Module 4: Nerves

Question 1

Explain the difference between excitable cells and non excitable cells

Answer 1

Excitable cells can have action potentials and have a lower resting membrane potential than non-excitable cells. Examples of an excitable cell include: neurons and muscle cells. An example of a non-excitable cell is a red blood cell

Question 2

Draw and label the soma, axon, dendrites, axon hillock, myelin sheath, nodes of Ranvier, terminal boutons, typical neuron

Answer 2

EDIT LATER

Question 3

Describe voltage-dependent sodium and potassium channels

Answer 3

Found: nerve and muscle
They are essential for generating an action potential
Open when the cell is more positive (depolarization)

Question 4

Draw a diagram of an action potential and the permeability changes of sodium, potassium. Use it to describe the mechanisms of the action potential

Answer 4

UPDATE AFTER

Question 5

What is the absolute refractory period?

Answer 5

The time period when an action potential is in progress and inactivation is closed. The channel won’t open regardless of the strength of stimuli

Question 6

What is the relative refractory period?

Answer 6

The timing right before an action potential where it could be possible for another action potential to be triggered but it would require a high stimulus.

Question 7

Action potential:

Describe the conventional direction of current flow

Answer 7

The direction goes from areas that are more positive to areas that are negative

• remember opposites attract
• current is carried by positive ions (Na+)

Question 8

Describe how an action potential propagates Dow’s a cell membrane of an excitable cell

Answer 8

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Question 9

Describe the saltatory conduction of action potentials in myelinated fibers. What are the advantages of saltatory conduction?

Answer 9

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Question 10

Describe what is meant by an all or nothing principle of action potential conduction

Answer 10

A certain threshold (usually -55mV) has to be met to trigger an action potential. If it is less, it won’t be enough to trigger one.

Question 11

depolarization

Answer 11

when the cell becomes way more positive (+35mV)

caused by the opening of sodium voltage gated channels

Question 12

repolarization

Answer 12

when the cell comes back down to normal conditions (-70mV). triggered by the opening of the potassium voltage gated channels

Question 13

overshoot

Answer 13

this is the top of the parabola when the cell is doing from depolarization to repolarization.
This happens when the sodium voltage gated channels start to close and the potassium voltage gated channels start to open.

Question 14

hyperpolarization

Answer 14

This is the period of the action potential where the cell becomes more negative than usual (approximately -90mV). This happens because it takes longer for the potassium voltage gated channels to close, letting more potassium leave.

Question 15

What happens at the neuromuscular junction?

Answer 15

1. action potential reaches the presynaptic axon terminal
2. voltage gated Ca++ voltage gated channels are triggered to open with the presence of the action potential
3. Ca++ comes in and releases acetylcholine from the vesicles. (acetylcholine is a neurotransmitter)
4. Acetylcholine diffuses across the synaptic cleft.
5. acetylcholine binds to receptors on the postsynaptic muscle fiber.
6. The binding of acetylcholine increases the permeability to ligand gated sodium ion channels
7. sodium enters the muscle cell through the ligand gated sodium ion channels
8. The increase of sodium in the muscle cell results in depolarization
9. once enough sodium enters the muscle cell an action potential is triggered.

Question 16

Resting Membrane Potential

Answer 16

• more negative on the inside (-70mV)
• Ions stay where they are because the membrane is selectively permeable
• changes when voltage gated channels open at depolarization

Question 17

How is the initial depolarization started?

Answer 17

The dendrites sense stuff

The receptors receive signals to let some ions in (usually sodium) which causes the action potential to happen

Question 18

How many gates are there in the sodium voltage gated channel

Answer 18

2

Question 19

Where are voltage gated channels located?

Answer 19

• end plate
• axon terminal
  Role: triggers end plate potential

Question 20

sodium ligand gated channel

Answer 20

• membrane protein!
• opening is triggered by acetylcholine
• it is located in the muscle end plate