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Biology 449 - Animal Physiology |
Fall 2006 |
Answers in italics
Fill in your scantron form as follows:
· Write and bubble in your name in the upper left (last name first).
· Follow any additional instructions provided in class.
· Sign your form in the upper right.
Multiple choice: As always, choose the best answer for each multiple-choice question. Answer on your scantron form. Each question is worth 3 points.
1. Claude Bernard referred to the blood and interstitial fluids of the vertebrate body as
a. the extracorporeal fluids.
b. the internal fluids.
c. the internal environment.
d. the biological bilge waters.
e. soup.
2. In biological systems, regulation is normally achieved through
a. conscious control.
b. negative feedback loops.
c. positive feedback loops.
d. eliminating influx and efflux.
e. allowing equilibration with the environment.
3. In the system that increases blood calcium levels when they drop too low, the parathyroid hormone that triggers increased calcium release from bones serves as the
a. sensor.
b. afferent pathway.
c. integrating center.
d. efferent pathway.
e. effector.
4. Which of the following might reasonably be expected to induce an increase in cutaneous vasoconstriction?
a. a decrease in body temperature.
b. a decrease in environmental temperature.
c. a decrease in body temperature setpoint.
d.
Two of the above might induce increased shivering cutaneous vasoconstriction. [a and b]
e.
All of the above might induce increased shivering cutaneous vasoconstriction.
Sorry - I rewrote this one the morning of the exam, and while the question got changed from "shivering" to "cutaneous vasoconstriction," the answers in d and e did not. The changes above show how it should have read. Everyone got credit for this question.
5. While remodeling your home, you hire Done-Rite Discount Heating & Cooling to install a new furnace and air conditioner. Unfortunately, they wire up the thermostat so that if the air temperature is higher than the temperature you set, the heater turns on, and if it’s lower, the air conditioner turns on. This is an example of
a. a negative feedback loop.
b. a feedforward system.
c. a positive feedback loop.
d. conformation.
e. the kind of wiring job Dr. Cullum would do.
6. The phrase that best describes the concept of secondary active transport is
a. “family-friendly.”
b. “two-for-one sale.”
c. “unlimited free minutes.”
d. “pump now, pay later.”
e. “channel-tastic.”
7. Water does not move across cell membranes by
a. simple diffusion across the lipid bilayer.
b. permeation through channel proteins.
c. transport via carrier proteins.
d. Water only moves across cell membranes by one of the above routes.
e. Water does not move across cell membranes by any of the above routes.
8. The region of the central nervous system that has primary control of the heartbeat is the
a. brainstem.
b. cerebellum.
c. cerebral cortex.
d. spinal cord.
e. thalamus.
9. In the Nernst equation, the equilibrium potential across a membrane is influenced by all of the following except
a. ion valance.
b. ion concentration differences.
c. ion permeability.
d. temperature.
e. All of the above are included in the Nernst equation.
10. In most vertebrate cells, the ion with the greatest influence on normal membrane potential is
a. calcium.
b. chloride.
c. phosphate.
d. potassium.
e. sodium.
11. Which of the following is not a characteristic of action potentials?
a. They exhibit a consistent peak depolarization.
b. They have a consistent duration.
c. They include a period of hyperpolarization.
d. One action potential can be followed immediately by another.
e. They do not occur in all cell membranes.
12. A voltage-gated sodium channel is molecularly engineered so that it lacks an activation gate, and is then embedded in a cell membrane. The membrane potential is first set below threshold, then raised above threshold for a number of milliseconds, and then lowered back below threshold again. Which of the following best describes the likely pattern of opening and closing in the altered channel, assuming the inactivation gate behaves normally?
a. The channel starts closed and stays closed throughout the voltage changes.
b. The channel starts open and stays open throughout the voltage changes.
c. The channel starts closed, opens once the voltage goes above threshold, and then closes again when the voltage goes back below threshold.
d. The channel starts closed, opens once above threshold, and then stays open back below threshold.
e. The channel starts open, closes once above threshold, and then opens again back below threshold.
