121. What is the role of the myelin sheath? Describe the two types of cells that make the myelin sheath.
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122. Using motor and sensory neurons as examples, explain the difference between afferent and efferent.
| ANSWER: | An afferent axon brings information into a structure whereas an efferent axon carries information away from a structure. Sensory neurons detect sensory information (e.g., light, pressure) and convert that energy into neural impulses. That information is sent to the brain via afferent pathways. Motor neurons carry information from the brain and spinal cord to muscles and glands via efferent pathways. |
123. Mr. Doyal has been diagnosed with Parkinson’s disease (which is the result of damaged dopamine signaling). Instead of giving him dopamine, his doctors have given him a derivative of dopamine called L-DOPA to take. Given what you know about substances entering the nervous system, why do you think Mr. Doyal was given L-DOPA instead of dopamine?
ANSWER: Mr. Doyal was likely given L-DOPA instead of dopamine because of the blood-brain barrier. Dopamine cannot cross the blood-brain barrier so giving it to Mr. Doyal would not relieve his symptoms. His doctors gave him L-DOPA since it would cross the blood-brain barrier and could then be converted into dopamine in the brain.
124. Jena has been assigned a project for school where she is asked to demonstrate the activity of the sodium-potassium pump using yellow marbles to represent sodium and green marbles to represent potassium. How many marbles will Jena need and explain how she could demonstrate the movement of the ions through the pump?
ANSWER: Jena needs to explain to the class that the sodium-potassium pump pushes three sodium ions out of the cell and brings in two potassium ions. So she will need three yellow marbles to represent the sodium and two green marbles to represent the potassium. She should show that the pump moves the three yellow marbles out of the cell and brings in the two green marbles.
125. Bryson is having a cavity filled at the dentist and was given Novocain to prevent feeling any pain. Later, he explains to his roommate how the Novocain worked to stop the pain. What did he tell his roommate?
| ANSWER: | Bryson told his roommate that Novocain works by binding to the sodium channels on the axons of neurons and prevents sodium from entering. Because sodium cannot enter the axon, the neuron cannot produce an action potential. Therefore, the pain message was never sent to Bryson’s brain from his mouth. |