Cell Membrane and Sodium-Potassium Pump Quiz G 5

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Questions and Answers

What is the role of the sodium-potassium (Na+-K+) pump in the cell membrane?

It allows free movement of both sodium and potassium ions across the membrane.

It is responsible for maintaining a neutral charge inside the cell by balancing sodium and potassium ions.

It transports sodium and potassium ions against their concentration gradients, requiring energy. (correct)

It primarily transports sodium ions out of the cell, creating a positive charge inside.

Why is the sodium-potassium pump considered an electrogenic pump?

It maintains a neutral charge inside the cell by balancing ion movement.

It moves three sodium ions out for every two potassium ions in, creating a net negative charge inside the cell. (correct)

It generates electrical energy through the movement of ions.

It pumps both sodium and potassium ions in equal amounts, creating a balanced charge.

What is the typical concentration of sodium ions inside and outside the cell?

140 mEq/L inside, 4 mEq/L outside.

14 mEq/L inside, 142 mEq/L outside. (correct)

142 mEq/L inside, 14 mEq/L outside.

4 mEq/L inside, 140 mEq/L outside.

How does the sodium-potassium pump contribute to the membrane potential?

It creates a negative charge inside the cell due to the outward movement of sodium ions. (B) Signup and view all the answers

Which of the following statements accurately describes the sodium-potassium pump?

It is an active transport system that requires energy to move ions against their concentration gradients. (D) Signup and view all the answers

Which of the following processes is directly involved in the movement of sodium and potassium ions across the cell membrane?

Active transport (C) Signup and view all the answers

What is the primary source of energy for the sodium-potassium pump?

ATP (D) Signup and view all the answers

What is the typical voltage at which a sudden conformational change occurs in the voltage-gated potassium channel?

-55 millivolts (D) Signup and view all the answers

What is the typical resting state membrane potential?

-70 millivolts (A) Signup and view all the answers

What is the name of the process that causes the membrane potential to become less negative?

Depolarization (A) Signup and view all the answers

What is the name of the state of the voltage-gated potassium channel during the resting state?

Deactivated (B) Signup and view all the answers

What is the name of the state of the voltage-gated potassium channel during activation?

Activated (B) Signup and view all the answers

What is the unit of measurement for conductance?

mmho/cm2 (A) Signup and view all the answers

What is the name of the electrode that measures the membrane potential?

Voltage electrode (A) Signup and view all the answers

What is the name of the electrode that measures the current?

Current electrode (D) Signup and view all the answers

What is the name of the device that provides a command voltage?

Signal generator (C) Signup and view all the answers

What is the name of the device that amplifies the feedback signal?

Feedback amplifier (B) Signup and view all the answers

What is the primary function of the myelin sheath in nerve fibers?

To increase the speed of nerve impulse transmission. (B) Signup and view all the answers

What is the name given to the gaps between the myelin sheath along the nerve fiber?

Nodes of Ranvier (A) Signup and view all the answers

How does the saltatory conduction of nerve impulses increase the speed of transmission?

By allowing the nerve impulse to jump between nodes of Ranvier, skipping the myelinated sections. (B) Signup and view all the answers

Which of the following statements regarding myelinated and unmyelinated fibers is TRUE?

Unmyelinated fibers are more common in a typical nerve trunk. (D) Signup and view all the answers

What is the primary component of the myelin sheath that gives it its insulating properties?

Sphingomyelin (A) Signup and view all the answers

What happens to the activity of the sodium-potassium pump as the internal sodium concentration increases from 10 to 20 mEq/L?

The activity of the pump increases by a factor of eight. (C) Signup and view all the answers

What is the primary reason the recharging process of a nerve fiber can be set rapidly into motion?

The rapid action of the sodium-potassium pump. (B) Signup and view all the answers

How does the transmission of each action potential along a nerve fiber affect the concentration differences of sodium and potassium?

It slightly reduces the concentration differences. (C) Signup and view all the answers

What is the defining characteristic of a plateau potential in nerve fibers?

A sustained depolarization for a prolonged period before repolarization. (C) Signup and view all the answers

What is the main consequence of the diffusion of sodium ions to the inside during depolarization?

It contributes to the slight reduction of the concentration differences. (D) Signup and view all the answers

According to the Goldman equation, what is the primary factor determining the membrane potential in a nerve fiber under normal conditions?

The permeability of the membrane to potassium ions (B) Signup and view all the answers

What is the approximate difference in millivolts between the resting membrane potential of a nerve fiber and the potassium potential as mentioned in the text?

2 (C) Signup and view all the answers

What is the relative permeability of the membrane to potassium compared to sodium in a normal nerve fiber?

100:1 (A) Signup and view all the answers

Which of the following is NOT a contributing factor to the resting membrane potential of a nerve fiber?

The action potential (D) Signup and view all the answers

What is the primary function of the sodium-potassium pump in maintaining the resting membrane potential?

To maintain the concentration gradients of sodium and potassium ions (B) Signup and view all the answers

What is the approximate resting membrane potential of a skeletal muscle cell?

-90 millivolts (B) Signup and view all the answers

What is the primary mechanism by which nerve signals are transmitted?

Action potentials (A) Signup and view all the answers

What is the characteristic change in membrane potential during an action potential?

From negative to positive (C) Signup and view all the answers

What is the concentration of potassium ions outside of the cell?

4 mEq/L (A) Signup and view all the answers

What is the ratio of sodium ions inside the cell to sodium ions outside the cell?

1:10 (B) Signup and view all the answers

Which ion is more permeable across the cell membrane?

Potassium (C) Signup and view all the answers

What is the main factor responsible for establishing the resting membrane potential?

