Mamm phys module 2

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? (Hint: All cells exhibit an electrical potential difference across their plasma membranes. Only excitable cells can alter this difference by generating action potentials. Thus, an excitable cell, like a neuron, exhibits both a resting and an excited state). Positive membrane potential Resting membrane potential (RMP) Action potential Threshold potential

Resting membrane potential (RMP)

Extracellular [Cl-] is far greater than intracellular [Cl-]. In the membrane of a resting nerve cell, when chemically gated Cl- channels open,

Cl- ions enter the cell and the cell becomes hyperpolarized.

Extracellular [Cl-] is far greater than intracellular [Cl-]. In the membrane of a resting nerve cell, when chemically gated Cl- channels open, Cl- ions leave the cell and the cell becomes hyperpolarized. Cl- ions enter the cell and the cell becomes hyperpolarized. Cl- ions leave the cell and the cell becomes depolarized. Cl- ions enter the cell and the cell becomes depolarized.

Cl- ions enter the cell and the cell becomes hyperpolarized.

At rest (in a resting neuron, so we're talking about the resting membrane potential), there is a little bit more ___ than ______ Na+ influx; K+ efflux Na+ efflux; K+ influx K+ influx; Na+ efflux K+ efflux; Na+ influx

K+ efflux; Na+ influx

When ligand - gated K+ channels of a resting neuron open,

K+ leaves the neuron.

When ligand - gated K+ channels of a resting neuron open, K+ leaves the neuron. K+ leaves the neuron and the neuron depolarizes. K+ enters the neuron.

K+ leaves the neuron.

Image a world without electrical gradients (this is a hypothetical situation that does not exist). What would happen to the K+ concentration gradient? (assume there are leak channels to K+ so K+ can move) K+ would leak out but at some point it would stop and the concentration gradient will be maintained K+ would leak out of the cell until the K+ concentration inside the cell equaled the K+ concentration outside K+ would not move The concentration gradient would flip, with more K+ outside than inside the cell.

K+ would leak out of the cell until the K+ concentration inside the cell equaled the K+ concentration outside

The following is important for maintaining a negative resting membrane potential: Leak channels specific to ____ in a membrane causes this ion to leave the cell, while ___ cannot follow this ion. A-;Na+ Na+; A- A-; K+ K+; A-

K+; A-

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

Leak channels

When voltage - gated Na+ channels of a resting neuron open, Na+ leaves the neuron and the neuron depolarizes. Na+ enters the neuron and the neuron depolarizes. the neuron depolarizes. Na+ enters the neuron.

Na+ enters the neueon and the neuron depolarizes

Image a world without electrical gradients (this is a hypothetical situation that does not exist). What would happen to the Na+ concentration gradient? (assume there are leak channels to Na+ so Na+ can move) Na+ would leak in but at some point it would stop and the concentration gradient will be maintained Na+ would leak into the cell until the Na+ concentration inside the cell equaled the Na+ concentration outside Na+ would not move The concentration gradient would flip, with more Na+ inside than outside the cell.

Na+ would leak into the cell until the Na+ concentration inside the cell equaled the Na+ concentration outside

The concentration gradients for sodium and potassium between the ICF and the ECF are maintained by the ___

Na+/K+ ATPase pump

The ____ can be used to calculate the equilibrium potential of a specific ion for a given concentration gradient differential equations Nernst equation Goldman-Hodgkin-Katz equation

Nernst equation

Sodium levels are increased in a patient in the ECF. Assuming that all else remains unchanged (this means that intracellular sodium levels are the same as in a normal person), how will this affect the membrane potential? it will become more negative than -70 mV (e.g. -80 mV) because the concentration gradient of sodium is steeper, so there will be more movement of sodium down its electrochemical gradient. it will become less negative than -70 mV (e.g. -60 mV) because the concentration gradient of sodium is steeper, so there will be more movement of sodium down its electrochemical gradient.

it will become less negative than -70 mV (e.g. -60 mV) because the concentration gradient of sodium is steeper, so there will be more movement of sodium down its electrochemical gradient.

Extracellular [Cl- ] is far greater than intracellular [Cl- ]. The equilibrium potential of chlorine is

negative

The membrane potential at rest is negative positive neither negative nor positive

negative

The equilibrium potential of sodium is

positive

The resting membrane potential results from activity of the sodium/potassium pump only. differences in membrane permeability to Na+ and K+ only. uneven distribution of ions across the cell membrane only. uneven distribution of ions across the cell membrane and differences in membrane permeability to Na+ and K+.

uneven distribution of ions across the cell membrane and differences in membrane permeability to Na+ and K+.

