Neuronal Communication

Question 1

What are the steps involved with synaptic transmission?

Answer 1

1. Action potential reaches the presynaptic knob, depolarising the presynaptic membrane
2. Calcium ion channels open and calcium ions diffuse into the presynaptic knob
3. Synaptic vesicles fuse with presynaptic vesicles
4. Synaptic vesicles release NT into the synaptic cleft by exocytosis, and NT diffuse across the synaptic cleft
5. NT bind with specific receptors on the postsynaptic membrane, and the receptors change shape
6. Sodium ion channels open in response to binding, and sodium enters the postsynaptic neurone, depolarising it
7. If this passes a threshold level, it triggers an action potential in the postsynaptic neurone

Question 2

How does the sarcoplasmic reticulum contribute to muscle contraction?

Answer 2

1. The sarcoplasmic reticulum stores calcium ions
2. The action potential travels along the sarcolemma via the T-tubules, which are connected to the sarcoplasmic reticulum
3. When the action potential reaches the sarcoplasmic reticulum, calcium ion channels open
4. Calcium ions flow into the sarcoplasm, stimulating muscle contraction

Question 3

What happens when a nerve impulse reaches a neuromuscular junction?

Answer 3

1. Calcium ion channels open and calcium flows into the end of the neurone
2. This triggers the release of acetylcholine from vesicles
3. Acetylcholine binds to receptors on the sarcolemma
4. Sodium ion channels open and the sarcolemma depolarises
5. Acetlycholinesterase breaks down acetylcholine to prevent overstimulation
6. Depolarisation of sarcolemma spreads along T tubules towards the sarcoplasmic reticulum