Nerves and synapses

Question 1

Describe the release, action and inactivation of acetylcholine as a typical neurotransmitter.

Answer 1

1. Ach made from choline and acetyl coA
2. IN synaptic cleft, Ach is rapidly broken down by acetylcholinerase
3. choline is transported back into axon terminal by co-transport w/ Na+
4. Recycled choline used to make more Ach

Question 2

What are the differences between pre- and post-synaptic potentials?

Answer 2

Postsynaptic potentials are saller in amplitude and longer in duration. This allows summation of many postsynaptic potentials to be generated. A single action potential from presynaptic nerve is not enough so long duration = more time for summation of presynaptic APs. Postsynaptic potential magnitude directly related to amount of neurotransmitter released.

Question 3

What is summation; how does it work?

Answer 3

Summation is the combined effect of numerous presynaptic end bulbs releasing neurotransmitter at the same time resulting in a genreated nerve impulse.

Question 4

Describe temporal and spatial summation.

Answer 4

Temporal

• At one Axon terminal, multiple impulses arriving. NT builds in the synapse allowing a greater postsynaptic potential.
• Frequency modulate potential

Spatial

• Postsynaptic membrane recieving multiple graded potentials from immediate neighourhood.

Question 5

What is the difference between excitatory and inhibitory synapses? Provide examples for both and explain what happens at the post-synaptic membrane.

Answer 5

Impulses are the same for inhibitor and excitatory postsynaptic potential, but neurotransmitters vary.

EPSP: Opens ligand gated Na+channels and causes PostSP to more likely depolarise.

IPSP: ligand-gated K+ or CL- channels. PostSP is less likely to depolarise due to negative contribution to membrane potential

Question 6

What is pre-synaptic inhibition?

Answer 6

The inhibition of an excitatory fibre by an inhibitory fibre.

Question 7

Why is pre-synaptic inhibition regarded as being selective and post-synaptic inhibition, non-selective?

Answer 7

Postsynaptic memrbane inhibition is non-selective as it affect all presynaptic axon terminals of that neuron to some degree. Presynaptic inhibition is selective as it only effects that pre-synaptic terminal.