synapses

Question 1

what is a synapse?

Answer 1

A junction between a neurone and a neurone
or
A neurone and an effector cell

Question 2

what is the synaptic cleft

Answer 2

The gap between cells at a synapse

Question 3

what happens when an action potential reaches the end of a neurone

Answer 3

Neurotransmitters are released into the synaptic cleft, and they diffuse across to the postsynaptic membrane and binds to specific receptors.

Question 4

what could happen when a neurotransmitter binds to a receptor

Answer 4

An action potential could be fired, muscle contraction, hormone secretion etc

Question 5

why are neurotransmitters removed from the synaptic cleft and how does this happen?

Answer 5

-Removed from the cleft so the “response” does not keep happening.

This can happen by:

1) neurotransmitters are taken back into the presynaptic neurone
2) Neurotransmitters can be broken down by an enzyme

Question 6

what is acetycholine ( ACh)

Answer 6

A neurotransmitter

“noradrenaline” is another example of a neurotransmitter

Question 7

What are cholinergic synapses

Answer 7

Synapses that use acetylcholine

The neurotransmitters bind to cholinergic receptors.

Question 8

what enzyme breaks down neurotransmitters that bind to cholinergic receptors

Answer 8

Broken down by acetylcholinesterase (AChE)

Question 9

How do neurotransmitters transmit nerve impulses between neurones (3 stages)

Answer 9

1) An action potential triggers a calcium influx
2) Calcium influx causes neurotransmitters to release
3) The neurotransmitters trigger an action potential in the post synaptic neurone

Question 10

1) Action potential triggers calcium influx:

Answer 10

• An ACTION POTENTIAL arrives at the synaptic knob of the presynaptic neurone.
• This stimulates voltage gated calcium ion channels to open in the presynaptic neurone.
• Calcium ions diffuse into the synaptic knob

Question 11

2) Calcium influx causes neurotransmitters to be released:

Answer 11

• Influx of calcium ions in the synaptic knob, causes synaptic vesicles to fuse with the presynaptic membrane, and release neurotransmitters into the synaptic cleft by exocytosis.

Question 12

3) Neurotransmitter triggers action potential in the postsynaptic neurone:

Answer 12

• neurotransmitters diffuse across synaptic cleft and bind to specific receptors on the postsynaptic membrane
• Which causes sodium ion channels on the post synaptic membrane to open.
• THE INFLUX of sodium ions in the postsynaptic neurone causes depolarisation
• IF the threshold is reached action potential on the post synaptic neurone is generated
• Neurotransmitter is removed from synaptic cleft so response doesn’t keep on happening.

Question 13

what are the two different types of synapses:

Answer 13

1) excitatory

2) inhibitory

Question 14

what is the difference between excitatory and inhibitory synapses:

Answer 14

• At and excitatory synapse, neurotransmitters DEPOLARISE the post synaptic membrane, making it fire an action potential if the threshold is reached.
• At an inhibitory synapse, neurotransmitters bind to receptors in the postsynaptic membrane and HYPERPOLARISE the membrane( decreases P.D even more)
• Which prevents an action potential from being fired

Question 15

what is synaptic divergence

Answer 15

When one neurone connects to many other neurones, causing information to be dispersed to different parts of the body

Question 16

what is synaptic convergence

Answer 16

When many neurones connect to one neurone, information can be amplified.

Question 17

What is summation

Answer 17

Where the effect of neurotransmitters is combined

Question 18

What does spatial summation do

Answer 18

Allows signals from multiple stimuli to be coordinated into a single response

( Many neurones release excitatory neurotransmitters)

Question 19

spatial summation:

Answer 19

• when neurones converge, the small amount of neurotransmitter released from each neurone, could be enough to reach threshold in the post synaptic neurone and fire an action potential

Question 20

What happens if a neurone releases inhibitory neurotransmitters?

Answer 20

no action potential is fired

Question 21

Temporal summation:

Answer 21

When nerve impulses arrive in quick succession from the SAME presynaptic neurone.

• Which makes an action potential more likely to occur , because neuro transmitters are released into the synaptic cleft.

Question 22

Why is it that only the post synaptic membrane has receptors?

Answer 22

This is so the synapses make sure the nerve impulses can only travel in one direction