Chapter 4 Flashcards
The rising phase is characterized by:
A rapid depolarization of the membrane. This change in membrane potential continues until the membrane potential reaches a peak of about 40 mV
What is the overshoot?
The part of the action potential where the inside of the neuron is positively charged with respect to the outside
What is the falling phase?
a rapid repolarization until the membrane is actually more negative than the resting potential
What is the undershoot or after-hyperpolarization?
The last part of the falling phase when the membrane potential is more negative than the resting potential
What is threshold?
The critical level of depolarization that must be crossed in order to trigger an action potential
Graph of an action potential:
What is the absolute refractory peroid?
The (about) 1msec during which it is impossible to initiate another action potential after one is initiated
What is the relative refractory period?
The several milliseconds after the absolute refractory period during which it is relatively difficult to initiate another action potential
Depolarization of the cell during the action potential is caused by ________________ and repolarization is caused by ____________
The influx of sodium ions across the membrane,
The efflux of potassium ions
IK=gK (Vm-EK)
Iion=gion(Vm-Eion)
Where:
Iion is the electric current of the ion in question
gion is the electrical conductance of the ion in question
Graph of the action potential WRT sodium and potassium channels:
What is a voltage-gated sodium channel?
The protein that forms a pore in the membrane that is highly selective to Na+ ions. The pore is opened and closed by changes in the electrical potential of the membrane
What is the threshold for voltage-gated sodium channels?
-40 mV
What is a channelopathy?
A human genetic disease caused by alterations in the structure and function of ion channels
Threshold:
The membrane potential at which enough voltage-gated sodium channels open so that the relative ionic permeability of the membrane favors sodium over potassium
Rising Phase:
When the inside of the membrane has a negative electrical potential, there is a large driving force on sodium ions. Therefore, sodium ions rush into the cell through teh open sodium channels, causing the membrane to rapidly depolarize
Overshoot:
Because the reative permeability o the membrane greatly favors sodium, teh membrane potential goes to a value close to ENa, which is greater than 0 mV
Falling Phase:
The behavior of two types of channel contributes to the falling phase. First, the voltage-gated sodium channels inactivate. Second, the voltage-gated potassium channels finally open (triggered to do so 1msec earlier by the depolarization of the membrane). There is a great driving force on potassium ions when the membrane is strongly depolarized. Therefore, potassium ions rush out of teh cell through the open channels, causing the membrane potential to become negative again.
Undershoot:
The open voltage-gated potassium channels add to teh resting potassium membrane permeability. Because there is very little sodium permeability, the membrane potential goes toward EK, causing a hyper-polarization relative to teh resting membrane potential until the voltage-gated potassium channels close again
Absolute refractory period:
Sodium channels inactivate when the membrane becomes strongly depolarized. They cannot be activated again, and another action potential cannot be generated, until the membrane potential goes sufficiently negative to deinactivate the channels
Relative refractory period:
The membrane potential stays hyperpolarized until teh voltage-gated potassium channels close. Therefore, more depolarizing current is required to bring the membrane potential to threshold
