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PHGY 209 > nerve/synapse lectures 3-4 > Flashcards

nerve/synapse lectures 3-4 Flashcards

1
Q

what are sodium and potassium gradients maintained by

A

sodium potassium pump

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2
Q

describe sodium potassium pump

A

uses energy produced by ATP hydrolysis to pump sodium out and potassium in (against concentration gradients)

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3
Q

what happens if sodium potassium pump doesnt work

A

resting membrane potential goes down to zero

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4
Q

describe how pumps create the gradients

A

concentration gradient created by ATP energy - used to drive sodium potassium pump
concentration gradient creates potential energy gradient

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5
Q

where is sodium potassium pump found

A

neuron membrane

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6
Q

describe how the sodium potassium pump works - gen

A

uses ATP energy = binds and hydrolyzes ATP and uses energy
grabs sodium and pump out of cell against concentration gradient
grabs potassium from outside and pumps inside
maintains concentration gradients for sodium and potassium

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7
Q

what do axons do

A

propagate info from one region of the nervous system to another by electrical impulses = action potentials

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8
Q

where do action potentials start and go towards

A

start at initial segment of axon and propagate down length of axon to presynaptic terminals

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9
Q

describe action potential - informally

A

signal
electrical pulse = very rapid change in membrane potential of neuron
propagates like wave
self regenerating = will propagate through whole length

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10
Q

definition of action potential

A

transient depolarizing spike that moves down axon

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11
Q

describe membrane potential at the action potential peak

A

membrane potential approaches Ena

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12
Q

describe beginning of AP

A

membrane potential spikes for 1/1000 of sec to positive value +30mv then drops back to -70mv

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13
Q

how to simulate action potential

A

use stimulating electrode to change membrane potential by injecting current
will make initial segment more positive = depolarization

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14
Q

what is hyperpolarization

A

make more negative
inject negative current using simulator if reverse polarity (-70 to -80 mv)

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15
Q

when is action potential initiated

A

when membrane potential depolarizes to a threshold level

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16
Q

what is threshold determine by

A

properties of ion channels in the axon membrane (especially the voltage gated sodium channels)

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17
Q

what is threshold potential level

A

-50mv

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18
Q

what happens if membrane depolarizes from -70 to -65mv

A

will just go back to resting potential
nothing will happen

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19
Q

what happens if membrane depolarizes from -70 to -50mv

A

action potential
will not just go back to resting
action potential will start and no way to stop it

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20
Q

what is the rising (depolarizing) phase of action potential caused by

A

sodium ions flowing into cell through voltage gated sodium channels

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21
Q

name the 3 critical properties of sodium channels

A

1 - closed at resting membrane potential, open when membrane depolarizes
2 - selective for Na+
3 - open channel rapidly inactivates and stops flow of sodium ions

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22
Q

why does resting membrane have little permeability to sodium

A

since voltage gated sodium channels are closed

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23
Q

when voltage gated sodium channel is open

A

allows sodium to flow into cell through pore of voltage gated channels

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24
Q

where are voltage gated sodium channels concentrated

A

in axon
allows it to propagate

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25
Q

if sodium channel is inactivated can it open again

A

not directly
must be converted back to closed state before they can open again

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26
Q

the rising phase of the AP is…

A

a regenerative process

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27
Q

what does depolarization of the membrane to threshold potential activate

A

small amount of sodium channels
further depolarizes membrane and activates more sodium channels

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28
Q

what kind of mechanism is AP

A

positive feedback

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29
Q

describe positive feedback effect of ap

A

maximal activation of sodium channels
a large sodium influx
depolarization of membrane from resting level to near Ena

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30
Q

what does inactivation do

A

terminates sodium influx
causes membrane to relax back to its original resting level
potassium flows out and brings back to -70mv

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31
Q

describe what happens when 100% of sodium channels are open

A

very permeable to sodium
so membrane potential will go up near equilibrium potential of sodium
after 1 milisec sodium channels inactivate and drops back to potassium equilibrium potential

