Membrane Electrophysiology: Action Potentials Flashcards by Matt Stanton

action potential

rapid change in membrane potential away from normal, negative resting voltage to positive voltate

followed by a return back to negative RMP

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what is required of excitable cells?

ability to alter permeability

-gated channels exist in different activation states

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leak channels

always open

unregulated ion flow

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gated channels

typically ion specific

can be:
1 closed (but can be activated)
2 open
3 closed and inactivated

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voltage-gated channels

respond to changes in membrane potential

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depolarization

flow of + ions into cells

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hyperpolarization

flow of + ions out of cell

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polarization

either positive or negative (other than 0mV)

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hypopolarization

less negative than resting

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depolarization

loses negative polarity

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repolarization

return to RMP

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hyperpolarization

membrane more polarized than RMP

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threshold

action potential only occurs if threshold is reached

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ungated potassium channel

always open

K+ efflux

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voltage-gated sodium channels

generation of action potential in n. and skeletal muscles

closed at RMP
open quickly then close and inactive

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voltage gated potassium channels

closed at RMP

open slowly and slowly close

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three phases of voltage-gated sodium channel

closed but capable of activation
-at RMP

open
-threshold to peak

closed and inactivated
-peak to resting

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phases of voltage gated potassium channels?

closed or open

act slowly**

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what generates action potential?

rapid opening of sodium followed by inactivation

slow opening of potassium

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depolarization?

sodium into cell

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repolarization?

potassium out of cell

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hyperpolarization?

caused by the slow delayed potassium channels

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threshold depends on what?

strength and duration of stimulus

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initial depolarization

stimulus reaches threshold

sodium channels open
sodium influx, depolarized membrane

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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