3 - Equilibrium, Resting Membrane, and Action Potentials

Potential difference that exists across membranes in the period between action potentials

resting membrane potential (RMP)

RMP is established by _____

diffusion potentials

RMP is defined as the potential difference generated across a membrane when a charged ion diffuses [up/down] a concentration gradient

down

A RMP can be positive or negative. True or false?

true

A RMP can be positive or negative, depending on what?

charge of ion

A RMP is set by _____ and maintained by _____

K+ leak channels; Na+/K+ ATPase pump

Ions with high permeabilities contribute [most/least] to RMP

most

K+ and Cl- are ions with [high/low] permeabilities, and therefore contribute most to RMP

high

K+ is not separated from immobile anions inside cell. True or false?

false

What is usually the RMP range?

-70 to -90 mV

Na+/K+ ATPase helps maintain _____ concentration gradient across the cell membrane and set _____ diffusion potential

K+; K+

Resting membrane potential always close to potassium equilibrium potential. True or false?

true

RMP is negative because more _____ ions outside cell than _____ ions inside cell

Na; K

Membrane is [more/less] permeable to K+ than Na+

more

K equilibrium potential is _____ to _____ mV

-85; -90

K+ is in equilibrium when cell is 85-90 mV [higher/lower] than EC environment

lower

_____ is point at which movement of K+ INTO cell because of negative electrical potential is balanced by diffusion of K+ OUT of cell due to concentration gradient

K+ equilibrium potential

K+ equilibrium potential is point at

which movement of K+ [into/out] cell

because of negative electrical

potential is balanced by diffusion

of K+ [into/out] of cell due to

concentration gradient

into; out

At K+ equilibrium, electrical and diffusion forces are _____ and _____

equal; opposite

What is the typica equilibrium potential value for Na+?

+65 mV

What is the typica equilibrium potential value for Ca2+?

+120mV

What is the typica equilibrium potential value for K+?

-85 mV

Review

reviewed

Difference between the measured membrane potential and the ion's calculated equilibrium potential

driving force

When driving force is negative, ion will enter cell if it is a _____ and leave cell if it is an _____

cation; anion

When driving force is [positive/negative], ion will enter cell if it is a cation and leave cell if it is an anion

negative

Membrane potential is too negative - try to bring it towards _____ potential

equilibrium

Transmit information in nervous system and all muscle

action potential (AP)

AP occurs in excitable cells - rapid _____ followed by _____

depolarization; repolarization

Membrane potential is less negative with [depolarization/ hyperpolarization]

depolarization

Membrane potential is more negative with [depolarization/ hyperpolarization]

hyperpolarization

[Inward/outward] current is the flow of positive charge into cell

inward

[Inward/outward] current is the flow of positive charge out of cell

outward

What is A?

resting potential

What is B?

threshold of excitation

What is C?

peak action potential

What is D?

repolarization

What is E?

hyperpolarization

What is A?

depolarization

What is B?

overshoot

What is C?

repolarization

What is D?

hyperpolarization

Membrane potential at which an AP is inevitable

threshold potential

Portion of AP where membrane potential is positive

overshoot

Portion of AP where membrane potential is more negative than RMP

undershoot

Period during which another AP can't be generated

refractory period

When the RMP is -70 mV, K+ conductance is [low/high] and Na+ conductance is [low/high]

high; low

During repolarization, inactivation gates on _____ channels close and _____ channels open

Na+; K+

During undershoot (hyperpolarization), K+ conductance is [higher/lower] than at rest

higher

During upstroke of AP, the membrane is depolarization to _____ (-60mV)

threshold

Excitable cells unable to produce normal APs during _____

refractory periods

-Overlaps with most of the AP

-No stimulus can occur to cause another AP

absolute refractory period (ARP)

No stimulus can occur to cause another AP during the absolute refractory period (ARP). True or false?

true

-From end of ARP until through most of hyperpolarization

-AP occurs with greater than normal depolarization

relative refractory period (RRP)

During the relative refractory period (RRP), AP occurs with [greater/lesser] than normal depolarization

greater

The activated state of the refractory period is _____ and _____ gated

voltage; ligand

During the _____ state of the refractory period, time and return to RMP is required for reset

inactivated

Review

reviewed

What are the 3 main characteristics of AP?

