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Cellular And Molecular > Lecture 6 - Synapses > Flashcards

Lecture 6 - Synapses Flashcards

1
Q

How many synapses are there in the human cortex?

A

Neurons - 20 billion
Over 1000 synapses per neuron
Total: 20 trillions I.e > 20 x 10^12

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2
Q

What are some synapses?

A

Excitatory

Increasing the response of a post-synaptic neuron

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3
Q

What are some examples of excitatory neurotransmitters?

A

Glutamate

ACH

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4
Q

What are some examples of inhibitory neurotransmitters?

A

GABA

Glycine

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5
Q

What determines the neurotransmitter action?

A

The properties of the receptors

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6
Q

Why did B.Katz win the Nobel prize?

A

Understanding quintal neurotransmission

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7
Q

What did B.Katz work on?

A

Nerve muscle junction

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8
Q

How are neurotransmitters released into a synapse?

A

Packaged vesicles called quanta

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9
Q

What does one quantum generate?

A

Miniature end plate potential

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10
Q

What is miniature end plate potential?

A

Smallest amount of stimulation that one neuron can send to another neuron

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11
Q

What is Quantal release a mechanism of?

A

Most traditional endogenous neurotransmitters are transmitted throughout the body

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12
Q

What 2 types of molecules does chemical neurotransmission rest on?

A

Chemical messengers

Chemically gated receptors

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13
Q

What plays an important role in giving rise to a negative membrane potential?

A

Electrochemical gradient for K+ ions

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14
Q

Why is ACH receptor not selective between sodium and potassium ions?

A

It has a reversal potential of 0 millivolts

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15
Q

Ena

A

Positive

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16
Q

Ek

A

Negative

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17
Q

NACh receptors

A

Ionotropic receptors

Respond to chemical stimulus and incorporate an ion channel

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18
Q

What is the structure of NACh receptors?

A

Formed from 5 subunits

Subunits have alpha helical domain

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19
Q

What happens in the absence of ACH?

A

H20 is being excluded

Alpha helices are stuck together

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20
Q

What holds the channels closed?

A

Hydrophobic interactions

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21
Q

Where does ACH bind?

A

At C loops on the alpha subunit

Outside the inter membrane domain

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22
Q

What helps shape the ACH binding pockets?

A

Gamma or delta subunit

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23
Q

Where was 2 sharp micro electrode inserted into muscle fibre?

A

One close to NMJ

The other can move at flick of switch

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24
Q

How is synaptic potential generated?

A

When you send action potential down the motor axon that is connected to muscle fibre

