Biology Lecture Series C: Ionic Flux and Membrane Potential Concepts

Because the cell membrane is impermeable to ions, it has the ability to _____.

Separate charges

_____ is defined as an electrical potential created by the separation of charged ions.

The variable is _____.

It is measured in _____.

Voltage

V

Volts

_____ is defined as any net flow of charge.

The variable is _____.

It is measured in _____.

Current

I

Amperes (amps) (A)

_____ is defined as a measure of the ease of current flow between two points.

The variable is _____.

It is measured in _____.

Conductance

G

Siemens (s)

What is the relationship (formula) between conductance and resistance?

G = 1 / R

or

R = 1 / G

* G is conductance

* R is resistance

Resistance is measured in _____.

Ohms

Ohm's law describes the relationship between _____, _____, and _____.

Voltage

Current

Resistance

The formula for Ohms law is _____.

V = I * R

or

I = V * G

_____ is defined as a measure of the ability to separate charge.

The variable is _____.

It is measured in _____

Capacitance

C

Farads (s)

A pure _____ is one of nature's best capacitors.

Phospholipid bilayer

The total capacitance of a cell is proportional to the _____ of the membrane.

Surface area

_____ is defined as the voltage at which there will be no net movement of an ion through an open conductance.

Equilibrium potential

Equilibrium potential is also referred to as _____.

Reversal potential

True/False:

Every permeant ion has its own equilibrium potential.

True

The two primary driving forces that set an equilibrium potential for an ion are the _____ and the _____.

Chemical gradient

Electrical gradient

Let's say a membrane has K+ ions and Cl- ions in the intercellular space and no ions in the extracellular space.

If an open channel suddenly appeared in the membrane, the ions would travel to the _____.

These ions would be moving _____ their concentration gradients.

The movement of these ions will stop when _____.

To the extracellular space

With

[Ion] outside membrane = [Ion] inside membrane

True/False:

Separation of charge occurs just outside and inside the lipid bilayer.

True

The _____ equation is used to calculate the equilibrium potential of a specific ion.

Nernst

True/False:

Having membrane potential means that one side of the membrane is charged and the other side is uncharged.

False

* Having membrane potential means there is an electric field across the membrane

The size of the ionic flux needed to product a voltage change across the membrane depends on the _____ of the cell.

The effect of ionic flux on ionic gradients depends on the _____ of the cell.

Surface area

Volume

The _____ gradient is defined by the voltage across the membrane.

Electrical

The _____ gradient is defined by the concentration of the ion in the bulk solution.

Chemical

The equilibrium potential for an ion is reached when the driving force for the electrical and chemical gradient are _____ and _____.

Equal

Opposite

_____ is defined as the voltage across the membrane of a cell at rest.

Resting membrane potential

_____ is defined as the weighted average of the equilibrium potentials for all permeant ions.

Resting membrane potential

The resting membrane potential is closest in value to the equilibrium potential for _____ ion.

This means that this ion has an important role in setting the _____.

K+

Resting membrane potential

The _____ equation is used to calculate resting membrane potential given the concentration gradient and relative permeability of all permeant ions.

Goldman

Sodium ions will flow _____ of the cell based on their chemical gradient and _____ the cell based on their electrical gradient.

Into

Into

Potassium ions will flow _____ of the cell based on their chemical gradient and _____ the cell based on their electrical gradient.

Out of

Into

If sodium ions are flowing into the cell based both on their chemical AND electrical gradient, while potassium ions are flowing into the cell ONLY on their chemical gradient, how is there an equal flux of sodium and potassium in and out of the cell?

Sodium has a large "driving force" into the cell but low permeability at rest

Potassium has a small "driving force" into the cell but high permeability at rest

True/False:

Generally, more sodium ions are flowing into the cell than potassium ions are flowing out.

False

* The net flux of each ion is generally even

Resting membrane potential is very sensitive to the equilibrium potential for _____.

K+

The peak of an action potential is very sensitive to the equilibrium potential for _____.

Na+

_____ is defined as a brief, regenerative, all-or-none, electrical potential that originates in a neuronal cell body and propagates along an axon.

Action potential

True/False:

Only the concentration of K+ ions affect membrane voltage.

False

* There are other influences, but none as big

True/False:

At rest, a membrane is much more permeable to Na+ than K+.

False

* At rest, a membrane is more permeable to K+

An all-or-none action potential is created when there is a regenerative spike in _____ levels.

Na+

After a regenerative spike, the rising phase is terminated by the loss of a(n) _____ for Na+ or by _____ of Na+ channels.

Driving force

Inactivation

The regenerative spike causes _____.

a) Depolarization

b) Hyperpolarization

c) Repolarization

a) Depolarization

The initial efflux of K+ ions causes _____.

a) Depolarization

b) Hyperpolarization

c) Repolarization

c) Repolarization

The efflux of K+ ions drops the membrane potential below resting membrane potential, which is characterized as _____.

a) Depolarization

b) Hyperpolarization

c) Repolarization

b) Hyperpolarization

Once _____ gates are closed, a membrane can return to its resting membrane potential.

K+

The two main variables that effect the speed of propagation are _____ and _____.

Axial resistance (Ra)

Capacitance (Cm)

True/False:

Axial resistance means resistance of flow across a cell membrane.

False

* Axial resistance means resistance to flow down the length of an axon

True/False:

Speed of propagation increases as Ra * Cm decreases.

True

* They are indirectly proportional

True/False:

As diameter of an axon increases, axial resistance decreases.

True

True/False:

As diameter of an axon increases, capacitance decreases.

False

* As diameter of an axon increases, capacitance increases.

True/False:

As diameter of an axon increases, Ra is decreasing MORE than Cm is increasing, and that is why the net effect causes an increase in speed of propagation.

True

_____ if defined as the wrapping of axons with a myelin sheath.

Myelination

True/False:

Myelination is a method of increasing speed of propagation WITHOUT changing axial resistance.

True

The two types of glial cells that produce myelin are _____ in the CNS and _____ in the PNS.

Oligodendrocytes

Schwann cells

True/False:

Wrapping myelin around an axon is functionally equivalent to increasing the thickness of the axonal membrane.

True

* Increasing the thickness means the membrane is not as good of a capacitor, which is better for speed

True/False:

Action potential would travel faster down an axon if Nodes of Ranvier were absent.

False

* Node of Ranvier allow for action potential to regenerate

True/False:

Action potential jumps relatively slow from one node to another.

False

* Action potential moves very quick