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202 Theme 1 > Lecture 1 Synaptic transmission > Flashcards

Lecture 1 Synaptic transmission Flashcards

1
Q

what is a synapse

A

a specialised junction where part of a neuron contacts and communicates with another neuron or cell type (muscle or glandular)

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2
Q

what are the two main categories of synapses

A

chemical (majority) and electrical (minority)

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3
Q

how do electrical; synapses compare to chemical

A 
simpler structure and function
faster
passive signal transmission
bidirectional 
minority (common in development)
allow synchronised electrical activity among populations of neurons
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4
Q

how do chemical synapses work simply

A

Arrives as electrical and converted to chemical and back to electrical in chemical synapses

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5
Q

what is a drug

A

a chemical substance, which when administered to a living organism, produces a biological effect
drugs affect how signals are communicated at a synapse
eg caffeine
affects learning and memory

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6
Q

what are the types of synapse

A

axodendritic
axosomatic
axoaxonic

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7
Q

what is the presynaptic element

A

upstream neuron, source of current

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8
Q

what is the postsynaptic element

A

downstream neuron, into which current flows

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9
Q

how does synapse location link to function

A

where they are affected how strongly they affect the postsynaptic neuron

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10
Q

what is an axodendritic synapse

A

presynaptic axon to dendrite in postsynaptic neuron

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11
Q

what is an axosomatic synapse

A

presynaptic contact to postsynaptic soma (more synaptic weight)

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12
Q

what is an axoaxonic synapse

A

presynaptic axon contacts axon of another cell before attaching to postsynaptic soma, affects communication as can cancel each other out (signal integration to determine excitation/inhibition)

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13
Q

what is the chemical synapse

A

synaptic bouton - presynaptic element
cytoskeleton - aid function and passing signals
mitochondria
synaptic vesicles - cont nt
synaptic granules ^
active zone - membrane of presynaptic cell to optimise conditions of membrane for communication
synaptic cleft - gap btwn AZ and postsynaptic cell

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14
Q

what is the neuromuscular junction

A

similar to chemical synapse
one synapse innervates many muscle fibres
vesicles contain Ach, received by muscle fibres converted to electricity for contraction

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15
Q

what is the postsynaptic membrane at the neuromuscular junction called

A

motor end-plate

folds to inc SA for more powerful reception of signals

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16
Q

how does synaptic transmission occur

A

as an action potential reaches the synaptic terminal, nt molecules are released from presynaptic neuron and diffuse across cleft to post synaptic membrane

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17
Q

what do receptors on the postsynaptic membrane recognise

A

specific neurotransmitters to initiate a response

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18
Q

what are the types of responses

A

direct excitatory or inhibitory (on or off) neurotransmission

neuromodulation - lots of possible effects (dynamic so important in development and memory)

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19
Q

what is direct excitatory or inhibitory transmission

A

the membrane of the next cell becomes slightly depolarised (ex) or hyperpolarised (in)

20
Q

what is neuromodulation

A

alters the presynaptic cell’s ability to release more transmitter or the postsynaptic cell’s ability to respond

21
Q

how much transmitter is released

A

released in specific packages (quanta)

22
Q

what criteria define a neurotransmitter

A

synthesised in the neuron
present in presynaptic terminal and released to exert a defined effect on postsynaptic neuron or effector organ
administered exogenously it mimics action of endogenously released transmitter
specific mechanism exists to remove it from cleft

23
Q

what is the first step of typical chemical synapse transmission

A

transmitter synthesised then stored in vesicles

24
Q

what is the 2nd step of typical chemical synapse transmission

A

action potential invades the presynaptic terminal

25
Q

what is the 3rd step of typical chemical synapse transmission

A

presynaptic. terminal depolarises causes opening voltage gated ca2+ channels

26
Q

what is the 4th and 5th step of typical chemical synapse transmission

A

influx of Ca2+ causing vesicles to fuse with presynaptic membrane

27
Q

what is the 6th and 7th step of typical chemical synapse transmission

A

transmitter released int synaptic cleft by exocytosis

binds to receptor molecules in postsynaptic membrane

28
Q

what is the 8th and 9th step of typical chemical synapse transmission

A

opening or closing of postsynaptic channels

postsynaptic current causes ex or in potential that changes the excitability of the postsynaptic cell

29
Q

what is the 10th and 11th step of typical chemical synapse transmission

A

remove nt by glial uptake or enzymatic degradation

retrieve vesicular membrane from plasma membrane

30
Q

where and how are vesicles anchored in the presynaptic cell

A

pool of vesicles anchored to cytoskeleton by synapsin

31
Q

how does action potential flow through the cell

A

action potential to presynaptic terminal, voltage gated ca2+ channels open so ca2+ flows to cytoplasm activate calmodulin activated kinase II (CaMKII) which phos synapsin

32
Q

How are synaptic vesicles released and recycled

A

activates calmodulin activated kinase II (CaMKII) which phos synapsin
P-synapsin can no longer bind to cytoskeleton, allows vesicles to dock to active zone to start fusion/exocytosis
vesicles reused

33
Q

what is a SNARE complex

A

at active zone

enzyme (ATPase) docks vesicles to plasma membrane as a helical protein with v and t SNAREs

34
Q

what are the mechanisms of exocytosis during neurotransmitter release

A

vesicle docks
entering Ca2+ allows binding to membrane
SNARE complex form to pull membranes together
entering Ca2+ binds to synaptotagmin
ca2+ bound synapto catalyses membrane fusion by binding SNAREs to plasma membrane

35
Q

how are vesicles recycled

A

rapidly recovered by endocytosis (10-20 sec), new vesicles bud off and refilled with transmitter
whole cycle about 1min

36
Q

how are SNARE proteins affected by clostridial toxins

A

sites of proteolysis blocking nt release
target amino acids in SNAREs
botox and tetanus prevent transmission release

37
Q

how does botulinum toxin affect SNAREs

A

stops neuromuscular transmission of Ach - paralysis by relaxation (treatment for muscle paralysis)

38
Q

how does tetanus toxin affect SNAREd

A

interneurons at spinal cord, GABA/gly to stop inhibitors - permanent contraction

39
Q

where are botulinum and tetanus toxins from

A

from bacteria Clostridium botulinum and tetani respectively

40
Q

what diseases affect the presynaptic terminal

A

cong myasthenia syndromes - impaired vesicle recycling
latrotoxin - trigger vesicle fusion
botox and tetanus
cog disorders impair transsynaptic signalling
LEMS attacks presynaptic Ca2+ channels

41
Q

how are vesicular transporters powered

A

proton gradient
ATPase proton pump loads up vesicles with H+ to make acidic (pH 5.5 comp to cytoplasm 7.2)
eg 1 glut traded for 1 H+ (counter transport)

42
Q

how are plasma membrane transporters powered

A

by electrochemical gradient
Na+ higher outside and K+ inside
eg glut co transported in with 2 Na+

43
Q

what do glia do

A

part of tri-partite synapse - support and regulate
support synaptic transmission
express nt receptors (can respond to synaptic activity by changing intracellular Ca2+)
coordinate synapse formation and elimination with secreted and cell surface associated signals

44
Q

what do glia control

A 
synapse formation
function
plasticity
elimination 
crucial in development, learning, memory and disease
45
Q

how do glia link to disease

A

reactive gliosis post injury (relevant to CNS regeneration)
aberrant synapse formation (link to epilepsy and neuropathic pain)
brain cancer
HIV induced dementia
neuroinflammatory response (depression)
neurodegernative diseases (Alzheimers, glaucoma, prion disease through aberrant synaptic stripping)

202 Theme 1 (6 decks)

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