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Neuroscience 1 > Changing membrane potentials > Flashcards

Changing membrane potentials Flashcards

1
Q

capacitance

A

two conducting materials separated by an insulator

stores charges of opposite sign on two opposing surfaces

amount of charge stored is inversely proportoinal to the thickness of the capacitor

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2
Q

difference between capacitive current and ionic current

A

the initial injection of a current into a capacitor rearranges the distribution of charges within the capacitor- capacitive current

as the ions rearrange, it changes the distribution of ions on the other side of the membrane, changing the voltage- this is the ionic current

this takes time, and is responsible for the lag in the change in membrane potential

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3
Q

time constant

A

the time required to rise to approximately 64% of the total change in potential
usually b/t 1-10 milliseconds

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4
Q

why is the time constant important?

A

the rate at which the membrane changes in respone to an individual stimulus and its subsequent relaxation determines how closely spaced sequential stimuli must be befre there is a summation of their effects

cells w/ short time constants sum their potentials more easily

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5
Q

temporal summation

A

depolarization events add together and through their combined influence depolarize the cell enough to reach threshold for firing an action potential

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6
Q

cable properties

A

the electrical characteristics involved in the spread of current and voltage changes along an axon

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7
Q

Ri

A

resistance to current flow through the inside of the axon

related to axon size- big axons = less resistance

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8
Q

the length constant

A

the distance at which ~37% of the original change in membrane potential still occurs

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9
Q

speed of propagation

A

is proportional to 1/ (sqrt(membrane resistance * membrane capacitance * internal resistance to current flow))

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10
Q

how is axon diameter related to capcitance and resistance

A

proportional to capacitance

inversely proportional to membrance membrane resistance

inversely proportional to the square of internal resistance to current flow

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11
Q

action potential

A

rapid depolarization and then repolarization of the membrane to a membrane depolarization of sufficient magnitude, but not hyperpolarization

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12
Q

resting membrane potential

A

-70 to 80 mV

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13
Q

describe the events occuring during an action potential

A

Na channels open in response to depolarization. It is only open for about 1 ms before it is closed also by depolarization. the membrane must be repolarized before they open again. (DEPOLARIZATION PHASE)

delayed rectifier K channels also open in response to depolarization, but w/ a slight delay. these channels do not inactivate until repolarization of the membrane. (REPOLARIZATION PHASE)

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14
Q

afterhypolarization

A

d/t residual k channel activity, resulting from their lag in response to membrane potential

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15
Q

threshold

A

the membrane potential at which the inward current through the NA channels that are opening up is finally greater than the outward K current through other channels

(Ina > Ik + Ileak)

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16
Q

refractory period

A

a period in time in whihc another AP cannot be generated (absolute refractory period) or can only be generated w/ some difficulty (relative refractory period)

result of:

Na channel inactivation

High levels of K channel activation

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17
Q

describe what proportion of ions move during an AP

A

very low, overall concentrations change very little

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18
Q

how important is the Na/K ATPase to APs?

A

not at all. important to maintaining the resting potential

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19
Q

general features of voltage gated channels

A

4 homologous domains/channels
6 transmembrane regions/domain

  1. pore loops- selectivity filter (region that does not quite become a transmembrane region)-

2 voltage sensors- 4th domain

3 inactivatoin loops

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20
Q

how does the pore loop confer selectivity?

A

done by size of hyrated molecule and energy required to remove water from ion

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21
Q

properties of the S4 voltage gates

A

go through all-or-none transitions between discrete conformations

S4 region has positively charged AAs inside the membrane every 3rd electron

depolarizing the membrane repels the positive charges, moving it in a helical twist

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22
Q

ball and chain model

A

cluster of positively charged amino acids, as the membrane becomes depolarized, the “ball” will plug the channel

applies to K channels

Na channels have n analagous loop of positively charged amino acids that flip up and clog the membrane

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23
Q

t vs l type Ca channels

A

t- transient response to depolarization- involved w/ transmitter

l- longer response to depolarization

24
Q

how does the speed of Ca and Na channels compare?

