal to Fo divided by Fi and to Vi divided by Vo.

(4) The fulcrum is at the ankle joint.

(5) Yes they do! (6) A high MA favors a high Vo/Vi (needed by the cat), whereas a low MA favors a high Fo/Fi (needed by the armadillo). The closer the muscle insertion is to the joint, the lower that Li, Li/Lo, and MA will be. Thus the cat has a low Li relative to the armadillo.

(7) Answers will vary. For example, some people are baffled by the line, "How do you amplify a whisper to a shout?", which is a rather oblique way of noting that levers can serve as force multipliers.
Insecty Things(1) Spiracles are like the human airway and lungs in allowing air into the animal. The trachea are like the human circulatory system in delivering oxygen to the various tissues that need it.

(2) Plants have stomata that let gases pass in and out when open, and that conserve water when shut, so stomata are similar to spiracles in these ways.
Ion Channels(1) Voltage-gated channels are the ones that generate action potentials. However, ligand-gated channels in the dendrites and soma contribute to action potentials indirectly by generating graded depolarizations that bring voltage-gated channels to their threshold.

(2) In a typical neuron, voltage-gated channels are pre-synaptic (in the axon) and ligand-gated channels are post-synaptic (in the dendrites and soma).
It's All Connective!(1) Connective tissue, epithelial tissue, muscle tissue, and nervous tissue.

(2) Mesenchyme tissue is immature connective tissue that differentiates into the other connective tissue types listed in the song.

(3) Epithelial cells, which coat the exterior and interior surfaces of the body and are shed as they wear out.

(4) Connective tissue proper: adipose, areolar, ligaments, reticular, tendons. Fluid connective tissue: blood, lymph. Supporting connective tissue: bone, cartilage.
Keratin and Melanin(1) Keratin.

(2) Keratin.

(3) Keratin.

(4) Melanin.
Kidney Wonderland(1) Creatinine is a small (molecular weight 113), nitrogen-containing organic molecule. It is a breakdown product of the creatine phosphate found in muscles. It is humans' second-most-abundant organic waste product for nitrogen excretion, behind urea but ahead of uric acid.

(2) An elevated serum creatinine often indicates a reduced glomerular filtration rate (GFR), which may reflect kidney disease. However, such elevations can also be caused by muscle damage from intense exercise, excessive intake of meat or other creatine-containing products, drugs that inhibit creatinine secretion by renal tubules (e.g., trimethoprim), etc.

(3) In principle, a Wearable Artificial Kidney (WAK) should free patients from the need to spend many hours (e.g., four hours per day, three times per week) in hospitals where dialysis is traditionally performed, potentially improving both quality of life and compliance. However, since WAKs are a new technology, they may malfunction more frequently than traditional dialysis machines, and those malfunctions may not be noticed and corrected as quickly or as easily as if the patient was receiving traditional hospital dialysis.

(4) Answers will vary. A person's ability to get a K award may predict future success in obtaining research funding, which is important in many academic positions. However, the addition of new faculty who currently have their own funding raises questions about departments' and universities' long-term commitment to these people. What will happen to them if their funding eventually dries up?
Lactose Bends the Protein(1) Jacques Monod and Francois Jacob.

(2) The "energetic landscape" refers to a graph of the energetic stability of all of the possible 3D structures that a protein could theoretically adopt. A protein settles into the 3D shape that is most energetically stable. This most stable shape will be different in the presence of a ligand such as lactose than in the absence of it.

(3) The operator.

(4) When the repressor dissociates from the operator, RNA polymerase becomes able to bind to the promoter and to transcribe the DNA to RNA.
Lateral Inhibition(1) The first "Low/High" line simply illustrates in the absence of lateral inhibition; there is simply a spatial transition from cells receiving low-intensity stimuli (represented by the low notes, each sung as the word "low") to cells receiving high-intensity stimuli (represented by the high notes, each sung as the word "high"). The second "Low/High" line shows how this edge between "low" and "high" is exaggerated by lateral inhibition; the "low" note closest to the high ones is made even lower, and the "high" note closest to the low ones is made even higher.

(2) The phrase "branching wires" is used metaphorically. Cells, especially neurons, conduct electrical signals in ways that resemble physical wires. For lateral inhibition to occur, the raw sensory information must be sent out via branches to adjacent cells.
Leaving for the Membrane(1) SRP is the Signal Recognition Particle, which mediates cotranslational transport of proteins into the endoplasmic reticulum (ER).

(2) Residues are individual amino acids making up the protein.

(3) These blood types reflect difference in oligosaccharide groups attached to membrane proteins, and differences in their recognition by antibodies.

(4) Based on the line that "the cell surface is my home," this protein seems ultimately destined for the plasma membrane (cell membrane).
The Length Constant(1) Rm is the resistance to the flow of electrical charge across the cell membrane. Ri is the internal resistance to flow (sometimes abbreviated Ra for axial resistance).

(2) Myelin increases Rm; as axon diameter increases, Ri decreases.

(3) This phrase is an encapsulation of the expression for length constant. The two terms are RESISTANCES: Rm and Ri. These are arranged in a RATIO, i.e., Rm is the numerator and Ri is the denominator. And we have to take the square ROOT of that ratio to solve for the length constant.

(4) The length constant has units of length, such as millimeters (mm) or centimeters (cm). This is potentially confusing because the ratio Rm/Ri would seem to be unitless; however, the units for the two are different. For example, Rm could be in units of ohms*cm3 while Ri could be in units of ohms*cm.

(5) This is the length by which a signal -- in this case, a change in voltage -- has declined to 37% of the original value at distance 0. (This 37% is 1/e, that is, 1 over the mathematical constant e.)

(6) The equation applies to passive spread of electrical signals through all parts of the neurons. It is most commonly discussed in the context of the dendrites and the soma; however, it also governs the spread of signals between nodes of Ranvier along the axon, for example.

(7) Answers will vary. For example, it may be confusing that the overall form of the equation is given in the verse ("a root of a ratio of resistances"), but the ratio itself is not specified until the chorus ("Rm over Ri").
Leptin Versus Ghrelin(1) The main source of ghrelin is the cells in the wall of the stomach.