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32
Q

why at the peak of ap the Na+ permeability swaps for the resting permeable of K+

A

density of voltage gated sodium channels in axon membrane is much higher than density of the leak potassium channels

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33
Q

what contributes to falling phase of action potential

A

sodium channel inactivation
delayed activation of voltage gated potassium channels

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34
Q

describe voltage gated potassium channels

A

open when membrane is depolarized
much slower than sodium
channel opens after a delay (1 milisec after sodium channels open)
open when sodium channels inactivate
during falling part of ap

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35
Q

what happens when voltage gated potassium channels are open

A

potassium leaks out
helps bring membrane down to resting potential faster
shut when membrane repolarizes

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36
Q

what 2 factors help make action potentials short

A

sodium channels inactivate fast
potassium channels open and allow potassium to flow and repolarize membrane

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37
Q

why do we want action potentials to be short

A

since then you can send more
neuron can send many aps per second or in a short amount of time

38
Q

what happens without voltage gated potassium

A

ap would still happen but just repolarizes slower

39
Q

what happens to sodium and potassium gradients when many aps

A

they run down faster
neuronal activity must be maintained by pumps (sodium potassium pump)

40
Q

what happens if sodium potassium pump didnt work

A

gradients will just run down over time since neurons will still fire aps

41
Q

name something that can block sodium potassium pump

A

south american tree frogs make a toxin that can block pump
toxin is deadly

42
Q

describe role of sodium potassium pump in maintaining gradients when many aps

A

pump constantly and move sodium out and potassium in to maintain concentration gradients, so they are not run down by the aps

43
Q

what is action potential propagation caused by

A

spread of electronic currents from site of ap - which excites adjacent regions of axon
due to properties of voltage gated sodium ion channels

44
Q

describe ap propagation

A

membrane depolarizes and has more + charges, will attract - charges from part of membrane not depolarized (right next to it)
+ flows towards - and depolarizes next part of membrane and initiates ap

45
Q

will the action potential ever go backwards, why?

A

NOOOOO
due to inactivation of sodium channels
they are refractory - will not open again
must convert back to being closed, only happens when membrane goes back to resting potential
segment of axon behind ap is unexcitable

46
Q

what does refractory mean

A

Unresponsive

47
Q

what is absolute refractory period

A

few milisecs after ap
sodium channels are inactivated and membrane is completely unexcitable

48
Q

what is relative refractory period

A

longer period
voltage gated potassium channels open
membrane potential overshoots its resting level
axon is less excitable and unlikely to fire ap
membrane becomes closer to potassium equilibrium level

49
Q

what determines how fast axon fires aps

A

duration of absolute and especially relative refractory period

50
Q

each ap is an…

A

all or none event

51
Q

how do neurons send info

A

time and frequency and pattern of aps
each ap is a binary event
encode info by how fast aps come and by patterns and timing

52
Q

what does intensity of stimulus correspond to (Transduction of pressure on skin surface into neuronal activity)

A

frequency of aps

53
Q

what are the molecular targets for naturally occurring neurotoxins

A

sodium channels
all different kinds of ion channels in neurons and other excitable cells like muscle are also targets

54
Q

describe puffer fish

A

tetrodotoxin = extremely potent inhibitor of sodium channels
binds with high specificity and affinity
10^-8 M is enough to block all sodium channels

55
Q

describe phyllobates frogs (south american tree frogs)

A

secrete from skin batrachotoxin = powerful sodium channel activator
binds to sodium channels and irreversibly opens them, so neurons will fire aps like crazy, super dangerous
animals who come in contact have a bunch of seizures

56
Q

what are sodium channels also modulated by

A

pyrethroid insecticides
scorpion and anemonae toxins

57
Q

what important therapeutic drugs block sodium channels

A

local anesthetics
antiepileptic agents

58
Q

describe local anesthetics

A

lidocaine
benzocaine
tetracaine
cocaine

block voltage gated sodium channels so aps will not get past the area (will not feel stimulus)

59
Q

describe antiepileptics

A

phenytoin (dilantin)
carbamazepine (tegretol)

epileptic seizure = electrical storm in brain, drugs block voltage gated sodium channels just enough to suppress seizures