Maintaining a polarized membrane potential at rest requires energy yes yes but it requires no ATP no no but it requires some ATP

yes

Maintaining a polarized membrane potential at rest requires energy? yes yes but it requires no ATP no no but it requires some ATP

yes

The equilibrium potential of ion 'X' is the membrane potential of a hypothetical cell that is very permeable to ion 'X' at a given concentration gradient. Does that mean the equlibrium potential of ion 'X' changes when the concentration gradient of 'X' is increased?

yes, the equilibrium potential will change because with a steeper concentration gradient, more of ion 'X' can move across the membrane and cause an even greater charge differences between the in and outside of the plasma membrane

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 Na+ /K+ pump moves three positive ions out of and two into the cell. Which statement is FALSE regarding the pump? It transports Na+ out of the cell and K+ into the cell. It maintains the Na+ and K+ concentration gradients Its activity requires the expenditure of metabolic (cellular) energy. The net efflux of positively charged ions is directly responsible (and the major determinant of) for the negative resting membrane potential

The net efflux of positively charged ions is directly responsible (and the major determinant of) for the negative resting membrane potential

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. Hint: Diffusion across the plasma membrane: The phospholipid bilayer is a largely hydrophobic permeability barrier. Small, lipid-soluble substances readily diffuse through it. However, small, water-soluble substances do not. There are two conditions that must be met in order for diffusion of small, water-soluble substances to take place. What are these two conditions? The presence of concentration gradients and Na+-K+ pumps The presence of concentration gradients and voltage-gated channels The presence of concentration gradients and leak channels The presence of a resting membrane potential and leak channels

The presence of concentration gradients and leak channels

The plasma membrane is much more permeable to K+ than to Na+. Why? Hint: There are several K+ channel types. Some are voltage sensitive. Others are calcium sensitive. Others still allow for the movement of K+ into cells down electrical gradients. Finally, there are certain K+ channels that are always open and available to K+.

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

True or false? The equilibrium potential of sodium is the membrane potential of a hypothetical cell that is very permeable to sodium at a given concentration gradient. For sodijm, the equilibrium potential is positive

True

Ionic current (across the membrane of within the cell) is defined as a difference in concentration of a specific ion between two regions a difference in the net charge between two regions flow of an electrical charge

a difference in concentration of a specific ion between two regions

The electrical gradient is defined as

a difference in the net charge between two regions

When sodium channels open, sodium rushes into the cell. This will cause

depolarization

When calcium channels open, calcium rushes into the cell. This will cause depolarization (inner side of the membrane becomes more positively charged) hyperpolarization

depolarization (inner side of the membrane becomes more positively charged)

If a small amount of cations is leaked into the cell, the cell would

depolarize

The membrane potential is defined as the fact that the body has more anions than cations electrical disequilibrium between the ICF and the ECF (ions are not distributed evenly between the ECF and the ICF, especially across the membrane) the fact that the body has more cations than anions

electrical disequilibrium between the ICF and the ECF (ions are not distributed evenly between the ECF and the ICF, especially across the membrane)

Potassium levels are ____ inside the cell than outside the cell

higher

If a small amount of anions is leaked into the cell, the cell would repolarize hyperpolarize depolarize

hyperpolarize

If a small amount of chlorine is leaked into the cell, the cell would

hyperpolarize

A neurotransmitter binds to a receptor, resulting in the opening of more sodium channels. How will this affect the membrane potential? it will become more negative it will become less negative (and thus more positive)

it will become less negative (and thus more positive)

Sodium levels are increased in a patient in the ECF. Assuming that all else remains unchanged (this means that intracellular sodium levels are the same as in a normal person), how will this affect the membrane potential?

it will become less negative than -70 mV (e.g. -60 mV) because the concentration gradient of sodium is steeper, so there will be more movement of sodium down its electrochemical gradient.

Sodium levels are increased in a patient in the ECF. Assuming that all else remains unchanged (this means that intracellular sodium levels are the same as in a normal person), how will this affect the membrane potential? it will become more negative than -70 mV (e.g. -80 mV) because the concentration gradient of sodium is steeper, so there will be more movement of sodium down its electrochemical gradient. it will become less negative than -70 mV (e.g. -60 mV) because the concentration gradient of sodium is steeper, so there will be more movement of sodium down its electrochemical gradient.

it will become less negative than -70 mV (e.g. -60 mV) because the concentration gradient of sodium is steeper, so there will be more movement of sodium down its electrochemical gradient.