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Neuro > Synaptic Transmission And Intergration > Flashcards

Synaptic Transmission And Intergration Flashcards

1
Q

What are the 2 types of synapses

A

Electrical and chemical

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2
Q

Definition of synapse

A

A specialised junction where an axon terminal contacts another neuron or cell type

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3
Q

What are electrical synapses linked by

A

Gap junction

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4
Q

What do electrical synapses consist of

A

Precisely aligned paired channels in pre and post synaptic membranes

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5
Q

What is the gap junction channel formed by in electric synapses

A

2 hemispheres channels

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6
Q

What is a hemichannel

A

Connexon
Connexon composed of Connexon subunits

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7
Q

How is the pore of gap junction opened

A

Connexins rotate

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8
Q

Describe the passage of current in electric synapse

A

Connexon rotate to open pore in gap junction
Ionic current generated t presynaptic membrane flow passively into post synaptic neuron
Current can pass in both directions (bidirectional/non-rectifying synapse)
Pass in one direction (unidirectional/rectifying)
Rapid and allows ATP and 2nd messenger exchange
Synchronise electrical activity among neuron populations

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9
Q

What are the requirements for chemical synaptic transmission

A

-Mechanism for synthesising and packing NT into vesicles
-Mechanism for causing vesicle to spill contents into synaptic cleft in response to action potential
-mechanism for producing an electrical or biochemical response to NT in post-synaptic neuron
-mechanism for removing transmitter from synaptic cleft
-must be carried out very rapidly

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10
Q

Describe the synaptic cleft in chemical synapses

A

20-50nm wide
Held together by a fibrous extracellular matrix

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11
Q

What is the synaptic bouton in chemical synapse

A

Presynaptic element
Contains synaptic vesicles and secretory granules called large dense core vesicles

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12
Q

What are the membrane differences in chemical synapses

A

Accumulations of proteins on either side of the synaptic cleft
Active zones - presynaptic site of NT release
Postsynaptic density - contains receptors to translate intracellular signal (NT) into a intracellular signal (chemical change or membrane potential change)

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13
Q

What can synapses be categorised by

A

Connectivity (which part of the neuron is postsynaptic to the axon terminal)
Synapse anatomy (appearance of the pre and postsynaptic membrane differentiations, size and shape)

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14
Q

Describe axodendritic/axospinous synapses

A

Postsynaptic membrane on dendrite of another neuron
30% of neurons in the CNS

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15
Q

Describe axosomatic synapses

A

Post synaptic membrane on cell body of another neuron
6% of neurons in the CNS

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16
Q

Describe dendrodendritic synapses

A

Dendrites synapse with one another
Rare

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17
Q

Describe axoaxonic synapses

A

Postsynaptic membrane on the axon of another neuron
Rare

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18
Q

Describe Gray’s Type 1 synapse

A

Postsynaptic membrane thicker than the presynaptic membrane
Asymmetrical membrane differentiations
Excitatory

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19
Q

Describe Gray’s Type II synapse

A

Post and pre synaptic membranes similar thickness
Symmetrical membrane differentiations
Inhibitatory

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20
Q

What are synaptic junctions outside the CNS

A

Junctions between autonomic neurons and glands, smooth muscle, and heart

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21
Q

Describe the neuromuscular junction

A

Transmission is fast and reliable due to large size with many active zones and a motor end plate with specialised folds for more receptors
One motor neuron innervates one muscle fibre
Only Ach and nicotinic receptors

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22
Q

What are neurotransmitters

A

Molecules released by pre-synaptic neurons and are the means of communication at the chemical synapse
They are specific for the receptor they bind to and result in either an excitatory or inhibitory signal and can be put into 2 categories based on size (neuropeptides or small molecule NT)

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23
Q

What are neuropeptides

A

Relatively large transmitter molecules composed of 3 to 36 amino acids

24
Q

What are small molecule NTs

A

Include individual amino acids such as glutamate and GABA
Also include the transmitters Ach and the bio genie amines dopamine, noradrenaline, adrenaline, serotonin and histamine

25
Q

What does fast transmission use

A

Amino acids or Ach

26
Q

What does slow transmission use

A

Any of the three types of NTs

27
Q

Describe Glutamate

A

Most common, excitatory in CNS
Iono tropic receptors
Influx of cations into postsynaptic neurons
Metabotropic receptors modulate ion channels

28
Q

Describe GABA and Glycine

A

Inhibitory in the CNS
Halfinhibitory synapses in spinal cord use glycine
Bind to ionotropic receptors
Influx of Cl- into post synaptic neurons
Metabotropic receptors activate K+ channels and block Ca2+
Net loss of positive charge

29
Q

Describe acetylcholine

A

Used in both PNS ganglia of visceral motor system and CNS, forebrain
Ionotropic receptors - nicotinic
Metabotropic receptors - muscarinic

30
Q

what are the 5 biogenic amines

A

Dopamine
Noradrenaline
Adrenaline
Histamine
Serotonin

31
Q

Describe dopamine

A

Involved in many forebrain circuits
Associated with emotion, motivation, reward
Acts on G-protein coupled receptors
Excitatory (via D1 receptors)
Inhibitor (via D2 receptors)

32
Q

Describe noradrenaline

A

Involved in wakefulness and attention
Acts on the Metabotropic alpha-adrenergic and beta-adrenergic receptors, both of which are excitatory

33
Q

Describe adrenaline

A

Acts on the same receptors but its concentration in the CNS is much lower than that of noradrenaline

34
Q

Describe Histamine

A

Binds to an excitatory Metabotropic receptor in the CNS and is involved in wakefulness

35
Q

Describe serotonin

A

Both an excitatory or inhibitory effect
Involved in a regulation of mood, emotion and several homeostatic pathways
Most receptors are Metabotropic
One ionotropic serotonin receptor which is a non selective cation channel and therefore excitatory

36
Q

Describe the purine ATP

A

Cotransmitter
Can be broken down into adenosine, a purine which binds to the same receptors as ATP

37
Q

Purinergic receptors can be….

