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BIOL 241 – Spring 13
Exam 5 – 100 pts
Instructions: Please type your answers on a numbered MS Word, rtf, open office, or pdf
document. (If you don’t have acces to any of these programs, you can cut and paste your
answers into an email). Save the document as “Your name – Biology 241 Final Exam” and
send it to me at [email protected] by 11:59pm on Friday, Dec 14th.
You may use your book, notes, or other resources to answer the questions but there are two
absolute rules: 1. No collaborating with other students or anyone else – this test should be
completed independently. 2. No cutting and pasting from other sources – use your own
words. Violation of either rule will result in loss of points and possible failure of the exam.
Very Short Answer Questions: Answer questions 1-12 with one word or phrase as needed.
(2 points each)
1. What is the net (total) electrochemical force (its size and direction) acting on Na+ at
the resting potential (-70mV)?
2. What is the net (total) electrochemical force (its size and direction) acting on Na+ at
the peak of the action potential (+30mV)?
3. What is the net (total) electrochemical force (its size and direction) acting on Na+ at
the equilibrium potential for sodium (+66mV)?
4. Action potentials are all the same. So, how do neurons signal that a stimulus is of great
intensity (like a bright light or firm pressure)?
5. Where along the cell does a presynaptic input (synapse) have the greatest effect on
determining whether a postsynaptic neuron fires an action potential or not?
6. Head trauma often leads to greatly increased pressure inside the skull, so doctors must
drill into the skull and drain off some CSF to reduce the pressure. Where do they need
to drill to in order to do this?
7. During brain surgery to resect (remove) a tumor, surgeons “map” the brain by
stimulating different regions of the cerebral cortex while the patient is awake and
observing how the patient responds. If the surgeon stimulates the brain and the patient
moves his left arm, where in the brain must the doctor be stimulating?
8. In an adult human, what would you find if you drilled into the L4 level of the vertebral
column?
9. Where would you find the cell bodies of the cells responsible for motor function in the
brain (aka. the upper motor neurons)?
10. In all the afferent sensory pathways below the neck, where is the cell body of the first
order neuron found?
11. The regions of skin that are monitored for sensation by a pair of spinal nerves at a
specific level in the spinal cord (e.g. T7) are called what?
12. Why don’t you feel the shirt you are wearing (unless you focus your attention on it - like
you are probably doing right now)? There are two possible reasons that we talked about,
you just need to provide one of them.
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Short Answer Questions Answer questions 13-20 with 1-2 sentences as needed
(2 points each)
13. In the popular press, you may hear the statement that “M.S. is a disease that attacks the
nerves.” Is this a true statement? Briefly explain.
14. If you had a brain tumor that affected the cerebral cortex and the neurosurgeon said she
was going to operate based on textbook descriptions of the locations of functional brain
areas, what would you tell her and why?
15. What would be the result of an injury to the dorsal horn of the spinal cord in the lumbar
region? Would someone still have reflexes in the affected region?
16. If someone has a brain injury that destroys the primary motor cortex, will they still have
spinal reflexes such as the stretch reflex discussed in class? Why or why not?
17. Which region of the spinal cord has the most (largest amount of) white matter? Why?
18. At the resting potential, which ion is a cell most permeable to? Why is the cell most
permeable to that ion?
19. Explain why an action potential normally does not flow backwards, toward the cell body.
Would it be different if you injected Na+ into the middle of the axon? Why?
20. What was your favorite topic that we discussed in this class? Why?
Essay Questions (12 points each; you will answer five total)
Answer the following question:
A: Explain the reason that the resting potential for neurons is around -70mV. Be sure to
include the roles of the K+ and Na+ concentration gradients, electrical forces, passive
ion channels and the relative permeabilities of K+ and Na+. Now, say that an alien race
was discovered from a distant galaxy. Their cells have a higher concentration of Na+
inside than outside their cells and a higher concentration of K+ outside than inside. If
this race’s neurons had the same relative permeability to K+ and Na+ at rest that Earth
organisms have, what might an approximate value of the resting potential of these
alien’s cells be? Why?
Choose FOUR of the following seven questions (B – H) to answer. REMEMBER TO
PUT THE LETTER OF THE OPTION YOU CHOOSE AT THE START OF EACH
OF YOUR ANSWERS.
B: The local anesthetics your dentist uses such as Novocaine work by blocking voltagegated Na+ channels from opening. Explain why this is effective in preventing the
transmission of pain. Include a description of how Na+ and K+ channels normally
function at all the points along the action potential graph (and the reason those channels
open when they do). Does Novocaine block sensation or perception? Explain. Why is it
not a good idea to give a systemic (whole body) dose of Novocaine?
C: Describe how an action potential propagates along a myelinated and an unmyelinated
axon, including how the potential is spread along the membrane. What two benefits do
myelinated axons have over unmyelinated ones? Provide one way in which a
myelinated axon is similar to an electrical wire and one way in which an axon is
different than a wire. How are these two processes similar and how are they different?
Why does multiple sclerosis (MS) prevent transmission in myelinated axons (that is,
why can’t these axons just propagate the action potential in the same way that an
unmyelinated axon does)?
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D: The central nervous system (CNS) is composed of billions of discrete cells that are not
directly connected but are instead connected by synapses, which require
neurotransmitters to pass a signal between cells. Why is this an advantage over a CNS
in which all the cells are directly connected? That is, what do we gain by having our
brains made up of individual cells that don’t automatically fire an action potential when
they are stimulated?
E: What are the consequences of a spinal injury in the thoracic region of the spinal cord if
the damage is to the gray matter? What about a complete transection of the white matter
in the thoracic region? What body regions and functions that would be disrupted? Why
is a white matter injury in the upper cervical region worse than one lower down in the
cord? How do white matter injuries affect reflexes? How do gray matter injuries affect
reflexes?
F: Explain the relationship between cortical representation in the primary sensory cortex
and receptive field size. Is there also a relationship between the size of the body part
and cortical sensory representation? Then, explain the relationship between cortical
representation in the primary motor cortex and motor unit size. Again, is there a clear
relationship between the size of a body part and cortical motor representation? Finally,
what would you expect the cortical sensory and motor representation to be if we had a
sixth finger that had high touch sensitivity and very good fine motor control?
G: fMRI (functional magnetic resonance imaging) is a relatively new technology that
allows researchers to see which areas of the brain are receiving the most blood flow
when a subject is performing an activity. Why would blood flow to particular parts of
the brain change when the brain is performing specific tasks? That is, what does this
tell you about the functional division of the brain? What is in the blood that specific
brain regions need when they become more active? What do active neurons require so
much energy (what is using up all the energy)?
H: Describe what happens to people who have Parkinson’s disease. What cells are affected
and where do they project to? What is the consequence on motor behavior and why?
How does PD relate to Huntington’s disease (aka Huntington’s chorea)? One
experimental treatment for PD involves injecting stem cells that produce a particular
neurotransmitter into the brain: what neurotransmitter do you think it is and where do
you think surgeons implant the cells?
Extra Credit Question
As humans grow from babies to adults, our brains become less and less able to repair
themselves after brain injury. Though our brains retain an amazing capacity for change,
they no longer are able to repair injuries caused by a stroke, head trauma, or neurological
disease. Why do you think is? Provide an explanation for why this occurs. Your
explanation can be either evolutionary (that is why hasn’t evolution led to humans whose
adult brain can repair itself?) or physiological (what important changes might cause this
transition from babies to adults?). HINT: Don’t just copy something from the internet or
you’ll get no points.
Take a deep breath.
Enjoy the break!
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