Synapses (5)

Question 1

Describe the structure of a synapse and the knobs.

Answer 1

• presynaptic knob has many mitochrodria and synpatic vesicles which contain neurotransmitters
• synaptic cleft is that gap between two synaptic knobs
• the postsynaptic knob has receptor molecules and also has mitochondria

Question 2

Name two types of neurotransmitters

Answer 2

Acetylcholine and dopamine

Question 3

Name the 3 stages of a nerve impulse transmission between two neurones.

Answer 3

1. calcium influx
2. neurotransmitter release
3. action potential generation

Question 4

What happens in the first stage, when an action potential reaches the presynaptic knob?

Answer 4

The action potential stimulates voltage-gates calcium ion channels to open in the presynaptic neurone. This causes a calcium influx as calcium ions diffuse into the synaptic knob. (they are later pumped out by active transport hence the high numbers of mitochondria)

Question 5

What happens at the second stage?

Answer 5

• the clacium influx causes the synaptic vesicles to move to the presynaptic membrane and fuse with the membrane to release the neurotransmitters by exocytosis.

Question 6

What happens at the third stage?

Answer 6

• the neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane
• this causes sodium ion channels to open
• the influx of sodium ions causes depolarisation and if this depolarisation reaches or surpasses the threshold an action potential will be generated.
• the neurotransmitter is then released from the synaptic cleft so the response doesn’t keep happening.

Question 7

What are three functions of synapses in the nervous system?

Answer 7

1. Synaptic diverge - when one neurone connects to many so info can be dispersed
2. synaptic converge - where many neurones connect to one so info can be amplified
3. Summation - when the effect of neurotransmitters released from many neurones ( or one which has been repeatedly stimulated) is added together