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Label the parts of the neuron. Try not to look at
your notes!
NEURON
Dendrites
Dendrites – receive messages from other cells
and conduct impulses toward the cell body
NEURON
Dendrites
Cell Body
Cell Body – the cell’s life-support center
NEURON
Dendrites
Cell Body
Axon
Axon – the extension of a neuron through which messages
are sent to other neurons or to muscles or glands
NEURON
Dendrites
Cell Body
Axon
Myelin Sheath
Myelin Sheath – a layer of fatty cells covering
the axon, helps speed up neural impulses
NEURON
Dendrites
Axon Terminals
Cell Body
Axon
Myelin Sheath
Axon Terminals – where impulses leave the
neuron as neurotransmitters
Video: How do nerves work?
• https://www.youtube.com/watch?v=uU_4u
A6zcE&list=PLhfdMF9uC2pAaqiNgm9tvRu9
gWbGVNwc4&index=18
Neurons – How do they work?
• Neurons send messages to other
neurons – this is what keeps every
part of our body in communication with
every other part.
• Neurons “fire” – send an impulse
(message) down their length
dendrite
Axon
cell body
cell
body
TYPICAL MOTOR
NEURON
synapse
muscle
tissue
Action Potentials
• This “firing” of impulse messages is
called the action potential.
• An action potential is a brief
electrical charge that travels down
the axon of the neuron.
What causes an impulse to
fire or not fire?
• When a neuron is at rest, it is called the
resting potential
• There are electrically charged particles
(ions) inside and outside of the neuron
• During the resting potential, there is a
negative charge on the inside of the
neuron compared to the outside.
Neuron Communication
Resting Potential
Action Potentials, cont.
• Stimulation from inputs to dendrites causes
the cell membrane to open briefly
• Positively charged sodium ions flow in
through the cell membrane
• If resting potential rises above threshold,
an action potential starts to travel from the
cell body down the axon
• Refractory period The “recharging phase”
when a neuron, after
firing, cannot generate
another action potential
Neuron Communication
All-or-None Principle
• The principle that if a neuron
fires it will always fire at the
same intensity
• A strong stimulus can trigger
more neurons to fire, and to
fire more often, but all action
potentials are of the same
strength and speed.
• A neuron does NOT fire at
30%, 45% or 90% but at
100% each time it fires.
Just like a gun,
there is no
“part-way”
firing
How is a neuron firing similar to a
toilet flushing?
• Consider the following concepts:
– All-or-none principle
– Direction of impulse
– Refractory period
– Threshold
– Resting potential
– Action potential