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Physiology 2410 > Lecture 10- synaptic transmission > Flashcards

Lecture 10- synaptic transmission Flashcards

1
Q

what is a synapse?

A

connection between two neurons or a neuron and another cell that is specialized for the transfer of information

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2
Q

what ways do we classify synapses? (2)

A

functional
location on post synaptic cell

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3
Q

what is functional classification in respect to synapses?

A

electrical vs chemical

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4
Q

what locations on the post-synaptic cell can synapses be on?

A

axodendritic
axosomatic
axoaxonic

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5
Q

what does synaptic activity cause?

A

graded potentials in the postsynaptic cell

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6
Q

what is a depolarizing synaptic potential also called?

A

excitatory postsynaptic potential (EPSP)

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7
Q

what is a hyperpolarizing synaptic potential also called?

A

inhibitory postsynaptic potential (IPSP)

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8
Q

what does an IPSP do?

A

brings membrane more (-)
makes it harder to fire action potentials

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9
Q

describe the structure of a gap junction

A

there are two connexons, each made of 6 connexin monomers, thus a complete channel is 12 connexins. each gap junction must align to form a functional channel

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10
Q

how far apart is the postsynaptic cell and the presynaptic cell?

A

3.5nm

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11
Q

what is an example of an electrical signal?

A

action potential

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12
Q

how does electrical information get transported between two cells?

A

directly carried by the movement of ions between cells

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13
Q

where are electrical synapses commonly found?

A

some neurons
cardiac muscle
smooth muscle

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14
Q

how can an electrical signal be bidirectional?

A

under experimental conditions (not physiological)

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15
Q

what are two important reasons why electrical synapses exist?

A

fast communication (has short synaptic delay of 0.2ms)
allows groups of cells to fire action potentials nearly synchronously

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16
Q

cells with electrical gap junctions are said to be connected by what?

A

cytoplasm

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17
Q

what are chemical synapses a specialized form of?

A

exocytosis

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18
Q

what do chemical synapses do?

A

release of neurotransmitter from presynaptic cells to influence electrical activity in postsynaptic cell

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19
Q

neurons communicate with post- synaptic targets, what are 3?

A

other neurons
muscle cells
glands

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20
Q

how many synapses are in our brains?

A

100-600 trillion

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21
Q

how does a chemical signal work?

A

electrical signal from one neuron is converted to a chemical signal to cross a synaptic cleft, then is often converted back to an electrical signal

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22
Q

what are the classic neurotransmitters? 3

A

acetylcholine
amines (norepinephrine, dopamine, histamine, serotonin)
amino acids (glutamate, GABA)

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23
Q

what are the novel neurotransmitters (recognized in the past 25+ years)? 2

A

peptides (oxytocin, melanocortin)
purines (ATP)

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24
Q

explain the general mechanism of a neurotransmitter?

A
  1. action potential travels down axon. depolarization opens voltage gated Ca++ channels (allows Ca++ to enter presynaptic terminals)
  2. Ca++ entry causes some synaptic vesicles to fuse with presynaptic membrane and release their neurotransmitter contents into the synaptic cleft
    3.neurotransmitter binds to postsynaptic receptors. some receptors are ion channels, some are GPCR, the postsynaptic response depends on the type of receptor
  3. neurotransmitter is removed from the cleft
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25
Q

when neurotransmitter is removed from the cleft of the general mechanism, what are 4 different destinies of the neurotransmitters?

A
  1. destroyed in the synaptic cleft by a degradative enzyme
  2. transported back into the terminal by active transport. recycled and repackaged back into vesicles.
  3. diffuses away from synapse
  4. taken yp into postsynaptic cell by endocytosis
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26
Q

what is the process of synthesis and recycling of acetylcholine?

A
  1. acetylcholine is made from choline and acetyl CoA
  2. in the synaptic cleft ACh is rapidly broken down into choline and acetic acid by the enzyme acetylcholinesterase
  3. choline is transported back into the axon terminal by cotransport with Na+
  4. recycled choline is used to make more ACh
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27
Q

what is the synapse of acetylcholine called?

A

cholinergic synapse

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28
Q

what is acetylcholine neurotransmitter used by?

A

motorneurons
every pathway of the autonomic nervous system
used diffusely throughout the central nervous system as a neuromodulator

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29
Q

what does acetylcholine do for motor neurons?

A

causes excitation of skeletal muscle

30
Q

what are the two kinds of receptors for ACh?

A

receptor channels
GPCR

31
Q

what receptor does ACh use for receptor channels?

A

nicotinic receptor (nicotine is agonist for receptor)

32
Q

what receptor does ACh use for GPCR?

A

muscarinic receptor

33
Q

what does binding of ACh to a receptor channel cause?

A

opening of channel
entry of Na+ and exit of a small amount of K+

34
Q

what does movement of (+) charge into cell cause in respect to acetylcholine?

