lecture 19 - synaptic transmission Flashcards

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1
Q

How is information transferred between cells?

A

Chemically- via synaptic interactions

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2
Q

What are the features of a synapse? (7)

A

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

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3
Q

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

A

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

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4
Q

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

A

Trigger synaptic vesicles to release neurotransmitters via exocytosis

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5
Q

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

A

Exocytosis

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6
Q

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

A

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

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7
Q

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

A

They are released and broken down by enzymes.

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8
Q

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

A

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

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9
Q

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?

A

AChE

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10
Q

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

A

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.

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11
Q

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

A

Cholinergic synapse.

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12
Q

What is the overall process of synaptic transmission?

A

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.

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13
Q

What kind of synaptic junction is involved in electrical synapses?

A

Gap junction

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14
Q

What are gap junctions?

A

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

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15
Q

What is an electrical synapse?

A

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)

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16
Q

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

A

Cells will have gap junctions and will undergo electrical synapses.

17
Q

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

A

Depolarisation (always produce a like voltage change)

18
Q

Why are electrical synapses rare?

A

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.

19
Q

What does EPSP stand for?

A

Excitatory Post Synaptic Potential

20
Q

What does IPSP stand for?

A

Inhibitory Post Synaptic Potential

21
Q

What is an EPSP?

A

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

22
Q

What is an IPSP?

A

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.

23
Q

What are the excitatory neurotransmitters used to create EPSP?

A

Acetylcholine (ACh), norepinephrine, epinephrine and glutamate

24
Q

What are inhibitory neurotransmitters used to generate IPSPs?

A

GABA

25
Q

What are the two forms of postsynaptic potential summation?

A

Temporal and spatial summation

26
Q

What is temporal postsynaptic potential summation?

A

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.

27
Q

What is spatial postsynaptic potential summation?

A

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.

28
Q

What is a neuromuscular junction?

A

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

29
Q

Are synapses small or large at a neuromuscular junction?

A

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

30
Q

How many neurons are received by an individual muscle fibre?

A

1