Module 4: Membrane & Action Potentials

Question 1

What are the primary ions involved in establishing membrane potentials?

Answer 1

Sodium (Na+) and Potassium (K+)

Question 2

What is the role of the sodium-potassium pump?

Answer 2

It maintains the chemical concentration gradients of Na+ and K+ across the cell membrane.

Question 3

What is the typical resting membrane potential of a cell?

Answer 3

Approximately -70 mV

Question 4

How does the cell membrane become polarized?

Answer 4

The cell membrane is somewhat leaky, but K+ and Na+ leak at different rates, and in different directions, with K+ leaking at an initially faster rate.

Question 5

Why does K+ leak at a faster rate?

Answer 5

A greater concentration gradient and more potassium leak channels

Question 6

At rest, after establishment of the resting membrane potential the inside of the cell membrane is __, and the outside of the cell membrane is __. This is considered a steady state for the cell, also called the __

Answer 6

negative, positive, resting membrane potential

Question 7

What happens to the membrane potential during depolarization?

Answer 7

The inside of the cell becomes less negative, moving closer to zero.

Question 8

What occurs during hyperpolarization?

Answer 8

The inside of the cell becomes more negative than the resting potential.

Question 9

What is the electrochemical gradient?

Answer 9

The combined effect of concentration gradients and electrical gradients on ion movement.

Question 10

What type of cells use changes in membrane potential to send signals in the body?

Answer 10

neurons and muscle cells

Question 11

graded potential

Answer 11

local changes in membrane potential that decrease in intensity with distance

Question 12

action potential

Answer 12

all-or-nothing events that propagate along the axon.

Question 13

transmembrane potential

Answer 13

Potential difference between the inside and outside of the cell membrane

Question 14

What is responsible for the transmembrane potential?

Answer 14

The current caused by the electrochemical gradient

Question 15

what two things do ions do when gated channels in the membrane open at resting membrane potential?

Answer 15

they move according to chemical concentration and electrical gradient, together called electrochemical gradient

Question 16

What is the effect of opening gated Na+ channels?

Answer 16

It typically causes depolarization of the membrane.

Question 17

What happens when K+ channels open?

Answer 17

K+ rushes out of the cell, leading to hyperpolarization.

Question 18

What is the ion composition of intracellular fluid (ICF)?

Answer 18

High concentration of K+ and low concentration of Na+, with negatively charged proteins trapped inside.

Question 19

What is the ion composition of extracellular fluid (ECF)?

Answer 19

High concentration of Na+ and low concentration of K+, with chloride ions as the main anions.

Question 20

What causes the cell membrane to become polarized?

Answer 20

The differential leakage of K+ and Na+ ions through their respective channels.

Question 21

What is the role of chloride ions in membrane potential?

Answer 21

Chloride ions can move in and out of the cell, influenced by both concentration and electrical gradients.

Question 22

What is meant by ‘current’ in the context of membrane potentials?

Answer 22

Current refers to the movement of electrical charge across the membrane.

Question 23

What is the effect of a graded potential on the membrane?

Answer 23

It can lead to either depolarization or hyperpolarization, depending on the type of ion channel that opens.

Question 24

What happens during repolarization?

Answer 24

The membrane potential returns toward -70 mV after depolarization.

Question 25

What is the difference between local flow of current and action potentials?

Answer 25

Local flow of current decreases in intensity with distance, while action potentials propagate without decrement.

Question 26

What is the role of negatively charged proteins in the cell?

Answer 26

They contribute to the negative charge inside the cell and are too large to cross the membrane.

Question 27

How does the concentration gradient affect ion movement?

Answer 27

Ions move from areas of high concentration to areas of low concentration.

Question 28

What is the significance of the resting membrane potential in neurons and muscle cells?

Answer 28

It is crucial for the ability to generate action potentials and transmit signals.

Question 29

What initiates the depolarization of a neuron?

Answer 29

The influx of Na+ ions into the cell down its electrochemical gradient.

Question 30

What is the threshold level for generating an action potential?

Answer 30

Approximately -55 mV.