60
Q

what is rapid propagations of aps important for

A

survival
rapid reflexive responses

61
Q

describe how squids send fast moving signals from one end of body to other

A

giant axons
1000 times fatter than human axons

62
Q

what is propagation rate of ap proportional to

A

axon diameter

63
Q

what happens if put hand on stove

A

put hand on stove
5-10 sec later = pain
slow burn conveyed from hand to CNS by axons called C fibers (slow, propagate at 0.2m/s)

64
Q

what are fastest and slowest aps

A

fastest = 100m/s
slowest = 0.2m/s

65
Q

there will be evolutionary selection pressure that will want…

A

to select axons that can propagate aps as fast as possible

66
Q

why is a fatter axon faster

A

imagine a hose, wider = more water than a thinner hose

67
Q

why are squid axons giant

A

evolution can select for axons to get fatter - common in invertebrates
giant squid axon runs down middle of squid - good since squids escape mechanism is to run away, signal must be sent fast

68
Q

are fat axons good for humans

A

noo
100 billion axons and if each were big - our heads would be be huge
solution is to insulate axons instead (caused by evolutionary selection pressure for complex nervous systems like mammals and humans, higher vertebrates)

69
Q

what are axons wrapped in (in vertebrate neurons)

A

insulator called myelin

70
Q

what is myelin formed by

A

schwann cells in PNS
oligodendrocytes in CNS
cells sit next to neuron and send out these extensions and wrap around axon to create insulation

71
Q

is myelin wrapped around whole neuron

A

no
not continuous
has gaps

72
Q

what does myelin do

A

acts as electrical insulator
enables charge to travel farther and faster down axon

73
Q

what is myelin interrupted by

A

periodic gaps called node of ranvier

74
Q

what do node of ranvier contain

A

very high concentrations of voltage gated sodium channels
Enables signal to be regenerated at periodic intervals

75
Q

do all axons have myelin

A

no - shorter ones do not
long ones tend to be myelinated, like for sensory and memory

76
Q

what happens if no myelin on longer axons

A

depolarization will spread but since myelin regions have no/little sodium channels depolarization will just die and ap will stop

77
Q

describe saltatory conduction - generally

A

ap starts at initial segment
starts to fizzle out in areas where there is myelin
then hits node just in time and influx of sodium since many channels are open at nodes
faster than just having ap propagate down length of axon

78
Q

what is multiple sclerosis caused by

A

loss of myelin

79
Q

what is multiple sclerosis

A

autoimmune disorder
episodes in which immune system attacks and degrades myelin and leads to deficits associated with an episode of MS (sensory, movement and cognitive dysfunctions)
immune system then settles down and myelin grows back but then another episode
each time urs harder for myelin to come back

80
Q

what is white matter

A

regions of brain and spinal cord that contain mostly myelinated axons
myelin makes things white

81
Q

what is grey matter

A

cell bodies
dendrites
synapses

82
Q

what is synapse

A

place where one axon makes contact with another neuron

83
Q

what is upstream and downstream synapse

A

upstream = presynaptic
downstream = postsynaptic

84
Q

name the 3 types of synapses

A

axodendritic
axosomatic
axoaxonic

85
Q

name and describe axodendritic synapses

A

spine synapse
shaft synapse
on dendrites (most synapses are on dendrites)

86
Q

describe spine synapse

A

between presynaptic terminal and dendritic spine (sticks out on dendrite)
like neurons in cerebral cortex
mainly excitatory

87
Q

describe shaft synapse

A

synapse on shaft of dendrite directly
mainly inhibitory

88
Q

describe axosomatic synapse

A

Synapses on cell body

89
Q

describe axoaxonic synapses

A

presynaptic terminal of neuron to presynaptic terminal of another neuron

90
Q

how many synapses can one neuron make

A

make synapses with many other neuron due to branching axon
each neuron has one axon bur can branch and make many synapses
only one ap tho, sent equally in all directions of branches

PHGY 209 (19 decks)

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