Module 3.1 Neurons and Action Potentials

Review questions/terms at the end of the chapter.

Sensory Neuron

detects and transmits sensory information to CNS

Interneuron

integrates information and connects neurons

Motor Neuron

sends commands from CNS to muscles or glands

Dendrites and Cell Body

receive signals from other neurons

Axon Hillock

initiates the action potential

Axon

conducts the action potential to the terminals

Synaptic Terminals

release neurotransmitters to communicate with next call

Polarization

charge difference across membranes.

Resting Membrane Potential

-70 mV; the inside of the neuron is negative compared to the outside.

Depolarization

membrane becomes less negative (more positive)

Hyperpolarization

membrane becomes more negative than resting.

Graded Potential

local, small, stimulus-proportional voltage change

Action Potential

all-or-none electrical signal propagated along axon.

Rising Phase

sodium influx, depolarization.

Falling Phase (Repolarization)

sodium channels close, potassium exits

Undershoot and Refractory Period

hyperpolarization and temporary inability to fire

EPSP

excitatory; moves membrane toward threshold

IPSP

inhibitory; moves membrane away from threshold

Neurotransmitter Removal

enzymatic breakdown or reuptake

Action Potentials Step #1

Resting membrane potential at -70mV

Action Potentials Step #2

stimulus depolarizes membrane to threshold (-55 mV), sodium channels open

Action Potentials Step #3

rising phase - sodium floods in, cell becomes positive

Action Potentials Step #4

sodium channels inactivate, stopping sodium influx

Action Potentials Step #5

potassium channels open, potassium exits → repolarization

Action Potentials Step #6

potassium channels slow to close → hyperpolarization (undershoot)

Action Potentials Step #7

refractory period prevents another action potential

Action Potentials Step #8

membrane returns to resting potential (-70 mV)