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physio- exam 1 > Excitable cells > Flashcards

Excitable cells Flashcards

1
Q

Excitation =

A

activation to initiate an event

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2
Q

Extracellular fluid is also referred to as:

A

interstitial fluid

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3
Q

what is the composition of interstitial/extracellular fluid?

A
  • primarily ions, proteins
  • similar to plasma in ion content
  • High NaCl level
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4
Q

what is the composition of intracellular fluid (aka cytosol)

A
  • much higher [ ] of proteins

- Main salt in cytosol- KCl

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5
Q

CHanges in permeability, that are ________ and ________ are essential to excitation in cells

A

ion-specific and exquisitely timed

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6
Q

Simple diffuision:

A

random diffusion, diffusion down electrical gradient or concentration gradient

-organic molecules or ions

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7
Q

________ organic molecules diffuse rapidly through the membrane. why is this?

A

non-polar organic molecules

  • this is because they are readily soluble in the lipid membrane
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8
Q

Ions cross membranes through ______

A

channels

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9
Q

what is flux?

A

amount of substance crossing a surface per unit of time

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10
Q

________ is the difference between the two unidirectional fluxes

A

net-flux

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11
Q

what happens during mediated transport?

A
  • ligand binds to a transporter in the membrane
  • transporter undergoes a conformational change
  • ligand is released on other side of membrane
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12
Q

what are the 2 types of mediated transport?

A

1) facilitated diffusion

2) active transport

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13
Q

what are the three factors that determine the rate of flux?

A

1) number of transporters in the membrane
2) extent of transporter saturation
3) rate of transporter conformational change

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14
Q

what are the types of channels involved in mediated transport?

A

a) ligand-sensitive
b) voltage-sensitive
c) mechanosensitive

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15
Q

Osmolarity =

A

total solute concentration in a solution

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16
Q

1 mole NaCl = ______ osmoles

A

2 osmoles

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17
Q

what is the osmolarity of extracellular fluid?

A

300 mOsm

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18
Q

what is the mOsm of an isotonic solution? hypertonic? hypotonic?

A

isotonic- 300 mOsm

hypotonic- less than 300 mOsm

hypertonic- greater than 300 mOsm

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19
Q

a hypoosmotic solution contains what?

A

less than 300 mOsm of non-penetrating plus penetrating solutes

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20
Q

what is a hyperosmotic solution?

A

greater than 300 mOsm of non-penetrating plus penetrating solutes

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21
Q

What is endocyctosis? Pinocytosis? phagocytosis?

A

Endocytosis- engulfment of fluid and particles

Pinocytosis- small particles with/without small volume of ECF

Phagocytosis- large particles or cellular debris

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22
Q

Voltage (V) = ________

A

current (I) x resistance (R)

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23
Q

Conductance (G) = ________

A

Current (I) divided by Voltage (V)

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24
Q

conductance is the _______ of resistance

A

reciprocal

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25
Q

current across cell membranes is an _________

A

actual flow of electrons

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26
Q

what is the definition of equilibrium?

A

balance of voltage and concentration

-note: voltage and concentrations can differ between the 2 solutions and they can still be in equilibrium

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27
Q

the nernst equation yields the __________ of a single ionic species

A

equilibrium potential (AKA the equilibrium voltage)

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28
Q

diffusion potentials occur due to an _______

A

asymmetric ion flow- an imbalance in the flow of an ion between 2 compartments

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29
Q

a _________ can also be maintained at a steady level over time

A

diffusion potential

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30
Q

there are higher concentrations of ______ inside the cell, and higher concentrations of _____ outside

A

Potassium (K) - higher inside the cell

Sodium (Na) - higher outside the cell

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31
Q

there is a ____________ across the plasma membrane for potassium

A

concentration gradient

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32
Q

Pk (permeability of K+) is much higher than ____

A

PNa

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33
Q

at what voltage is the membrane potential when equilibrium is reached for potassium?

A

-70 to -90 mV

this is close to the equilibrium potential for K+…. -100mV

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34
Q

Na+ diffuses into the cells own both of its _______ and ________

A

concentration gradient and electrical gradient

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35
Q

at rest, what ion diffuses out of the cell and what ion diffuses into it?

A

K+ goes out of the cell

Na+ goes into the cell

36
Q

change of the membrane potential toward 0mV is referred to as “________”

A

depolarization

37
Q

what is hyper polarization?

A

increase in membrane potential from the resting value

  • becoming MORE negative
38
Q

without the Na/K ATPase pump, what would happen to the resting membrane potential?

A

it would slowly dissipate to 0 mV

39
Q

T/F: even large changes in membrane potential will not effect the overall concentration of ions

A

true- an extremely small fraction of total ions moving can cause a large membrane potential

40
Q

the most common change in membrane potential is referred to as the _________

A

action potential

41
Q

where are the most common sites of action potentials in the body?

A

neurons and muscle cells

42
Q

action potentials are _______ events that are _______ over a distance

A

active events

propagated over a distance

43
Q

action potentials usually first develop in the ___________ of the axon

A

initial segment

44
Q

what is the first step in the development of the action potential?

A

increase in the membrane permeability to sodium ions

45
Q

sodium enters the cell, being driven by what?

A

the electrical and concentration gradients

46
Q

as sodium rushes across the cell membrane, what happens to the membrane potential?

A

it moves closer to 0 mV

47
Q

if the depolarization is sufficiently large, a point will be reached, the “______”, which causes additional Na channels to open

A

Threshold

48
Q

the Na channels that open during a threshold depolarization are know as _______-regulated

A

voltage

49
Q

during an action potential, the membrane potential overshoots 0mV and reaches a peak at what voltage?

