Biology B3 Synapses

Question 1

What are synapses ?

Answer 1

Synapses are the connection between 2 neurones

Question 2

what happens at synapses ?

Answer 2

The nerve signal is transferred by chemicals which diffuse across the gap. These chemicals then set off a new electrical signal in the next neurone

Question 3

What is the process of a synapse using a Presynaptic Neurone ?

Answer 3

1. Calcium channels open
2. Neurotransmitter Release
3. Sodium Channels
4. New action potential
5. Acetylcholinesterase
6. Remaking acetylcholine

Question 4

What happens when the Calcium Channels open ?

Answer 4

The Incoming action potential causes depolarisation in the synaptic knob.
This causes Calcium Channels to open . Calcium Ions flood into the synaptic Knob

Question 5

What happens at neurotransmitter release ?

Answer 5

The Influx of Calcium Ions cause Synaptic vesicles to fuse with the presynaptic membrane. This releases Neurotransmitter in to the cleft so calcium ions cause the release of neurotransmitter.

Question 6

What happens at the sodium channels ?

Answer 6

Neurotransmitter ( acetylchloine) is released into the synapatic cleft. Acetycholine binds to the receptor site on the sodium ion channels. Sodium ion channels open.

Question 7

What happens to The Neurotransmitter Acetlycholine ?

Answer 7

It is released into the synaptic cleft . it binds to the receptor site on the sodium ion

Question 8

What happens fully at the sodium channels ?

Answer 8

Neurotransmitter Acetylcholine binds to the receptor site on the sodium ion channels.
Sodium ion channels open
Sodium ions diffuse in down steep gradient
Postsynaptic neurone depolarises

Question 9

What happens at the new action potential ?

Answer 9

Deplorisation inside the postsynaptic neurone must be above a threshold value. If the threshold is reached a new action potential is sent along the axon of the post synaptic neurone

Question 10

What is Acetylcholinesterase and what happens ?

Answer 10

It is an enzyme that hydroylses acetylcholine in to separate acetyl - ethanoic acid and choline.
It breaks up acetycholine - Neurotransmitter into acetyl ( ethnoic acid) and choline
Once the acetylcholine is removed, the sodium ion channels closes. The two bits diffuse back across the cleft into the presynaptic neurone. This allows the neurotransmitter to be recycled

Question 11

Why break down acetlycholine in the synapses ?

Answer 11

If the neurotransmitter is not broken down , this could allow it continously generate new action potentials
Breaking down acetlycholine prevents this.
The products of the breakdown of the neurotransmitter move to receptors on the presynaptic neurone and are taken up by the neurone to be recycled

Question 12

What happens at remaking Acetcholine ?

Answer 12

It is released by mitochondira and is used to recombine acetyl and choline thus recycling the acetlycholine
This is stored in synaptic vesicles for future use
More Acetylcholine can be made at the SER
Sodium ion channels close in the absence of acetylcholine at their receptor sites
The synapse is now ready to be used again