Electric Potential of Cells Flashcards
Potential (Potential difference)
The voltage difference between two points due to separated electrical charges of opposite sign; these separated charges have the potential to do work
Membrane potential
The voltage difference between the inside and outside of a cell
Equilibrium potential
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 that same ion
- where the net flow through any
open channel is 0
- indicates that the chemical and electrical
forces for that ion are in balance
Resting membrane potential (Vm)
The steady potential of an unstimulated cell
- RMP of ALL cells is NEGATIVE; -50 to -90mV in excitable cells and -5 to -15mV for non-excitable cells
Graded potential
A potential change of variable amplitude and duration that is conducted decrementally (further away from stimulus); has no threshold or refractory period
Can be:
- depolarizing OR hyperpolarizing
- vary in size d/t stimulus strength
- decay with distance from site of initial stimulus
Action potential
A brief all-or-none depolarization of the membrane, which reverses polarity in neurons; has a threshold and refractory period and is conducted without decrement
Synaptic potential
A graded potential change produced in the postsynaptic neuron in response to the release of a neurotransmitter by a presynaptic terminal; may be depolarizing (an excitatory postsynaptic potential or EPSP) or hyperpolarizing (an inhibitory postsynaptic potential or
IPSP)
Receptor potential
A graded potential produced at the peripheral endings of afferent neurons (or in separate receptor cells) in response to a stimulus
Pacemaker potential
A spontaneously occurring graded potential change that occurs in certain specialized cells
Threshold potential
The membrane potential at which an action potential is initiated
Energy
the ability of an object to do work on another object
Kinetic Energy
energy in motion
Potential energy
energy at rest
Effects of quantity and distance on separated charges
Force:
- INCREASES when charges are closer together
- INCREASES when there are MORE charges being separated
Ohm’s Law
V=IR
I=V/R
R = Resistance due to presence of the plasma membrane (measured in Ohms)
V = Difference in electric potential energy on either side of the membrane (measured in volts)
I = Flow of charged particles through “conductors” in the membrane (measured in Amperes
Capacitor
a device that can store energy by accumulating electric charges on two closely spaced surfaces that are insulated from one another
Insulator
structure that separates opposing surfaces so that the contents of one surface do not bleed into the other surface
Conductance (G)
a measure of how easily an ion moves through a membrane; reciprocal of resistance
- HIGH conductance= LOW resistance
- ion channels are conductors when open
Resistance (R)
a measure of how DIFFICULT an ion moves through a membrane; reciprocal of conductance
- HIGH resistance= LOW conductance
- ion channels are mini-resistors when closed
Determinant of resting membrane potential
- differences in [ion] in the ICF and ECF
- difference in membrane permeabilities to the ion
Nernst equation
describes the equilibrium potential of an ion
equation: 61/Z x log ([out]/[in])
E (Na+)
+60 mV
E (K+)
-90 mV
Net driving force
must consider both concentration and
electrical potential differences so can be calculated:
Vm-Eion
ex: E(Na+)= +60mV –> -70mV-60mV= -130mV which means driving force favors Na+ ENTERING the cell
