Molecular Basis of Action Potentials

Absolute Refractory period

During falling phase, voltage gated Na+ channels inactivate

It is the period during after-hyperpolarization when a neuron can fire another action potential.

What is the Relative Refractory Period?

They become reactivated.

What happens to voltage gated Na+ channels during the Relative Refractory Period?

It is below the resting membrane potential.

What is the membrane potential like during the Relative Refractory Period?

A greater depolarization current than at rest.

What is required to fire another action potential during the Relative Refractory Period?

spike-initiation zone

In sensory neurons: the spike-initiation zone is near the sensory nerve endings

In motor neurons: the axon hillock

-spread of action potential along membrane

-path of the + charge

-axonal excitability

-myelination

Factors influencing conduction velocity

-Inside the axon=faster

-Across the axonal membrane=slower

When is the + charge of an axonal path faster/slower?

bigger=faster

What does it mean if an axonal diameter is bigger?

orthodromic

action potential travels in one direction - down axon to the axon terminal

antidromic

backward propagation

10 m/sec

typical conduction velocity

~2 msec

typical length of action potential

role of myelin in conduction velocity

insulates the axon, increases membrane resistance, decreases capacitance, and allows the AP to travel faster by reducing current loss.

saltatory conduction

the jumping of action potentials from node to node, speeding up signal transmission in myelinated axons

nodes of Ranvier

Gaps in the myelin sheath to which voltage-gated sodium channels are confined, allowing AP regeneration during saltatory conduction

optogenetics

introduces into neurons foreign genes that express membrane ion channels that open in response to light