Chapter 3 B Action Potential Flashcards
What is depolarization?
Depolarization is a decrease in membrane potential. It is when the interior of the cell becomes less negative and closer to zero. Negative ions leave the cell and positive ions come in.
What is hyperpolarization?
The interior of the membrane becomes even more negative and farther from zero. Negative ions come into the cell and positive ions leave the cell.
What is a graded potential?
A stimulus will cause a small changes in the membrane potential.
Stimuli that depolarize enough to reach the threshold will produce a what?
An action potential.
Pacinian Corpuscles are sensitive to?
Vibration & pressure.
Graded potentials vary depending on the size of the?
Stimulus
Action potentials are very quick large electrical pulses in the membrane of the what?
Axon.
A change in resting membrane potential has to occur for them to be initiated.
Action potentials. They are voltage dependent.
Action potentials are characterized by a rapid reversal of the membran potential from what voltage to what voltage and then back down to what?
-40mV to + 40mV and then back down to -70mv. They are “all or none” they either reverse the membrane potential to +40mv or they do not.
Action potentials begin where?
At the axon hillock and always travel down to the terminal button.
Amplitude is independent of stimulus size. True or false?
True
What are the five phases of an action potential?
- Depolorization. Threshold. Rising. Falling. Hyperpolarized ( undershoot)* two refractory periods.
Define depolarization
Inside of a cell becomes more positive because of an excitatory stimulus. ( Graded potentials or positive current injected via a microelectrode.
Threshold phase
This is the level of stimulation required for a neuron to produce an action potential. It represents the opening of voltage-gated ion channels.
Where are voltage gated sodium channels located?
At the axon hillock.
Voltage-gated sodium channels
Are closed at membrane potential -60 mv. Then open for a milisecond when the membrane is depolarized to about -40mv at the threshold.
What is the rising phase?
The membrane potential becomes more positive because sodium rushes into the cell through voltage-gated sodium channels. Voltage-gated potassium channels begin to open.
Falling Phases
Potassium rushes out of the cell via voltage-gated potassium channels causing membrane potential to become more negative.
Hyperpolarized ( undershoot phase)
Voltage gated potassium channels close slowly , and potassium leaves the cell, until the membrane potential becomes more negative than normal.
What do sodium/potassium pumps do?
They restore membrane potential to resing membrane potential. Passive ions are also open and allow chloride to come in.
Absolute & relative refractory period
The time the neruon is insensitive to further stimulation and therefore it is impossible to elicit an action potential. It starts at the peak or the action potential and continues through the falling phase. Inactivation gate blocks channel and does not reset until membrane has reached RMP.
Relative Refractory Period
Follows the absolute refractory period. A neuron can generate another action potential, but is has to be stronger than a normal stimulus.
Intensity of a stimulus is encoded by the?
Firing rate of a neuron and the number of neurons firing an action potential. The more intense stimuli can cause more neurons to fire an action potential.
