Synaptic transmission

Question 1

What is a synapse?

Answer 1

A junction between a neurone and another neurone or between a neurone and an effect cell

Question 2

What is a synaptic cleft?

Answer 2

The tiny gap between the cells at a synapse

Question 3

What is synaptic knob?

Answer 3

A swelling on the presynaptic neurone that contains synaptic vesicles filled with chemicals called neurotransmitters

Question 4

What causes neurotransmitters to be released into the synaptic cleft?

Answer 4

When an action potential reaches the end of a neurone

Question 5

What do neurotransmitters do?

Answer 5

Diffuse across to the postsynaptic cleft and bind to specific receptors

Question 6

What happens when neurotransmitters bind to receptors?

Answer 6

Trigger a response

Question 7

What do synapses ensure?

Answer 7

Make sure impulse are unidirectional

Question 8

Why are the neurotransmitters removed from the synaptic cleft?

Answer 8

To make sure the response doesn’t carrying on happening

Question 9

How are the neurotransmitters removed?

Answer 9

Taken into the presynaptic neurone or broken down by enzymes

Question 10

What neurotransmitter do cholinergic synapses use?

Answer 10

Acetylcholine

Question 11

How is a nerve impulse transmitted across a cholinergic synapse?

Answer 11

1. An action potential arrives at the synaptic knob of the presynaptic neurone.
2. The action potential stimulates voltage-gated calcium ion channels in the presynaptic neurone to open.
3. Calcium ions diffuse into the synaptic knob.
4. The influx of calcium ions into the synaptic knob causes the synaptic vesicles to move to the presynaptic membrane. They then fuse to the presynaptic membrane.
5. The vesicles release acetylcholine (ACh) into the synaptic cleft (exocytosis).
6. ACh diffuses across the synaptic cleft and binds to specific cholinergic receptors on the postsynaptic membrane.
7. This causes sodium ion channels in the postsynaptic neurone to open.
8. The influx of sodium ions causes depolarisation. An action potential on the postsynaptic membrane is generated of the threshold is reached.
9. ACh is removed from the synaptic cleft. It is broken down by an enzyme acetylcholinesterase. The products are reabsorbed by the presynaptic neurone.

Question 12

What are excitatory neurotransmitters?

Answer 12

Neurotransmitters that depolarises the postsynaptic membrane, making it fire an action potential if the threshold is reached

Question 13

What are inhibitory neurotransmitters?

Answer 13

Neurotransmitters that hyperpolarises the postsynaptic membrane preventing it from firing an action potential

Question 14

Describe a spatial summation

Answer 14

When many neurones connect to one neurone. The small amount of neurotransmitter released from each of these neurones can be enough altogether to reach the threshold on the postsynaptic neurone and trigger an action potential.
If some neurones release an inhibitory neurotransmitter then the total effect of all the neurotransmitters might be no action potential

Question 15

Describe a temporal summation

Answer 15

When two or more nerve impulses arrive in quick succession from the same presynaptic neurone.
This makes an action potential more likely because neurotransmitter is released into the synaptic cleft

Question 16

What is a neuromuscular junction?

Answer 16

A synapse between a motor neurone and a muscle cell.
They use acetylcholine which binds to cholinergic receptors called nicotine cholinergic receptors

Question 17

How do neuromuscular junctions work?

Answer 17

The postsynaptic membranes have lots of folds that form clefts. The clefts store the enzymes that break down the acetylcholinesterase.
Have more receptors than other synapses

Question 18

How do drugs affect synaptic transmission?

Answer 18

• have the same shape as neurotransmitters so mimic their action at receptors so more receptors are activated.
• block receptors so they cannot be activated by neurotransmitters which means fewer receptors can be activated.
• inhibit the enzyme that breaks down the neurotransmitters which means there are more neurotransmitters in the synaptic cleft to bind to receptors and will be there for longer
• stimulate the release of neurotransmitters from the presynaptic neurones so more receptors are activated
• inhibit the release of neurotransmitters from the presynaptic neurone so receptors are activated