Lecture 6 (AP, Synapse neurotransmitters)

Question 1

Explain the steps of an action potential

Answer 1

1. A stimulus triggers Na+ channels to open and allow inward Na+ diffusion. This causes the membrane to depolarize.
2. As the threshold potential (-70 mV) is reached, voltage-gated Na+ channels open
3. As more Na+ enters the cell through voltage-gated Na+ channels, the membrane depolarizes even further.
4. The magnitude of the action potential peaks (at +30mV) when voltage gated Na+ channels close.
5. Repolarization begins when voltage-gated K+ channels open, allowing outward diffusion of K+
6. After a brief period of hyperpolarization, the resting potential is restored by the Na+/K+ pump and the return of ion channels to their resting sate.

Question 2

What’s the difference between absolute and relative refractory period?

Answer 2

• Absolute refractory period cannot generate AP (during spike (depolarization))
• Relative refractory period needs larger stimulus for immediate 2nd AP (during hyperpolarization)

Question 3

What are the 2 ways to increase velocity of conduction?

Answer 3

1) Axon has a large diameter (larger wire)
2) Axon is myelinated (insulated)

Question 4

Why are Myelin sheaths useful?

Answer 4

Myelin sheaths produced by oligodendrocytes and schwann cells insulate axon an improve conduction

Question 5

Describe what the Nodes of Ranvier are

Answer 5

Gaps in myelin, sites for action potential

Question 6

Explain continuous conduction

Answer 6

One after the other
AP moves along the axon like a domino
Slow

Question 7

Explain Saltatory conduction

Answer 7

Leaping
AP jumps from one node of Ranvier to the next node
Very fast

Question 8

What is multiple sclerosis?

Answer 8

• Neurological disorder involving the progressive loss of myelin sheaths (from scars)
• Slows and short circuits conduction of nerve impulses
• Symptoms: heaviness, weakness of muscles, double vision
• Cause: autoimmune

Question 9

Define synapses

Answer 9

Synapses are intercellular junctions

Question 10

What’s the difference between a presynaptic and postsynaptic cell?

Answer 10

• Presynaptic cell transmits action potential
• Postsynaptic cell receives it

Question 11

What are the 3 structures that make up a chemical synapse?

Answer 11

1) A synaptic knob
2) A synaptic cleft
3) The plasma membrane of postsynaptic neuron

Question 12

Describe the steps in the transmission of action potentials

Answer 12

1) Voltage-gated Ca2+ channels open and allow extracellular Ca2+ to enter into the presynaptic cell

2) The Ca2+ triggers the rapid exocytosis of neurotransmitter molecules from vesicles in the knob

3) Neurotransmitter diffuses into the synaptic cleft and binds to receptors initiating an action potential int he postsynaptic neuron.

Question 12

Describe the synaptic knob

Answer 12

The synaptic knob contains synaptic vesicles with neurotransmitters

Question 12

What is the fate of neurotransmitters?

Answer 12

After synaptic transmission, the signal must be stopped by removing neurotransmitters form the synaptic cleft.

Therefore, many neurotransmitters are:
- Transported back into the presynaptic neuron in a process called reuptake
- Go through enzyme degradation (breakdown)
- Diffuse out of cleft and into glial cells

Question 12

What are the 2 types of neurotransmitters?

Answer 12

• Excitatory: depolarization + new action potential
• Inhibitory: hyperpolarization = harder to generate new AP