Biology Assigment
ANP 213 BIOL 241 – Spring 22 Exam 5 – 100 pts Instructions: Please type your answers in a numbered Word, rtf, open office, pages, or pdf document (no pics or screenshots please). Upload your answers document to the Exam 5 assignment page found in module 11 of the course Canvas site by 11:59pm on Friday, June 17th. You may use your book, notes, or online resources to answer the questions but there are two absolute rules: 1. DO NOT discuss the exam or collaborate with other students or anyone else – this test should be completed independently. 2. DO NOT copy and paste from any other source (not even from the lecture notes) – you must 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 (size and direction) acting on Na+ at the resting potential (-70mV)? 2. What is the net (total) electrochemical force (size and direction) acting on Na+ at the peak of the action potential (+30mV)? 3. What is the net (total) electrochemical force (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. ( 3 ) 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 and why? Essay Questions (12 points each; you will answer five total) 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 otherwise 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? B: The local anesthetics your dentist uses such as lidocaine work by blocking voltage-gated 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 lidocaine block sensation or perception? Explain. Why is it not a good idea to give a large systemic (whole body) dose of lidocaine? Finally, what if a patient had a genetic mutation that prevented lidocaine from binding to their voltage-gated Na+ channels, but it did block their mechanically-gated Na+ channels; would it still work for this patient? What if it blocked chemically-gated receptors? C: Describe how an action potential propagates along a myelinated and an unmyelinated axon, including how the potential is spread along the membrane. How are these two processes similar and how are they different? 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. 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)? Finally, what if a drug was developed that allowed M.S. patients to use continuous propagation for all of their neurons all the time; what would be the impact of such a drug? 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? What are the drawbacks of the chemical synaptic nervous system? Can you think of an idea of how to organize a nervous system that might improve upon the one we already have? 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? Is the same true of gray matter injuries? How do white matter injuries affect reflexes? How do gray matter injuries affect reflexes? Finally, what is your idea of why the spinal cord is organized in the way it is (white matter surrounding gray matter)? 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? What would the sensory homunculus look like if there was perfect correlation between body part size and cortical representation? G: fMRI (functional magnetic resonance imaging) is a 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)? How can fMRI be used to help monitor recovery from brain injuries and stroke? Given the neuroplasticity of the brain, what would you expect to see in the fMRI of someone recovering from such damage? 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 (HD)? How does the number of CAG repeats in the HTT gene determine onset of HD and, as we discussed in class, is it really 100% penetrant? How is PD fundamentally different than the movement disorders ALS and polio? 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? If you could design the perfect treatment for PD, what would it be? I: As humans grow from babies to adults, our brains become increasingly 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 (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?). Enjoy the break!