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Neurobiology > Synaptic Transmission > Flashcards

Synaptic Transmission Flashcards

0
Q

What are 3 roles of electrical synapses?

A

1) network activity (synchronization of electrical activity/info across many neurones)
2) communication between glia
3) coordination of growth in embryonic development (Bear et al)

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1
Q

What protein forms a gap junction?

A

Connexin (6 subunits from a connexon = hemichannel)

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2
Q

Which type of synapse has a role in epilepsy?

A

Electrical

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3
Q

Which type of synapse is the most common form of communication in the CNS?

A

Chemical

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4
Q

Chemical synapses occur between a presynaptic element, most commonly _______, and postsynaptic elements such as ________

A

Axon terminals

Dendrites, soma, axon terminals

(I.e. Axoaxonic, axosomatic, axodendritic)

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5
Q

Why is chemical transmission greatly flexible?

A

Many different NTs and receptors
Can modulate expression of NT and receptors
=> huge modulatory activity

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6
Q

What is the distance across the synapse for a) electrical synapses?
and b) chemical synapses?

A

Electrical - 0.35nm

Chemical - 30-50nm

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7
Q

What is the synaptic delay at:

a) electrical synapse?
b) chemical synapse?

A

a) none

b) min 0.3ms, usually 1-5ms

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8
Q

What is the direction of transmission for chemical and electrical synapses?

A

Chemical - unidirectional

Electrical - bidirectional

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9
Q

What are the 4 types of major NT?

A

Ach
Amines
AAs
Peptides

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10
Q

Small molecule NTs are synthesised in______ and stored in _____?

A

Synaptic terminal using enzymes from cell body

Small clear vesicles (40-60nm)

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11
Q

Large NTs are synthesised in _____ and stored in _____?

A

Cell body using RER and Golgi

Large dense core vesicles (90-250nm)

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12
Q

Where does Ca enter the presynaptic terminal?

A

Active zone

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13
Q

What is a MEPP?

A

Miniature end plate potential

=> spontaneous release of a single vesicle (quanta) (not due to AP)

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14
Q

What is/what causes an EPP?

A

Multiple MEPPs due to AP dependent release of many vesicles

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15
Q

Are axo-dendritic synaptic connections usually inhibitory or excitatory?

A

Excitatory

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16
Q

Are axo-somatic synaptic connections usually inhibitory or excitatory?

A

Inhibitory

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17
Q

Synapses where influence neurone firing the greatest?

A

At the initial segment / axon hillock

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18
Q

Which type of synaptic connection is modulatory and controls NT release?

How does it control NT release?

A

Axo-axonic

Controls Ca influx in presynaptic neurone

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19
Q

What is the name of the axo-axonic connection that increases NT release?

A

Presynaptic facilitation

Decreases K+ current, increases Ca current

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20
Q

What is integration?

A

Summation of all EPSPs and IPSPs

21
Q

Where does integration occur?

A

Axon hillock

22
Q

What is convergence?

A

Many neurones synapse onto one neurone

23
Q

What is divergence?

A

One neurone communicates with many via axon collaterals

24
Q

What is temporal summation?

A

Summation of PSPs arriving in quick succession (only needs one synaptic input)

25
Q

What is spatial summation?

A

Summation of PSPs from different inputs across membrane surface

26
Q

How does frequency affect NT release?

A

Increased frequency = increased release

27
Q

What NTs require higher frequency APs for release?

A

Peptides

28
Q

Why is an AP?

A

Self-propagating wave of depolarization

29
Q

What is the normal direction of an AP?

A

Orthodromic

30
Q

Synaptobrevin is what type of SNARE and what does it do?

A

V-SNARE

Binds T-SNAREs: SNAP-25 and syntaxin forming SNARE complex (docking and priming)

31
Q

Which SNARE protein is a Ca sensor?

What does it trigger?

A

Synaptotagmin

SNARE complex formation and Fusion (Ca dependent)

32
Q

What do synapsins do?

A

Restrain vesicles - bind NT to cytoskeleton

33
Q

How are vesicle released from synapsins?

A

Ca dependent phosphorylation of synapsin

34
Q

What occurs in targeting and docking?

A

Vesicle moves towards and binds to active zone

35
Q

What is priming?

A

Vesicles are prepared for fusion

36
Q

What is fusion?

A

Pore opening

37
Q

What is the process (each step) of NT release from vesicles?

A

1) vesicles restrained (synaspsin)
2) targeting + docking
3) priming
4) fusion
5) exocytosis
6) endocytosis

38
Q

How long does it take for vesicles to be recycled after release?

A

30-60 sec

39
Q

What is the role of Clathrin proteins and dynamin?

A

Endocytosis;
- Clathrin binds and distorts vesicle membrane, pulls it into cell
- once fully invaginated dynamin “pinches off” vesicle
(Energy dependent GTP -> GDP)

40
Q

What do zinc endonucleases and clostridium toxins do?

A

Cleave SNARE proteins actively involved in fusion

41
Q

What are clostridium toxins?

A

Botulinum and tetanus

42
Q

Which toxins is synaptobrevin cleaved by?

A

Tetanus and botulinum B, E, F + G

43
Q

Which toxins are snap-25 and syntaxin cleaved by?

A

Snap25: botulinum A + E

Syntaxin: botulinum C

44
Q

What does botulinum toxicity cause?

A

Blocks neuro transmission at peripheral Cholinergic synapses

45
Q

Do vesicle transporters have high or low specificity?

A

LOW (many NTs use same transporter)

46
Q

Do membrane tansporters have high or low specificity?

A

High (each NT has dif transporter)

47
Q

What are vesicular transporters?

What else do they require to function?

A

Proton dependent antiporters
(NT in, H+ out)

ATPase: transports H+ into vesicle creates electro chem gradient

48
Q

What is a membrane transporter?

Which NTs have these?

A

Na- dependent symporter

Choline, 5-HT, DA, GABA, glutamate

49
Q

What is disinhibition?

A

Inhibition of inhibitory neurones

Generation of excitation by transient inhibition of a tonically active neurone

50
Q

Describe how disinhibition works in the basal ganglia to excite the motor cortex

A

1) striatum excited (by excitatory input from cortex)
2) increased inhibition of globes pallidus
3) decreased inhibition of VL/VA of thalamus (it is disinhibited)
4) allows excitation of motor cortex

Neurobiology (9 decks)

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