Na+/K+ Pump

The Na+-K+ pump actively transports both sodium and potassium ions across the membrane to compensate for their constant leakage. In which direction is each ion pumped?

Na+ is pumped out of the cell and K+ is pumped into the cell.

What prevents the Na+ and K+ gradients from dissipating?

Na+-K+ ATPase

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?

Resting membrane potential

Which of the following best describes the Na+ and K+ concentrations across a neuron's plasma membrane?

The Na+ concentration is higher outside the cell compared to inside. The K+ concentration is higher inside the cell compared to outside

Why does the action potential only move away from the cell body?

The areas that have had the action potential are refractory to a new action potential.

ATP hydrolysis

What is the Na+/K+ pump driven by?

Na+

Which diffuses into the cell, K+ or Na+?

K+

Which diffuses out of the cell, K+ or Na+?

An action potential is self-regenerating because __________.

depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment

A vesicle fuses with the plasma membrane and releases its contents to the extracellular fluid. This statement describes _____.

exocytosis

The majority of water molecules moving across plasma membranes by osmosis do so via a process that is most similar to ____.

facilitated diffusion

What is the major role of the Na+-K+ pump in maintaining the resting membrane potential?

maintaining the concentration gradients for Na+ and K+ across the cell membrane

A primary active transport process is one in which __________.

molecules move through transport proteins that have been activated by ATP

Which of the following would increase the membrane permeability to K+?

more K+ leak channels

Which of the following best explains diffusion?

movement of molecules from an area of high concentration to an area of low concentration

The sodium-potassium pump uses ATP to move sodium and potassium ions across the plasma membrane. This statement describes _____.

primary active transport

Which of the following processes allows cells to concentrate material that is present only in very small amounts in the extracellular fluid?

receptor-mediated endocytosis

the opening of voltage-gated K+ channels

slow closing of voltage-gated K+ channels

Which of the following is least likely to increase the rate of diffusion?

small concentration gradient

The repolarization phase of an action potential results from __________.

the opening of voltage-gated K+ channels

The depolarization phase of an action potential results from the opening of which channels?

voltage-gated Na+ channels

What is the magnitude (amplitude) of an action potential?

100mV

How is an action potential propagated along an axon?

An influx of sodium ions from the current action potential depolarizes the adjacent area.

More K+ leak channels

Are there more or less K+ leak channels compared to Na+ leak channels?

Negatively charged

Is the cell more negatively charged or positively charged?

Some transport processes use transport proteins in the plasma membrane, but do not require ATP. This type of transport is known as _____.

facilitated diffusion

Which of the following is NOT a characteristic of peroxisomes?

They contain powerful enzymes called acid hydrolases.

The sodium-potassium pump ejects two Na+ from the cell and then transports three K+ back into the cell in order to maintain the concentration gradients for sodium and potassium.

False

2 K+

How many K+ are pumped into the cell?

3 Na+

How many Na+ are pumped out of the cell?

What is the basic difference between simple diffusion and facilitated diffusion across a cell membrane?

In facilitated diffusion, molecules only move with the aid of a protein in the membrane.

Which of the following is a difference between primary and secondary active transport?

In primary active transport, the transport protein gets phosphorylated; in secondary active transport, the transport protein is not phosphorylated.

K+

In the resting cell, there is a high concentration of what inside the cell?

Na+

In the resting cell, there is a high concentration of what outside of the cell?

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.

During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.

K+ ions diffusing through voltage-gated channels

The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.

K+; Na+

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak Channels

Which statement best describes exocytosis?

Membrane organelles fuse with the membrane and release contents out of the cell.

The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?

Na+

Which of the following is most likely to move through the cell membrane by facilitated diffusion?

Na+

The concentrations of which two ions are highest outside the cell.

Na+ and Cl-

During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?

Na+ is entering the cell

Why does regeneration of the action potential occur in one direction, rather than in two directions?

The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane is much more negatively charged than the outside surface.

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

The presence of concentration gradients and leak channels

Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane?

The resting membrane potential would become less negative (more positive).

Suppose a drug is developed that blocks K+ leakage channels. The drug prevents ions from passing through those channels. If this drug was applied to a neuron, what would be the most immediate effect on that neuron?

The resting membrane potential would become less negative (more positive).

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane

Opening K+ or Cl- channels in a postsynaptic membrane would produce an inhibitory postsynaptic potential (IPSP).

True

During the hyperpolarization phase of the action potential, voltage eventually returns to the resting membrane potential. What processes are primarily responsible for this return to the resting membrane potential?

Voltage-gated K+ channels close. K+ and Na+ diffuse through leakage channels.

During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?

Voltage-gated K+ channels close. K+ and Na+ diffuse through leakage channels.

What is a membrane potential?

a voltage or electrical charge across the plasma membrane

During depolarization, which gradient(s) move(s) Na+ into the cell?

both the electrical and chemical gradients

What is the electrochemical gradient of an ion?

the sum of the electrical and concentration gradients for that ion