(2)NPY stands for Neuropeptide Y; POMC stands for pro-opiomelanocortin. Both are neurotransmitters that are released by neurons in the hypothalamus and that impact neurons in other parts of the hypothalamus, such as the lateral hypothalamus area (LHA) and paraventricular nucleus (PVN).

(3) NPY release make you feel hungrier, while POMC release suppresses appetite.

(4) Ghrelin stimulates NPY release; leptin suppresses NPY release and stimulates POMC release.
LH Surge(1) LH stands for luteinizing hormone.

(2) LH is produced and secreted by the anterior pituitary gland. Its production is stimulated by GnRH from the hypothalamus.

(3) LH is a dimeric protein, with an alpha subunit of 92 amino acids (in humans) and a beta subunit of 120 amino acids (in humans).

(4) In women, LH acts primarily on the ovaries, where it promotes estrogen production, follicular growth, and ovulation. In males, LH promotes testosterone production.

(5) A large increase in the levels of LH circulating in the blood, causing ovulation.

(6) GnRH is not released continuously, but rather in pulses. These pulses can be frequent or less frequent; the latter is described here as a "slow, slow dirge."

(7) Progesterone in birth control pills slows the frequency of GnRH pulses, thus keeping LH release low and avoiding ovulation. Sometimes estrogen is used in combination with or instead of progesterone.

(8) Answers will vary. For example, "oocyte on the verge" might be considered unclear (on the verge of WHAT?). The sudden mention of sperm might also be considered unclear, since the rest of the song is about the LH surge and ovulation.
Malfunctioning Sphincter Blues(1) Esophageal, pyloric, ileocecal, anal. (This order is the opposite of the order in which they are mentioned.)

(2) The upper esophageal sphincter and the external anal sphincter -- the sphincters at the two ends of the alimentary canal. Also, the external urethral sphincter, and the orbicularis oris and orbicularis oculi.

(3) The sphincters we voluntarily control are made of skeletal muscle; the others are made of smooth muscle.
Mama Glia [poem](1) Glial cells exchange metabolites (nutrients and wastes) with neurons, provide myelin sheaths for axons, provide scaffolding for developing neurons to follow, secrete growth factors, engulf damaged cells and pathogens, etc.

(2) In the CNS: astrocytes, ependymal cells, microglia, and oligodendrocytes. In the PNS: satellite cells and Schwann cells.

(3) Probably the PNS. The neuron has apparently healed from a past injury, and this repair is much more common and effective in the PNS than the CNS.

(4) In general, the frequency of action potentials conveys the intensity of the stimulus.

(5)The reference to a "blanket of insulation" around the axon suggests that this neuron is indeed myelinated.

(6) The word "glue" implies that glial cells simply maintain the structural integrity of the nervous system. However, as covered by question #1, glial cells do much more than this.
Maximum Jump(1) The length-tension curve and the power-velocity curve.

(2) Vmax is the maximum shortening velocity, a theoretical value that would occur if the load were 0.

(3) Muscles convert the chemical energy of ATP into mechanical force, so in this sense they are machines.
Medulla Oblongata(1) The spinal cord.

(2) The hindbrain includes the pons and the medulla. The brainstem includes the hindbrain plus the midbrain.
Medulla's in the Middle(1) The medulla oblongata.

(2) Answers may vary. The adrenal gland is an important example because its cortex secretes different hormones than its medulla.

(3) The words "medulla's in the middle" are on a single note in the middle of the scale ("mi"); the words about the cortex bounce up and down above and below the medulla's note, thus "wrapping around" the medulla melodically.
Meet My Threshold(1) EK represents the equilibrium potential of potassium.

(2) PSPs are (excitatory or inhibitory) Post-Synaptic Potentials.

(3) When some voltage-gated sodium channels open, sodium enters the neuron, further depolarizing the membrane and causing even more voltage-gated sodium channels to open, thus ensuring that the neuron goes through a full action potential.
Membrane Permeability(1) Substances that are hydrophobic, or lipophilic, can generally diffuse freely across membranes. Substances that are hydrophilic, or lipophobic, cannot.

(2) Simple diffusion across membranes does not require any sort of protein, whereas facilitated diffusion involves a protein channel (pore).

(3) Some membrane proteins, such as ion channels, are simple pores; they merely provide an opening in the membrane through which a substance can pass. Other proteins -- usually called carriers, pumps, or transporters -- bind to a substance on one side of the membrane, then change configuration and release it to the other side of the membrane.

(4) Free fatty acids: simple diffusion. Na+ ions: simple diffusion, primary active transport, and cotransport (secondary active transport). Glucose: facilitated diffusion and cotransport (secondary active transport). Full-length proteins: endocytosis and exocytosis.
Metaphase(1) A chromatid is one half of a duplicated chromosome.

(2) Once the sister chromatids separate (during anaphase), they are referred to as chromosomes rather than chromatids.

(3) Yes.

(4) The two sister chromatids are about to migrate toward opposite poles of the cell -- one to the left, and one to the right.

(5) No -- the phases of mitosis only cover the sorting of the chromosomes. The splitting of the cytoplasm is considered a separate process called cytokinesis.
Microvilli, Cilia, Flagella(1) Sense surrounding fluid: cilia and microvilli (the hair cells in the cochlea, confusingly, have projections called stereocilia but more like microvilli than cilia). Move surrounding fluid: cilia. Move cells through surrounding fluid: flagella. Take things from surrounding fluid: microvilli.

(2) The cytoskeleton of microvilli is based on actin filaments, while the cytoskeletons of cilia and flagella are based on microtubules made of tubulin.

(3) Sperm are the only human cells with flagella; thus, only human males have cells with all three types of cellular projections.

Mitosis(1) The chromosomes condense into a more compact form so that they may be more easily seen.

(2) The "sphere" is the about-to-divide cell (which is often roughly spherical in shape, but not always).

(3) The process is NOT random; one copy of each chromosome is distributed to each daughter nucleus, such that both daughter nuclei wind up with the same genetic material.

Muscles of the Face(1) The first muscle performs the first function and the second muscle performs the second function. An "exception" is that "close your mouth and shut you up" is really only one function and is true of both the masseter and temporalis.

(2) "Oris" means "mouth" (think of the word "oral"). "Oculi" means "eye" (think of the word "ocular").
Myofibrils(1) A myofibril is a bundle of muscle proteins, including several copies of the thick and thin filaments. There are many myofibrils within a single muscle cell.

(2) Myofilament (smallest), myofibril, muscle fiber, muscle (largest).

(3) Muscle cells and whole muscles shorten when myosin and actin slide past each other. The lengths of these individual proteins do not change, but the degree of overlap between them increases so that the muscle cells and the muscle shorten.

(4) Motor neurons.

(5) In skeletal muscle, calcium is released from the sarcoplasmic reticulum (SR) when the SR receives notice of depolarizations of the sarcolemma (plasma membrane), as carried inward by T-tubules. In cardiac muscle, a small amount of extracellular calcium enters the cell and triggers the release of additional calcium from the SR.

(6) Calcium ions bind to troponin, whose change of shape causes tropomyosin (an adjacent protein) to roll out of the way of myosin's binding site on actin, so that myosin can now bind to actin, leading to contraction.

(7) ATP is split into ADP and Pi (inorganic phosphate) by myosin shortly after it binds to ATP and detaches from actin.

(8) The calcium pumps that put calcium back into the sarcoplasmic reticulum (SR).

(9) Answers will vary. For example, one could take issue with the imprecision of "rides the nerve to the muscle" (which nerve(s)? which muscle(s)?), or with "add a little calcium," which could be taken to mean that calcium is being delivered to the muscle cells from somewhere else, rather than being released from intracellular stores.
The Nernst Equation(1) For any given ion, the equilibrium potential is the electrical gradient across a membrane that is just sufficient to perfectly counterbalance the chemical gradient. This is important in the nervous system because ions flow into or out of cells according to these gradients, and electrical signals spread through the nervous system based on these ion flows.

(2) A quotient is the answer to a division problem. Here the extracellular ion concentration is being divided by the intracellular ion concentration.

(3) No -- this "constant" varies with temperature. At an internal body temperature of 37 degrees Celsius, the value is 61 mV.

(4) Ion valence is the charge carried by an ion, such as -1 or +2.

(5) E, an electrical potential, generally is reported in units of millivolts.

(6) E is the equilibrium potential -- the electrical gradient across the membrane needed to perfectly counterbalance any concentration gradient, such that there is no net driving force driving the given ion from one side of the membrane to the other.

(7) The electrical gradient is attracting K+ into the cell, but the chemical gradient is pulling K+ out of the cell; the strengths of these two gradients are equal and opposite at a membrane potential of -90 mV.

(8) Answers will vary. For example, the lyrics are not as clear as they could be on which ion concentration (extracellular or intracellular) is the numerator of the ratio; one has to get the order from the mention of "ions out and in." (Since the extracellular concentration is mentioned first, it is the numerator.)
Neural Modulation of Skeletal Muscle Force(1) A motor unit is a motor neuron and all of the muscle cells that it controls.

(2) Firing frequency refers to the frequency with which the motor neurons fire action potentials, which dictates the frequency with which the muscle cells depolarize.

(3) This arrangement (weak before strong) means that a given change in force (as additional motor units are added or dropped) will be proportional to the total "baseline level" of force. In other words, when you are working at low forces, you can modulate the level of force more precisely than when you are working at high forces.

(4) Tetanus is a muscle's state of maximal force production. To achieve it, each muscle cell in the muscle must be recruited and stimulated at a firing frequency that maximizes that cell's force (i.e., that does not permit relaxation in between stimuli).
Neuroendocrine Cell(1) A neuroendocrine cell is a cell that is a neuron or has neuron-specific properties (e.g., depolarizing in response to receiving neurotransmitter), but that secretes a hormone rather than a neurotransmitter.

(2) First, note that some of the hypothalamic neuroendocrine cells extend into the posterior pituitary gland, so that too can be a location. Second, the adrenal medulla can also be considered a location of neuroendocrine cells. Postganglionic cells there make epinephrine (adrenaline) and norepinephrine (noradrenaline) that are released into the blood as hormones.

(3) In general, a reflex is a rapid, predictable response to sensory input. A neuroendocrine reflex is one in which the response is the release of a hormone; the "neuro" part of the reflex reports the sensory input and triggers the release of the hormone (the endocrine part). In the example of the uterus, the pressure in the cervix is reported by the nervous system, leading to the release of the hormone oxytocin from neurons that originate in the hypothalamus and terminate in the posterior pituitary.

(4) No. The neuron could be making a regulatory hormone bound for the anterior pituitary (such as GnRH, GHRH, TRH, or CRH), or it could be making antidiurectic hormone (ADH) or oxytocin to be released from the posterior pituitary. The mention of "distant targets" suggests that the neuron is a producer of ADH or oxytocin, which have far-away target cells.

(5) This kind of neuron is not especially rare. Note the answer to #4 above, which lists many different hormones, all produced by different neuroendocrine cells in the hypothalamus.

(6) The basic idea of this phrase is that, by sending hormones all over the body, endocrine cells, influence cells that neurons cannot directly communicate with. In that sense, neuroendocrine cells do reach cells "of which other neurons can only dream," though it's shameless anthropomorphizing to imagine that individual neurons or small networks of them can do anything like "dream." Also, note that some neurons are themselves quite long and thus reach "distant targets" that way.

(7) Brooks' original lyrics indicate that a person can adopt more than one non-mutually-exclusive role, e.g., be both a child and a mother. Similarly, the cells of this song belong partly to the nervous system and partly to the endocrine system; it would be misleading to force them only into one category or the other.

(8) Answers will vary. For example, the opening line could be considered misleading, since it focuses on one particular neuron with a "secret," but there are many neurons that fit the description in the song, and there is nothing especially secretive about these neurons.
Neurons Like Nephrons(1) The analogy is reasonable in the sense that the neuron can be considered the functional unit of the brain, while the nephron can be considered the functional unit of the kidney. However, the parallels are not perfect. For example, most nephrons are similar in processing the filtrate from glomerular capillaries, whereas most neurons are used to process only certain types of information (e.g., neurons on the occipital cortex process visual stimuli).

(2) HCO3 is also known as bicarbonate and carries a -1 charge.

(3) If the plasma is too acidic (pH less than 7.4), nephrons will increase their secretion of protons and their reabsorption of bicarbonate. If the plasma is too basic (pH higher than 7.4), nephrons will decrease their secretion of protons and their reabsorption of bicarbonate.
The Nirenberg Concerto(1) This phrase refers to the process of translation, in which sequences of RNA bases (A, C, G, and U) are converted into sequences of amino acids.