A

Either ionotropic or Metabotropic

38
Q

Ionotropic receptors are..

A

Coupled to non-specific cation channels and are excitatory

39
Q

Metabotropic receptors act on..

A

G protein coupled signalling pathways

40
Q

What are neuropeptides

A

Group of peptides that include molecules involved in pain perception and modulation
Eg substance P, metenkephalin and opioids
Other neuropeptides are involved in the neural response to stress such as corticosteroid-releasing hormone and adrenocorticotropin

41
Q

Describe ligand (chemically) gated ion channels (ionotropic receptors)

A

Similar structure to other ion channels and incorporate a ligand binding site (receptor) in the extracellular domain
Control the fastest synaptic events in the NS
Activation generally rapid and is mediated by amino acids and amines
Speed of this response implies that the coupling between the receptor and ion channel is direct
No intermediate biochemical steps involved in transduction phase
NT binding causes channel to open
Consequence depends on specific ions that pass through the pore
Na+ and K+ channels cause depolarisation and are excitatory
Cl- channels cause hyperpolarisation and are inhibitory

42
Q

GABAa receptor is the site of…

A

Action of many iimportant drugs and compounds
Barbiturates, benzodiazepines and alcohol cause hyperpolarisation Cl- influx

43
Q

Describe type 2 G protein couples Metabotropic receptors

A

Largest super family of receptors
Despite diversity of signal molecule they all have a single polypeptide chain that threads back and forth

44
Q

Describe the action of G protein coupled receptors

A

Either by:
- opening ion channels
- by activating enzymes that synthesise second messenger molecules. Tend to be slower, longer lasting and have greater diversity than ligand gated ion channels
Ligand may bind to a family of receptors with different effects due to specific receptor type

45
Q

What is the role of G proteins

A

Membrane resistant proteins
Recognise activated GPCRs ad pass on the message

46
Q

How do G proteins carry out their action?

A

-Composed of 3 subunits, alpha beta gamma
-Achored to the membrane and coupled to the G protein through prenylation
-Freely diffusable within the plane of the membrane
-Interact with several receptors and effectors
-Unstimulated the a subunit has GDP bound (idle)
-Signal causes α subunit to exchange GDP for GTP
• Α subunit & GTP detaches from βγ complex
• The released α subunit and βγ complex are active
• Diffuse within the membrane and interact with target proteins relying signal to other parts of the cell.
• Βγ mediated effects occur at higher levels of receptor occupancy
• α subunit association with target enzymes cause activation or inhabitation
• Signal terminated when α subunit GTP is hydrolysed to GDP (GTPase)
• Self limiting
• Single receptor agonist complex can activate several G-proteins to produce product molecules
• Product molecules often a second messenger

47
Q

How to modulate synaptic transmission in progress

A

Limit further release of transmitter
May act as a break on the release of NT

48
Q

example of auto inhibition

A

Noradrenaline in sympathetic neurons

49
Q

Synthesis and storage of NTs

A
  1. Vesicle and peptide NT precursors and enzymes synthesised in the cell and are released from Golgi
  2. Vesicles travel through the axons on microtubule tracks via fast atonal transport. Peptide NTs are already in some vesicles
  3. A non peptide NT is synthesised in the nerve terminal and transported into a vesicle
50
Q

Why must NTs be cleared from the synapse

A

To permit another round of synaptic transmission

51
Q

How are NTs cleared from the synapse

A

Diffusion
Enzymatic degradation in the synapse
Presynaptic reuptake followed by degradation or recycling
Uptake by glia
Uptake by the post-synaptic neuron and desensitisation

52
Q

NTs in the CNS can act on numerous…

A

Subtypes of receptors

53
Q

Low-frequency stimulation…..

A

Low-frequency stimulation preferentially raises the Ca2+ concentration close to
the membrane, favoring the release of transmitter from small clear-core vesicles
docked at presynaptic specializations. High-frequency stimulation leads to a more
general increase in Ca2+, causing the release of peptide neuro transmitters from
large dense-core vesicles as well as small-molecule neurotransmitters from small
clear-core vesicles.

54
Q

Describe synaptic integration - inhibition

A

IPSP are generated when ion channels are opened casing hyperpolarisation of the membrane ie GABA or glycine opens Cl- channels
Shunting inhibition - inward movement of Cl- anions will negate the flow of positive ions

55
Q

Describe the generation of excitatory postsynaptic potential

A
  1. An impulse arriving in the presynaptic terminal causes the release of NT
  2. Molecules bind to transmitter-gated ion channels in the post synaptic membrane. If Na+ enters the post-synaptic cell through the open channels., the membrane will become depolarised
  3. The resulting change in membrane potential (Vm) are recorded by the microelectrode in the cell , is the EPSP
56
Q

What are 2 excitatory NTs

A

ACh and glutamate

57
Q

Describe the generation of an Inhibitory Postsynaptic Potential

A
  1. An impulse arriving in the pre-synaptic terminal causes the release of NT
  2. The molecules bind to the transmitter-gated ion channels in the post-synaptic membrane. If CL- enters the post-synaptic ell through the open channels, the membrane will become hyper polarised
  3. The resulting change is the IPSP

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