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MCAT Biology > Membrane and Action Potentials > Flashcards

Membrane and Action Potentials Flashcards

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1
Q

Concentration of K+ is greater __________.

A

Inside a cell

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2
Q

Concentration of K+ inside of cell

A

120-140 mM

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3
Q

Concentration of K+ outside of cell

A

5 mM

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4
Q

Concentration of Na+ is greater __________.

A

Outside of cell

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5
Q

Concentration of Na+ inside of cell

A

10-15 mM

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6
Q

Concentration of Na+ outside of cell

A

150 mM

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7
Q

Concentration of Cl and HCO- is greater _________.

A

Outside of cell

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8
Q

Concentration of Cl inside of cell

A

5-40 mM

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9
Q

Concentration of Cl outside of cell.

A

130 mM

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10
Q

Concentration of HCO- inside of cell

A

12-25 mM

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11
Q

Concentration of HCO- outside of cell

A

25 mM

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12
Q

Electroneutrality

A

Cations and Anions balancing each other outside of cell (155 mM)

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13
Q

Ions want to move _____ their concentration gradients.

A

down

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14
Q

When ions continue to move down their concentration gradients, what happens?

A

The sign of their charge begins to accumulate where they diffuse to (so they began to be pushed in the opposite direction across the membrane – b/c they want to work down their electrical AND concentration gradient – remember that like charges repel)

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15
Q

Responsible for asymmetrical concentration gradient across the cell membrane

A

ATPase Pump

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16
Q

ATPase Pump

A

pumps three sodium ions out of the cell for every two potassium ions pumped in

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17
Q

What can be used to calculate the membrane voltage across a cell’s membrane?

A

Nernst equation

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18
Q

What is Nernst equation?

A

(2.3) x (RT/ZF) x [Log(Concentration of ion on outside/concentration of ion on inside)]

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19
Q

What is R in the nernst equation?

A

8.314 J/(mol x K)

20
Q

What is T in the nernst equation?

A

Temperature in kelvin

21
Q

What is Z in the nernst equation?

A

Ion’s valence

22
Q

What is F in the nernst equation?

A

Faraday’s Constant: 96,500 C/mol

23
Q

Under standard conditions, what is (2.3) x (RT/ZF) in the nernst equation equal to?

A

60

24
Q

What the membrane voltage of the membrane if only K+ is permeable across the membrane?

A

-87 mV - inside the cell with respect to outside the cell

only K+ gradient determines this voltage if it is the only permeable ion

25
Q

What the membrane voltage of the membrane if only Na+ is permeable across the membrane?

A

+60 mV - inside the cell with respect to outside the cell

26
Q

What are the units of the nernst equation?

A

mV (1 mV = 0.001 V)

27
Q

What happens if we stimulate a nerve and it leaves its resting state?

A

It enters it’s active state and makes Na+ ions to become more permeable (causing them to want to work down their electrochemical and concentration gradients; This happens when too much K+ has left the cell)

28
Q

Increasing the membrane’s Na+ permeability can lead to ________.

A

Depolarization (decrease in membrane potential)

29
Q

How can depolarization be accomplished?

A

By stimulating a nerve

30
Q

What happens when when the initial depolarization exceeds the threshold potential (specific minimum value of the membrane potential for a cell to trigger action potential)?

A

Na+ ions burst into the cell and trigger an action potential

31
Q

When an action potential is generated, which ion becomes more permeable across the membrane and in what direction does it move?

A

Na+ ions, They burst into the cell

32
Q

When does the influx of Na+ ions into the cell discontinue?

A

When the membrane potential reaches the equilibrium potential for Na+ (60+)

33
Q

What occurs when the membrane potential reaches the equilibrium potential for Na+ (60+)?

A

The membrane potential (inside the cell) is balanced with the concentration gradient of Na+

34
Q

What happens during the refractory period?

A

1) Na+ channels close and becoming temporarily inactive

2) The neuron will not generate an action potential b/c the Na+ channels are closed (to prevent further depolarization)

35
Q

What happens during re-polarization?

A

1) Na+ channels close shut
2) K+ channels open and leave the cell
3) hyper-polarization

36
Q

What is hyper-polarization?

A

When the membrane potential passes above it’s normal resting potential (the cell eventually reach equilibrium)

37
Q

Multiple action potentials can happen at once in one cell? (TRUE/FALSE)

A

FALSE - ONLY ONE AP can happen AT ONE POINT IN TIME IN A CELL

38
Q

The ability of a neuron to conduct a current depends on what?

A

The cross-sectional area of the neuron

39
Q

Neurons with larger cross-sectional area conduct an AP ______ and ________ than a small diameter neuron.

A

farther, faster (more efficient)

40
Q

Which of the following increases the rate at which action potentials are conducted?

A. Myelinated
B. Unmyelinated

A

Myelinated

41
Q

What types of cells help to myelinate neurons?

A

Glial cells (they attach themselves to unmyelinated regions of neurons, rotate around the neuron a number of times to create a myelin sheath)

42
Q

Nodes of Ranvier

A

1) Regions between myelin on a myelinated neuron (AP “jumps” from node to node)
2) Plasma membrane at each node depolarizes during an AP
3) High density of Na+ channels for depolarization

43
Q

Which nervous system are oligodendrocytes (type of glial cell) located in?

A

CNS

44
Q

Which nervous system are schwann cells (type of glial cell) located in?

A

PNS

45
Q

What does myelin act as?

A

an electrical insulator that prevents transfer of ions across plasma membrane of the axon (Thus, there are only channels (Na+ in particular) at the nodes of Ranvier)

46
Q

Saltatory Conduction

A

Impulse jumping from node to node on an axon that is myelinated

MCAT Biology (7 decks)

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