Graded Potentials and Action Potentials (exam 3 A&P)

Graded potentials Effect

Happens when a stimulus opens an ion channel (like ligand gated Na+ channels) changing the Resting membrane potential of the cell.

Graded Potentials

Depolarization, Repolarization, Hyperpolarization. Usually received on the dendrites of a neuron. Which leads to an action potential releasing a neurotransmitter from the synaptic knobs.

Depolarization

Cell becomes less negative (approaches zero)

Repolarization

Removal of the stimulus (neurotransmitter) the Transmembrane potential returns to normal resting state.

Repolarization (function)

Potassium leak channels and the action of the sodium potassium pump, positive charges leave the cell.

Hyperpolarization

The cell for a little while becomes more negative than RMP (-70mV).

Action potential

Neuron transmitting an electrical disturbance down the length of an axon.

Process of Action Potential

A stimulus arrives at the plasma membrane of the neuron and causes ligand gated sodium channels to open.

Threshold

If the stimulus is large enough the neuron will reach threshold (-55mV) triggering an action potential. When threshold is reached the voltage-gated sodium channels open and sodium rushes into the cell. Causing the cell to depolarize.

Sodium Channel Inactivation

Once the inside of the cell reaches +30 mV, the inactivation gates begin to close and sodium can no longer enter the cell.

Hyperpolarization

The cell is re polarizing, the inside of the cell may actually become slightly more negative than it was prior to depolarization.

The refractory period

The time where cells can’t become electrically excited by another stimulus. (exhausted)

The absolute refractory period

An extremely large stimulus cannot evoke another action potential because VG Na + channels are already open or beginning to close.

Relative refractory period

Requires a larger than normal stimulus to cause an action potential because it needs a bigger leap to jump back from hyper polarization. (ex: -80 to -55)

All or none law

The conduction of an action potential (electrical impulse through a neuron) once threshold is reached the action potential is generated. Same strength/magnitude

Continuous conduction

Axons that lack myelin, slower.

Saltatory conduction

Myelinated axons, faster (prevents ions from diffusing)

Propagation speed (Type A fibers(axon))

Myelin and large diameter, motor neurons/sensory (300 mph) (sharp pain)

Type B fibers

Myelin and smaller diameter, visceral motor neurons (40 mph)

Type C fibers

Lacks myelin and has the smallest diameter out of all of the other axons. (sensory, fastest) (2 mph) (slow, buildup pain)