Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

SL12100 Health and Disease Y1 > Lecture 22 : Synapses and Neurotransmission > Flashcards

Lecture 22 : Synapses and Neurotransmission Flashcards

1
Q

Define a synapse

A

The point at which electrical signals move from one nerve cell to another. Allows neurons to pass electrical/chemical signals to another neuron or to the target effector cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Give the general outline for how they work

A
  • The arrival of an action potential at the synaptic terminal will trigger channels in the presynaptic membrane to open and release neurotransmitters into the synaptic cleft
  • These neurotransmitters bind to the receptors in the membrane of the dendrites or in the cell body of the postsynaptic neuron.
  • The receptors are activated and generate a graded potential in the postsynaptic neuron.
  • The postsynaptic potential may be inhibitory or excitatory.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Name the two types of synapses

A

electrical and chemical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Electrical synapses are also known as…

A

gap junctions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What makes electrical synapses different to chemical synapses?

A

There is a direct point of contact between the cytoplasm of two adjacent neurons- pre and postsynaptic neurons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the three parts of an electrical synapse?

A
  • presynaptic neuron
  • postsynaptic neuron
  • connexons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Gap junctions in electrical synapses are formed by connexons in both cell membranes. What is a connexon?

A

channels/pores which allow the direct passage of ions and small molecules through them. They connect the cytoplasm of the presynaptic and postsynaptic neuron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

electrical synapses are hard to control. Why?

A

very rapid transfer of signals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Where do we find electrical synapses?

A

non-mammalian and invertebrate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

electrical synapses work in both…

A

directions - bidirectional

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Chemical synapses are the most…

A

common

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How do chemical synapses differ to electrical?

A

The presynaptic and postsynaptic neuron are physically separated by the synaptic cleft.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the three parts of a chemical synapse?

A

presynaptic neuron, postsynaptic neuron, the synaptic cleft.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What crosses the synaptic cleft in the chemical synapses. What is the effect of this?

A

The presynaptic neuron releases a neurotransmitter which diffuses across the synaptic cleft and bind to receptors on the postsynaptic membrane and chemically stimulates the postsynaptic cell. Takes time to release neurotransmitters and for it to diffuse, so we have synaptic delay

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Chemical synapses only work in…

A

one direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Where are chemical synapses found?

A

In the CNS and NMJ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

There are three types of synapses in the CNS. Name them

A

Axo-dendritic
Axo-somatic
Axo-axonal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Axo-dendritic synapse

A

axon of one neuron synapses with a dendrite of another

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Axo-somatic synapse

A

the axon terminal of one neuron projects onto a cell body of another nerve cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Axo-axonal synapse

A

the axon terminal of one neurone projects onto the axon of another neuron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Synapses vary in…

A

size and shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Pre-synaptic terminals contain vesicles arranged at…

A

active zones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

The postsynaptic membrane is specialised how?

A

contains clusters of neurotransmitter receptors and signalling molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is a neurotransmitter?

A

a chemical messenger that is released from the pre-synaptic neuron. After release, the neurotransmitter crosses the synaptic cleft and attaches to receptors on the post synaptic neuron, either exciting or inhibiting the postsynaptic neuron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What does the suffix -ergic apply to?

A

neurons which release neurotransmitters. For example, dopaminergic neuron releases dopamine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Neurotransmitters are released from the presynaptic neurone by exocytosis. Explain the process.

A
  • When the action potential reaches the terminal, there is an influx of sodium ions in the terminal of presynaptic neuron.
  • This causes depolarization of the terminal
  • Voltage gated calcium channels are activated and calcium ions diffuse into the terminal.
  • The influx of calcium ions through VGCC initiates the exocytosis process that leads to neurotransmitter release.
  • Calcium interacts with a vesicle bound protein called synaptotagmin. This protein is a calcium sensor and when calcium is present the synaptotagmin interacts with the SNARE proteins.
  • Synaptic vesicle membranes fuse with presynaptic membrane. Exocytosis occurs and the neurotransmitters are released.
  • The neurotransmitters bind to receptors on the postsynaptic membrane either exciting or inhibiting the neuron.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How are neurotransmitters removed form the synaptic cleft?

