Anatomy and Phys lecture 6

1. depolarization of membrane to threshold
2. rapid opening of voltage-gated Na+ channels
3. Na+ entry causes rapid depolarization
4. Voltage-gated Na+ channels inactivate
5. Voltage-gated K+ channels open
6. K+ exits cell causes rapid repolarization
7. after-hyperpolarization due to K+ efflux
8. voltage-gated K+ channels close and the membrane returns to its resting value

steps of the action potentials

contains voltage-gated channels that respond to local electrical changes

axon

the depolarization phase is characterized by __________

rapid sodium entry

the repolarization phase is accelerated by _________

potassium efflux

voltage-gated potassium channels reach peak permeability, part of absolute refractory period

repolarization phase

potassium channels still open, inactivation gate on sodium channels opens, relative refractory period - cell is hyperpolarized, so requires greater stimulus to reach threshold

hyperpolarization phase

potassium permeability reduced, membrane potential goes back to resting value

after-hyperpolarization phase

T or F, open sodium channels accelerate the repolarization phase of an action potential

false

involves entire membrane surface, proceeds in series of small steps, occurs in muscle and unmyelinated axons

continuous conduction

involves patches of membrane exposed at nodes AP leads from node to node, proceeds in series of large steps, occurs in myelinated axons

saltatory conduction

action potential is 'recharged' at each membrane segment by fresh flow of Na+ through newly opened voltage-gated channels in the neighboring membrane

action potential propagation

______ axons = faster action potential propagation

wider

myelin produced by Schwann cells and oligodendrocytes, acts as electrical insulation

myelination

neurotransmitters released from the axon terminal of the pre-synaptic cell bind to receptors on the post-synaptic cell often ligand-gated channels which results in a change in the membrane potential of the post-synaptic cell

chemical synapses