Propagation of action potential Flashcards
Axon diameter compared to conductance velocity
Larger diameter = faster conductance
How can conduction velocity be measured?
Nerve fibre consists of axons with different diameters stimulus one end crush other end (so cant conduct) record extracellular action potentials plot graph
Local current theory
Injection of current into an axon will cause the resulting charge to spread along the axon and cause immediate local change in membrane potential
What is capacitance?
Ability to store charge
Membrane resistance?
depends on number of ion channels open
low resistance = lots of open channels
what does high capacitance mean?
voltage changes more slowly in response to current injection
High resistance meaning
Change in voltage spreads further along axon
What does spread of current depend on?
Capacitance and membrane resistance
increase membrane resistance and in decrease capacitance = more time for current to spread
How does an action potential spread along an axon?
Local currents depolarise adjacent section above threshold
action potential continues down
(cant go backwards as Na+ channels inactivated)
What does myelination do?
increases length constant as it is a good insulator
local currents can depolarise next node above threshold
Unmyelinated sections called and what they contain
Nodes of Ranvier - lots of V gated Na+ channels
How is a myelin sheath formed?
Schwann cells coil around axon
What do action potentials do in myelinated axons?
‘Skip’ myelinated sections - SALTATORY CONDUCTION
Action potentials occur at nodes of ranvier
faster conductance velocity
Na+ distribution unmyelinated axon vs myelinated
unmyelinated: Evenly across whole of axon
Myelinated: High Na+ channels at nodes
Myelinated axons vs unmyelinated axons velocity
myelinated axons: velocity is proportional to diameter
unmyelinated: velocity is proportional to square root of diameter