A
  • degradation: enzyme changes the structure of the neurotransmitter so it can no longer be recognised by receptor
  • diffusion: the neurotransmitter diffuses away from the receptor
  • reuptake: the whole neurotransmitter is actively transported back into the presynaptic axon terminal for reuse
  • Enzymatically transformed into inactive substances
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Give the four main criteria for neurotransmitters.

A
  • Must be synthesized and stored within the presynaptic neuron
  • The transmitter must be released by the presynaptic neuron in response to presynaptic depolarization by action potential – release should depend upon calcium ions
  • Must be a specific receptor for the substance in the postsynaptic cell to mediate postsynaptic response
  • There should be a mechanism for the removal/breakdown of the neurotransmitters
29
Q

Give the four main categories of neurotransmitter

A

amines
amino acids
peptides
purines

30
Q

Give the four types of amine neurotransmitters

A

histamine
acetylcholine
indoleamines
catecholamines

31
Q

Give three examples of catecholamine neurotransmitters

A

noradrenaline
dopamine
adrenaline

32
Q

Give four examples of amino acid neurotransmitters

A

glutamate, aspartate, GABA and glycine

33
Q

Give two examples of peptide neurotransmitters

A

endorphins
neurokinins

34
Q

Give two examples of purine neurotransmitters

A

adenosine
ATP

35
Q

What is a neurotransmitter receptor/neuroreceptor?

A

a membrane receptor protein that is activated by a neurotransmitter.

36
Q

Name the two types of neuroreceptors

A
  1. ionotropic receptor
  2. metabotropic receptor
37
Q

Describe ionotropic receptors.

A

ligand gated ion channel – these open up to allow ions like sodium, potassium, calcium and/or chlorine ions to pass through the membrane in response to the binding of a neurotransmitter. The effects can be excitatory (glutamate/aspartate) or inhibitory (GABA/Glycine).

38
Q

Describe metabotropic receptors

A

– G protein coupled receptor – GPCR. Neurotransmitter binds to the receptor, activating G proteins, activating second messenger cascade, activating voltage gated ion channels on membrane. These receptors can remain open from seconds to minutes.

39
Q

What is a neuromuscular junction?

A

a chemical synapse between a motor neuron and a muscle fibre – skeletal, smooth or cardiac. It allows the motor neuron to transmit a signal to the muscle fibre, causing muscle contraction

40
Q

Disease of the NMJ can cause…

A

muscle weakness through mechanisms which can effect presynaptic, synaptic and postsynaptic portions of the NMJ.

41
Q

Name three main diseases that involve the NMJ

A

= MG - myasthenia gravis, Botulism, Lambert-Eaton syndrome

42
Q

What are three parts of the NMJ?

A

presynaptic = nerve terminal, postsynaptic = motor endplate, synaptic cleft- area between nerve terminal and motor endplate

43
Q

What is the motor endplate?

A

The motor endplate is the thickened portion of the muscle plasma membrane that is folded to form depressions called junctional folds. The terminal nerve ending fit into these folds

44
Q

Junctional folds of the motor endplate are covered in what type of receptor? Describe them - how do they work?

A

The junctional folds have nicotinic ACh receptors concentrated at the top.
The receptors are ACh gated ion channels - the binding of acetylcholine to these receptors opens channels and allows sodium ions to diffuse into the muscle membrane so the endplate potential changes and an AP is transmitted to muscle membrane

45
Q

How is acetylcholine synthesised?

A
  • ACh is synthesized in the pre-synaptic terminal from choline and acetyl-CoA by the enzyme choline acetyltransferase, ChAT.
  • ACh goes through a series of modifications before packaged into vesicles
46
Q

How is acetylcholine released from NMJ?

A
  • action potential travels down axon and causes the voltage gated calcium channels to open, resulting in an influx of calcium ions into the presynaptic nerve terminal.
  • This causes the vesicles to move towards the nerve terminal membrane and fuse with it.
  • Exocytosis of Ach into the synaptic cleft
  • ACh bind to receptors and trigger the opening of Ach gated ion channels that allow the influx of sodium ions into the muscle. The membrane potential of the postsynaptic membrane changes from -90mV to -45mV. This decrease in the membrane potential is called endplate potential.
  • In the NMJ, endplate potential is strong enough to propagate action potential over the skeletal muscle membrane which ultimately results in muscle contraction.
47
Q

Why and how is acetylcholine broken down in the synaptic cleft of the NMJ?