(2) Nirenberg pioneered cell-free protein synthesis. He could add a specific mRNA molecule to his expression system and see what protein came out of it.

(3) Nirenberg's first step toward cracking the genetic code was to determine that an mRNA molecule whose only base was uracil (UUUUUU...) was translated into a protein whose only amino acid was phenylalanine. It eventually became clear that each UUU codon coded for one phenylalanine.
Obstructive and Restrictive Lung Disease(1) FVC stands for Forced Vital Capacity or Functional Vital Capacity. It is the maximum volume of air that you can exhale if starting from maximally inflated lungs.

(2) FEV1 is the Forced Expiratory Volume in 1 second, i.e., the maximal volume of air that you can exhale in 1 second when starting from maximally inflated lungs.

(3) People with restrictive lung disease have low FVCs; that is, they can't inflate their lungs fully. Consequently, the FEV1 may also be low simply because they don't have a lot of air available for exhalation. A low FEV1 secondary to a low FVC may be revealed by calculating the FEV1/FVC ratio; this ratio should be normal for patients with purely restrictive diseases.

(4) The pulmonary system consists of a trachea branching into two bronchi, which branch further into smaller bronchi and then bronchioles. Thus, the system has the branching structure of a tree.
Okazaki Fragments(1) Thymidine (one of the four nucleotide building blocks of DNA) that has been radioactively labeled with "heavy hydrogen" (tritium or H-3).

(2) "Semidiscontinous" means half discontinuous. One of the two new DNA strands is synthesized continuously; the other new strand is synthesized discontinuously.

(3) If all DNA replication was continuous, Okazaki would have found that all just-made pieces of DNA were long. However, he found that some pieces were short, presumably as a result of discontinuous replication.
Orbital Groove(1) "Orbital" refers to the eye socket -- the indentation in the skull where the eye resides.

(2) A foramen is a hole, whereas a fissure is a longer slit or groove.

(3) Since "superior" means "above" and "inferior" means "below," the superior orbital fissure is above the inferior orbital fissure.

(4) Since "supra" means "above" and "infra" means "below," the supraorbital foramen is above the eye and the infraorbital foramen is below the eye.
Oxidative Phosphorylation(1) Mitochondria.

(2) Oxygen is a substrate that accepts electrons passed along the electron transport chain, forming water. Carbon dioxide is a product of Krebs cycle reactions in the mitochondrial matrix.

(3) The matrix is the fluid interior of the mitochondria. The intermembrane space is the area between the mitochondria's inner membrane and outer membrane.

(4) Adenosine diphosphate (ADP) and inorganic phosphate (Pi.

(5) As electrons are passed along the electron transport chain, some of the energy lost by those electrons is redirected into pumping protons against their gradient out of the mitochondrial matrix.

(6) "Oxidative" generally refers to the losing of electron pairs -- in this case, electron pairs are harvested from high-energy molecules and passed down the electron transport chain in order to pump protons (H+) out of the mitochondrial matrix. "Phosphorylation" generally means adding a phosphate (-PO4) group onto something -- in this case, adding it to ADP to regenerate ATP.

(7) Yes! Even if a person isn't physically moving around, cells consume lots of ATP on maintenance, growth, and repair, and oxidative phosphorylation is their main way of replacing this ATP.

(8) Answers will vary. For example, the description of mitochondria as "cigar-shaped" is not necessarily helpful, since cigars come in different shapes.
Pee Values(1) Na+, K+, Cl-, Ca2+, glucose, urea, various hormones, etc.

(2) Secretion will increase excretion.

(3) Filtration occurs only within the renal corpuscle; water and small solutes move from the glomerulus to the glomerular capsule (Bowman's capsule).

(4) Filtration only moves substances down their concentration gradients; reabsorption and secretion can go either down or against a gradient.

(5) Secretion and reabsorption can sometimes require ATP use. For example, reabsorption of NaCl in the ascending limb of the loop of Henle is ATP-dependent.

(6) Yes. If a substance is not filtered or reabsorbed or excreted, the excretion rate would be 0. The excretion rate would also be 0 if the amount filtered is completely returned to the blood via reabsorption.

(7) Answers will vary. For example, the direction of each process is implicit in the equation, but the lyrics do not spell out that filtration and secretion move solutes from the plasma to the pre-urine, while reabsorption does the opposite.
Pennate or Parallel?(1) Pennate.

(2) a. Some people classify the biceps brachii as parallel because the fibers are indeed parallel. Others put this muscle in a separate (not necessarity mutually exclusive) category: convergent (muscle fibers taper down to a much narrower tendon) and/or fusiform (the belly of the muscle is much thicker than the tendons). b. Parallel or convergent (see part a above). c. Neither (it is circular). d. Parallel. e. Pennate. f. Parallel.
Photosynthesis Calypso(1) Carbon fixation is the process of converting carbon atoms from an inorganic form (CO2) into organic forms (in which the carbon atoms are generally bound to other carbon and/or nitrogen atoms).

(2) The Calvin cycle.

(3) Six is the number of carbon atoms in glucose (C6H12O6), the product of photosynthesis.

(4) Starch is many glucose molecules linked together, collectively called a polysaccharide. Sucrose is one glucose molecule linked to one fructose molecule (a similar sugar), collectively called a disaccharide.
Phototransduction(1) The sodium gates are open.

(2) Rhodopsin is a complex consisting of a small organic molecule (retinal) and a protein (opsin).

(3) Rhodopsin activates the G protein (which is trimeric, i.e., it has 3 subunits).

(4) Phosphodiesterase.

(5) This PDE converts cGMP to 5'-GMP.

(6) The inward sodium current that takes place when it is dark.

(7) Light leads to hyperpolarization of the membrane because the depletion of cGMP closes the cGMP-dependent sodium channels, and less sodium entry means less depolarization of the membrane.
A Physiologist's Blessing(1) "May your gradients drive the flows you need to thrive" refers to the core concept of flow down gradients. "May your cells transmit well at their junctions" refers to the core concept of cell-cell communication. "May your setpoints hold in weather hot or cold" refers to the core concept of homeostasis through feedback. "And your structures stay aligned with your functions" refers to the core concept of structure-function matching.

