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Flashcards in Excitable cells Deck (87):
1

Excitation =

activation to initiate an event

2

Extracellular fluid is also referred to as:

interstitial fluid

3

what is the composition of interstitial/extracellular fluid?

- primarily ions, proteins
- similar to plasma in ion content
- High NaCl level

4

what is the composition of intracellular fluid (aka cytosol)

-much higher [ ] of proteins
- Main salt in cytosol- KCl

5

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

ion-specific and exquisitely timed

6

Simple diffuision:

random diffusion, diffusion down electrical gradient or concentration gradient

-organic molecules or ions

7

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

non-polar organic molecules

- this is because they are readily soluble in the lipid membrane

8

Ions cross membranes through ______

channels

9

what is flux?

amount of substance crossing a surface per unit of time

10

________ is the difference between the two unidirectional fluxes

net-flux

11

what happens during mediated transport?

-ligand binds to a transporter in the membrane
-transporter undergoes a conformational change
-ligand is released on other side of membrane

12

what are the 2 types of mediated transport?

1) facilitated diffusion

2) active transport

13

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

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

14

what are the types of channels involved in mediated transport?

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

15

Osmolarity =

total solute concentration in a solution

16

1 mole NaCl = ______ osmoles

2 osmoles

17

what is the osmolarity of extracellular fluid?

300 mOsm

18

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

isotonic- 300 mOsm

hypotonic- less than 300 mOsm

hypertonic- greater than 300 mOsm

19

a hypoosmotic solution contains what?

less than 300 mOsm of non-penetrating plus penetrating solutes

20

what is a hyperosmotic solution?

greater than 300 mOsm of non-penetrating plus penetrating solutes

21

What is endocyctosis? Pinocytosis? phagocytosis?

Endocytosis- engulfment of fluid and particles

Pinocytosis- small particles with/without small volume of ECF

Phagocytosis- large particles or cellular debris

22

Voltage (V) = ________

current (I) x resistance (R)

23

Conductance (G) = ________

Current (I) divided by Voltage (V)

24

conductance is the _______ of resistance

reciprocal

25

current across cell membranes is an _________

actual flow of electrons

26

what is the definition of equilibrium?

balance of voltage and concentration

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

27

the nernst equation yields the __________ of a single ionic species

equilibrium potential (AKA the equilibrium voltage)

28

diffusion potentials occur due to an _______

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

29

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

diffusion potential

30

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

Potassium (K) - higher inside the cell

Sodium (Na) - higher outside the cell

31

there is a ____________ across the plasma membrane for potassium

concentration gradient

32

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

PNa

33

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

-70 to -90 mV

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

34

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

concentration gradient and electrical gradient

35

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

K+ goes out of the cell

Na+ goes into the cell

36

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

depolarization

37

what is hyper polarization?

increase in membrane potential from the resting value

- becoming MORE negative

38

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

it would slowly dissipate to 0 mV

39

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

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

40

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

action potential

41

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

neurons and muscle cells

42

action potentials are _______ events that are _______ over a distance

active events

propagated over a distance

43

action potentials usually first develop in the ___________ of the axon

initial segment

44

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

increase in the membrane permeability to sodium ions

45

sodium enters the cell, being driven by what?

the electrical and concentration gradients

46

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

it moves closer to 0 mV

47

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

Threshold

48

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

voltage

49

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

+40 mV

50

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

potassium (K)

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

51

what happens to the cell during the "falling phase"?

- K+ ions diffuse out of the cell, carrying the positive charge with them

- membrane potential abruptly reverses directly and returns to resting value

52

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

true

53

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

Sodium (Na+)

54

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

potassium (K+)

55

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

foot

56

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

suprathreshold stimulus

57

T/F: local responses move along the membrane

FALSE

they do NOT move along the membrane

58

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

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

59

how does a graded potential differ from an action potential?

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

60

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

absolute- cell cannot propagate another AP

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

61

Important stimulus parameters for neurons:

1) intensity (amplitude)

2) duration

3) rate of change

4) frequency

62

what is "adaptation" of a neuron?

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

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

adaptation of the neuron


accommodation of the ion channels

64

T/F: passive currents will propagate

false

65

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

anode --> cathode

66

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

extracellular fluid and inside the cell

67

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

a depolarizing potential change at that site

-will cause local currents around that site

-cause depolarization of adjacent regions

68

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

true

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

69

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

local currents from the adjacent site

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

70

_______ cells surround the axons of neurons

schwann cells

71

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

nodes of ranvier

72

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

salutatory conduction

73

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

refractory period

- will lower the maximal AP firing frequency

74

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

composite of several AP's

75

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

Velocity dependent on diameter

76

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

FALSE

larger diameter= higher velocity

77

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

- 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

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

- 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

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

TRUE

80

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

MEPP's

(miniature endplate potentials)

81

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

FALSE

only MEPPs are spontaneous

82

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

BOTH are confined to the end-plate region

83

what is the role of acetylcholinesterase? (AChE)

breakdown ACh

creates acetic acid and choline

84

how does the botulinum toxin differ from curare and organophosphates?

botulinum toxin blocks ACh release

Curare- blocks AChR's

organophosphates- block AChE

85

what is a “Rheobase”?

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

86

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

Utilization time

87

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

“Chronaxie”

(can be used to compare excitability of different cells.)