3 - Equilibrium, Resting Membrane, and Action Potentials

resting membrane potential (RMP)

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

diffusion potentials

RMP is established by _____

down

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

true

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

charge of ion

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

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

A RMP is set by _____ and maintained by _____

most

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

high

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

false

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

-70 to -90 mV

What is usually the RMP range?

K+; K+

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

true

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

Na; K

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

more

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

-85; -90

K equilibrium potential is _____ to _____ mV

lower

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

K+ equilibrium potential

_____ 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

into; out

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

equal; opposite

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

+65 mV

What is the typica equilibrium potential value for Na+?

+120mV

What is the typica equilibrium potential value for Ca2+?

-85 mV

What is the typica equilibrium potential value for K+?

reviewed

Review

driving force

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

cation; anion

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

negative

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

equilibrium

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

action potential (AP)

Transmit information in nervous system and all muscle

depolarization; repolarization

AP occurs in excitable cells - rapid _____ followed by _____

depolarization

Membrane potential is less negative with [depolarization/ hyperpolarization]

hyperpolarization

Membrane potential is more negative with [depolarization/ hyperpolarization]

inward

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

outward

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

resting potential

What is A?

threshold of excitation

What is B?

peak action potential

What is C?

repolarization

What is D?

hyperpolarization

What is E?

depolarization

What is A?

overshoot

What is B?

repolarization

What is C?

hyperpolarization

What is D?

threshold potential

Membrane potential at which an AP is inevitable

overshoot

Portion of AP where membrane potential is positive

undershoot

Portion of AP where membrane potential is more negative than RMP

refractory period

Period during which another AP can't be generated

high; low

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

Na+; K+

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

higher

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

threshold

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

refractory periods

Excitable cells unable to produce normal APs during _____

absolute refractory period (ARP)

-Overlaps with most of the AP

-No stimulus can occur to cause another AP

true

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

relative refractory period (RRP)

-From end of ARP until through most of hyperpolarization

-AP occurs with greater than normal depolarization

greater

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

voltage; ligand

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

inactivated

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

reviewed

Review

1. Size and shape typical for a given cell type

2. Propagation

3. All-or-none response

What are the 3 main characteristics of AP?

local currents

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

reviewed

Review

reviewed

Review: Propagation of APs

conduction velocity

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

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

depolarizes; Na+

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

resistance; capacitance

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

length constant

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

resistance; internal resistance

Membrane _____ and _____ affect length constant

increase

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

decreases

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

true

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

myelinate

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

increase; decrease

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

nodes of Ranvier

Breaks in myelin sheath every 1-2mm

saltatory conduction

APs jump from node to node

1. increase size of the nerve fiber

2. myelinate the nerve fiber

3. breaks in myelin sheath every 1-2mm

What are the 3 ways to increase conduction velocity?

increase; smaller

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

reviewed

Review: Changing Conduction Velocity:

length constant

How far depolarization current will spread along a nerve

saltatory conduction

APs jump from node to node

potassium

Which ion is always high inside the cell?

out; down

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

outside

Sodium is high [inside/outside] the cell

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

What do K+ leak channels do?

negatively

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

high

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

potassium

Resting membrane potential is determined by _____

inside of the cell

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

-85 to -90 mV

What is usually the RMP range for potassium?

potassium equilibrium

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

equilibrium potential

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

positively

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

movement stops (-85 to -90 mV)

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

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

What is the point of an action potential?

depolarize; repolarize

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

make membrane potential less negative

What does it mean to depolarize a cell?

membrane potential more negative than the resting membrane potential

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

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

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

refractory period

Period at which you cant get another action potential

more

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

inward

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