Membrane Electrophysiology: Action Potentials Flashcards
action potential
rapid change in membrane potential away from normal, negative resting voltage to positive voltate
followed by a return back to negative RMP
what is required of excitable cells?
ability to alter permeability
-gated channels exist in different activation states
leak channels
always open
unregulated ion flow
gated channels
typically ion specific
can be:
1 closed (but can be activated)
2 open
3 closed and inactivated
voltage-gated channels
respond to changes in membrane potential
depolarization
flow of + ions into cells
hyperpolarization
flow of + ions out of cell
polarization
either positive or negative (other than 0mV)
hypopolarization
less negative than resting
depolarization
loses negative polarity
repolarization
return to RMP
hyperpolarization
membrane more polarized than RMP
threshold
action potential only occurs if threshold is reached
ungated potassium channel
always open
K+ efflux
voltage-gated sodium channels
generation of action potential in n. and skeletal muscles
closed at RMP
open quickly then close and inactive
voltage gated potassium channels
closed at RMP
open slowly and slowly close
three phases of voltage-gated sodium channel
closed but capable of activation
-at RMP
open
-threshold to peak
closed and inactivated
-peak to resting
phases of voltage gated potassium channels?
closed or open
act slowly**
what generates action potential?
rapid opening of sodium followed by inactivation
slow opening of potassium
depolarization?
sodium into cell
repolarization?
potassium out of cell
hyperpolarization?
caused by the slow delayed potassium channels
threshold depends on what?
strength and duration of stimulus
initial depolarization
stimulus reaches threshold
- sodium channels open
- sodium influx, depolarized membrane
peak Na+ conductance
reached right before action potential peak
-at peak, many Na+ are open
however, Na+ influx is actually minimal as Vm becomes closer to ENa+
early repolarization
voltage-gated potassium still opening and sodium are locking
potassium efflux repolarizes membrane
peak K+ conductance
mid-repolarization
-force on K+ is lower as voltage is approaching EK+
however, efflux greater due to greater conductance
Na/K ATPase
always gradually restoring RMP
refractory period
key for ensuring unidirectional propagation***
time period after AP when subsequent AP cannot, or likely will not, be generated
absolute refractory period
no AP, regardless of stimulus can trigger
result of sodium channnel h gates (inactivation)
relative refractory period
AP can be produced if large stimulus
result of slow-closing K+ channels - hyperpolarization
two implications for refractory periods?
prevents rebound effect
sets upper limit to AP firing frequency
characteristics of action potential?
undiminished propagation that regenerates an identical AP
**all or none law
nervous system interpretation of AP?
frequency and number of APs
graded potentials
sub-threshold**
can be summed
-duration and strength depend on stimulus
decremental - spread but die out
ex/ EPSP, IPSP, receptor, end-plate at NMJ
no refractory
axon hillock
where the action potentials are initiated (lowest threshold)
contiguous conduction
local event opening adjacent channels down entire membrane
saltatory conduction
**with myelinated axons
allows for impulse “jumping” - faster
nodes or ranvier
where AP is generated in myelinated axon during saltatory conduction
schwann cells
myelinate PNS
oligodendrocytes
myelinate CNS
myein
insulating resistance
diameter and conduction velocity?
increased diameter causes increased velocity
**decreased internal resistance to flow (ohms law)
synaptic cleft
where info transmitted cell to cell
subsynaptic membrane
receptors
two categories of synaptic communication
electrical and chemical
electrical synapse
connexon channels of gap junctions
low resistance
reciprocal - both direction
rectifying - unidirectional
chemical synapse
unidirectional
ionotropic
rapid activation of receptor
-nicotinic ACh, NMJ
metabotropic
slower activation of receptor
-G-protein liked receptor
voltage gated calcium channels
responsible for an AP generating the influx of calcium
**calcium INFLUX
calcium influx?
causes the neurotransmitter release
convergence
single cell may be influenced by thousands of presynaptic cells (sensory)
diverence
single axon terminal affects thousands of postsynaptic cells (motor)
postsynaptic potential
get graded potential convergent at soma
EPSP
excitatory postsynaptic potential
- depolarizes/hypopolarizes membrane
- always excitatory
IPSP
inhibitory postsynaptic potential
hyperpolarizes membrane
always inhibitory
excitatory signal?
sodium influx
potassium efflux
inhibitory signal?
chloride influx
potassium efflux
temporal summation
signals at same TIME
-frequency important
spatial summation
signals in same SPACE (DISTANCE)
-multiple inputs combine to reach threshold
cancellation
EPSPs and IPSPs cancel each other out