13. The direct trigger for the release of synaptic vesicles from the cytoskeleton in an axon terminal is
a. an influx of calcium ions.
b. activation of voltage-gated docking proteins.
c. activation of G-protein complexes.
d. depolarization of the vesicle membrane.
e. contraction of the axon terminal.
14. Ligand-gated ion channels opened by the arrival of a neurotransmitter normally close again fairly quickly. Which of the following is not a mechanism promoting this closure?
a. Diffusion of the neurotransmitter out of the synaptic cleft.
b. Enzymatic breakdown of the neurotransmitter.
c. Reuptake of the neurotransmitter by the presynaptic neuron.
d. Closure of inactivation gates in the ion channels.
e. All of the above promote channel closure in post-synaptic neurons.
I meant to write “voltage-gated inactivation gates” for d. Since we never discussed how ligand-gated channels actually close, I gave credit for d or e here.
15. Which of the following is an example of a neuroactive peptide?
a. Endorphins
b. Epinephrine
c. Dopamine
d. GABA
e. Glutamate
16. A general name for sensory cells showing very rapid adaptation is
a. interoceptive receptors.
b. nociceptors.
c. phasic receptors.
d. proprioceptors.
e. tonic receptors.
17. In cutaneous sensory cells that detect pressure changes, which of the following is likely to be found in the receptor membrane region?
a. G-protein-controlled ion channels.
b. ligand-gated ion channels.
c. mechanically-gated ion channels.
d. proton channels.
e. voltage-gated ion channels.
18. For which of the following is there no known taste receptor?
a. Protons
b. Sodium
c. Sugars
d. Amino acids
e. Fats
19. The correct function of the semicircular canals depends on
a. hair follicle receptors.
b. otoliths.
c. G-protein complexes.
d. the inertia of the fluid they contain.
e. rapid adaptation.
20. The transducin in rod cells is a particular type of
a. channel protein.
b. G-protein.
c. ionotropic receptor.
d. secondary messenger.
e. photon-absorbing molecule.
Short answer: Write a concise answer to each of the following questions. Your answers should fit in the spaces provided. Diagrams may be used but must be accompanied by written explanations. Each question is worth 8 points.
21. Consider two solutions, A and B, of equal volume and separated by a membrane. Side A contains solute X at 500mM and solute Y at 400 mM, while side B contains solute Z at 1000mM. X, Y and Z are all uncharged and none of them dissociate.
a.
If the membrane was permeable only to water, in which direction (if
either) would water move, and why?
The total osmolarity on side A is 500 + 400 = 900 mOsm, on side B it is
1000 mOsm. That means side B is hyperosmotic relative to side A and will draw
water in along its osmotic gradient.
b.
If instead the membrane was permeable only to X, how would X move,
and what would be the expected equilibrium state?
Since X is uncharged it can diffuse independently of other particles. It
will move down its concentration gradient from side A to side B until it reaches
a concentration equilibrium. Since the water volume is equal on both sides,
this will be approximately 250 mM on each side.
c.
How would your answer to question b above change if X was a
charged particle?
This phrasing was poorly thought through on my part, but there are two
ways you could have interpreted this question. The first way is that the system
starts with charge balance on side A. In this case, as the concentration gradient
starts to drive X across the membrane, an excess of positive charge will build
up on side B and oppose further diffusion while X is still almost all on side
A. The other interpretation is that, with X as the only charged particle,
it can diffuse to equal concentration on both sides since this will also result
in equal charge on both sides.
22. Two parts:
a.
Describe the process by which action potentials are propagated in an
unmyelinated axon. You do not need to discuss all the details of the
action potential itself.
Once a portion of the axon is raised above threshold and an initial action
potential occurs, it will trigger further AP's along the axon. The depolarization
of the initial AP raises the membrane potential of adjacent regions of the
membrane (via very rapid current flow); the amount of depolarization decreases
with distance from the original AP. In all regions of the membrane raised
above threshold potential, additional AP's will be triggered. These AP's then
trigger additional AP's further along the axon, etc. The rate at which AP's
propagate is determined by the furthest distance from each AP that is depolarized
above threshold. Current carries further in axons with better cable properties,
and thus action potentials propagate more quickly.
b.