1. Size and shape typical for a given cell type

2. Propagation

3. All-or-none response

APs start close to the cell body of a neuron, spread down the axon via _____

local currents

Review

reviewed

Review: Propagation of APs

reviewed

-Speed at which an AP travels along a nerve or muscle fiber

-How quickly a membrane depolarizes in response to inward Na+ current

conduction velocity

Conduction velocity is how quickly a membrane _____ in response to inward _____ current

depolarizes; Na+

Membrane _____ and _____ affect the time constant when it comes to conduction velocity of APs

resistance; capacitance

How far depolarization current will spread along a nerve, in association with conduction velocity of APs

length constant

Membrane _____ and _____ affect length constant

resistance; internal resistance

To increase conduction velocity, we need to [increase/decrease] the size of the nerve fiber

increase

By increasing diameter of a fiber, internal resistance [increases/decreases]

decreases

There are anatomical limits to nerve size. True or false?

true

To increase conduction velocity, we need to _____ the nerve fiber

myelinate

Insulation of nerves with lipid will [increase/decrease] membrane resistance and [increase/decrease] capacitance

increase; decrease

Breaks in myelin sheath every 1-2mm

nodes of Ranvier

APs jump from node to node

saltatory conduction

What are the 3 ways to increase conduction velocity?

1. increase size of the nerve fiber

2. myelinate the nerve fiber

3. breaks in myelin sheath every 1-2mm

The myelin coating [increases/decreases] the thickness of the membrane, making the capacitance [smaller/larger]

increase; smaller

Review: Changing Conduction Velocity:

reviewed

How far depolarization current will spread along a nerve

length constant

APs jump from node to node

saltatory conduction

Which ion is always high inside the cell?

potassium

Potassium diffuses [in/out] of the cell, [up/down] its concentration gradient

out; down

Sodium is high [inside/outside] the cell

outside

What do K+ leak channels do?

allow potassium to leak out of the cell slowly, carrying a positive charge

Because K+ leaks out of the cell, and takes a positive charge with it, the inside of the cell is _____ charged

negatively

Ions that have really [high/low] permeability will contribute most to resting membrane potential

high

Resting membrane potential is determined by _____

potassium

When there is an action potential, sodium will go where?

inside of the cell

What is usually the RMP range for potassium?

-85 to -90 mV

Because RMP is determined by potassium in most cells, its always going to be close to the _____ potential

potassium equilibrium

Point at which the movement of potassium into the cell (because of negative electrical potential) is balanced by diffusion of potassium out of the cell due to its concentration gradient

equilibrium potential

Potassium wants to move out because its high inside the cell -> leaking out -> creating negative charge inside cell -> attraction of _____ charged ions back into the cell

positively

At K+ equilibrium, electrical & diffusion forces are equal and opposite. What happens after?

movement stops (-85 to -90 mV)

What is the point of an action potential?

how you get info transmitted in the nervous system & muscle (leads to contraction)

In order to get an action potential, you need to _____a cell & excite it, and then _____ it to get it back to the resting membrane potential

depolarize; repolarize

What does it mean to depolarize a cell?

make membrane potential less negative

What does it mean when a cell is hyper-polarized?

membrane potential more negative than the resting membrane potential

While a cell is in the hyper-polarized state, is it harder or easier to get another action potential during that time? Why?

harder b/c it has to reach threshold of excitation again

Period at which you cant get another action potential

refractory period

The further away you are from a threshold, the [more/less] stimulus is required to reach it

more

There has to be an [inward/outward] current of an ion in order to get an action potential

inward