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neurophysiology Flashcards

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USMLE® Step 1 flashcards
1
Q

coulomb

A

charge of one electron (1.6E-19C)

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2
Q

faraday constant

A

total charge of one mole of charge

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3
Q

potential difference

A

work required to move a charge from point A to B

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4
Q

ampere

A

current (coulombs per second)

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5
Q

ohm

A

resistance (measured in ohms per cm^2)

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6
Q

ohms law

A

E = IR

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7
Q

siemen

A

conductance (reciprocal of resistance/ohm)

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8
Q

ionic equilibriam potential

A

balance between ion gradient and charge gradient

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9
Q

capacitance

A

storage of electric charge

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10
Q

nernst equation

A

E = (58mV/z) * log([outside]/[inside])

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11
Q

when is the nernst eq valid?

A

ONLY when the system is in equilibrium

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12
Q

what value does nernst eq. give?

A

the membrane potential at equilibrium

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13
Q

principle of electrical neutralitiy states

A

[cation]=[anion] in any compartment

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14
Q

donnan equilibrium means that?

A

the electrical potential across the membrane must balance the concentration gradient

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15
Q

donnan equilibrium equation

A

[K+]outside * [Cl-]outside = [K+]inside * [Cl-]inside

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16
Q

goldman equation accounts for

A

permeability (P)

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17
Q

permeability is expressed relative to ___

A

K+

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18
Q

3 things that affect transmembrane potential

A

transmembrane resistance; axial resistance; membrane capacitance

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19
Q

membrane resistance

A

measures how sensitive something is to an applied current LONGITUDINALLY; R(m)

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20
Q

internal resistance equation

A

R (in) = delta V / I

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21
Q

resistance durastically changes when..

A

radius increases (because the surface area of the cell gets way bigger and the charge diffuses across that area)

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22
Q

R(m) is proportional to

A

lambda. Since the membrane doesn’t take on the charge it travels farther down the axon

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23
Q

lambda equation

A

lambda = sqrt((Rm) / (Rin))

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24
Q

what does diameter do to lambda

A

lambda is inversely proportional to Rin which is inversely proportional to r. As diameter increases, so does lambda

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25
Q

membrane time constant

A

time needed for electronic potential to decrease to 37% of original

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26
Q

time constant depends on?

A

membrane resistance (Rm) and membrane capacitance (Cm)

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27
Q

larger time constant means?

A

less decay over time, so there is a larger chance for the impulse to trigger an action potential

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28
Q

hyperpolarization

A

an increase in membrane potential; proportional to the current increase; makes it harder to start an AP

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29
Q

hypopolarization

A

a decrease in membrane potential; makes it easier to start an AP

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30
Q

AP triggered by

A

depolarization; of 10-20mV from the resting membrane

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31
Q

all or nothing means

A

an AP is triggered, or it is not; the amplitude is the same no matter the strength of the trigger

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32
Q

stimulus strength dictates?

A

the frequency of the all or nothing AP

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33
Q

speed of AP

A

relatively slow

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34
Q

AP decrements?

A

no, it is regenerative and propagates without diminishing

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35
Q

overshoot

A

when the AP goes positive

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36
Q

undershoot

A

when the AP goes extra negative

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37
Q

absolute refractory period

A

you can’t over excite the cell during this period. Its impossible

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38
Q

inward current of AP is from

A

sodium, proved by nernst equation and tetrodotoxin and ion substitution

39
Q

outward current of AP is from

A

potassium, proved by tetraethylammonium

40
Q

seizures are from

A

defective sodium channel that leaks TOO MUCH and you get an unwanted AP; treat with phenotoitin

41
Q

hyperkalemic periodic paralysis from

A

too much K so you lose muscle tone especially after a meal with high carbs or high K; this is due to a defective Na channel that responds to a high [K] by shutting down; treat with insulin and glucose

42
Q

hypokalemic periodic paralysis from

A

low K that prevents generation of AP; treat by giving them K (bananas or strawberries)

43
Q

driving force of ions across membrane?

A

ohms law says its due to the difference in membrane potential and the equilibrium potential

44
Q

Na and K conductances depend on

A

voltage: the conductances increase as the neuron is depolarized

45
Q

Which ion conductance peaks first?

A

Na before K

46
Q

Why does the Na depolarization level out?

A

as Na enters the cell, the conductance of sodium increase and therefore, the cell loses its driving force

47
Q

What causes the hyperpolarization?

A

voltage change opens pores so that K leaves the cell; conductance of K increases more than during rest and this causes hyperpolarization

48
Q

why Is depolarization regenerative?

A

Na progressively depolarizes the cell, and when it runs out of energy, it activates K to release from the cell which repolarizes it back to the resting state voltage potential

49
Q

the speed of an action potential depends on

A

the diameter and myelination of the nerve

50
Q

relatively refractory period =

A

when membrane voltage is being changed by outward flow of K

51
Q

relationship between myelin and Rm

A

myelination decreases the amount of lost energy, so Rm decreases

52
Q

relationship between axon diameter and Ri

A

increasing diameter, lowers internal resistance of the axon

53
Q

where are ion channels located?

