Transmission across a Synapse

Question 1

Gist

Answer 1

Chemicals called neurotransmitters released from the ends of an axon

The neurotransmitters diffuse across the gap (known as the synaptic cleft) and attach to receptors on the membrane of the next neuron.

Question 2

Step 1)

Answer 2

1) A wave of action potential travels along the presynaptic neuron, until it reaches the synaptic end bulb.

Question 3

Step 2)

Answer 3

2) Depolarisation of the membrane at the synaptic end bulb causes the Ca2+ channels to open.

Question 4

Step 3)

Answer 4

3) Ca2+ ions flow into the presynaptic membrane.

Question 5

Step 4)

Answer 5

4) Increase in Ca2+ inside the cell activates vesicles containing the neurotransmitter.

Question 6

Step 5)

Answer 6

5) Vesicles fuse with membrane, releasing neurotransmitter (via exocytosis) into synaptic cleft

Question 7

Step 6)

Answer 7

6) Neurotransmitter diffuses across the synaptic cleft and binds to a neurotransmitter receptor molecule (specific to neurotransmitter) on the postsynaptic neuron.

Question 8

Step 7)

Answer 8

7) Binding of neurotransmitter causes the receptor molecule to be activated. This causes an action potential in the postsynaptic neuron or stimulus for an effector (muscle or gland).

Question 9

Step 8)

Answer 9

8) Neurotransmitter molecules eventually break loose from receptor molecule and drift away (through synaptic cleft towards the presynaptic neuron).

Question 10

Step 9)

Answer 10

9) The neurotransmitter is deactivated by an enzyme in the synaptic cleft and is reabsorbed (endocytosis) by the presynaptic neuron to be reused.