Synapses

Question 1

What is a synapse?

Answer 1

A joining point between two neurones or an effector etc which an impulse can pass.

Question 2

What is the synaptic cleft?

Answer 2

Neurones don’t really touch so the synaptic cleft is that small gap.

Question 3

Describe the presynaptic neurone.

Answer 3

It has a swelling called the synaptic knob that contains synaptic vesicles filled with neurotransmitters e.g. acetylcholine.(It also contains mitochondria)

Question 4

How does the synapse transmit and impulse?

Answer 4

1. Action potential arrives & membrane depolarises. Ca2+ channels open & Ca2+ enter neurone.
2. Ca2+ cause synaptic vesicles containing neurotransmitter to fuse with the presynaptic membrane.
3. Neurotransmitter released into synaptic cleft. It binds to specific receptors on postsynaptic membrane. Cation channels open and Na+ flow through the channels.
4. Membrane depolarises and initiates action potential. The neurotransmitter will then be reuptaken or broken down by enzymes.

Question 5

What is the name of the neurotransmitter you need to know?

Answer 5

Acetylcholine.

Question 6

What is the name of the enzyme that breaks down acetylcholine?

Answer 6

Acetylcholinesterase.

Question 7

Why do Ca2+ diffuse across the membrane into the cytoplasm of the neurone etc.?

Answer 7

Because there is a greater concentration of CO2 outside membrane than inside.

Question 8

How does the vesicles that contain the neurotransmitter fuse with the membrane?

Answer 8

Via exocytosis.

Question 9

In a post-synaptic neurone, what does the extent of depolarisation depend on?

Answer 9

The amount of acetylcholine reaching the post synaptic membrane ie a single impulse isn’t enough to generate enough neurotransmitter to depolarise the membrane. Multiple are needed.

Question 10

Why is the neurotransmitter removed in the end?

Answer 10

To prevent the response from continuously happening.

Question 11

What are the two main roles of synapses?

Answer 11

1. Control of nervous pathways, allowing flexibility of response.
2. Integration of information from different neurones, allowing coordinated responses.

Question 12

What two factors will affect the liklihood that a post synaptic membrane will depolarise?

Answer 12

1) the type of synapse 2) the number of impulses received

Question 13

What are two types of synapses?

Answer 13

1) inhibitory 2) Excitatory

Question 14

What is the function of excitatory synapses?

Answer 14

They make the post synaptic membrane more permeable to Na+ ions. However, a single excitatory synapse does not depolarise the membrane enough to produce an action potential, but several impulses arrive at once will.

Question 15

What are the two types of summation?

Answer 15

Spatial and Temporal.

Question 16

What is spatial summation?

Answer 16

• Impulses are from different synapses, usually from different neurones.
• The number of different sensory cells stimulated can be reflected in the control of the response.
• BASICALLY, IMPULSES FROM SEVERAL DIFF. NEURONES PRODUCE AN AP IN THE POST SYNAPTIC MEMBRANE

Question 17

What is summation?

Answer 17

Summation is basically the addition of post-synaptic potentials.

Question 18

What is temporal summation?

Answer 18

Several impulses arrive at a synapse having travelled along a single neurone one after the other. Their combined release of neurotransmitter generates an action potential in post synaptic membrane.

Question 19

What do inhibitory synapses do?

Answer 19

They make it less likely that an action potential will result in the post synaptic cell.