A
  • To prevent sustained depolarization and muscle contraction and to allow for repolarization, acetylcholine is metabolised by acetylcholinesterase into its subunits choline and acetate.
  • Choline is reused for synthesis of ACh.
48
Q

What type of neurone produces the neurotransmitter acetylcholine?

A
  • produced by neurons called cholinergic neurons
49
Q

Acetylcholine acts on which parts of the nervous system? What is its role in the PNS?

A
  • In the PNS it plays a role in skeletal muscle movement as well as regulation of smooth and cardiac muscle.
  • It acts on the CNS, ANS and NMJ
50
Q

Generally, ACh receptors at the NMJ are what type of receptors?

A

Nicotinic ACh receptors, which are ligand-gated ion channels

51
Q

Generally, ACh receptors in the CNS and ANS are what type?

A

muscarinic ACh receptors which are G protein coupled receptors

52
Q

We call process that enhance ACh function………… and processes that inhibit ACh function are ……………

A

cholinergic
anticholinergic

53
Q

Amino acids are the main brain neurotransmitters. Name the two types of neurotransmitters and give an example of amino acid neurotransmitter for each.

A

excitatory- glutamate and inhibitory- GABA

54
Q

What is an excitatory neurotransmitter?

A

generates an electrical signal in the postsynaptic neuron

55
Q

What is the role of glutamate

A
  • the main excitatory transmitter in the CNS. Activates both ionotropic- ligand gated and metabotropic receptor- G protein coupled receptor.
  • Glutamate is important for learning and memory
56
Q

What is an inhibitory neurotransmitter?

A

Inhibitory neurotransmitters stop a specific response from other cells in the body- it prevents an excitatory response

57
Q

GABA is the main inhibitory neurotransmitter in the CNS. What is it’s role?

A
  • it reduces the activity of neurons, leading to increased relaxation, reduced stress, more calm, decreased pain, improved sleep and concentration. It is also involved in immune and endocrine systems and appetite, metabolism, motor control and vision.
  • Activates small family of ionotropic and metabotropic receptors
58
Q

Draw Glutamate and GABA

A
59
Q

What is an Excitatory postsynaptic potential, EPSP? What neurotransmitter would produce this?

A
  • Glutamate generates an excitatory postsynaptic potential -EPSP
  • This is a synaptic potential that makes a postsynaptic neuron more likely to produce an action potential.
60
Q

How does an EPSP occur?

A
  • presynaptic cell releases neurotransmitters into the synapse
  • some of them bind to receptors on the postsynaptic cell. Many of these receptors are ionotropic receptors and generally allow sodium ions into the cell, generating an excitatory postsynaptic current
61
Q

What are inhibitory postsynaptic potentials and what neurotransmitter produces them?

A
  • GABA generates an inhibitory postsynaptic potential – IPSP.
  • This is a kind of synaptic potential that makes the postsynaptic neuron less likely to generate an action potential
62
Q

Describe how IPSPs occur.

A
  • Inhibitory presynaptic neurones release neurotransmitters which bind to the postsynaptic receptors, inducing a change in the permeability of the postsynaptic membrane to certain ions- usually allow flow of negative ions into the cell or positive ions out of the cell. - - This allows for a more negative postsynaptic potential to be generate – the membrane potential becomes more negative -hyperpolarisation, which makes depolarisation less likely and no action potential in postsynaptic neuron occurs
63
Q

EPSPs and IPSPs are graded potentials. Graded potentials decay with…

A

time and distance

64
Q

Explain temporal summation.

A

Graded potentials decay with time and distance. However, if they happen close enough in time, their effects may be additive- temporal summation

65
Q

Explain spatial summation

A

Graded potentials decay with time and distance but if they occur near the same part of the neuron their effects may be additive - spatial summation

66
Q

When multiple EPSPs occur on a single patch of postsynaptic membrane, their combined effect results in…

A

a greater membrane depolarisation, increasing the likelihood of reach threshold and an action potential being fired

67
Q

If excitatory and inhibitory potentials of the same size occur at same time and place…

A

they may cancel each other out and membrane potential may not change.

68
Q

In most neurons one excitatory event is not enough to reach threshold. An action potential is therefore initiated by…

A

the combined effects of many excitatory synapses - temporal / spatial summation

SL12100 Health and Disease Y1 (18 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions