Neurons+AG

Neuron Structure 1. Insert an image of the basic neuron structure that includes cell body, dendrites, and axon. p. 249

Myelin Sheath 2. Insert an image of a neuron with a myelin sheath.

3. What is the myelin sheath made of? Where is it located? What is its function? White, fatty material, derived from the membrane of shwann cells that forms a covering for nerve fibers.

4. What is the difference between the "gray matter" and "white matter" in the brain? p.249 The gray matter is gray because it contains no myelinated axons; the white matter is white because it does contain them.

5. What causes multiple sclerosis? P.249 Caused by loss of myelin from the axons and in an attack on the myelin by the body’s immune system.

Nerve Impulse p.250-252 5. Where are the sodium and potassium ions when the axon is at rest? What is the charge inside the axon? When at rest, sodium is outside the axon and potassium is more inside that causes polarization. There is a negative charge on the insides of the axon.

6. Which ions can cross the membrane and enter the axon? Potassium or sodium? Sodium flows into the axon across the membrane.

7. What happens to the charge inside the axon when sodium gates open? Where does sodium go? The membrane potential changes from -65mV to +40 mV. The charge of the axon changes from negative to positive which is called a depolarization.

8. What happens to the charge inside the axon when the potassium gates open? Where does potassium go? The potential changes from +40 to -65 as the potassium flows outside the axon.

9. Look at the graph on page 251. What do you think depolarization means? What do you think repolarization means? Depolarization is the charge changing from negative to positive; repolarization is when the inside of the axon resumes a negative charge as the potassium exits the axon.

10. What causes depolarization of the axon? Depolarization occurs when Na+ gates open and Na+ moves to the inside of the axon.

11. What causes repolarization of the axon? Repolarization occurs when K+ gates open and K+ moves to outside the axon.

12. What is an action potential? A rapid change in polarity across axonal membrane as the nerve impulse occurs.

13. How does the sodium potassium pump reestablish the resting potential during the refractory period? As soon as an impulse has passed by each successive portion of an axon, it undergoes a refractory period, during which the sodium gates are unable to open, ensuring that the action potential cannot move backward and instead always moves down an axon toward its branches.

14. What is a synapse? Each terminal lies very close to either the dendrite or the cell body of another neuron; this region of close proximity is called a synapse.

15. What is a synaptic cleft? A small gap that separates the sending neuron from the receiving neuron.

16. What is a neurotransmitter? Molecules called neurotransmitters, which are stored in synaptic vesicles in the axon terminals, carry out transmission across a synapse.

17. Since neurons don't touch, how is the signal from one neuron transmitted to another neuron? Transmission across a synapse from one neuron to another occurs when a neurotransmitter is released and diffuses across a synaptic cleft and binds to a receptor in the membrane of the receiving neuron.

18. Insert an image showing an action potential.

19. Insert an image showing a synapse.