The Action Potential Flashcards
What is the function of voltage-gated ion channels?
They facilitate the selective permeability of certain ions across the cell membrane.
Define selectivity filter.
A region in ion channels that allows specific ions to pass while excluding others.
What are permeant ions?
Ions that can pass through the selective filter of ion channels.
What are impermeant ions?
Ions that cannot pass through the selective filter of ion channels.
What does selective permeability refer to?
The ability of a membrane to allow certain ions to pass while blocking others.
List the main cations involved in action potentials.
- K+
- Na+
- Ca2+
What is the primary anion involved in action potentials?
Cl-
What is the knock-on mechanism in ion channels?
A process that involves the movement of ions due to charge interactions.
- Selectivity filter strips off hydration shell and ion moves into the channel
- Entry of ion into the channel pushes one of the other ions occupying the channel out the other side
- In K+ channel, oxygen atoms stabilise the ion as it crosses the membrane & strips off the hydration shell
True or False: Sodium channels open slowly and inactivate rapidly.
False
How quickly do sodium channels inactivate after opening?
After approximately 1 ms.
How do potassium channels behave compared to sodium channels?
Potassium channels open more slowly and can also inactivate.
What is an action potential?
A transient reversal of the membrane potential.
What is the duration range of action potentials?
From a few milliseconds (nerve, skeletal muscle) to a few hundred milliseconds (heart).
What is the threshold potential for action potential generation?
~ -55 mV.
What happens to action potentials with larger stimuli?
The size of the action potential remains fixed regardless of stimulus size.
How does the body code stimulus intensity?
By changes in frequency of action potentials, not size.
Fill in the blank: The probability of _______ is greater than the probability of closing during depolarization.
opening
What are the phases of an action potential?
- Resting potential
- Rising phase
- Peak
- Falling phase
- Undershoot (after hyperpolarization)
Define absolute refractory period.
A period during which another action potential cannot be produced (due to all or nothing principle)
What characterizes the relative refractory period?
The cell is less excitable and requires a larger stimulus to produce an action potential (there is a raised threshold)
What causes the refractory period?
Inactivation of Na current and activation of K current.
What is the concentration of Na+ outside the cell before an action potential?
150 mM
What is the concentration of K+ inside the cell before an action potential?
100 mM
What is the concentration of Cl- outside the cell before an action potential?
150 mM
