resting membrane potential Flashcards
what ions are involved for bioelectricity?
K+, Na+, Cl-, Ca2+
what ions have higher/lower concentration inside/outside the cell?
K+ and organic anions are present in higher concentration inside the cell.
Na+ and Cl- are present in higher concentration outside the cell.
resting membrane potential: define
the steady potential difference across the cell membrane of an unstimulated cell.
(under resting conditions, cells have a potential difference across their plasma membranes. the ICF is negatively charged, while the ECF is positively charged.
electrical potentials are generated across cell membranes because:
- there are differences in the concentrations of ions across cell membranes.
- membranes are selectively permeable to some of these ions.
resting membrane potential (RMP) results from the combined effects of:
- the diffusion of ions down their gradients through plasma membrane, provided there are channels available.
- selective permeability of the membrane, allowing some ions to pass more readily than others.
- the electrical attraction between cations and anions, and the repulsion between like charges.
what are some types of channels that enable diffusion?
mechanically gated, voltage-gated, ligand-gated, leaky channels
mechanically gated channels
channel is physically opened in response to mechanical change in surrounding tissue, like pressure, touch and temperature.
voltage gated channels
opens when the transmembrane voltage changes. contribute to action potential
ligand gated channels
opens when a ligand binds to the extracellular region of the channel
leaky channel
has an intrinsic rate of switching between open and closed states. very important for resting membrane potential.
what are channels and why are they needed?
channels are proteins in the membrane. the ions cannot pass directly through the hydrophobic lipid region of the membrane, because they are charged. the channel proteins provide a hydrophilic tunnel across the membranes.
how is resting membrane potential determined?
it is a weighted mean of the equilibrium potentials of the different permeant ions.
equilibrium potential: define
the voltage difference across a membrane that produces a flux of a given ion species that is equal but opposite to the flux due to the concentration gradient of the same ion.
what is the equation used to calculate the membrane potential with multiple ions?
the GHK equation
movement of chloride and RMP
Cl- does not influence RMP, instead membrane potential passively influences Cl- distribution. when membrane potential changes, Cl- moves into/out of the cell.
excitable cell: define
a cell that is able to be electrically excited, resulting in the generation of action potential.
how is a neuron resting membrane potential produced?
see notion notes: Class notes A/resting, graded and action potential
is the cell membrane more permeable to K+ or Na+?
K+. there are considerably more K+ leaky channels than Na+ leaky channels.
ion channels are selective.
For example, a small channel lined with negatively charged groups will be selective for _____ and exclude ____ and _________. Conversely, a small channel lined with positively charged groups will be selective for ______ and exclude _____ and ____________.
small cations; anions; large solutes;
small anions; cations; large solutes.
what does the conductance of a channel depend on?
the probability that the channel is open. The higher the probability that a channel is open, the higher the conductance, or permeability.
how to calculate the equilibrium potential at a given concentration difference of a permeable ion across a cell membrane?
using the Nernst equation.
what is the resting membrane potential of a cell?
-70mV.
what is the K+ equilibrium potential?
-85mV
what is the Na+ equilibrium potential?
+65mV
what is the effect of a concentration gradient?
Substances tend to diffuse down a concentration gradient provided there are channels of transport/communication available
how many times more concentrated is ICF K+ than Na+?
40
how many times more concentrated is ECF Na+ than K=?
12
how many times more permeable is the cell membrane to potassium than to sodium?
25-30 times more.
is the 3Na/2K/ATPase pump passive or active?
the pump is a mode of active transport. it uses ATP.
what is the principal ECF anion, and how is it transported?
Cl- is the principal ECF anion.
it is highly permeant and passively diffuses across the cell membrane.
what is the equilibrium potential of Cl-?
-70mV.
what does the Na/K pump do?
it pumps 3 Na+ out of the cell, and 2 K+ into the cell.
