Action Potential Flashcards
Where is a graded potential located?
dendrites or cell bodies
Where is an action potential located?
Trigger zone (axon hillock)»_space; Axon
What type of ion channels are involved with a graded potential?
any type
What type of ion channels are involved with an action potential?
Voltage only (Na+, K+ only)
What type of signal is a graded potential?
Depolarizing or hyperpolarizing
What type of signal is an action potential?
Depolarizing only
What is the strength of a graded potential?
Depends, summation possible
What is the strength of an action potential?
Always the same
Cannot be summed
Refractory period obeyed
How is a graded potential initiated?
Ions through channel
How is an action potential initiated?
Above threshold graded potential at the axon hillock
What is an action potential?
A regenerating depolarization of membrane potential that propagates along an excitable membrane
Key features of an action potential
- All-or-none event
- Need to reach threshold
- Have constant amplitude
- Do not summate
- Initiated by depolarization
- Involve changes in permeability
- Rely on voltage-gated ion channels
3 Functions of Action Potentials
- Information delivery to CNS
- Information encoding
- Rapid transmission over distance (nerve cell APs)
What do local anesthetics do to action potentials?
Block APs in nerve cells
What happens after a local anesthetic is used?
Produces analgesia without paralysis
Why do local anesthetics work?
They are more effective against a small diameter
Large Surface Area:Volume ratio
C-fibers more than a-motor neurons
Can amplitude change for APs?
No
What does the speed of transmission depend on?
fiber size and whether it is myelinated or not
What does the AP do to non-nervous tissues?
Initiates a range of cellular responses
Ex:
Muscle contraction
Secretion
What are the steps of an AP?
1- Resting membrane potential
2- Depolarizing stimulus
3- Membrane depolarizes to threshold. VG-Na+ channels open. Na+ enters cell. VG-K+ channels open slowly.
4- Rapid Na+ entry depolarizes cell
5- Na+ channels close, Slow K+ channels open
6- K+ moves out from cell to ECF
7- K+ remains open, additional K+ leaves cell. Hyperpolarization
8- VG-K+ channels close, less K+ leaks out of cell
9- Cell returns to resting ion permeability and RMP
