Lecture 4 Flashcards
What are other names for action potential?
spike
nerve impulse
discharge
What is action potential?
A rapid reversal of membrane potential where the inside becomes positively charged for 2-3 msec
What is synaptic transmission?
transfer of information from neuron to neuron
- frequency and pattern of action potentials constitute the code used by neurons to transfer information from one to another
How does action potential travel?
Starts at axon hillock (zone of integration) and travels down the axon to the presynaptic terminal (zone of output) = neurotransmitter release
Define depolarization
membrane voltage is more positive
Define hyperpolarization
membrane voltage is more negative
What results in depolarization?
Positive ion influx and negative ion efflux
What results in hyperpolarization?
positive ion efflux and negative ion influx
How is action potential generated?
Requires depolarization current
- occurs naturally via excitatory synaptic transmission
- artificially via current injection current into a neuron with microelectrode
What does the depolarizing current tell you about firing frequency from the generation of multiple action potentials?
Firing frequency reflects the magnitude of the depolarizing current.
Action potential firing rate increases as the depolarizing current increases
- if the current doesn’t depolarize the membrane to threshold, no action potential is generated
- if injected current depolarizes beyond threshold, action potentials will be generated
What’s the difference between electrical properties of neurons vs glia?
Neurons: electrically active - fire action potentials
Glia: electrically silent cells
What are the properties of the action potential?
- caused by depolarization of membrane beyond threshold
- All or None
- Chain reaction
What is the graph readings of an action potential?
1) Resting potential
2) Rising phase
3) Overshoot
4) Falling phase
5) Undershoot (after-hyperpolarization)
What are the necessary characteristics for action potentials?
1) ~10 mV depolarization above rest for initiation
2) below threshold = none, above threshold = all
3) Always depolarizing
4) Constant amplitude ~100 mV
5) Constant duration ~2-3 msec
6) Propagate without decrement
7) 2 part refractory period: absolute during falling phase and relative during undershoot
What is depolarization and repolarization in terms of Na+ and K+?
Depolarization: influx of Na+
Repolarization: efflux of K+
What is membrane current?
net movement of K+ across membrane
potassium current = flow and driving force
What’s the equation that links current, conductance, and driving force?
current = conductance* (membrane voltage - driving force)
What’s the ins and outs of action potential?
Rising phase: inward sodium current
Falling phase: outward potassium current
Define law of permeability.
Membrane potential is always driven toward the equilibrium potential of the ion to which the membrane is most permeable.
What’s the purpose of Hodgkin and Huxley model?
Demonstrates properties of action potentials using patch-clamp electrophysiology
- rising phase = transient increase of influx of Na+ ions
- falling phase = increase in efflux of K+ ions
What’s the structure of the voltage-gated sodium channels?
transmembrane domains and ion-selective pore
What’s the difference between voltage when the voltage-gating sodium channel when it’s open vs. closed?
Closed: -65 mV
Open: -40 mV
How does the voltage-gated sodium channel selective permeability?
Size exclusion filter
- partially hydrated Na+ ion fits
- partially hydrated K+ doesn’t fit
What is the cycle of the voltage gated sodium channel?
Closed (-65 mV) -(~10 mV Depolarization)->
Open (-55 mV) -(~1 ms delay)->
Inactivated -(channel requires -Vm reset)->
Closed
