Lecture 3 Flashcards
Action Potential?
Rapid + transient change in the membrane potential (Vm) of a cell (ex. neuron)
Basis of electrical signaling in body?
Action Potential
Action Potentials usually initiate at?
Axon Hillock
Action Potentials are propagated by?
Voltage-Gated Ion Channels along the axon
Action Potential is an _____ phenomenon?
“All-or-Nothing”
AP will NOT fire if Vm is?
Under threshold
Minimum depolarization needed to?
Fire AP
S4 segment senses change in?
Voltage
“Voltage Sensors” with Ion Selectivity?
1) Na+ Channel
2) K+ Channel (Tetramer)
Voltage-Gated Na+ Channels?
3 Conformational States (Open, Inactivated, Closed)
Activation of the voltage-gated Na+ channels leads to?
Increased flow of ions and depolarization
Inactivation of the voltage-gated Na+ channels leads to?
Stops the flow of ions and leads to repolarization
Voltage-Gated K+ Channels?
1) Depolarization triggers opening of voltage-gated K+ channels
2) K+ ions rush OUT OF cell
3) Transient efflux (high Pk) leads to Hyperpolarization
Depolarization triggers?
Opening of Voltage-Gated K+ channels
Hyperpolarization is built in defense against?
Hyperexcitability (Negative feedback decreases probability of activating more channels)
Na+ and K+ Channel Synchrony?
1) Rapid activation of Na+ channels causes depolarization
2) Na+ channel inactivation STOPS depolarization
3) Slower activation of K+ channels contributes to depolarization and eventual hyperpolarization
Propagation?
Movement down axon
Non-Propagated Depolarization?
Spreads passively through local current flow (“Electronic Conduction”)
Depolarization attenuates as it?
Moves down axon
Peak membrane potential during an AP remains?
Consistently depolarized
AP propagation takes?
Time (to charge membrane)
Myelination increases?
Conduction velocity
Depolarization decreases as it?
Moves down axon
Propagated Depolarization (Concept 1)?
Depolarization attenuates as it moves down axon
Propagated Depolarization (Concept 1) is caused by?
1) Membrane Resistance (Rm)
2) Interaxonal Resistance (Ri)
Membrane Resistance?
Barricade on cell surface that is preventing passive flow of ions out
Interaxonal Resistance?
Resistance inside axon (“like traffic”)
Length Constant?
Distance it takes to reach 37% of Vmax
Length Constant is directly proportional to?
Rm
Length Constant is inversely proportional to?
Ri
Propagated Depolarization (Concept 2)?
Peak membrane potential along an axon during an AP remains consistently depolarized
Propagated Depolarization (Concept 2) is caused by?
Refractory Periods
Refractory Periods keep it?
Moving down the axon
Absolute Refractory Period?
A 2nd Ap can NOT fire
(Na+ channels can not be reactivated) (either in open or inactivated state)
Relative Refractory Period?
A much greater depolarization required for an AP to fire (Active K+ channels hyperpolarizing the cell)
Propagated Depolarization (Concept 3)?
AP propagation takes time (time is needed for the membrane to charge as the AP moves along the axon)
Time needed to charge membrane = ?
Rate limiting event of AP propagation
Time Constant?
Time it takes for the change in Vm to reach 63% of its final value
Time Constant is directly proportional to?
Rm
Time Constant is directly proportional to?
Cm
Greater the size of the axon?
Greater the time it takes for the membrane to charge
Capacitance?
Ability for something to hold a charge
Propagated Depolarization (Concept 4)?
Myelination increases the conduction velocity by:
1) Increasing Rm –> Increases length constant
2) Decreasing Cm –> Decreases time constant
Myelination increase = ?
Membrane Resistance will increase
Saltatory Conduction?
Propagation of APs along myelinated axons from 1 node of Ranvier to the next node
Multiple Sclerosis?
An autoimmune, degenerative disease of axon demyelination
MS increases?
Passive current flow
MS decreases?
AP conduction velocity
MS results in?
Muscle Functions being messed up
