Communication between excitable cells Flashcards
How does the diameter of an axon affect AP propagation?
Increase in diameter increase speed
Increases in axon diameter decreases axoplasm resistance, allowing local currents to flow more easily so speed increases.
For unmyleinated axons: V is proportional to the root of the diameter
How does myelination of axons affect AP propagation?
Myelination increases speed
Myelinated regions of axon membrane lack v-g ion channels forcing local currents to ‘jump’ from node of ranvier to the next - ‘Saltatory Conduction’.
Myelination increases axon diameter, increasing the internodal distance so ‘jumps’ are longer thus speed increases.
For myelinated axons: V is proportional to the diameter
How does temperature influence AP propagation?
As temperature decreases, speed of AP also decreases.
What is the range of conduction velocities for:
unmyelinated, small diameter axons?
myelinated, small diameter axons?
myelinated, large diameter axons?
0.5 - 2.5 ms
2 - 15 ms
60 - 100 ms
What is the conduction velocity range for autonomic axons?
5-25 ms
What stimuli are sensed by fast sensory axons?
touch
vibration
muscle length
What stimuli are sense by slow sensory axons?
temperature
‘ache’ (poorly-localised pain)
How can conduction of APs along an axon be blocked?
Reversible or Irreversible blockade of axonal sodium channels
Give an example of a local anaesthetic that reversibly blocks axonal sodium channels?
Lidocaine
What are the 2 ways in which APs are transmitted from cell to cell?
- At chemical synapses
- between neurons; between motor neurons and muscle - At low-resistance electrical gap junctions
- between cardiomyocytes; between SMCs; between neurons via electrical synapses
Binding of transmitter to post-synaptic receptors results in what 2 events?
- Opening or closing of integral ion channel
2. Activation of enzyme system which modulates opening of nearby ion channels
What is the delay (in ms) of neuromuscular transmission in setting up of an AP receiving cell?
0.5 - 1 ms
At low-resistance electrical gap junctions, what connects the cytoplasms of each cell to allow the continuous flow of electrical current between cells?
Aligned Connexons that have water-filled pores.
Because of the direct connection between cells using low-resistance electrical gap junctions to propagate APs, what are the differences compared to synaptic transmission?
The direct connection means that no transmitter is required and there is no delay in transmission.
Bi-directional transmission is possible.
Gap junctions make poor pharmacological targets.
Where are the cell bodies of sensory neurons located?
Just outside the spinal cord (still part of the PNS)