What are the different phases of the action potential?
1) Resting State
4) Repolarization continues
Define Resting State:
Voltage gated Na+ channels are at rest while voltage gated K+ channels are closed. Ready to accept information.
-70 mV to -50 mV (threshold) opens Na+ channel activation gates. The influx of Na+ further depolarizes the membrane until the membrane polarity is reversed (absolute refractory period)
Depolarization also opens the K+ voltage gated channels. As K+ rushes out of cell it closes the voltage gated Na+ channels. The outflow of K+ restores membrane potential.
Define Local Current Flow: Where does it occur?
KNOW Propagation of Action Potential
As AP's move down (forward only) the axon they leave behind a depolarized area to resting membrane potential while being attracted to the next negative charge to reach threshold and therefore depolarizing the axon down the vessel.
Why do AP's only move forward?
Because of the refractory period the membrane behind the AP is not ready to receive a threshold.
Define Saltatory Conduction:
Ap jumping over areas covered by myelin sheath in which ions can not cross the membrane and spark and action potential, thus the "skip".
Is local conduction faster than saltatory?
No, saltatory is faster.
Speed of impulse conduction (propagation) is determined by what two factors?
1) presence or absence of myelin sheath
2) the size (diameter) of the axon
Define characteristics of Type A Fibers:
Largest axons (4-20 um) in diameter
Speed (up to 300 mph)
Carry info. to the CNS concerning position, balance skin sensations
Ex: Motors neurons sending info. to skeletal muscles use type A
Define characteristics of Type B fibers:
smaller (2-4 um) in diameter
messages from organs (less important info. than A fibers)
Define type C fibers:
Unmyelinated and under 2um in diameter, tiny
moves at speed of 2 mph (less important than A fibers)
The site where information is transferred from one cell to another. (The neurotransmitter is released at the synapse following an AP)
KNOW page 9 of Synapse talk: Read over as well in notes
Axondendritic Synapse (why?)
Axoaxonic synapse (Always on exam and final) Inhibiting the flow of Ca2+. It does not immediately effect a Neuron of interest, it modifies the neurotransmitter released by another neuron to the Neuron of interest.
Define Chemical Synapse:
A synapse at which neurotransmitters are released.