Action potential

Neurons

nerve cells that are capable of initiating and conducting electrical activity throughout the body

Neuroglia

cells that support the neurons

Function of nerve cells

is rapid communication and quick, localized control of body movement

Dendrites

receive incoming signals at synapses in the form of passive, “electronic” graded potentials

Cell body

“integrates” multiple incoming signals via summation

Axon

carries the output signal; all-or-none action potential

summation

cumulative effect of multiple individual stimuli that combine to trigger a response

Graded Potential

• travel short distances

• many different sizes

• small positive or negative voltage deflection (EPSP or IPSP)

• can be made quickly or even simultaneously

• propagate in all directions

Action Potentials

• travel very long distances

• all the same size

• rapid positive voltage deflection (depolarization)

• travel in only one direction in the axon

Action potential firing

an all-or-none wave of elevated potential that will result in some Ca⁺ driven action part of the cell. Also called spikes.

AP’s are ____ driving ____ action

Potentials; calcium mediated

Action Potentials Sodium gated

Na channels have two gates activation and inactivation

Na channels open

Soduim flows IN cell depolarizes

Na channels activate…

fast

Na channels inactivate…

slow

Action Potential Sodium Channels Activation part 1

at resting membrane potential, the activation gate closes the channel

Action Potential Sodium Channels Activation part 2

Depolarizing stimulus arrives at the channel. Activation gate opens.

Action Potential Sodium Channels Activation part 3

With activation gate open, Na enters the cell

Action Potential Sodium Channels Activation part 4

inactivation gate closes and Na⁺ entry stops

Action Potential Sodium Channels Activation part 5

during depolarization caused by K⁺ leaving the cell the two gates reset to their original positions

Action Potentials: Potassium Channels gates

K channels have ONE gate: activation only

Action Potentials: Potassium Channels

K channels open: potassium flows OUT cell re-polarizes

With positive voltage: K channels activate slow, K channels dont

Action Potentials: Ion permeabilities

With negative voltage

Na channels de-activate fast

K channels de-activate slow

In which predominant states are Na+ channels at point 7?

closed, unblocked

In which predominant state are K+ channels at point 7?

closing, slowly

The neuron NEEDS the after-hyperpolarization (AHP) phase to:

unblock Na+ channels, close K+ channels, reset ionic gradients return to rest