Question

1. The release of the transmitter is directly governed by

1. Sodium influx
2. Sodium efflux
3. Potassium influx
4. Potassium efflux
5. Calcium influx

(Please note: please describe the process of neurotransmitter release in detail.)

2. On a myelinated fiber, where is the site of the fastest conduction velocity? Why?

Answer 1

1.

D. Calcium channel.

Step 1.

Depolarization (action potential) in presynaptic cell. Results in calcium channels opening at axon terminal.

Step 2.

Calcium influx into presynaptic cell occurs

Step 3.

Calcium mobilizes synaptic vesicles.

Step 4.

synaptic vesicles fuse to presynaptic terminal bouton membrane.

Step 4.

synaptic vesicles fuse to presynaptic terminal bouton membrane.

Step 5.

Exocytosis occurs.

Step 6.

Neurotransmitter substance diffuses across the synaptic cleft.

Step 7.

Neurotransmitter attaches to receptor sites on post synaptic membrane.

Step 8.

Neurotransmitter affects the chemical gates of the postsynaptic membrane, changing membrane permeability.

2.

Node of Ranvier.

In myelinated axons, conduction is fast
(saltatory conduction). Myelin keeps current in
axons (voltage doesn't decay much). APs are
generated only in the myelin sheath gaps and
appear to jump rapidly from gap to gap.