MT - Neuronal Function (Part 3): Axonal Physiology Flashcards
What electrical components make up each area of an axon?
3 resistors and a capacitor.
What are the 3 “resistors” inherent to an area of the axon?
- Extracellular fluid
- Membrane
- Intracellular fluid
What components make up the axon “capacitor”?
2 conducting materials (ICF and ECF) + an insulating layer (phospholipids).
What is the relative amplitude of an action potential in the brain? What about in the spinal cord? What about in a peripheral motor neuron?
They are all the same.
What term is used to describe the movement of an action potential along an axon?
Electrotonic current spread (or saltatory conduction under different terms).
In what 2 ways can the conduction velocity of an axon be increased?
- Myelination
2. Increased diameter
What 2 factors combine to influence the speed of axonal conductance?
- Electrotonic current flow
2. Ions flowing through voltage-gated channels
Which is faster: axons moving through solution or through opening/closing ion channels?
Ions moving through solution.
How does low membrane resistance influence the length constant (λ) and the conduction speed?
Length constant (λ): decreased Conduction speed: decreased
How does low internal resistance influence the length constant (λ) and the conduction speed?
Length constant (λ): increased Conduction speed: decreased
What equation gives the length constant (λ)?
λ = sqrt(membrane resistance / internal resistance)
What are potential disadvantages of having large axons?
- Take up a lot of space
- Expensive to produce and maintain
How does myelin increase conduction speed (in terms of electrophysiology)?
Increases membrane resistance and decreases the membrane capacitance.
What is the purpose of the nodes of Ranvier on a myelinated axon?
To boost depolarization and perpetuate the action potential.
Where along a myelinated axon are the Na+ channels concentrated?
At the nodes of Ranvier.
What mechanism ensures that action potentials are unidirectional?
Recently opened Na+ channels are deactivated (absolute and relative refractory period).
If you were to stimulate the middle of an axon, would the action potential propagation be unidirectional?
No, it would travel to both ends of the axon.
Why do large axons have lower membrane resistance?
They have greater surface area and therefore more room for leak channels.
Why do large axons have lower internal resistance?
They have larger volume and therefore allow more ions to travel through at one time.