How does propagation differ in a myelinated axon?
In myelinated axons, glial cells wrapped around the axons provide lengths
of insulation that alternate with regions of uncovered axon called the nodes
of Ranvier. The insulated regions have much better cable properties, and thus
when an AP occurs it can depolarize regions much further along the axon above
threshold. This greatly increases the rate of propagation of action potentials
in myelinated axons. The nodes of Ranvier are essential, however, because
myelinated regions of the axons are physically separated from the extra-cellular
fluid and thus cannot generate AP's. AP's do occur at the nodes, with the
AP at each node depolarizing the membrane above threshold at the adjacent
node. Since only the nodes show AP's, the type of propagation is referred
to as saltatory or jumping conduction.
23. Two parts:
a.
Explain what is meant by neuronal integration, and describe the difference
between temporal summation and spatial summation of post-synaptic potentials.
Neuronal integration refers to the summation of effects of all pre-synaptic
neurons on the membrane potential of the post-synaptic neuron. The resulting
membrane potential determines if and how frequently action potentials occur
in the post-synaptic neuron.
In temporal summation, action potentials arrive frequently enough at
a pre-synaptic neuron that their effects on the post-synaptic neuron can sum.
That is, the membrane is still somewhat depolarized (in the case of excitatory
post-synaptic potentials) or hyperpolarized (in the case of inhibitory post-synaptic
potentials) from the effects of the neurotransmitter released by one AP when
a second AP arrives and releases more NT, which further depolarizes or hyperpolarizes,
respectively, the membrane.
In spatial summation, AP's arrive at multiple pre-synaptic neurons
at approximately the same time, so that the effects of the released NT on
post-synaptic potential can add together. These psp's may be any combination
of excitatory and inhibitory.
b.
Give an example of a change in ion influx or efflux that could cause
a post-synaptic potential that is
Excitatory – Examples include Na+ and Ca2+ influx
Inhibitory – Examples include K+ efflux and Cl-
influx
24. Describe the process of lateral
inhibition, explaining how it helps augment perception of a mild sensory stimulus.
Lateral inhibition is a mechanism that allows the more effective perception
of a relatively mild stimulus. Sensory neurons innervate secondary afferent
neurons in two ways. They excite their "own" secondary neurons,
but also excite neurons that inhibit adjacent secondary neurons. As a result,
if a receptor is stimulated, it not only increases the AP frequency in its
secondary neuron, but also decreases the AP frequency in surrounding secondary
neurons. (All these neurons are normally producing AP's at some background
rate.) This means that the apparent intensity of the stimulus is increased
relative to that of the nearby receptors, with a greater differential than
would be seen without lateral inhibition.
25. Two parts:
a.
Describe the general mechanism by which the pressure waves produced
at the oval window are transduced into action potentials by the cochlea.
Pressure waves produced at the oval window travel through the fluid filling
the scala vestibuli of the cochlea. High pressure events push down on the
scala media (via the vestibular membrane), while low pressure events tend
to cause it to rise. Within the scala media are the organ of Corti, which
rests on the basilar membrane and contains sensory hair cells, and the tectorial
membrane, to which the sterocilia of the hair cells are attached. When the
scala media is moved up and down by the pressure changes in the scala vestibuli,
the mechanical arrangement is such that the tectorial membrane moves laterally
relative to the organ of Corti, bending the cilia of the hair cells. This
bending causes the hair cells to de- and hyperpolarize (due to the activity
of mechanically-gated K+ channels), changing the amount of neurotransmitter
released by the hair cells. This change in NT release in turn changes the
AP frequency in the afferent neurons that synapse with the hair cells.
b.
How is the frequency of a sound distinguished?
The acoustic properties of the
cochlea are such that high frequency sounds cause strong movement of the scala
media at the base of the cochlea, while low frequency sounds most strongly
affect the tip of the cochlea, with a contimuum of frequency sensitivities
in between.