Nerves Part 3

Question 1

What cells are targets in multiple sclerosis?

Answer 1

Oligodendrocytes; They also secrete inhibitory factors that limit the ability of CNS axons to regenerate

Question 2

Whats the function of Astrocytes?

Answer 2

Maintain the ionic environment of neurons during their electrical activity; Help remove neurotransmitter from synaptic cleft. Can be a guide for growing axons.

Question 3

Discuess Amyotrophic lateral sclerosis (ALS).

Answer 3

Astrocyte function is impaired, thus prolonging the action of the neurotransmitter glutamate on GSEs. Neurons get over-excited.

Question 4

What are the effects of damage to a neuron?

Answer 4

Axon damage will not necessarily cause death, but damage to the soma will.

Question 5

Explain the regrowth of damaged neurons.

Answer 5

New dendrites grow into regions of dying neurons.

Question 6

What happens when a cell reaches threshold?

Answer 6

The voltage gated sodium channels open; Both gates must be open to have depolarization.

Question 7

Describe the state of the sodium channels at resting membrane potential, depolarization, just after the peak and repolarization.

Answer 7

1. Rmp: A is closed, I is open
2. Threshold: A is open, I is open
3. Just after peak: A is open, I is closed
4. Repolarization: A is closed, I is open

Question 8

What happens to the voltage gated potassium channels in depolarization?

Answer 8

They open but after a small delay.

Question 9

When these channels open, do they all open at once?

Answer 9

NO; it is a graded response.

Question 10

Describe the state of the potassium channels at resting membrane potential, depolarization, just after peak and repolarization.

Answer 10

1. Rmp: Channel is closed
2. Threshold: Channel is closed.
3. Just after peak: Channel is OPEN
4. Repolarization: Channel is closed

Question 11

Discuss the cell’s permeability to potassium during resting membrane potential.

Answer 11

Many potassium leak channels are open; Giving potassium a high permeability.

Question 12

Discuss the refractory period.

Answer 12

A time period in which an action potential can’t be initiated; Since most sodium channels are inactivated, sodium can’t go in the cell. This sets the maximum frequency at which action potentials can form.

Question 13

How do local anesthetics work?

Answer 13

They block the formation of action potentials by blocking the opening of voltage gated sodium channels.

Question 14

Explain an action potential

Answer 14

1. Sodium enters an axon to make a small part positive instead of negative.
2. They repel each other and spread into neighboring bits of axon.
3. Oncoming positive charges depolarize this bit of axon and reaches threshold; Voltage channel opens and AP happens HERE.
4. Repeat

Question 15

What keeps an action potential from going backward?

Answer 15

Sodium channels are inactivated in the axon region behind the current action potential.