(2) Answers will vary.

(3) In general, a gradient is a change in the magnitude of something over space; for example, a color gradient might go from a light color on the left side of a page to a darker color on the right side of the page. Biologically relevant gradients include chemical/concentration gradients (e.g., oxygen passes from the blood into muscle cells via diffusion), electrical gradients (e.g., positively charged sodium ions are attracted to the negatively charged interior of cells), thermal gradients (e.g., heat is transferred from the body's core to colder, more peripheral areas), and pressure gradients (e.g., blood flows from regions of higher pressure to those of lower pressure).

(4) No. In endocrine communication, for example, a hormone molecule travels from the cell that produced it to the cell that receives it via the blood, so there is no "junction" where the two cells meet.

(5) A setpoint is a variable's ideal or target value, as maintained by negative feedback. For endotherms like mammals, the setpoint for core body temperature should be independent of environmental temperatures; however, temperature extremes may challenge an animal's ability to keep its temperature at this setpoint. Extreme heat might also lead to sweating and dehydration, which could bring the body's setpoints for arterial blood pressure and ECF osmolarity into play.

(6) Answers will vary. Of the four lines of the chorus, it could be argued that "may your setpoints hold in weather hot or cold" is the least clear and least complete summary of the four corresponding core concepts. It implies that setpoints might be a temperature-specific phenomenon, when setpoints are actually a general component of control systems; the phrasing "may your setpoints hold" suggests that the drifting of setpoints is a major challenge, whereas the drifting of observed values away from the corresponding setpoints is the usual challenge; and the phrase does not refer specifically to the feedback mechanisms by which observed values are pushed back toward the corresponding setpoints.
The Place Principle(1) The basilar membrane of the cochlea.

(2) The apex of the cochlea is most sensitive to low pitches, so the word "apex" is sung as a low note. Conversely, the base is most sensitive to high pitches, so the word "base" is sung as a high note.
Poiseuille's Law of Laminar Flow(1) Poiseuille's Law calculates the rate of blood flow through a single blood vessel of the circulatory system. Units should be volume of blood per unit time, e.g., milliliters per second.

(2) "r" stands for radius -- the radius of the blood vessel.

(3) Blood does flow in a circuit: from the left heart to the various tissues of the body, back to the right heart, to the lungs, to the left heart, out to the various tissues again, and so on.

(4) Resistance to flow (often abbreviated with a capital R) is inversely proportional to radius to the 4th power (r4). As radius increases, resistance decreases.

(5) Here delta P refers to a difference in hydrostatic pressure over the length of the vessel. It is not the same as the delta P in Fick’s Law of Diffusion. That delta P refers to a concentration difference of dissolved gases (whose concentrations are reported as partial pressures).

(6) Blood vessel radius. Since radius is raised to the fourth power, even a small change in radius will have a large effect on blood flow.

(7) Yes. Although the equation includes the radius, rather than the diameter, the two are directly related -- the diameter is twice the radius. If the diameter of a blood vessel increases by 30%, the radius will increase by 30% as well, so changes in diameter affect blood flow in the same way that changes in radius do.

(8) The equation can be rewritten as: Flow = (pi*r4*deltaP)/(8*length*viscosity).

(9) Answers will vary. For example, the long, flowing lines ("when the blood flows around and around and around...") could be taken to underscore the way blood flow through the body is continuous rather than intermittent.

(10) Answers will vary. For example, Poiseuille's Law only covers laminar (smooth) flow, not turbulent flow, but this distinction is not made in the song lyrics.
Polymerase (1) The lines "I saw a DNA strand growing in size/Polly was there, adding nucleotides" suggests that Polly is synthesizing DNA and therefore is a DNA polymerase.

(2) No. There are three stop codons; in terms of RNA sequence, they are UAA, UAG, and UGA. The UAA codon corresponds to ATT on the template DNA strand; UAG corresponds to ATC, and UGA corresponds to ACT. Since all of the DNA triplets have an A in them, which was the incorrect base ("it's got an A where a C belongs"), the stop codon could be any of the three.

(3) The DNA replication rate quoted in the song is 50 bases per second. A genome of 3,000,0000,000 base pairs -- 6,000,000,000 bases -- would thus take 120,000,000 seconds to copy if a single DNA polymerase molecule had to do the entire job. To speed this up, many copies of the polymerase are active simultaneously.
Polymers and Monomers(1) A polymer is a structure (not necessarily a biological one) made up up repeating subunits (i.e., monomers) that are linked together.

(2) Polysaccharides (e.g., starch) are polymers made up of monosaccharides (e.g., glucose); proteins are polymers made up of amino acids.
Positive and Negative Feedback(1) A setpoint is the default or "ideal" level of the regulated variable; a detector (or sensor or receptor) senses the current level of the regulated variable; an integrator compares the variable's current level (as indicated by the detector) with the setpoint to determine whether there is a discrepancy between the two; and the effector moves the regulated variable back toward the setpoint.

(2) Answers will vary. Examples include the opening of voltage-gated sodium channels along the axon of neurons, the increasingly strong contractions of the uterus during labor, the promotion of the "LH surge" by estrogen, and the formation of platelet plugs in response to bleeding.

(3) Answers will vary. Variables regulated by negative feedback include many properties of blood, including blood pressure, calcium level, glucose level, osmolarity, oxygen level, pH, and temperature.

(4) The line about positive feedback starts on a low pitch and then rockets higher and higher above its starting point. In contrast, the negative feedback melody is "regulated" to stay close to the starting point.
Positive- and Negative-Pressure Ventilation(1) Frogs.

(2) Negative-pressure ventilation.

(3) Positive-pressure ventilation can be said to PUSH air into the lungs; negative-pressure ventilation can be said to PULL air into the lungs.
Protease Cascades(1) The inactive precursor form of a protein often has a prefix like "pro" or a suffix like "ogen." When a piece of the protein is cut off, it becomes shorter (i.e., it now has fewer amino acids), and, likewise, its name becomes shorter too (e.g., prothrombin is converted to thrombin).

(2) Proteases are important for both activation and destruction of other proteins. A single cut to remove a regulatory peptide will often activate a protein; however, if that protein is cut repeatedly, it will be destroyed.

