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Neuroscience > L17 Synaptic Transmission > Flashcards

L17 Synaptic Transmission Flashcards

1
Q

what is a homomeric connexon?

A

consists of 1 type of connexin

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2
Q

what is a heteromeric connexon?

A

formed by a mix of different connexin isoforms

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3
Q

what are hemichannels?

A

connexins + pannexins

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4
Q

what are gap junctions?

A

only connexins

connexons may dock with an identical connexon to form a homotypic or a different connexon to form a heterotypic channel

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5
Q

what is the speed of transmission through gap junctions?

A

FAST (under 0.1ms)
unidireciton transmission
bidirectional transmission

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6
Q

what type of transmission is seen in electrical synapses?

A

gap junctions

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7
Q

what are gap junctions made of?

A

2 hemichannels (connexons) which are composed of 6 units of 4 membrane spanning regions (connexins)

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8
Q

where are gap junctions found (structures)?

A

CNS - spinal cord, hippocampus, mesensephalic nucleus and retina between horizontal cells

between astrocytes which allows them to function in sync when buffering K+ ions

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9
Q

are synapses most chemical or electrical?

A

chemical

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10
Q

what is a human disease with connexin mutation?

A

Charcot-Marie tooth syndrome

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11
Q

the postsynaptic membrane has extensive ___ regions?

A

dense - where NT is received in the postsynaptic membrane

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12
Q

what is an axodendritic synapse and what is an example?

A

excitatory on firing rate

cortical pyramidal cell’s dendrites

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13
Q

what is an axosomatic synapse and what is an example?

A

inhibitory on firing rate

cortical pyramidal cell’s soma

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14
Q

what is an axoaxonic synapse and what is an example?

A

inhibitory on NT release

cortical pyramidal neurons

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15
Q

what is a tripartite synapse?

A

between the presynaptic neuron
postsynaptic neuron
astrocyte endfeet - take in NT released by neurons and release others

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16
Q

define ionotropic receptor and give example?

A

ion channel proteins that open (or close) when they are hit by the NT which leads to a change in gm and Vm

consist of multimeric different proteins with 5 subunits and varying number of membrane spanning domain

nicotinic receptor

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17
Q

define metabotropic receptor and give example

A

mediate action via G protein influencing the activity of adjacent enzymes to induce changes in the 2nd messenger in the postsynaptic cell

muscarinic receptor

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18
Q

what is synaptic delay?

A

Delay between arrival of impulse and the onset of a response

from arrival of an impulse in the presynaptic nerve ending till the onset of the postsynaptic cell’s response after binding to a postsynaptic receptor and production and breakdown of 2nd messengers

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19
Q

what are the mechanisms for removing NT from the synaptic cleft?

A
  • diffusion - neuropeptide, all transmitters
  • extracellular enzymatic degradation Ach via acetylcholinesterase
  • uptake into nerve endings or glial - glutamate, GABA, catecholamines
  • intracellular enzymatic degradation
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20
Q

what are the 3 most important ionitropic glutamate receptors>?

A

NMDA
AMPA
kainate receptors

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21
Q

what is the role of the glutamate ionotrophic receptors?

A

cation channels that allow an influx of Na+ ions (NMDAR also Ca2+) and efflux of K+ ions
influx of Na+ ions exceeds efflux of K+ ions because the Na+ electrochemical gradient is larger than the K+ gradient

22
Q

what does the net entry of cations evoke?

A

depolarization = excitatory postsynaptic potential EPSP

23
Q

what does the amplitude of the EPSP reflect?

A

the amount of glutamate released by exocytosis in response to a presynaptic impulse

DEPOLARIZATIONS CAN BE GRADED IN SIZE DEPENDING ON THE APPLIED LICAL GLUTAMATE CONCENTRATION AND THE NUMBER OF OPEN GLUTAMATE-GATED CHANNELS IN POSTSYNAPTIC MEMBRANES

24
Q

what is the reversal potential for the excitatory response?

