SESSION 7 LT 1 ELECTRICAL EXCITABILITY - AP's AND IT'S PROPERTIES Flashcards
1
Q
DESCRIBE THE PROPERTIES OF AP
A
- Change in voltage across the membrane
- Depends on ionic gradients and relative permeability of the membrane
- AP only occurs if threshold is reached
- All/ nothing response
- Propagated without loss of amplitude
2
Q
Conductance what is it and its relation to membrane potentials?
A
- Conductance to any ion increased the membrane potential will move closer to EP for that ion
- Conductance of membrane to a particular ion- dependent upon the number of channels open for than Pom
Amount of ions move to produce ap is small to produce a relatively large change in membrane potential
3
Q
What happens to sodium channels during maintained depolarisation?
A
- During maintained depolarisation - Na+ channels close VIA INACTIVATION!- hence this is the way that the depolarising blocker succinylcholine works on nACHR
4
Q
What is the importance of reaching threshold potential?
A
- Once a certain potential is reached positive feedback occurs as Na+ channels begin to open
- This is the threshold for AP generation
5
Q
Diseases affecting the conduction of AP’s
A
CNS- MS - All CNS nerves
Deric’s disease - optic and spinal cord nerves only
PNS-
Landry Guillain Barre Syndrome
Charcot - Marie- Toot disease
6
Q
What are the properties of the axon will lead to high conduction velocity?
A
- High membrane resistance
- Low membrane capacitance
- Large axon diameter
7
Q
What is Capacitance?
A
- Ability to store charge
- Property of lipid belayer
8
Q
Membrane resistance is dependent upon what?
A
- Number of ion channels open
9
Q
Effect of myelination on axons
A
- Conduction velocity is increased considerably by myelination of axons
- Larger diameter axons - eg Motor neurones - myelinated
Smaller ones such as C-fibres are not
EFFECT OF MYELIN = INCREASED RESISTANCE AND REDUCED CAPACITANCE THEREFORE INCREASING CONDUCTION VELOCITY
