Synapses 2

Question 1

Define summation

Answer 1

Occurs when the effects of several excitatory post- synaptic potentials are added together.

Question 2

What kind of response is an action potential?

Answer 2

an all or nothing response.
once the action potential starts it will be conducted along the entire neurone.
the action potential does not vary in size or intensity.

Question 3

What happens during synaptic transmission?

Answer 3

The presynaptic membrane releases neurotransmitter molecules into the synaptic cleft. The post synaptic neurone responds to these molecules, which is an example of cell signalling.

Question 4

What do the cholinergic synapses consist of?

Answer 4

the molecule acetylcholine

Question 5

What is the main role of synapses

Answer 5

to connect two neurones together so that a signal can be passed from one to the other.

Question 6

What can nerve junctions involve?

Answer 6

• several neurones from different places converging to one neurone
  or
• one neurone sending signals out to several neurones that diverge to different effectors.

Question 7

What happens when one action potential passes down an axon to the synapse?

Answer 7

It will cause a few vesicles to move too and fuse with the presynaptic membrane.

Question 8

What is an excitatory post synaptic potential? (EPSP)

Answer 8

When the small number of acetylcholine molecules diffuse across the cleft producing a small depolarisation.

Question 9

Why is one (EPSP) not sufficient enough to cause an action potential in the post synaptic neurone?

Answer 9

takes several EPSPs to reach the threshold and cause an action potential.

Question 10

Summation

Answer 10

The effects of several EPSPs combine together to increase the membrane polarisation until it reaches the threshold.

Question 11

What can summation result from?

Answer 11

temporal summation
spatial summation

Question 12

What is temporal summation?

Answer 12

several action potentials in the same pre synaptic neurone.

Question 13

What is spatial summation?

Answer 13

action potentials arriving from several different pre synaptic neurones.

Question 14

What can some pre synaptic neurones also produce?

Answer 14

inhibitory post synaptic potentials (IPSPs)

Question 15

What can (IPSPs) do?

Answer 15

They can reduce the effect of summation and prevent an action potential in the post synaptic neurone.

Question 16

as nerve junctions may involve several neurones what does it enable?

Answer 16

It enables synapses to control the communication passed along the nervous system.

Question 17

When pre synaptic neurones converge on one post synaptic neurone what does it allow?

Answer 17

action potentials from different parts of the nervous system to contribute to generating an action potential in one post synaptic neurone- creating a particular response.

this is called spatial summation.

Question 18

When is spatial summation useful?

Answer 18

useful when several different stimuli are warning us of danger.

Question 19

How could the combination of several EPSPs be prevented?

Answer 19

by producing an action potential from one IPSP.

Question 20

What can one presynaptic neurone that diverges to several post synaptic neurones allow?

Answer 20

It allows one action potential to be transmitted to several parts of the nervous system.

Question 21

Why is this useful?

Answer 21

it is useful in a reflex arc. One post synaptic neurone elicits the response while another informs the brain.

Question 22

How do the synapses control communication?

Answer 22

They ensure action potentials are transmitted in the correct direction.
only pre synaptic bulb contains vesicles of acetylcholine.
so if an action potential was to start half way along a neurone and ends at the post synaptic membrane it will not cause a response in the next cell.

Question 23

Why do synapses filter out unwanted low level signals?

Answer 23

If a low level stimulus creates an action potential in the pre synaptic neurone it is unlikely to pass across a synapse to the next neuron because lots of vesicles of acetylcholine must be released to create an action potential in the post synaptic neurone.

Question 24

How can low level action potentials be amplified?

Answer 24

summation
it will generate several successive action potentials in the pre synaptic neurone.
the release of many vesicles of acetylcholine over a short period of time will enable the post synaptic EPSPs to combine together producing an action potential