Action Potential Flashcards
Do APs lose amplitude?
No
Where on the nerve is an AP initiated?
Axon Hillock
How can you measure ion currents across a membrane?
Voltage clamping
Do Na+ channels/K+ channels inactivate?
Na yes K no close
What effect does a larger diameter of axon have on the conduction velocity of an action potential?
Larger diameter increased conduction velocity
Talk through 3 stages of an action potential
1) Depol - VG Na+ channels open, positive feedback, more Na in
2) Inactivation - Na+ in inactivates Na+ channels and opens VG K+ channels - K+ out
3) Repol - K+ out + overshoot
What are the two stages of AP recovery?
Absolute refractory period - no AP can be elicited
Relative refractory period - with threshold can elicit another AP
What leads to propagation of an AP along an axon and how?
Local current theory - spread of depolarisation locally (does reduce in amplitude).
What’s resistance and capacitance and what’s its relevance in terms of AP propagation?
Resistance - of the membrane, increased resistance means the local depol will spread further along the axon.
Capacitance - ability of membrane to store charge, higher capacitance means the slower a depol will travel down axon.
What is the basic structure of Na+ channel (4) ? What do each bit do?
One alpha peptide subunit, 4 parts
Pore region = determines selectivity to ion
S4 of each of 4 parts = voltage sensor
Inactivation particle = When pore open succestible to inactivation - plug closes pore. Cell has to hyperpolarise before plug can release
What is the basic structure of K+ channel (1)? What is the nature of K+ open and closing?
4 alpha subunits - 4 x size of Na+ channel
Channels open and close in random manner - average of many openings.
What is the order of how local anaesthetics affect
1) small myelinated neurones
2) small unmyelinated
3) large myelinated
That order
How do Local anaesthetics block?
Na+ channels in a use dependent manner
