Chapter 4 - The action potential Flashcards
What are the phases of the action potential?
A rising phase (a rapid depolarization of the membrane), followed by a overshoot (a phase where the membrane is positively charged), the falling phase (a rapid polarization) and the undershoot (a hyperpolarization phase) finally there is a restoration phase of the resting potential.
How long does an action potential last?
About 2ms
What is the maximal frequency at which a neuron can fire?
About 1000hz
What is the absolute refractory period?
The period following an action potential during which the neuron can’t fire.
What is a voltage-gated sodim channel?
A protein which is selective to Na+ which is opened and closed by changes in the electrical potential of the membrane.
depolarization causes the gate to open.
What are the threshold phase of the action potential?
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.
What is a myelin sheath?
Many layers of membrane provided by glial support cells. These are Schwann cells in the peripheral nervous system and oligodendrogilai in the CNS.
It facilitates current flow down the axon.
What is multiple sclerosis and what causes it?
A neurological disorder with symptoms ranging from weakness, lack of coordination, impaired vision and speech.
It is caused by the degradation of myeling sheaths in the brain, spinal cord and optic nerves.
Explain the rising phase of the action potential?
Rising phase: Whe the inside of the membrane has a negative potential, there is a large driving force on Na+ ions. Therefore, Na+ ions rush into the cell through the open sodium channels. This causes the membrane to rapidly depolarize.
Explain the overshoot phase of the action potential?
Overshoot: The membrane potential goes to E_na which is greated than 0mV as there is much more sodium inside the membrane.
Explain the falling phase of the action potential?
The behavior of two types of channels contributes to the falling phase.
- Voltage-gated sodium channels inactivate
- Voltage-gated potassium channels finally open
- K+ rushes out of the cell, causing membrane to become negative again.
Explain the undershoot phase of the action potential?
Undershoot: The open voltage-gated potassium channels add to the resting potassium membrane permeability. The membrane goes toward E_k which causes a hyperpolarization.
What happens during the absolute refractory period?
Absolute refractory period: sodium channels are inactivated and cannot open again before the membrane potential goes sufficiently negative.