A

in nodes of ranvir

54
Q

saltatory conduction decrases

A

the amount of metabolic stress; otherwise, it would take to keep pumping ions out of the entire length of the axon

55
Q

guillan-barre from?

A

circulating peripheral anti-myelin Ab, so the pt. loses their myelin, but the nerves are still alive

56
Q

guillan-barre symptoms

A

peripheral neuropathy, usually had an intestinal virus 3-4 weeks prior

57
Q

guillan-barre treatment

A

purified IgG to down regulate natural production of their IgG; plasmaphoresis to get their Ab out

58
Q

multiple sclerosis from?

A

Ab against central myelin and the oligodendrocytes

59
Q

multiple sclerosis symptoms?

A

progressive gait problems, loss of vibratory and proprioception, pale optic disk

60
Q

multiple sclerosis treatment

A

selective immunosuppressive drugs that can enter the CNS; you cannot regenerate already lost myelin

61
Q

two types of synapses?

A

electrical synapse (gap jxn) and chemical synapse (NT)

62
Q

a gap jxn pore is not __

A

selective. If it fits through, it goes through.

63
Q

gap jxns are made of?

A

connexons with 6 protein subunits

64
Q

what types of things usually pass through gap jxn

A

sodium, potassium, cAMP

65
Q

What can close a gap jxn

A

a lowering of cytoplasmic pH or an elevation of Ca2+ can make the conexxon parts rotate and close the pore

66
Q

gap jxns are appropriate for?

A

cells that are directly adjacent that will work by passive electrotonic potentials; example: cardiac muscle, or something that needs synchrony

67
Q

another cellular fxn of a gap jxn

A

passing nutrition; example: schwaan cell does this, also your cornea does this because it doesn’t have a blood supply.

68
Q

drawback of gap jxn?

A

they are bidirectional. You can’t mandate the flow of something to only go one way

69
Q

what signals a NT to release?

A

the action potential allows Ca2+ into the cell

70
Q

end plate potential

A

transient depolarization of the post synaptic membrane

71
Q

What blocks postsynaptic ach receptors

A

curare

72
Q

result of increased extracellular [ca] in neuromm. Jxn

A

you hit the threshold more, there is a higher amplitude response (from extra quanta released) but the concentration within each quanta is the same

73
Q

__ has the lowest threshold for AP

A

the axon hillock because the voltage sensitive Na and K channels are concentrated there

74
Q

examples of excitatory NT. Cause?

A

ach, glu. Increase Na permeability @ postsynaptic membrane and depolarize it

75
Q

What is the break even point for epsp?

A

the reversal potential. No net potential occurs at -11mV

76
Q

what typs of NT for ipsp? Cause?

A

GABA. Increase the Cl permeability at postsynaptic membrane

77
Q

where is the break even point for ipsp

A

reversal potential for this one is at -80 mV

78
Q

2 pieces of info that cns carries

A

WHERE the info comes from, INTENSITY

79
Q

What is the Ach binding site made of

A

a disulfide bond from cysteins in the N terminal domain

80
Q

what lines the pore of Ach receptor

A

TM2 sections from the 5 protein subunits

81
Q

what happens when Ach binds its receptor

A

the alpha helicies rotate and allow the kink in the TM2 to spin out of the way so that ions can pass through the pore

82
Q

Ach receptor belongs to what category?

A

ionotropic. It directly lets ions through a pore

83
Q

glutamate importance

A

most important NT in CNS. Almost all EPSPs in CNS are glutamatergic

84
Q

two ionotropic receptors for glutamate

A

AMPA and NMDA

85
Q

what does TM2 look like in glutamate receptor

A

it has a hairpin loop within the membrane and it reenters the cytoplasm

86
Q

glycine receptors are

A

inhibitory ionotropic glycine gated Cl channels

87
Q

which type of channel is most prevalent

A

chemically activated (vs. voltage activated)

88
Q

crossbridge cycle: when is ADP released?

A

when the energized myosin binds to the actin

89
Q

where is a voltage gated Ca channel

A

in the t-tubule that causes the calcium ion channels in the SR to open

90
Q

what triggers smooth m contraction

A

variety of NT and hormones. This triggers a cascade of reactions with IP3, Ca, phosphorylation of MLCK and calmodulin

91
Q

innervation ratio

A

number of mm that are activated by 1 neuron. Usually 10-10,000

92
Q

size principle is due to

A

the fact that smaller cells are depolarized easier than bigger ones. If you have a small signal, only the small (slow twitch) muscles are activated to work

93
Q

ryanodine receptor

A

regulates the release of Ca in skeletal muscle; diseased state is malignant hypothermia

94
Q

muscle force depends on

A

the number of cross bridges being utilized

medical physiology (9 decks)

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