Transmission Across A Synapse

Question 1

What is a Choligenic synapse

Answer 1

One in which the neurotransmitter is a chemical called acetylcholine

Question 2

How do drugs stimulate the nervous system by creating more action potentials in post synaptic neurones

Answer 2

A drug may do this by mimicking a neurotransmitter, stimulating the release of more neurotransmitter m, or inhibiting the enzyme that breaks down the neurotransmitter. The outcome is to enhance the body’s responses to impulses passed along the postsynaptic neurone

Question 3

How do drugs inhibit the nervous system by creating fewer action potentials in postsynaptic neurones

Answer 3

A drug may do this by inhibiting the release of neurotransmitter or blocking receptors on sodium/potassium ion channels on the postsynaptic neurone. The outcome is to reduce the impulses passed along the postsynaptic neurone.

Question 4

Suggest the likely effect of drugs lie morphine and Codeine on the body. Explain how it might be brought about

Answer 4

They will reduce pain

They act like endorphins by binding to the receptors and therefore preventing action potentials being created in neurones of the pain pathway

Question 5

Suggest a way that the drug Prozac might affect serotonin within synaptic clefts l. And explain how it makes proazac a good antidepressant

Answer 5

Prozac might prevent the elimination of serotonin from the synaptic cleft

By increasing the conc of serotonin in the synaptic cleft, it’s activity is increased, reducing depression, which is caused by serotonin activity

Question 6

Suggest the likely effect of Valium on the nerve pathways that cause muscle contractions. Explain your answer

Answer 6

It will reduce muscle contractions as Valium increases inhibitory effects of GABA so therefore there are fewer action potentials on the nerve pathways that cause muscles to contract

Question 7

Describe the mechanism of transmission across a choligenic synapse

Answer 7

1. The arrival of an action potential at the end of the pre synaptic neurone causes the calcium ion protein channels to open and calcium ions enter the synaptic knob by facilitated diffusion
2. The influx of calcium ions into the pre synaptic neurone causes synaptic vesicles to fuse with the pre synaptic membrane, releasing acetylcholine into the synaptic cleft
3. Acetylcholine molecules diffuse across the narrow synaptic cleft very quickly because the diffusion pathway is short. Acetylcholine then binds to receptor sites on sodium ion protein channels in the membrane of the postsynaptic neurone. This causes the sodium ion protein channels to open, allowing sodium ions to diffuse rapidly along a concentration gradient
4. The influx of sodium ions generates a new action potential in the postsynaptic neurone
5. Acetylcholinesterase hydrolyses acetylcholine into choline and acetyl, which diffuses back across the synaptic cleft into the pre synaptic neurone. In addition to recycling the choline and acetyl, the rapid breakdown of acetylcholine also prevents it from continuously generating a new action potential in the post synaptic neurone, and do leads to discrete transfer of info across synapses
6. ATP released by mitochondria is used to recombine choline and acetyl into acetylcholine. This is stored in synaptic vesicles for future use. Sodium ion proteins channels close in the absence of acetylcholine in the receptor sites