TEST 2: Membrane Potentials Flashcards
Resting Membrane Potential (RMP)
-70 mV
RMP created/ maintained by
- 50-75x greater membrane permeability to K+ than to Na+
- Na+/K+ pump
Polar
carries a charge
Graded Potentials
- Localized changes in membrane potentials
- May be strong at area of initiation on dendrites, but only 1-2 mV in strength by the time they reach the axon hillock- decremental spread because of leak channels over surface of cell body
- caused by opening of neurotransmitter (NT)- gated ion channels
Can be two types
- depolarizations or EPSPs, membrane becomes less negative
- hyperpolarizations or IPSPs, membrane becomes more negative
Why do we have IPSPs?
provides a way for one set of signals to offset another. often involved in protecting body from injury
+ ion with high concentration on outside of cell
open a channel for it \+ ion moves down concentration gradient into cell positives going in inside becomes less negative creates a DEPOLARIZATION (EPSP)
+ ion with high concentration on inside of cell
open a channel for it \+ ion moves down concentration gradient out of cell positives going out inside becomes more negative creates a HYPERPOLARIZATION (IPSP)
- ion with high concentration outside of cell
open a channel for it -ion moves down concentration gradient into cell negatives going in inside becomes more negative creates a HYPERPOLARIZATION (IPSP)
-ion with high concentration inside of cell
open a channel for it -ion moves down concentration gradient outside of cell negatives going out inside becomes more positive creates DEPOLARIZATION (EPSP)
Most sum of all GPs at axon hillock
if you reach or exceed threshold potential then action potential sent out axon
- temporal summation
- spatial summation
temporal summation
one presynaptic neuron in rapid fire
spatial summation
many presynaptic neurons firing simultaneously
What happens if summation result in hitting or exceeding Threshold Potential?
Action Potential is sent down axon
Why is Summation Important?
So that we have discrimination as to what info we act upon and what we don;t
Why have IPSPs in addition to EPSPs?
Finer degree of decision making capability provides a war for one set of signals to offset another set
Threshold Potential
-55mV
All ion channels involved in Action Potential are :
voltage gated and all triggered at Threshold Potential
Depolarization
opening of Na+ activation gates. Na+ rushes into cell, changing membrane potential to +30 mV
Repolarization
Na+ inactivation gates close- stops the influx of Na+. K+ gates open: K+ flows out of cell —-> inside more negative again
Refractory Period
- AP is self-generating, unlike GP
- Absolute Refractory Period
- Relative Refractory Period
Absolute Refractory Period
impossible to restimulate membrane because Na+ gates have not yet reset- occurs from the pout where TP reached until Na+ gates reset
Relative Refractory Period
possible, but harder to restimulate membrane because K+ gates haven’t closed yet- somewhat hyper polarized at this time, so stimulus has to be greater to reach TP
-occurs after absolute refractory until back to -70 mV as K= gates all close
Major significance of refractory periods
-keeps impulse going in 1 direction because area upstream of area that is currently depolarizing is an absolute refractory, so signal can only spread forward and not backward
Restoration of Normal Resting Concentrations of K+ and Na+
During AP, some K+ moved outside and some Na+ moved inside, so we need to get concentrations back to normal. This is accomplished via the Na+/K+ pump
Does AP increase or decrease in intensity as it spreads?
AP does not decrease in intensity as it spreads (self-generating, no decremental spread) due to myelin. Myelin insulates the axon from loss of charge as the signal passes down axon. Other major function of myelin is to speed the conduction of the AP. Remember, APs only occur at axon hillock and nodes in myelinated neurons-myelination allows for saltatory conduction