A

depolarization (cell becomes more positive)

35
Q

is the postsynaptic potential inhibitory or excitatory? (ACh)

A

excitatory (EPSP)

36
Q

is ACh a fast or slow process?

A

fast (happens after a delay of miliseconds)

37
Q

what does binding of ACh to GPCR cause?

A
  1. generation of second messengers
  2. activation of kinases
  3. phosphorylation of proteins in the postsynaptic membrane
  4. some of the proteins that get phosphorylated are phosphorylation gated ion channels
  5. phosphorylation gates K+ leakage channels closed
38
Q

is the bind of ACh to GPCR a fast or slow process?

A

slow (happens after a delay of seconds and effects may last seconds to hours)

39
Q

will all GPCR neurotransmitter receptors cause closure of K+ channels?

A

no, there are many possible targets in postsynaptic cells (depends on the cell and the receptor)

40
Q

what are some examples of cell types that may be targeted through GPCR neurotransmitter receptors?

A

Na+ leakage channels
Ca++ channels

41
Q

What synapse is associated with norepinephrine?

A

noradrenergic synapse
or
noradrenaline synapse

42
Q

where is the norepinephrine neurotransmitter used?

A

CNS
sympathetic branch of the ANS (autonomic NS)

43
Q

what are the subtypes of receptors that norepinephrine uses?

A

all subtypes are GPCR

44
Q

what specific receptors does Norepinephrine use?

A

alpha and beta receptors

45
Q

what synapse is associated with glutamate?

A

glutamatergic synapse

46
Q

what is unique about glutamate?

A

its the main excitatory neurotransmitter used throughout the CNS

47
Q

what are the two types of glutamate receptors?

A

receptor channels (ionotropic)
GPCR (metabotropic glutamate receptors)

48
Q

what are ionotropic recptors?

A

ionotropic receptors are typically ligand-gated ion channels, through which ions pass in response to a neurotransmitter

49
Q

what are metabotropic receptors?

A

metabotropic receptors require G proteins and second messengers to indirectly modulate ionic activity in neurons

50
Q

what are the two subtypes of receptor channels in glutamate receptors?

A

NMDA receptor
AMPA receptor

51
Q

what does the AMPA receptor do? (glutamatergic)

A

allows Na+ to pass (some K+)
depolarizes cell

52
Q

what does the NMDA receptor do? (glutamatergic)

A

allows Na+ and Ca++ to enter (some K+ leaves)
inward movement of Na+ and Ca++ depolarizes cell
normally is blocked by Mg++ but Mg++ gets ejected when membrane depolarizes

53
Q

what is the main inhibitory neurotransmitter used throughout the CNS?

A

gamma- amino- butyric acid (GABA)

54
Q

what synapse does GABA use?

A

GABAergic synapse

55
Q

what two receptors does GABA use?

A

receptor channel
GPCR

56
Q

what receptor channel does GABA use?

A

ionotropic GABAa receptor

57
Q

what GPCR does GABA use?

A

metabotropic GABAb receptor

58
Q

what does binding of GABA to GABAa receptor channel cause?

A

opening of channel
negatively charged Cl- allowed to enter cell

59
Q

because Cl- enters the cell in binding of GABA to GABAa what happens?

A

movement of (-) charge into cell causes hyperpolarization

60
Q

is the postsynaptic hyperpolarization of GABA neurotransmitter EPSP or IPSP

A

IPSP (inhibitory)

61
Q

what is the most fast inhibitory synaptic transmission in the vertebrate central nervous system?

A

binding of GABA to GABAa receptor channel

62
Q

which synaptic receptors, a receptor channel or GPCR causes a faster postsynaptic response? why?

A

receptor channel because GPCR has a lot more steps to it

63
Q

what is the fastest synatpic transmission?

A

electrical synapses

64
Q

what are different things that GPCRs do after activating second messenger pathway? (3)

A

alters open state of ion channels (closes or opens channels)
modifies existing proteins or regulates synthesis of new proteins
change gene expression

65
Q

what do chemically gated ion channels do?

A

open ion channels

66
Q

big difference between electrical and chemical synapses?

A

electrical: fast and simple
chemical: slow and complex

67
Q

why would electrical signals from one neuron get converted to a chemical signal to cross synaptic cleft, then get converted back to an electrical signal?

A

allows excitatory signals to become inhibitory
allows modulation of signals
very efficient

68
Q

what does modulation of signals mean?

A

switch from single AP to tonic to bursting (information processing)

69
Q

how is the process of changing from electrical to chemical to electrical signals efficient?

A

a few molecules of neurotransmitter can have a large electrical effect on a post synaptic cell

70
Q

what makes chemical synapses so complex?

A

theres a wide variety of receptors, even for a single neurotransmitter

71
Q

what receptor channels cause depolarization?

A

ACh
NMDA
AMPA

72
Q

does phosphorylation open channels in ACh, Norepinephrine, glutamate, GABA?

A

ACh: yes
norepinephrine: yes?
glutamate: yes?
GABA: no?

Physiology 2410 (21 decks)

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