Resting potential I

changes in membrane potential

information in the nervous system is encoded as __ in neurons

between cells, over long distance

Changes in membrane potential allow the transfer of information __ & __ within the cell.

electricity

flow of electrons around a circuit

chemical

electrical signal of first neuron is transduced into a ___ signal before being transduced into an electrical signal again in the second neuron.

ions

electrical signals are generated based on the flow of ___ across the plasma membranes.

potassium, sodium, calcium, chlorine

ions responsible for generating electrical signals in meurons

diffusion

process during which ions flow down their concentration gradient aka from high concentration to low concentration

Takes no energy

happens until there is no NET flow aka flow in = flow out

flows equal and opposite

closed

plasma membranes are similar to __ systems even though they are semi-permeable and have proteins acting as doors.

equilibrium

diffusion always proceeds toward an ___ where the concentrations are equal

entropy

highest ___ is better, nature like disorder

gibbs free energy

chemical force acting on ions until equilibrium is reached

higher

The change in free energy is proportional to the difference in concentration (inside vs outside).

___ ratio = ___ Gibbs free energy number = ___ number of molecules that have to move to reach equilibrium

voltage

separation of charge creates an electrical potential difference aka a ___

increases

electrical driving force on ion ___ as voltage increases

bigger

The bigger an arrow on a diagram, the ___ the magnitude of the force.

opposite, like

___ charges attract, ___ charges repel

neutral, inside, outside

both the inside and the outside of the phospholipid bilayer are about electrically ___, however, the negative charge arrange themselves closer to the membrane ___, and the positive charge arrange themselves closer to the membrane ___. This creates a negative resting potential.

inside, outside

convention is to write resting membrane potential as ___ relative to __.

resting membrane potential

results from separation of charge across the cell membrane

inside

positive charges are driven __

outside

negative charges are driven ___

ion channels, transporters

ions and charged particles need __ ___ or ___ to cross the plasma membrane.

voltage

separation of charges, or electrical potential difference

-40mV, -90mV

resting membrane potential caused by an uneven distribution of ions across membrane is usually between ___ and __ in mammalian cells.

denoted Vm

depolarization

positive swing in membrane potential

aka gets closer to 0, more postiive

hyperpolarization

negative swing in membrane potential

aka gets more negative

current

flow of charges (ions).

unit is Amperes (coulomb/sec)

direction of current flow = direction of flow of positive charges

ions

charge carriers in cells

encode, transmit, store

nerve cells generate electrical signals to ___, ___, or ___ information

stimulating electrode

inject current in nerve cell

recording electrode

measure membrane potential

ion channels

type of proteins that can have multiple transmembrane domains (usually alpha helix) creating a “pore” in the plasma membrane.

When the gates open, diffusion of ions is possible, NO energy required, following concentration gradient.

Some might be selective to a certain ion, other might be selective to multiple ions.

selectivity

__ of ion channels is possible due to the size differences between ions, leading to a difference in the size of their hydration shell.

Ex: sodium is smaller than potassium and therefore will have a largely bigger hydration shell than K+

hydration shell

water molecules surrounding ions to stabilize them, so they dissolve better in water.

transporters

type of proteins that usually needs energy in the form of either ATP or from the movement of another molecule/ion down its concentration gradient, all of that in order to move an ion AGAINST its concentration gradient

couples 2 ions/molecules together

no pre/opening whatsoever

CREATE concentration gradient

rest

at equilibrium, aka at ___, inside of cell is negative & outside of cell is positive

decreases

In cell, concentration ever ___ like this due to Kother transporters pumping ions back in

aka concentration never changes over time due to transporters activity

electrochemical equilibrium

exact balance between the concentration gradient causing K ions to move from inside to outside & an opposing electrical gradient that increasingly tends to stop K+ from moving across the membrane

calcium

cells tend to hate ___ so the concentration inside biological cells is very low

10:1

the biological system ratio of concentration in and outside neurons tend to be ___

ion concentrations inside cells

Na+ 15mM

K+ 145mM

Cl- 10mM

Ca2+ 0.0001 mM

ion concentrations outside of cells

Na+ 145mM

K+ 5mM

Cl- 105 mM

Ca2+ 2 mM

0

chemical energy + electrical energy = __ at electrochemical equilibrium

Nernst equation

equation used to predict/calculate membrane resting potential aka potential at equilibrium

depends on the concentration ratio

change in concentration means changes in where the cell comes to rest

negative

increase in potassium concentration inside the cell leads to a more __ membrane resting potential because more ions will leave the cell

positive

decrease in potassium concentration inside cell leads to a more ___ membrane resting potential because less ions swill leave the cell

leaking potassium channels

opens and closes randomly, thought of as always open

selectively permeable for K+

faster

the bigger the axon diameter, the ___ the speed of the action potential

Hodgkin & Katz

giant squid nerve cells experiment in 1949

despite different ion concentrations in squid compared to mammalians the concentration ratios are similar

difference in temperature was considered

steeper

The ___ the concentration ratio, the further away from zero the resting potential gets, aka more negative

0

equal concentrations mean resting potential is at __

shallow

the more ___ the concentration ratio is, aka the closer the numbers are, the more positive the resting potential gets

raised

Vm (resting potential) becomes more positive when extracellular K+ is __

Vm agrees with Nernst equation

for large concentration, the experimental resting potential agrees well aka at high concentration neurons are predominantly permeable to potassium at rest

for low concentrations, non-biological concentrations, mathematical predictions deviate from experimental values

primary

K+ permeability is the __ source of resting potential, Na+ has NO effect on resting potential

reasons for resting potential

• resting neuron more permeable to K+ than any other ion

• there is more K+ inside cell than outside

• selective permeability cause by K+ leaky channels open at rest

• K+ transporters create and maintain concentration gradient

can

changing the concentration ratio of an ion __ affect the resting membrane potential

depolarize

make membrane potential more positive

make concentration ratio shallower

inject + current

increase outside K+ concentration

decrease inside K+ concentration

ABOVE normal resting potential

hyperpolarize

make membrane potential more negative

make concentration ratio steeper'

increase inside K+ concentration

decrease outside K+ concentration

BELOW normal resting potential

overcome

electrical potential can ___an ionic concentration gradient

greater

the further from equilibrium, the __ the force applied to the ion is