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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
if sodium channel is inactivated can it open again
not directly must be converted back to closed state before they can open again
26
the rising phase of the AP is...
a regenerative process
27
what does depolarization of the membrane to threshold potential activate
small amount of sodium channels further depolarizes membrane and activates more sodium channels
28
what kind of mechanism is AP
positive feedback
29
describe positive feedback effect of ap
maximal activation of sodium channels a large sodium influx depolarization of membrane from resting level to near Ena
30
what does inactivation do
terminates sodium influx causes membrane to relax back to its original resting level potassium flows out and brings back to -70mv
31
describe what happens when 100% of sodium channels are open
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
32
why at the peak of ap the Na+ permeability swaps for the resting permeable of K+
density of voltage gated sodium channels in axon membrane is much higher than density of the leak potassium channels
33
what contributes to falling phase of action potential
sodium channel inactivation delayed activation of voltage gated potassium channels
34
describe voltage gated potassium channels
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
35
what happens when voltage gated potassium channels are open
potassium leaks out helps bring membrane down to resting potential faster shut when membrane repolarizes
36
what 2 factors help make action potentials short
sodium channels inactivate fast potassium channels open and allow potassium to flow and repolarize membrane
37
why do we want action potentials to be short
since then you can send more neuron can send many aps per second or in a short amount of time
38
what happens without voltage gated potassium
ap would still happen but just repolarizes slower
39
what happens to sodium and potassium gradients when many aps
they run down faster neuronal activity must be maintained by pumps (sodium potassium pump)
40
what happens if sodium potassium pump didnt work
gradients will just run down over time since neurons will still fire aps
41
name something that can block sodium potassium pump
south american tree frogs make a toxin that can block pump toxin is deadly
42
describe role of sodium potassium pump in maintaining gradients when many aps
pump constantly and move sodium out and potassium in to maintain concentration gradients, so they are not run down by the aps
43
what is action potential propagation caused by
spread of electronic currents from site of ap - which excites adjacent regions of axon due to properties of voltage gated sodium ion channels
44
describe ap propagation
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
will the action potential ever go backwards, why?
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
what does refractory mean
Unresponsive
47
what is absolute refractory period
few milisecs after ap sodium channels are inactivated and membrane is completely unexcitable
48
what is relative refractory period
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
what determines how fast axon fires aps
duration of absolute and especially relative refractory period
50
each ap is an...
all or none event
51
how do neurons send info
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
what does intensity of stimulus correspond to (Transduction of pressure on skin surface into neuronal activity)
frequency of aps
53
what are the molecular targets for naturally occurring neurotoxins
sodium channels all different kinds of ion channels in neurons and other excitable cells like muscle are also targets
54
describe puffer fish
tetrodotoxin = extremely potent inhibitor of sodium channels binds with high specificity and affinity 10^-8 M is enough to block all sodium channels
55
describe phyllobates frogs (south american tree frogs)
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
what are sodium channels also modulated by
pyrethroid insecticides scorpion and anemonae toxins
57
what important therapeutic drugs block sodium channels
local anesthetics antiepileptic agents
58
describe local anesthetics
lidocaine benzocaine tetracaine cocaine block voltage gated sodium channels so aps will not get past the area (will not feel stimulus)
59
describe antiepileptics
phenytoin (dilantin) carbamazepine (tegretol) epileptic seizure = electrical storm in brain, drugs block voltage gated sodium channels just enough to suppress seizures
60
what is rapid propagations of aps important for
survival rapid reflexive responses
61
describe how squids send fast moving signals from one end of body to other
giant axons 1000 times fatter than human axons
62
what is propagation rate of ap proportional to
axon diameter
63
what happens if put hand on stove
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
what are fastest and slowest aps
fastest = 100m/s slowest = 0.2m/s
65
there will be evolutionary selection pressure that will want...
to select axons that can propagate aps as fast as possible
66
why is a fatter axon faster
imagine a hose, wider = more water than a thinner hose
67
why are squid axons giant
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
are fat axons good for humans
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
what are axons wrapped in (in vertebrate neurons)
insulator called myelin
70
what is myelin formed by
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
is myelin wrapped around whole neuron
no not continuous has gaps
72
what does myelin do
acts as electrical insulator enables charge to travel farther and faster down axon
73
what is myelin interrupted by
periodic gaps called node of ranvier
74
what do node of ranvier contain
very high concentrations of voltage gated sodium channels Enables signal to be regenerated at periodic intervals
75
do all axons have myelin
no - shorter ones do not long ones tend to be myelinated, like for sensory and memory
76
what happens if no myelin on longer axons
depolarization will spread but since myelin regions have no/little sodium channels depolarization will just die and ap will stop
77
describe saltatory conduction - generally
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
what is multiple sclerosis caused by
loss of myelin
79
what is multiple sclerosis
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
what is white matter
regions of brain and spinal cord that contain mostly myelinated axons myelin makes things white
81
what is grey matter
cell bodies dendrites synapses
82
what is synapse
place where one axon makes contact with another neuron
83
what is upstream and downstream synapse
upstream = presynaptic downstream = postsynaptic
84
name the 3 types of synapses
axodendritic axosomatic axoaxonic
85
name and describe axodendritic synapses
spine synapse shaft synapse on dendrites (most synapses are on dendrites)
86
describe spine synapse
between presynaptic terminal and dendritic spine (sticks out on dendrite) like neurons in cerebral cortex mainly excitatory
87
describe shaft synapse
synapse on shaft of dendrite directly mainly inhibitory
88
describe axosomatic synapse
Synapses on cell body
89
describe axoaxonic synapses
presynaptic terminal of neuron to presynaptic terminal of another neuron
90
how many synapses can one neuron make
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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