ANPS: Graded Potentials & Action Potentials

Depolarization

membrane potential moves toward 0 mV, making the inner membrane become less negative than the outside

Repolarization

membrane potential increases, inside of the cell becoming more negative than the outside

Graded Potentials

• Small distances of incoming signals

• Local change in membrane potential at point of stimulus

• Size dependent on stimulus magnitude

• Decays down the axon

Where do graded potentials occur?

Dendrites and soma (synapses)

What type of gated ion channels are involved in graded potentials

Mostly chemically gated ion channels (neurotransmitter binding)

Ions involved in graded potentials

usually Na+, K+, Ca2+

Type of signal involved in graded potentials

depolarizing or hyperpolarizing

strength of signal in graded potentials

stimulus magnitude dependent

Action Potentials

• Long-distance signals of axons

• Triggered by graded potentials at the axon hillock

• “all or none”

• only in cells with excitable membranes

Importance of voltage gated K+ channels in action potentials

• selective for potassium only

• slower to open than Na+ channels

• TWO STATES:

  • open or closed

Importance of voltage gated Na+ channels

• selective for sodium ions only

• TWO MAIN GATES

  • activation- closed at rest, opens quickly following depolarization

  • inactivation- closes shortly after channel opens

• THREE MAIN STATES

  • closed, open, inactivated

Absolute refractory period

another action potential CANNOT be generated at this time

Relative refractory period

another action potential can be generated only if the stimulus is strong enough

The threshold value of the membrane potential is important to action potential generation because ___

it is the point at which depolarization becomes self-generating

Action potentials are generated where

Axon hillock (high concentration of voltage gated sodium channels)

What channels are needed in action potentials

Voltage gated ion channels (first sodium and then potassium)

In action potentials what is the direction of voltage change

Depolarization and then repolarization

In action potentials what is the amount and degree of voltage change

Relatively large change in voltage (from -70 mV to +30 mV) but the degree of change is always the same (shape and magnitude)

Duration of action potential event

travels the complete distance of the axon

Action potential change in intensity

amplitude of events will always be the same