The permeability of the cell membrane (C) Signup and view all the answers

Which of the following statements accurately describes the Na+-K+ pump?

It pumps sodium ions out of the cell and potassium ions into the cell. (D) Signup and view all the answers

What is the role of the concentration gradients of sodium and potassium ions in the resting membrane potential?

They create an electrical potential difference across the membrane. (A) Signup and view all the answers

What is the approximate resting membrane potential value discussed in the text?

-90 mV (A) Signup and view all the answers

Which factor contributes to the difference in permeability between sodium and potassium ions?

The presence of specific channels for each ion in the cell membrane. (A) Signup and view all the answers

Study Notes

Membrane Potentials and Action Potentials

Electrical potentials exist across cell membranes, crucial for nerve and muscle cells.
Membrane potentials are generated by ion concentration differences across a selectively permeable membrane.
In Figure 5-1A, potassium concentration is high inside, low outside, creating an outward diffusion tendency. This generates a membrane potential with negativity inside and positivity outside.
In figure 5-1B, high sodium concentration outside and low inside generates opposite polarity.
The Nernst equation calculates the diffusion potential for an ion, depending on its concentration difference.
EMF (millivolts) = ±61 x log (Concentration inside / Concentration outside)
Z is the electrical charge of the ion.
Cell types have different resting membrane potentials (Table 5-1).

Basic Physics of Membrane Potentials

Ion concentration differences create a diffusion potential across a selectively permeable membrane.
The Goldman equation calculates membrane potential considering multiple ion permeabilities.
EMF (millivolts) = -61 x log ( CNa+ PNa+ + CK+PK+ + CcPcr/ CNa+ PNa+ + CKPK+ + CCFPCr )
Sodium, potassium, and chloride are the most important ions involved.
Permeability of the membrane is crucial to determining the magnitude of the membrane potential.
Positive ion gradients from inside to outside cause electronegativity inside.
Rapid changes in sodium and potassium permeability are responsible for signal transmission.

Diffusion Potentials

Diffusion potential across a membrane opposes net diffusion of a particular ion.
It's determined by the ratio of ion concentrations on two sides of the membrane.
Greater concentration difference results in stronger diffusion potential.

The Nernst Equation

Calculates the equilibrium potential for an ion.
Relates the ion's diffusion potential to its concentration difference across the membrane
Formula: EMF (millivolts) = ±61 x log (Concentration inside / Concentration outside). Z is the ion's electrical charge.

Active Transport of Sodium and Potassium Ions

Sodium-Potassium (Na+-K+) pump constantly transports sodium out and potassium in, making the inside of the cell negative.
Creates large concentration gradients for both ions.
Na+ (outside): 142 mEq/L
Na+ (inside): 14 mEq/L
K+ (outside): 4 mEq/L
K+ (inside): 140 mEq/L

Leakage of Potassium

Potassium channels allow potassium to leak out even at rest.
This contributes significantly to the resting membrane potential.

Voltage-Gated Sodium Channels

Two gates: activation and inactivation.
Activation gate opens rapidly increasing sodium permeability.
Inactivation gate closes slowly, preventing further sodium entry.
Crucial for action potential generation and propagation.

Voltage-Gated Potassium Channels

Open more slowly than sodium channels.
Increased potassium permeability leads to repolarization.
Slow opening and closing are vital for action potential propagation.

Membrane Potential Measurement

Microelectrodes measure the potential difference across the membrane.
Voltmeters or oscilloscopes are used for recording.

Action Potentials

Rapid changes of membrane potential.
The action potential begins with a sudden shift from the normal negative resting membrane potential to a positive potential.
It ends with an equally rapid shift back to the negative potential.
This process propagates along the nerve fiber
Characteristics of Action Potential:
- Resting stage
- Depolarization Stage (fast Na+ channels open)
- Repolarization Stage (slow K+ channels open)

Propagation of Action Potentials

An action potential causes adjacent parts of a membrane to depolarize.
This process continues to propagate the action potential along the membrane (fiber).
The "all-or-nothing" principle governs propagation.

Re-establishment of Sodium and Potassium Gradients

Na+-K+ pump re-establishes concentration gradients after an action potential.
Requires energy, maintaining the "resting state."

Rhythmic Excitation of Excitable Tissue

Some tissues exhibit spontaneous repetitive discharge (e.g., heart, smooth muscle).
This arises from a combination of factors:
- Ion permeabilities allowing automatic depolarization
- This process is different in various excitable tissues

Myelinated and Unmyelinated Nerve Fibers

Myelinated fibers have a fatty myelin sheath that insulates the axon, drastically reducing ion leakage, thus increasing action potential propagation speed.
Unmyelinated fibers lack this insulation, leading to a much slower speed of propagation,
Saltatory conduction occurs in myelinated fibers; the action potential "jumps" between Nodes of Ranvier.

Excitation

Factors that initiate action potentials:
- Mechanical disturbances
- Chemical effects
- Electrical currents
Strength of stimulus influences whether an action potential develops.

Threshold for Excitation and Local Potentials

A minimum stimulus strength (threshold) is needed to initiate an action potential.
Weak stimuli cause local potentials that may or may not reach threshold.

Refractory Period

Period after an action potential during which a new one cannot be elicited.
Sodium channels are inactivated preventing further depolarization,

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Description

Test your understanding of the sodium-potassium pump and its role in cell membrane dynamics. This quiz covers key concepts such as ion concentrations, membrane potential, and the pump's electrogenic properties. Perfect for students studying cell biology and physiology.

Cell Membrane and Sodium-Potassium Pump Quiz G 5 - 1.4

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