Exam 2 Powerpoint 9 Flashcards
Both Na and K are dependent on
depolarizing currents
Need 8 to 9 milliseconds to fire another
action potential
Refractory Period
Short period following an AP, during which axon is resistant to further excitation 8-9 ms
Closed channel
can just open
Inactivated channels have to __________ before they can open again.
close
Threshold
Threshold is the membrane potential at which enough voltage-gated
sodium channels are open so that the relative permeability of the membrane is
higher for sodium ions than it is for potassium ions.
Rising Phase:
Rising Phase: When the inside of the membrane has a negative potential, there is a large driving force for on sodium ions. Therefore, sodium rushes in through the open sodium channels, causing a rapid depolarization of the membrane
Overshoot:
Because of the high permeability to sodium, the membrane potential
goes to a value that is close to the Equilibrium potential for sodium (depends on concentrations but somewhere above +50 mV)
Falling Phase:
Falling Phase: First, the voltage-gated sodium channels inactivate. Second, the voltage-gated potassium channels open (the delayed-rectifier potassium channels).
The driving force pushes potassium out of the cell, causing the membrane potential
to become negative again.
Undershoot:
Undershoot: The open potassium channels add to the normal resting membrane permeability to potassium, and drives the membrane potential close to the equilibrium potential for potassium, thus hyperpolarizing the membrane.
At rest, neuronal membranes more
permeable to
K+ than Na
During an action potential, membrane more permeable to
Na+
Than K
During repolarization,____ more
permeable than ____
K+
Na+
Positive feed back is fueled by
Na
Negative feed back is fueled by
K
AIS is rich in v
oltage-gated Na+ Channels
APs typically initiate here at the
AIS
Spread of AP down the axon
AP re-generates itself, activating
adjacent Nav channels
Leak channels work to________ APs re-generating itself
0.5 to 10m/s top speed (conduction velocity)
oppose
Speed at which action potential travels
0.5 to 10m/s
MYELIN ________ CONDUCTION VELOCITY to_______
Increases
150 m/s
Problem with myelin
Myelin is not a perfect insulator
Some charge leaks out
After a certain distance, the whole signal would be lost
Fix for myelin
Nodes of Ranvier – periodic interruption of myelin sheath
Nodes are rich in voltage gated Na+ channels
AP is regenerated at the node.
The current flows through the neuron to the next node at near the speed of light
This is called Saltatory Conduction
Multiple Sclerosis
Demyelination of axons in multiple sclerosis. Myelin ordinarily surrounds axons . In MS, axons lose myelin and can break as a result