Question 31

What happens when the threshold is reached in a neuron?

Answer 31

Voltage-gated Na+ channels open, causing a rapid depolarization known as an action potential.

Question 32

What is the all-or-none property of action potentials?

Answer 32

Once the threshold is reached, the action potential occurs fully and does not vary in magnitude.

Question 33

What is the role of the axon hillock in action potential generation?

Answer 33

It has a high concentration of voltage-gated Na+ channels and is where action potentials are initiated.

Question 34

Describe the process of repolarization after an action potential.

Answer 34

Voltage-gated Na+ channels close, voltage-gated K+ channels open, allowing K+ to exit the cell and restore resting membrane potential.

Question 35

What is the absolute refractory period?

Answer 35

The time during which no second action potential can be generated, regardless of stimulus strength.

Question 36

What is the relative refractory period?

Answer 36

The period immediately following the absolute refractory period when a second action potential may occur if the stimulus is strong enough.

Question 37

What is the difference between continuous conduction and saltatory conduction?

Answer 37

Continuous conduction occurs in unmyelinated axons, while saltatory conduction occurs in myelinated axons, where the action potential jumps between nodes of Ranvier.

Question 38

What is frequency coding in relation to action potentials?

Answer 38

Information about stimulus strength is conveyed by the frequency of action potentials rather than their strength.

Question 39

What is hypokalemia and how does it affect action potentials?

Answer 39

Hypokalemia is low potassium levels in the extracellular fluid, making it harder to depolarize and send action potentials, leading to symptoms like muscle weakness.

Question 40

What is hyperkalemia and its effects on action potentials?

Answer 40

Hyperkalemia is high potassium levels in the extracellular fluid, which can hinder repolarization and lead to severe muscle weakness and cardiac arrest.

Question 41

How does hypocalcemia affect neuronal excitability?

Answer 41

Low calcium levels can cause inappropriate opening of Na+ channels, leading to spontaneous action potentials and symptoms like cramps and spasms.

Question 42

What causes hyponatremia and its impact on action potentials?

Answer 42

Hyponatremia is low sodium levels in the extracellular fluid, making it harder to depolarize and leading to muscle weakness and neurological symptoms.

Question 43

What is the role of the Na+/K+ pump after an action potential?

Answer 43

It restores the normal concentrations of Na+ and K+ in the intracellular and extracellular fluids.

Question 44

What is the significance of the depolarization phase of an action potential?

Answer 44

It represents a rapid increase in membrane potential from -70 mV to +30 mV due to the influx of Na+.

Question 45

What triggers the opening of voltage-gated Na+ channels?

Answer 45

A sufficient depolarization of the membrane potential that reaches the threshold level.

Question 46

What is the effect of a strong stimulus during the relative refractory period?

Answer 46

It may generate a second action potential, but it is more difficult due to the hyperpolarized state of the membrane.

Question 47

What happens to the membrane potential during an action potential?

Answer 47

The membrane potential rapidly depolarizes and then repolarizes back to resting potential.

Question 48

What is the role of voltage-gated K+ channels during repolarization?

Answer 48

They open to allow K+ to exit the cell, which helps restore the negative membrane potential.

Question 49

What is the effect of a subthreshold stimulus on action potential generation?

Answer 49

A subthreshold stimulus will not generate an action potential.

Question 50

How does myelination affect the speed of action potential propagation?

Answer 50

Myelination increases the speed of propagation through saltatory conduction.

Question 51

What is the significance of the nodes of Ranvier in myelinated axons?

Answer 51

They are the sites where voltage-gated channels are concentrated, allowing for rapid conduction of action potentials.

Question 52

What is primarily responsible for ESTABLISHING the RESTING membrane potential of a cell?

Answer 52

faster leaking (greater permeability) to K+

Question 53

Describe the charge of the cell membrane potential of a neuron at rest

Answer 53

polarized

Question 54

A strong stimulus makes action potentials __ but not __

Answer 54

more frequent, stronger

Question 55

During the relative refractory period, can a second action potential be elicited?

Answer 55

Yes, by a threshold or suprathreshold stimulus