lecture 19 - synaptic transmission

Question 1

How is information transferred between cells?

Answer 1

Chemically- via synaptic interactions

Question 2

What are the features of a synapse? (7)

Answer 2

Pre-synaptic nerve terminal, synaptic cleft, post-synaptic cell, receptors, voltage gated Ca2+ channels, synaptic vesicles, neurotransmitter inactivation enzyme.

Question 3

When an action potential arrives at an axon terminal, what are triggered?

Answer 3

Voltage gated calcium channels, allowing Ca2+ to enter the terminal

Question 4

When calcium ions diffuse into the axon terminal during a synapse, what does this trigger?

Answer 4

Trigger synaptic vesicles to release neurotransmitters via exocytosis

Question 5

What is the fundamental process in which synaptic vesicles release neurotransmitters?

Answer 5

Exocytosis

Question 6

When neurotransmitters diffuse across the synaptic cleft, what occurs at the post-synaptic cell?

Answer 6

Neurotransmitters bind to chemically gated sodium ion channels, allowing them to open and release sodium into the cell, creating a graded depolarisation (local potential).

Question 7

When chemically gated sodium channels close after depolarisation in the post-synaptic cell, what happens to the neurotransmitters that were bound to the channel?

Answer 7

They are released and broken down by enzymes.

Question 8

When Acetylcholine is broken down after release from chemically gated sodium channels, what is formed?

Answer 8

AChE enzyme breaks it down into Acetate and Choline, which is reabsorbed by the axon terminal.

Question 9

What is the enzyme used to break acetylcholine down into acetate and choline after it is release from the post-synaptic chemically gated sodium channels?

Answer 9

AChE

Question 10

How does the axon terminal ‘recycle’ the neurotransmitter ACh?

Answer 10

The axon terminal reabsorbs choline from the synaptic cleft and combines it with Acetyl-CoA (from the mitochondria) to form acetylcholine which can then be released again via synaptic vesicles.

Question 11

What is the name for a synapse that uses the neurotransmitter Acetylcholine?

Answer 11

Cholinergic synapse.

Question 12

What is the overall process of synaptic transmission?

Answer 12

Action potential triggers Ca2+ channels, Ca2+ enters cells and triggers release of synaptic vesicles (containing neurotransmitters). neurotransmitters diffuse across synaptic cleft and bind to chemically gated Na+ channels creating a local potential. Neurotransmitters are release and broken down by enzymes before being reabsorbed by the terminal.

Question 13

What kind of synaptic junction is involved in electrical synapses?

Answer 13

Gap junction

Question 14

What are gap junctions?

Answer 14

Channels that connect the post- and pre- synaptic neuron that allow electrical signals to be passed on directly without chemical signals.

Question 15

What is an electrical synapse?

Answer 15

An electrical event that allows a presynaptic cell to trigger an electrical signal in the postsynaptic cell directly, without chemical signals. (Ca2+ channels or neurotransmitters)

Question 16

When pre- and post- synaptic cell membranes sit very close together, what will generally occur?

Answer 16

Cells will have gap junctions and will undergo electrical synapses.

Question 17

In an electrical synapse, will a depolarisation in the pre-synaptic cell lead to a depolarisation or hyperpolarisation in the post-synaptic cell?

Answer 17

Depolarisation (always produce a like voltage change)

Question 18

Why are electrical synapses rare?

Answer 18

They provide no opportunity for signal modulation - the sign of the potential cannot be changed to cause inhibition. i.e. depolarisation cannot lead to hyper-polarisation.

Question 19

What does EPSP stand for?

Answer 19

Excitatory Post Synaptic Potential

Question 20

What does IPSP stand for?

Answer 20

Inhibitory Post Synaptic Potential

Question 21

What is an EPSP?

Answer 21

An electrical charge on the post-synaptic membrane that briefly depolarises it towards threshold, sometimes facilitating the firing of an action potential.

Question 22

What is an IPSP?

Answer 22

An inhibitory electrical charge on the post-synaptic membrane that leads to a brief hyper-polarisation, moving the membrane away from the threshold, and inhibiting action potentials.

Question 23

What are the excitatory neurotransmitters used to create EPSP?

Answer 23

Acetylcholine (ACh), norepinephrine, epinephrine and glutamate

Question 24

What are inhibitory neurotransmitters used to generate IPSPs?

Answer 24

GABA

Question 25

What are the two forms of postsynaptic potential summation?

Answer 25

Temporal and spatial summation

Question 26

What is temporal postsynaptic potential summation?

Answer 26

When several stimulus arrive shortly after each other - i.e. secondary arrives before the first decays - the potentials sum allowing the threshold potential to be met, triggering an action potential.

Question 27

What is spatial postsynaptic potential summation?

Answer 27

When two stimuli are received from 2 nerve terminals that sit close together, the local potentials will add together allowing the threshold to be reached, propagating an action potential.

Question 28

What is a neuromuscular junction?

Answer 28

A junction, separated by a synaptic cleft, between an axon terminal and the sarcolemma of a muscle fibre.

Question 29

Are synapses small or large at a neuromuscular junction?

Answer 29

Huge, Action potential likely to bring muscle fibre to threshold.

Question 30

How many neurons are received by an individual muscle fibre?

Answer 30

1