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25
What happens to the micro electrode close to the NMJ?
Rapid rising of EPP
26
What is NMJ?
High-fidelity junction
27
What happens when you move the microelectrode further away?
The EPP gets smaller Rise of EPP gets smaller (Moving away from the source of depolarising current)
28
What does muscle fibre membrane have?
Capacitance
29
What is the source of excitation in muscle fibre?
End plate
30
What was NMJ initiating?
Excitation in the muscle fibre
31
What does a single quantum cause?
Only a slight depolarisation
32
What happens when the electrode is inserted into muscle fibre very close to the NMJ?
Send impulses down motor axon | Record AP
33
What occurs when electrode is recorded away from end plate?
No EPP is seen | Just AP
34
How are tiny little blips recorded?
If amplifier is increased when electrode is near NMJ
35
What occurs spontaneously in muscle fibre?
Tiny miniature potential
36
How is the release of neurotransmitters at NMJ controlled?
Electrically
37
What kind of recording is done in a muscle fibre?
Intracellular
38
What is the release of neurotransmitter from presynaptic terminal dependent upon?
Presence of Ca2+
39
Where must Ca2+ enter to trigger the release of neurotransmitter?
Pre-synaptic terminal
40
What is not random but related?
The relationship between releasing neurotransmitters and the size of EPP recorded in a muscle fibre
41
How is EPP generated?
Release of many N.T
42
What is present on the post-synaptic membrane?
Junctional folds
43
What is Acetylcholinesterase?
the enzyme that is responsible for breaking down ACH and terminating it’s action
44
What is the role of Snare proteins?
Mediate vesicle fusion
45
What is snare protein a primary target of?
Botulinum | Tetanus toxins
46
What does synaputogamin-1 induce?
Transduction the Ca2+ signal into membrane “bending”
47
What is present in the synaptic cleft?
Acetylcholinesterase
48
What can neurotransmitter breakdown be inhibited by?
Organophosphate nerve agent e.g. sarin (nerve gas) Insecticide
49
What is neurotransmitter breakdown medicinally inhibited by?
Neostigmine | Physostigmine
50
What are the reasons for chemical transmission at NMJ?
Presence of miniature and analysis of EPP amplitude suggest transmission is based on quantal mechanism Functional synaptic transmission requires entry of Ca2+ into presynaptic terminal Presynaptic terminal typically contain membrane bound vesicles EM: exocytosis of vesicles takes place with nerve stimulation, and that neurotransmitter is released into synaptic cleft Transmission is unidirectional Protein complex involved in exocytosis require Ca2+ entry Nicotine acetylcholine receptors are found expressed at postsynaptic membrane Immunohistochemical data puds Acetylcholinesterase in post junctional gold Blocking NT release or breakdown alters characteristic of transmission Autoantibodies against acetylcholine receptors cause myasthenia graves
51
What does neurotransmitter release in CNS cause?
EPSP IPSP In the postsynaptic cell
52
EPSP
1a afferent reflex arc Reflex that give rise to knee jerk Hamstring contain muscle spindle When you hit the ligament it is stretched Give rise to AP/impulse which go up the sensory pathway Make monosynaptic connection with a same motor neuron Alpha motor neuron sits in the central horn of spinal cord and connects to same muscle
53
What is Glutamate receptor?
Excitatory synapse that give rise to depolarisation | Glutamate receptor: ionotropic
54
What does a central axon lead to?
Pre-synapse
55
What are examples of glutamate receptors?
Kinate receptors NMDAR AMPA
56
What is Dales principle?
Each synaptic connection made by a single neuron utilises the same chemical transmitter
57
Renshaw Inhibition
The first functional central circuit to be discovered Inhibitory neuron: grey matter of spinal cord Associate 2 ways: Receive excitatory collateral from alpha neurons axon as they emerge from motor root and informed of how vigorously that neuron is firing Renshaw cell synapses with multiple neuron Elicit IPSP in alpha motor 1a inhibitory internueon and gamma motor neuron
58
What is reciprocal antagonist inhibition?
When the CNS sends a message to agonist muscle to contract, the tension in Antagonist muscle is inhibited by impulses from motor neuron and thus must simultaneously relax
59
Mechanism of IPSP
``` Glycine/GABA a receptor Ionotropic receptor Linked with an ion channel Cl- crosses the membrane Give rise to hyperpolarisation ```
60
What is Risus sardonicus?
High characteristic, abnormal sustained spasm of facial muscle that appears to produce grinning
61
Where is Glutamate taken up in?
Pre and post synaptic terminals and into adjacent glia | The transporter uses energy stored in the transmembrane Na* gradient to uptake glutamate
62
Synaptic plasticity
Long lasting potentiation Record extracellularly in dentate gyrus Extracellular recording is altered by tetanizing activating performant path at high frequency Synaptic depression and potentiation are both apparent in CA1 region of hippocampus
63
What is LTD linked with | ?
Activation of G protein coupled glutamate receptors morning
64
Dudek + Bear
CA1 hippocampus (pyramidal neurons) If you use 3hg to excite an input pathway to CA1 You can depress the synapse (LtD) If you use 10hg stimulation - no long term effect on synaptic strength 50hg briefly —> generate LTP
65
Long term synaptic plasticity
Memory storage
66
What is the molecular mechanism of sensitisation in Aplysia?
Activate 5HT receptors Release serotonin which acts on G protein coupled receptors Activated pka Action on potassium channels Increase pka = translocated into the nucleus Gives rise to the activation of protein synthesis When KREB1 and KREB2 are bound together in the nucleus of a sensory neuron - become inactive

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