A

+40 mV

50
Q

after a peak of 40 mV has been reached, ____ channels open

A

potassium (K)

-K ions move across the plasma membrane from the inside to the outside

51
Q

what happens to the cell during the “falling phase”?

A
  • K+ ions diffuse out of the cell, carrying the positive charge with them
  • membrane potential abruptly reverses directly and returns to resting value
52
Q

T/F: the afterpolarization phase can last much longer than the polarization/depolarization phases

A

true

53
Q

the peak of the action potential (at 40 mV) approaches the equilibrium potential for what ion?

A

Sodium (Na+)

54
Q

the end of the repolarization phase is close to the equilibrium potential for ______

A

potassium (K+)

55
Q

the latency period precedes the _____ of the AP which is that portion of the rising phase before threshold is reached

A

foot

56
Q

what is a stimulus that is greater than the threshold stimulus?

A

suprathreshold stimulus

57
Q

T/F: local responses move along the membrane

A

FALSE

they do NOT move along the membrane

58
Q

what happens to a AP after a supra threshold stimulus is reached?

A

the action potential continues to completion and propagates along the entire length of the axon

59
Q

how does a graded potential differ from an action potential?

A

a graded potential’s amplitude is proportional to the strength of the stimulus (its not “all-or-none”)

60
Q

what is the difference between the absolute refractory period and the relative refractory period

A

absolute- cell cannot propagate another AP

relative- a suprathreshold stimulus can still elicit an AP, but a normal threshold stimulus cannot

61
Q

Important stimulus parameters for neurons:

A

1) intensity (amplitude)
2) duration
3) rate of change
4) frequency

62
Q

what is “adaptation” of a neuron?

A

the transition from from closed-state to the open-state of the channels is dependent on the rate of stimulus change

basically, a nerve cell will respond to a quickly applied stimulus, but not a slowly applied one

63
Q

_______ is a property of the neuron and its due to __________ of ion channels

A

adaptation of the neuron

accommodation of the ion channels

64
Q

T/F: passive currents will propagate

A

false

65
Q

current flows from the _____, through the neuron, to the ________

A

anode –> cathode

66
Q

the cathode causes cations to move toward int, in both the ______ and __________

A

extracellular fluid and inside the cell

67
Q

the stimulus that occurs at the site of a cathode will result in what?

A

a depolarizing potential change at that site

  • will cause local currents around that site
  • cause depolarization of adjacent regions
68
Q

T/F: one AP does not actually move long the entire axon

A

true

-every site along an axon undergoes a change in membrane potential

69
Q

the initiation of the AP at each site of the neuron is dependent on what?

A

local currents from the adjacent site

-cause a depolarization of the membrane that opens Na+ channels

70
Q

_______ cells surround the axons of neurons

A

schwann cells

71
Q

what are the names for the periodic nodes found along a myelinated nerve cell

A

nodes of ranvier

72
Q

the action potential “skipping” along the axon of a myelinated cell is known as what?

A

salutatory conduction

73
Q

loss of myeline prolongs the __________. what will this cause?

A

refractory period

  • will lower the maximal AP firing frequency
74
Q

a peripheral nerve will express a _______ of several Action Potentials, due to its composition of axons of many neurons

A

composite of several AP’s

75
Q

the _______ of an action potential is dependent on the diameter of the axon

A

Velocity dependent on diameter

76
Q

T/F: axons with larger diameters will have slower velocities of conduction

A

FALSE

larger diameter= higher velocity

77
Q

what is the sequence of events from an AP in a motor neuron to the fusion of neurotransmitter to the motor endplate?

A
  • AP travels along motoneuron axon
  • AP invades presynaptic terminal
  • Calcium ion influx into presynaptic terminal
  • vesicle fusion with membrane of presynap terminal
  • release of ACh from fused vesicle
  • diffusion of ACh across cleft
  • binding of ACh to AChR (receptor) in postysnap membrane (motor endplate)
78
Q

once ACh receptors are activated on the motor plate, what happens?

A
  • Opening of Na+ and K+ channels
  • Na+ influx and small K+ efflux across motor endplate
  • generation of ENDPLATE potential
  • opening of voltage-regulated Na+ channels in SARCOLEMMA immediately surrounding endplate
  • AP is initiated in SARCOLEMMA
79
Q

T/F: endplate potentials are graded, are not all-or-none in amplitude, do no not propagate, and can undergo summation

A

TRUE

80
Q

_______ are small EPP’s that occur spontaneously and result from release of ACh

A

MEPP’s

miniature endplate potentials

81
Q

T/F: MEPP’s and EPP’s can be spontaneous

A

FALSE

only MEPPs are spontaneous

82
Q

are EPPs or MEPPs confined to the end-plate region?

A

BOTH are confined to the end-plate region

83
Q

what is the role of acetylcholinesterase? (AChE)

A

breakdown ACh

creates acetic acid and choline

84
Q

how does the botulinum toxin differ from curare and organophosphates?

A

botulinum toxin blocks ACh release

Curare- blocks AChR’s

organophosphates- block AChE

85
Q

what is a “Rheobase”?

A

“Rheobase”: magnitude of least intense stimulus that can elicit a response.

86
Q

__________ is the duration required to elicit a response by a stimulus with a rheobase magnitude.

A

Utilization time

87
Q

_________ is the duration required to elicit response for a stimulus that has a magnitude that is twice the rheobase magnitude

A

“Chronaxie”

can be used to compare excitability of different cells.

physio- exam 1 (8 decks)

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