Synapses

Question 1

Synapse

Answer 1

The point where the axon of one neurone connects with the dendrite of another or with an effector.

Question 2

Synaptic cleft

Answer 2

Small gap that separates neurones

Question 3

Presynaptic neurone

Answer 3

The neurone that releases the neurotransmitter

Question 4

Synaptic knob

Answer 4

Axon of the end of the presynaptic neurone which possesses many mitochondria and large amounts of E.R. required in the manufacturing of neurotransmitters.

Question 5

Synaptic vesicles

Answer 5

Where neurotransmitters are stored

Question 6

Postsynaptic neurone

Answer 6

The neurone which receives neurotransmitters released from synaptic vesicles with receptor molecules on its membrane.

Question 7

Functions of synapses

Answer 7

1. Allows a single impulse along one neurone to be transmitted to a number of different neurones at a synapse. -> a single stimulus can create a number of simultaneous responses
2. Allows a number of impulses to be combined at a synapse. Allows stimuli from different receptors to interact in order to produce a single response.

Question 8

When is a neurotransmitter released into the synapse?

Answer 8

When an action potential reaches the synaptic knob.

Question 9

How is an action potential generated in the postsynaptic neurone?

Answer 9

The neurotransmitter binds with the receptor molecules and sets up a new action potential in the postsynaptic neurone.

Question 10

Why are synapses unidirectional?

Answer 10

They can only pass impulses in one direction.

Question 11

What is summation?

Answer 11

A process by which a build-up of neurotransmitter in the synapse allows for sufficient amount of neurotransmitter to trigger a new a.p. in the postsynaptic neurone.

Question 12

What are the two types of summation?

Answer 12

1. Spatial summation - a number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone.
2. Temporal summation - a single presynaptic neurone releases neurotransmitter many times over a short period.

Question 13

Inhibitory synapses

Answer 13

Postsynaptic synapses with membranes where protein channels carrying Cl- are made to open, leading to an inward diffusion of Cl- so the inside of the postsynaptic membrane is even more negative than when it is at resting potential (hyperpolarisation) -> less likely that a new a.p. will be generated.

Question 14

Cholinergic synapse

Answer 14

Synapse where the neurotransmitter is acetylcholine

Question 15

Where are cholinergic synapses common?

Answer 15

In vertebrates, they occur in the CNS and at neuromuscular junctions

Question 16

How do drugs affect synapses?

Answer 16

1. Stimulate the nervous system by creating more action potentials in postsynaptic neurones
2. Inhibit the nervous system by creating fewer action potentials in postsynaptic neurones