Nervous System Part 2 Flashcards
1
Q
Overview of conduction down an axon
A
- Current decreases with distance
- Graded potentials only travel short distances
- Action potentials are needed to send signals longer distances
- Propagation of action potential by populations of VG Na+ channels along axon, at nodes of Ranvier
- 3 pathways for current in an axon
- Saltatory conduction; role of myelin in allowing nodes to be spaced further apart
- Local anesthetic affects small diameter axons (pain fibers) first
2
Q
Synapse overview
A
- VG calcium channels
- Calcium enters presynaptic knob
- Calcium binds to membrane (docking) proteins
- Fusion of vesicle membrane
- Exocytosis
- Diffusion, binds to receptors in postsynaptic cell
3
Q
What are the three pathways that current has in a neuron?
A
- Down the inside of the axon
- Through the cell membrane (open ion channels)
- To the cell membrane to charge up the capacitance
4
Q
Why use an action potential (instead of graded potential)?
A
- Axons are poor conductors (pathway 1 has a high resistance) and allow current to “leak” out making it weaker with distance.
- (Pathways 2 and 3 are significant drains on overall current.)
5
Q
Diagram showing how current is dispersed through the different pathways
A
6
Q
Graded potentials
A
- Graded potentials only travel a short distance before diminishing in amplitude.
- To send signals beyond a very short distance, action potentials must be generated and propagated along the entire length of neuron.
7
Q
Diagram showing the direction of action potential propagation
A
8
Q
Saltatory conduction
A
9
Q
Local anesthetic
A
- Local anesthetic blocks APs in small diameter axons (pain) first and spares
large diameter axons (touch, motor). - At the injection site, anesthetic spreads
a given distance and the effects are determined by how many nodes are blocked.
10
Q
Synapse diagram
A
