Unit 6 Synaptic Transmission

Question 1

Describe the sequence of events involved in transmission across a cholinergic synapse

Answer 1

1. Depolarisation of presynaptic membrane
2. Calcium channels open and calcium ions diffuse in
3. Synaptic vesicles fuse with presynaptic membrane and release acetylcholine
4. Acetylcholine diffuses across synaptic cleft
5. Acetylcholine attaches to receptors on postsynaptic membranes
6. Sodium ions enter postsynaptic neurone leading to depolarisation

Question 2

Describe how the influx negatively
charged ions can inhibit postsynaptic
neurones.

Answer 2

1. (Inside of postsynaptic) neurone becomes more
   negative/hyperpolarisation/inhibitory postsynaptic potential;
   Ignore K+
   Accept -75mV or any value below this as equivalent to more negative
   Accept ‘decrease in charge’
2. More sodium ions required (to reach threshold)
   OR
   Not enough sodium ions enter (to reach threshold);
   Accept Na+ for sodium ions
3. For depolarisation/action potential;
   Context must covey idea that depolarisation / action potential is less
   likely

Question 3

Explain how blocking the calcium ion channels
at some synapses can reduce impulses at the
post synaptic membrane

Answer 3

1. No/fewer calcium ions enter synaptic knob OR No/less calcium enter synaptic knob via
   calcium ion channels;
2. No/fewer synaptic vesicles move to/fuse with presynaptic membrane and no/less
   glutamate is released;
3. No/less neurotransmitter diffuses across (synaptic cleft);
4. No/less (neurotransmitter attaches) to receptors on the postsynaptic membrane;
5. No/fewer sodium ions enter (postsynaptic neurone) so no/ fewer impulses