A

Na is faster to activate and deactivate

25
Q

delayed rectifier K channels do not inactivate

A

ok

26
Q

A current potassium channel

A

inactivate rapdily

will counteract a depolarization that may lead to an AP, prolong the interval b/t APs

27
Q

HCN channels

A

cation selective- K and Na both pass

open in response to hyperpolarization, helping raise the membrane potential reach a new AP, shortening the interspike interval

responsive to cAMP

important in pacemaking cells

28
Q

tetrodotoxin and saxitoxin

A

bind w/ high affinity to external site of Na channels and block the pore

TTX- puffer fish

STX- from algae that occasionally proliferate and cause a red tide- cooking does not inactivate

29
Q

conus toxins

A

class of toxins specific to voltage gated Ca channels

30
Q

TEA

A

a K channel selective blocker

31
Q

procaine/lidocaine

A

block the flow of ions through the Na channels, preferentially binding inactivated Na channels

32
Q

neuroma

A

elevated Na channel expression occurs in perihperal sensory nerves that have been cut- causes phantom pain

33
Q

propogation of an AP depends on both active and passive membrane properties

A

ok

34
Q

why is AP propogation unidirectional

A

retrograde channels are in the refractory period

35
Q

axon hillock (AIS)

A

elaborate accumulatoin of proteins, lipids and cytoskeletal elements that serve as a barrier to diffusion, effetiely separating the axon component

site of AP start

36
Q

range of measured axon speeds

A

1 m/s to 120 m/s

37
Q

myelins effect on conduction velocity

A

increases velocity

decreases capcitance and increases resistance

causes an increase in the length constant

38
Q

myelination allows us to save space by creating quick neurons w/ small diameters

A

ok

39
Q

what cells are responsible for myelination?

A

CNS- oligodendrocytes- myelinate as many as axons as possible

PNS- schwann cells- only one at a time

schwann cells also “encase” PNS axons, not true myelination, SCs interact with many axons

40
Q

where are the channels located in myelinated axons

A

in the nodes of ranvier

41
Q

how many layers of glial cells make up myelin

A

10-150

42
Q

difference between control of myelin expression in CNS and PNS

A

CNS- independent of axon presence

PNS- dependent on axon contact

43
Q

neuregulins

A

transmembrane factors expressed in axons, and they interact w/ ErbB receptor tyrosine kinase on glial cells

help communication between the two

44
Q

how are are the locations of the nodes of Ranvier determined

A

some initial axon specialization, followed by glial cell contact and further specializatoin

45
Q

MAG

A

myelin associated glycoprotein- in both the PNS and CNS- expressed in the earliest stages of myelination and primarily in the first wrap of the glial cell

involved in initial axonal-glial recognition and myelination

46
Q

Po

A

a major structural protein of PNS myelin, accounting for over 50% of protein in SC

mediates myelin compaction

47
Q

PLP

A

proteolipid protein- Po equivalent in CNS

48
Q

MBP

A

myelin basic protein

found in both PNS and CNS. mediates close apposition of inner membrane

49
Q

saltatory conduction

A

AP is only regenerated at each node of Ranvier

saves energy b/c it leaves less work for Na/K pump

50
Q

dysmyelinating disorder

A

some myelin present, defected

ex. pelizaes-merzbacher disease

51
Q

demyelinating disease

A

myelin sheath is absent

52
Q

guillain-barre syndrome

A

myelin is deficient in PNS. primarily affects motoneurons associated w/ inflammatory damage to myelin

53
Q

charcot-marie-tooth

A

peripheral motor and sensory neuropathy. leg weakness, difficulty running, hand weakness.

decreased nerve conduction

associated w/ gap junctoin subunit (Cx32)

54
Q

MS

A

autoimmune disease where T cells cause gaps or lesions in myelin of CNS. characterized by plaques of demylination. results in the slowing or blocking of APs

most people develop symptoms 20-50

cause unknown- environmental and genetic. some evidence that viral infection causes increased permeability in the BBB to t lymphocytes

55
Q

MS treatment

A

immunosuppressives

56
Q

oligodendrocyte transplantation

A

replacement myelin, but it results in thinner myelin than original

potential MS treatment

Neuroscience 1 (13 decks)

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