(3) Fibrinogen/fibrin is not a protease, but rather a structural protein that ties blood components together into a clot.

(4) Proaccelerin (factor V) becomes accelerin (factor Va). Procarboxypeptidase becomes carboxypeptidase. Proconvertin (factor VII) becomes convertin (factor VIIa). Trypsinogen becomes trypsin.

(5) A serine protease does NOT cut proteins at serine residues; instead, a serine is a key part of its active site (as part of a catalytic triad that also includes a histidine and an aspartate).

(6) These proteases (and others) help digest each other; their amino acids are absorbed from the small intestine into the blood.
Quads and Hamstrings(1) The physical action of kicking is the extension of the knee, perhaps accompanied by flexion of the hip and dorsiflexion of the ankle.

(2) The four quadriceps muscles (vastus lateralis, vastus intermedius, vastus medialis,and rectus femoris) all contribute to knee extension, and the rectus femoris is also responsible for hip flexion. (The hamstrings, as antagonists of the quadriceps, re-flex the knee following a kick.)
Right Heart, Left Heart(1) Yes -- the left ventricle has a thicker wall, reflecting its need to pump more strongly.

(2) High pulmonary blood pressure would lead to excessive filtration out of the pulmonary capillaries, pulmonary edema, and impaired gas exchange at the lungs.
RNA Clover(1) Translation is the conversion of a sequence of the bases in mRNA into a sequence of amino acids that form a protein.

(2) tRNA carries amino acids to the ribosomes.

(3) Each mRNA codon matches a tRNA anticodon, ensuring that the correct amino acid gets incorporated into the chain.

(4) The tRNA molecule folds back on itself at various points to maximize intra-stand base-pairing (A with U and C with G). In a normal cellular environment, the "leaves" of tRNA do not extend outward that much into the surrounding cytoplasn; instead, they adopt the more energetically favorable position of curling somewhat around the main "stalk" of the molecule. This can be seen in the figures of the music video.
Scientific State of Mind(1) The questions cover both the basic workings of the natural world and more practical applied issues, and they cover phenomena observable with the naked eye as well as invisible or microscopic processes. Thus, this song offers a "big-tent" definition of science, treating all of these areas as appropriate for scientific investigation.

(2) The song presents the essence of science as asking questions, developing hypotheses, and testing those hypotheses via the collection of data. So it could be argued that any thinking that proceeds through these three stages represents a scientific state of mind.

(3) A lab coat and big goggles.

(4) Answers will vary. For example, the line, "I have a guess, and I'll test my hypothesis" implies that a hypothesis is simply a guess, but most scientists would define the term more narrowly than that, expecting a hypothesis to be well-grounded in logic and previous observations.
The Secondary Immune Response(1) The secondary immune response is the immune response to a previously encountered pathogen. This response is quicker and stronger than the original (primary) response because the memory B cells and memory T cells "remember" this pathogen.

(2) T-helper (Th) cells.

(3) B cells, once they differentiate into plasma cells, produce and secrete huge quantities of a single type of antibody; thus they may be considered "antibody factories."
Semi-Permeable Membrane(1) A semi-permeable membrane is a barrier (membrane) that lets some things pass through it while preventing other things from passing. Examples of a non-biological semipermeable membrane will vary (dialysis membrane, cloth mesh, sieve, etc.).

(2) The narrator seems to be lipophobic, or hydrophilic. It refers to itself as having polar bonds, which would make it hydrophilic, and it also refers to itself as "lipophobic" and as needing transporters to get across the cell membrane.

(3) N's and O's are nitrogen and oxygen atoms, respectively. These atoms have high electronegativities, which are highly attractive and result in polar bonds when the other half of the bond is, say, a C or an H.

(4) The cell membrane is made of lipids, but also contains many embedded proteins. The cell membrane is not as rigid as the word "wall" implies; it is often described as a fluic mosaic. Finally, the phrase "lipid wall" may make some people think of the cell wall, which is a structure different from the cell membrane.

(5) "Lipophobic" is synonymous with "hydrophilic" and "polar."

(6) We can't rule out the possibility that the narrator is a protein, but it seems unlikely. The narrator thinks that a (protein) transporter will be its ticket through the cell membrane, and a protein doesn't usually use a single other protein to get through the cell membrane; it usually requires a vesicle-related process (endocytosis or exocytosis).
Shine a Light on a Lumen(1) Lysosomes are organelles specialized for breakdown (lysis) of molecules into smaller molecules.

(2) In physics, a lumen is a unit of light intensity. The title of this song is a reference to that alternative meaning.

(3) Yes!
Shoulders Versus Hips(1) Both are ball-and-socket joints.

(2) The lines about the shoulder use a wide-ranging melody, whereas the lines about the hip use a more restricted melody, illustrating the relative ranges of motion of these two ball-and-socket joints.

(3) The more ligaments there are around a joint, and the stronger these ligaments are, the more stability the joint will have, but the less flexibility it will have.
Smooth or Striated?(1) Striated.

(2) Striated.

(3) Smooth.
The Sodium Jeer(1) Na (hence the "Na Na Na Na Na" jeer).

(2) Sodium normally cannot get into cells because it is charged and thus cannot pass through the cell membrane unaided, and the ion channels through which it can pass are closed in a normal "resting" cell.

(3) Sodium is much more concentrated outside cells.
Squeeze Me Tight ... or Squeeze Me Gently(1) Yes -- the left ventricle has a thicker wall, reflecting its need to pump more strongly.

(2) High pulmonary blood pressure would lead to excessive filtration out of the pulmonary capillaries, pulmonary edema, and impaired gas exchange at the lungs.
Strata of the Epidermis(1) The stratum basale is closest to capillaries. This makes sense because the epithelial stem cells in that layer are growing and dividing rapidly, and thus have a great need for the nutrients provided by the capillaries.

(2) The stratum basale, though extensions of their cytoplasm reach into more superficial layers.

(3) Keratin.

(4) The stratum lucidum.
Surface Area-to-Volume Ratio(1) Surface area should have units of distance squared (e.g., cm2 or m2). Volume could have units of distance cubed (e.g., cm3 or m3), or could be measured in milliliters or liters.

(2) The ratio reduces to the fraction 6/L.

