Lesson 13: The Membrane Potential Flashcards
what is the electrical potential?
the difference in concentration of charged particles between one point and another
(a type of potential energy (V))
what is a current?
the flow of a charged particle from one point to another
what is the resting membrane potential (RMP)?
the charge difference across the plasma membrane
what does a negative value for the resting membrane potential mean?
theres more negatively charged particles on the inside of the plasma membrane compared to outside
how are electrical currents in the body created?
they are created by the flow of ions through gated channels in the membrane
what is the difference between a leak/passive channel and a gated channel?
leak/passive channel: channels that are always open
gated channel: channels that are normally closed but can be stimulated to open
BOTH are specific for its specific ion
what are the 3 types of gated channels and what are their stimuli?
- chemically gated channel: binding of chemical (found on neuron cell body, dendrites)
- voltage gated channel: change in the membrane potential (found on neuron axon, skeletal and cardiac muscle membrane)
- mechanically gated channel: physical stress/deformation on cell plasma membrane (found on sensory receptors; touch, pressure, vibration)
what are the 3 states of gated channels?
- closed
- open
- inactivated: ions cant pass through the channel but not considered closed, inactivation gate blocks the channel
how are ions distributed between extracellular fluid and intracellular fluid?
the ions are unequally distributed
what occurs for the presence of a resting membrane potential?
THE COMBINED EFFECT OF
1. the diffusion of ions down their concentration gradients through the membrane
2. selective permeability of the membrane, allowing some ions to pass more easily than others
3. the electrical attraction of cations and anions to each other
which ion has the greatest influence on the RMP and why?
potassium (K+) because it is much more abundant in the ICF than the ECF. the cell membrane is more permeable to K+ than Na+ since there are more K+ leak channels
how does sodium (Na+) influence the RMP?
Na+ is more abundant in the ECf than the ICF but the membrane is not as permeable to Na+ as K+. since the inside of the cell is negative, Na+ enters down its concentration gradient causing some of the negative charge to be cancelled out by the influx of sodium (only by a little bit though)
what compensates for the Na+ leakage in and the K+ leakage out?
the sodium-potassium pump uses ATP to move 3 Na+ out and 2 K+ in, concentrating Na+ outside and K+ inside.
what is a local potential and how does it occur?
an electrical signal that occurs when a physical stimulus acted on a sensory neuron triggers a local, temporary change in the membrane potential
what are some characteristics of local potentials?
graded - vary in magnitude with stimulus strength (stronger stimuli will cause gated channels to remain open longer causing a larger depolarization for Na+ influx or hyperpolarization for K+ efflux
decremental - get weaker the farther they spread from the point of stimulation
reversible - if stimulation ceases, membrane voltage quickly returns to normal resting potential
can be excitatory or inhibitory (either promoting the generation of an electrical signal or inhibiting it)
what is depolarization?
when the cell’s internal charge becomes less negative (more positive)
depolarization & hyperpolarization. which is inhibitory and which is excitatory?
depolarization -> excitatory (makes a neuron more likely to fire an action potential)
hyperpolarization (membrane more negative)-> inhibitory (makes a neuron less likely to produce an action potential)
what is an action potential?
a rapid up & down change in voltage proceeded by the coordinated opening and closing of voltage-gated ion channels
where do action potentials occur and how does it occur?
where there is a high enough density of voltage-gated ion channels (trigger zone of axon)
if excitatory local potential reaches trigger zone and is still strong enough, it opens enough voltage gated Na+ channels to generate an action potential
name the steps of an action potential
- local potential spreads to axon hillock
- voltage at axon hillock must reach threshold (minimum voltage to open voltage gated channels)
- voltage gated Na+ channels open quickly
- Na+ enters the cell, depolarizing it past 0 mV
- when voltage reaches +35mV, Na+ voltage gated channels inactivate (different than closed)
- voltage gated K+ on membrane are stimulated to fully open at +35 mV, K+ flows out of the cell and repolarizes membrane (inside of cell is negative again)
- membrane potential returns back to RMP as Na+ leaks into cell raising the voltage inside
true of false: the concentration of Na+ and K+ on either side of the membrane change significantly during an action potential.
FALSE
name some characteristics of action potentials
all or none law - if threshold reached (-55mV), neuron fires up/depolarizes to the maximum voltage (+35 mV); if threshold not reached, it does not fire an action potential
non decremental - does not get weaker with distance. action potential is “regenerated” as it travels along the axon
irreversible - once started, an action potential travels all the way down the axon and cannot be stopped by normal means
what is the refractory period?
period of resistance to stimulation
what are the 2 phases in the refractory period?
- absolute refractory period - no stimulus of any strength will trigger another AP
(caused by inactivation of voltage gated Na+ channels) - relative refractory period - an unusually strong stimulus is needed to trigger a new AP
(during hyperpolarization, a larger depolarization (local potential) is required to reach threshold since it has to overcome the hyperpolarization)
how are the absolute and relative refractory periods related to the action potential?
during the absolute refractory period, the voltage gated Na+ channel is inactivated. during the relative refractory period, the channel is now back to its resting state, which is closed.
why do unmyelinated axons have continuous conduction?
