Synaptic Transmission

Question 1

What is a synapse?

Answer 1

A connection between 2 different neurones

Question 2

Desrcibe how synaptic transmission takes place.

Answer 2

Sends nerve impulse across the gap (synaptic cleft) using neurotransmitters (e.g. acetylcholine)

AP arrives at end of the presynaptic neurone

Ca2+ channels open

Ca2+ ions enter presynaptic neurone

Causes vesicles containing neurotransmitters to move to the presynaptic membrane

Vesicle binds to membrane releasing neurotransmitter into cleft

neurotransmitter diffuses across cleft

binds to complementary receptors on postsynaptic membrane

Na+ channels open, Na+ ions enter

If threshold is reached, AP occurs

Question 3

How does a synapse return to rest?

Answer 3

Enzyme used to breakdown neurotransmitters, e.g. acetylcholinesterase

breakdown acetylcholine into ethanoic acid and choline, diffuses back into presynaptic neurone, ATP used to reform neurotransmitter into vesicle and actively transport Ca2+ ions out.

Question 4

What are the Properties of Synapses?

Answer 4

unidirectionality
filters out low-level stimuli
summation
inhibitory

Question 5

How is a synapse unidirectional?

Answer 5

AP/nerve impulse travels in one direction, from pre to post, pre has the neurotransmitter, post has the receptors

Question 6

How does a synapse filter out low level stimuli?

Answer 6

Low level stimuli do not release enough neurotransmitter, therefore not enough Na+ ion channels open, therefore not enough Na+ ions enter postsynaptic neurone for threshold to be reached, therefore no AP produced.

Question 7

Temporal summation

Answer 7

Low-level stimuli present for an extended period of time
Where multiple nerve impulses from a single pre-synaptic neurone occur in succession.

Question 8

Spatial summation

Answer 8

Low-level stimuli from a few presynaptic neurons add together

Where multiple pre-synaptic neurones connect to the same post-synaptic neurone.