(3) Yes. The surface area of a sphere equals 4*pi*r2, where r is the radius. The volume of a sphere equals (4/3)*pi*r3. The surface area-to-volume ratio is 3/r, which decreases as r increases. Thus this ratio decreases with increasing size, regardless of whether the object is cube-shaped or spherical.

(4) Oxygen and heat are the usual answers. Other possibilities include carbon dioxide, nitrogenous waste products like urea, water, etc.

(5) The lyrics refer to the trend that mass-specific metabolic rate (e.g., milliliters of oxygen consumed per minute per kilogram of body mass) decreases with body size, so a mouse would have a much higher mass-specific metabolic rate than an elephant. However, an elephant would have a higher total rate of oxygen consumption per minute, since it is so much bigger.

(6) Answers will vary. For example, some people may find ambiguity in the lines, "If you're small, it's high; if you're large, it's low." Here "you" is the organism and "it" is the surface area-to-volume ratio of that organism.
Surface Area, Eh?(1) Fick's law is for diffusion rate; Fourier's law is for the transfer of heat via conduction.

(2) Elephant ears and a distended scrotum give off heat quickly. Microvilli increase the rate of absorption of nutrients from the small intestine, and the rate of reabsorption of nutrients from the proximal tubule of nephrons in the kidney. Lung alveoli and gill lamellae increase gas exchange (the transfer of oxygen and carbon dioxide) at the lungs and gills, respectively.

(3) Structures with a high surface area are often thin and therefore delicate and easily damaged. Also, a high surface area can increase the transfer of substance that you don't want to gain or lose. For example, the high surface area of the lungs is great for gas exchange, but also causes animals to lose more water vapor to the environment than they would otherwise.

(4) Microvilli are found on cells of the small intestine and proximal tubule, and on white blood cells.
Synovial Joints(1) These are prefixes to be combined with the root "axial": triaxial, biaxial, monoaxial, or nonaxial, reflecting the number of axes the joint has. (Monoaxial joints are also referred to as uniaxial.)

(2) Here, "a ton" means 3.

(3) Answers will vary. Here are some possibilities.... Ball-and-socket: shoulder, hip. Condylar: metacarpophalangeal joints (for metacarpals II through V). Gliding: acromioclavicular, claviculosternal, intercarpal, intertarsal, sacroiliac, vertebrocostal. Hinge: ankle, elbow, interphalangeal, knee. Pivot: atlantoaxial (top two cervical vertebrae), proximal radioulnar. Saddle: first carpometacarpal (trapezium to metacarpal I).
Take Me to the Liver(1) A lipid such as a triglyceride or cholesterol is singing to its lipoprotein carrier (which sings the words in italics). There are various hints of this, such as the main vocalist's request to "keep me out of water," meaning that it is a hydrophobic ("water-fearing") molecule, and its mention of endocytosis, which is a major uptake mechanism for lipids but not protein or carbohydrate.
The Three Planes (Coronal, Sagittal, Transverse)(1) The frontal plane.

(2) The transverse plane.

(3) A coronal or frontal slice.

(4) A parasagittal plane is a sagittal plane that splits the body into two unequal halves.
Tiny Cells (RBCs/Tiny Sperm)(1) Mature RBCs do not retain any membrane-bound organelles, but mature sperm have nuclei and mitochondria.

(2) The bloodstream and semen, respectively.

(3) Oocytes.

(4) Enzymes released from the acrosome of the sperm digest the corona radiata and zona pellucida surrounding the oocyte.
Total Lung Capacity(1) RV = Residual Volume; ERV = Expiratory Reserve Volume; VT = Tidal Volume; IRV = Inspiratory Reserve Volume; TLC = Total Lung Capacity.

(2) RV is the air that you cannot get out of your pulmonary system no matter how hard you try. ERV is the amount of air that you can exhale beyond your normal exhalation volume; similarly, IRV is the amount of air that you can inhale beyond your normal inhalation volume. VT is the amount of air that passes in and out during normal breathing. TLC is the maximum amount of air that your pulmonary system can hold.

(3) Dead space is the air that cannot participate in gas exchange because it is in the conducting structures (trachea, bronchi, larger bronchioles), rather than the respiratory structures adjacent to pulmonary capillaries. Thus, dead space is one (relatively small) component of RV.

(4) All of these terms are volumes of air, so they can be reported in milliliters or liters.

(5) VC is the maximal volume of air that can be exhaled from the lungs, so it differs from TLC in that TLC also includes the RV, which can't be eliminated from the lungs.

(6) VC = TLC - RV. Alternatively, VC = ERV + VT + IRV.

(7) Answers will vary. For example, the acronyms ERV, VT, and IRV are not defined in the song. Also, the lyrics do not say whether these values are constant for a given person, or can vary with conditions (e.g., rest vs. exercise).
Touch Me!(1) Yes -- for example, thermoreceptors and nociceptors (pain receptors).

(2) Other mechanoreceptors include the hair cells of the inner ear and the baroreceptors of the carotid artery and aorta, which likewise sense distortion of the plasma membrane.
Unnatural Blues(1) 42 degrees Celsius is 107.6 degrees Fahrenheit.

(2) Evaporative heat loss (e.g., sweating); relocation to cooler areas; and expression of heat shock proteins (HSPs), which help prevent other proteins from denaturing under warm conditions.
The Urethra Chorus(1) The fluid is urine. The storage chamber is the urinary bladder.

(2) These numbers are approximate averages. As with almost any biological measurement, there is natural variation from person to person.

(3) The male urethra goes through the penis, which extends its length considerably.

(4) This line is referring to the fact that urine is created out of components of blood. Water and small solutes in the plasma of the blood are filtered out of the glomeruli (capillary beds in the kidney) and into the glomerular capsule (Bowman's capsule). The composition of this filtrate is then adjusted via reabsorption and secretion along the renal tubule and collecting duct, at the end of which the urine has reached its final composition.

(5) A pale yellow color is normal. A dark, rich color might indicate dehydration or other problems.
The Uterus(1) The myometrium ("myo" means "muscle").

(2) The outermost layer -- the perimetrium or serosa.
Vasoconstriction(1) The autonomic nervous system includes the sympathetic nervous system, the branch responsible for "fight-or-flight" responses. In this way, the autonomic nervous system really is "sympathetic to your plight."

(2) Noradrenaline, produced by the adrenal gland.

