L14 Resting (Excitable) Cells Flashcards
Currents flow ___ in a direction denoted by the direction of movement of _____ in an electrical field
passively cations (+)
cations (+) in a solution will move by electrodiffusion to the ____
cathode - negative terminal
anions (-) in a solution will move by electrodiffusion to the ___
anode - positive terminal
where is electroneutrality seen?
in cytosol
in extracellular fluid
where is electroneutrality not conserved?
across the width of the membrane - there is charge separation across the bilayer
large anions cannot pass through into what?
from intracellular space to extracellular space
define membrane potential
potential of the interior of the cell measured relative to the exterior and is Vm
what is the resting membrane potential in neurons?
-65 mV
what channels do neurons have open?
LOTS of K+ channels open
some Cl- channels open
few Na+ channels open
what is the resting membrane potential for skeletal muscle fibers?
-90 mV
what channels do skeletal muscle fibers have open?
LOTS of K+ and Cl- channels open
few Na+ channels open
what is the resting membrane potential for photoreceptors (rods)?
-40 mV
what channels do photoreceptor (rods) have open?
more Na+ channels open than neurons and muscle fibers
what is the resting membrane potential of astrocytes?
-40 mV to -90 mV
what can alter the resting membrane potential?
small changes in ion flux
what ion is more inside the cell and outside the cell
K-inside
Na-outside
an influx of Na+ will move the Vm in what direction?
depolarizing
an efflux of K+ will move the Vm in what direction?
repolarize
what ions are high extracellularly?
Na+
Cl-
Ca2+
bicarb
what ions are high intracellularly?
K+
what does changing the concentration of K+ outside the cell do?
alters the resting potential - resting potential dependent on K+
what happens if you increase the value of [K+]o?
= reduction in the rate of L ion loss from the cell and the interior becomes LESS NEGATIVE because less DF for K ions
Depolarization
what happens if you reduce the value of the [K+]o?
=increase in the rate of K ion loss from the cell and the interior becomes more negative because more DF for K ions
Hyperpolarized!
in what ways are ions transported?
by passive and active means
how do ions pass through membrane ion channels?
electrodiffusion
how are ions actively transported across the membrane?
by ATPases
how are ions also transported?
by antiports and symports
what determines the membrane potential?
open channels
cell transmembrane potential is affected by what?
- ion channel activity
- type + # of open ion channels
- amount of current passing through while channel is open
- time channels spend in an open state
- frequency of channel openings
- maintain by pump/transporter activity
every ion channel has a probability of being___
open
what is the probability of channel opening (Po)?
the fraction of the total time of observation that the channel is in the open state
what acts as capacitor?
bilayer component
what acts as a conductor?
open ion channel
what do electrochemical gradients drive?
passive ion flux
how is equilibrium established at a selectively permeable membrane?
diffusion force = electrical force
each ion has its own_____
electrochemical gradient
what is the formula for Nernst Equation:
E= RT/ zF ln [ion outside]/[ion inside]
gives you the equilibrium potential for any ion
what is the total ionic current across the resting membrane?
zero
what is Channelopathies?
dysfunctional ion channels
what is cytotoxic edema?
affects grey matter cells more than white matter
what is vasogenic edema?
blood vessels become permeable and the fluid accumulates in the extracellular space causing further damage
what does resting membrane potential (Vm) depend on
# of open channels for ions conductances of the open ion channels equilibrium potentials for ions