A

E cation

25
Q

define reversal potential?

A

when the potential is set close to 0, the AMPA channel opening does not cause current to flow because the inlfux of Na+ ions is counterbalanced by the efflux of K+ ions. the potential at which no current flows!

26
Q

local interneurons release inhibitory transmitters onto _____

A

motor neurons

for examples - the afferents not only excite motor neurons via AMPA receptors but they also excite local interneurons via AMPA receptors

27
Q

what type of influence do interneurons have on motor neurons of antagonist muscle and why?

A

inhibitory action on the motor neurons of the antagonist muscles because they release glycine on to the motor neurons for the antagonist muscle

28
Q

an impulse in the interneuron evokes what?

A

an inhibitory postsynaptic potential IPSP

29
Q

what type of channels are ionotropic glycine or GABA receptors?

A

anion channels - mostly Cl-

30
Q

describe the IPSP

A

transient hyperpolarization with rapid falling phase and a slower repolarizing phase

31
Q

what is the reversal potential for this inhibitory response?

A

-65 mV

32
Q

where are EPSP generated and where are they found?

A

synapses

dendrites, soma and axon hillock

33
Q

do EPSPs spread with decrement?

A

Yes - the induced depolarization spread BUT decline in amplitude according to their distance from the sites

34
Q

what type of summation is seen in EPSP?

A

spatial and temporal

35
Q

what does the firing rate of the neuron depend on?

A

the combined effect of the spatial and temporal summation of EPSPs and IPSPs occurring at many sites in its soma and dendrites

36
Q

what does cocaine do?

A

block Na+ channels from inside - also blocks the transporters for reuptake of dopamine, noradrenaline and serotonin and thereby prolongs their presence in cleft

37
Q

what does morphine do?

A

acts as an agonist for the receptors mediating the presynaptic inhibition of C fiber terminals - which relay pain info to second order neurons in the spinal cord

38
Q

where does action of morphine take place?

A

nociceptors
spinal cord
supraspinal sites
limbic system

39
Q

transmitter action is ____ within the synaptic celft

A

brief

40
Q

define active zone

A

where exocytosis occurs in presynaptic membrane

41
Q

which receptor will have a longer delay?

A

metabotropic - >100 ms delay due to 2nd messenger system = SLOWER = MORE CONTROL!

ionotropic - 0.5 ms delay due to mech of NT release

42
Q

how many motor neurons does an 1a-afferent sensory neuron innervate?

A

about 100 motor neurons for the muscle it monitors

43
Q

if a muscle is stretched, how will the 1a afferents be excited?

A

GLUTAMATE

44
Q

the 1a afferent sensory fibers will use glutamate to make synapses with what 2 things?

A

each motor neuron

interneurons –> release glycine onto antagonist muscle –IPSP!

45
Q

define spatial summation

A

the sum of the excitatory currents will add to = a larger EPSP than either of them alone

46
Q

define temporal summation

A

multiple impulses arriving so close together – they add to one another because the effect of the previous impulse has no relaxed back to the resting state - add on top of eachother!

47
Q

what are examples of ionotripic receptors?

A

nicotinic AChR, GABAa, NMDA and AMPA receptors for glutamate

48
Q

what are examples of meabotropic receptors?

A

muscarinic AChR and NE receptors

49
Q

what does cocaine do?

A

local anesthetic
blocks sodium channels from inside
blocks the transport for reuptake of dopamine, seratonin, NE and prolongs their presence in hte clefts

50
Q

what does morphine do

A

analgesic
binds to the receptors for neuropeptide (mu-enkephalin) that are located on the terminals of C fibers (nociceptors) in the substantia gelatinosa in the dorsal horn

agonist for receptors mediated the inhibition of C fibers terminals which relay pain info to second order neurons in spinal cord

Neuroscience (54 decks)

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