(3) Catecholamines are a group of compounds including epinephrine (adrenaline) and norepinephrine (noradrenaline). Alpha-one adrenergic receptors bind to these compounds, but bind more strongly to norephinephrine than to epinephrine.

(4) Calcium causes phosphorylation of smooth muscle's myosin, which allows this myosin to bind to actin.

(5) "Vaso" means "vessel." "Myo" means "muscle." "Baro" means "pressure."

(6) If blood pressure falls, you will faint (i.e., "fall down down down"). Vasoconstriction helps maintain blood pressure so that you don't faint.
Veins(1) From the heart, blood travels first through the arteries, then smaller arterioles, then still-smaller capillaries, and then venules before reaching the veins.

(2) Words that sound the same as "vein" are vain -- the phrase "in vain" means "failing to achieve the desired outcome" -- and vane, as in a weather vane that moves in the breeze.

(3) The two main components of blood are cells and plasma. They are commonly separated by centrifugation.
Visual Pathway Branchpoints(1) The optic nerve is cranial nerve II.

(2) The optic nerve is the name given to the nerve leading away from the retina of the eye. The intersection of the left and right optic nerves is called the optic chiasm. The nerves leading away from the optic chiasm toward the brain are called the optic tracts.

(3) The inferior colliculus processes auditory (sound) information.

(4) The lateral geniculate nucleus (LGN).
Voltage-Gated Sodium Channel(1) This presumably refers to neurotransmitters reaching the post-synaptic neuron and binding to receptors there after swimming across the "ocean" of the synaptic cleft.

(2) PSP = Post-Synaptic Potential.

(3) When the channel opens, ions enter the cell (rather than exiting), which is consistent with the channel being for sodium (rather than, say, for potassium). Likewise, the spreading of the charge along the axon sounds like the action of sodium channels.
The Waltz of the Ribosomes(1) DNA to RNA = transcription; RNA to protein = translation.

(2) No, there is no stop codon here. The six RNA codons code for threonine, glutamate, proline, tyrosine, tryptophan, and serine, respectively.

(3) Genetic sequences are generally written 5' to 3'. If the DNA sequence and RNA sequence were both enumerated in this way, their complementarity would not be as obvious.

(4) The poem is written in a triplet or "waltz" rhythm because the genetic code is based on triplets. That is each set of three bases encodes one amino acid.
Welcome to the Human Body!(1) An organ system is a group of related organs working together to achieve a common function.

(2) Answers will vary, but the organ systems are listed in the order that is typical of most current human A & P textbooks (Amerman, Hole/Shier, Marieb, Martini, etc.).

(3) Answers will vary.

(4) There is overlap, since some organs contribute to more than one organ system. For example, the pharynx is part of both the respiratory and digestive systems, and the pancreas is part of both the digestive and endocrine systems.

(5) Answers may vary, as this is a question of opinion, but the songwriter meant the phrase in at least two parallel ways. The phrase is meant as a sincere and enthusiastic welcome to the academic study of the human body. However, students have been living with their bodies since birth, so the idea of introducing them to something with which they are already so familiar is a bit whimsical.

(6) Answers will vary. One could argue that "lymphatic-slash-immune" is ambiguous; does that refer to a single organ system that goes by two names, or something else? The lymphatic system and immune system certainly overlaps but are not exactly the same, and some argue that the immune system is not a true organ system but rather a functional system comprised anatomically of components of other organ systems.
When The Milk Comes In(1) The anterior pituitary (adenohypophysis) secretes prolactin, while the posterior pituitary (neurohypophysis) secretes oxytocin. In addition, it appears that in many animals, oxytocin is sent from the hypothalamus to the anterior pituitary as a prolactin-releasing factor (PRF).

(2) In general, an acinus is a cluster of epithelial cells. The mammary glands have many acini consisting of cuboidal epithelial cells that secrete milk into the "cul-de-sacs" of the acini.
Where Are Your Fontanelles, Philip Crowther?(1) Fontanelles allow the cranium to compress as it goes through the birth canal during delivery, and to expand as the brain grows in early childhood.

(2) By age 2 the fontanelles are generally gone.
Where Is That Sound?(1) LSO = Lateral Superior Olive; MSO = Medial Superior Olive.

(2) Binaural = from both ears.

(3) Spikes = action potentials.
Where Osmolarity is High(1) Osmolarity is the total concentration of all solutes (charged and uncharged). Water is attracted to solutes; that is, it diffuses from regions of lower osmolarity to regions of higher osmolarity.

(2) Water can only diffuse out of the collecting duct if water channels -- aquaporins -- are present in the membranes of the cells lining the collecting duct.

(3) Aquaporins are the protein pores referred to in the previous question.

(4) ADH is antidiuretic hormone (sometimes called vasopressin). It increases the installation of aquaporins in the membranes of the epithelial cells lining the collecting ducts, thus allowing water to escape the collecting duct and pass into the interstial fluid and, eventually, the blood.

(5) If you are "missin' water," you are dehydrated, so your body conserves the water that it still has, peeing out as little fluid as possible.

(6) Aquaporins are also found in many other cells, including red blood cells. Most relevant here is their presence along the descending limb of the loop of Henle. These aquaporins are NOT regulated by ADH; they are present all the time.

(7) The loop of Henle sets up and maintains the osmolarity gradient that ultimately pulls water out of the collecting duct so that it is not lost in the urine. However, water's exit from the collecting duct depends on aquaporins, as noted above, which are made and inserted into the cell membrane in response to ADH.
You've Got Edema!(1) Hydrostatic pressure is essentially the "weight" of the fluid; hydrostatic pressure within blood vessels is called blood pressure. Osmotic pressure is the force by which water is attracted from solutions of lower osmolarity to solutions of higher osmolarity.

(2) The interstitial space is the area outside of a blood vessel and between the cells of a tissue through which the blood vessel passes.

(3) The lymphatic ducts eventually return the fluid to the circulatory system. (Specifically, the thoracic duct empties into the left subclavian vein, and the right lymphatic duct empties into the right subclavian vein.)

(4) FEMA is the Federal Emergency Management Agency, an office of the United States government; it responds to natural disasters such as floods. FEMA is mentioned here not only because it rhymes with edema, but because edema is a flood of sorts, i.e., an unwanted accumulation of water.