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Part 3
Neurons and
Action Potentials
What is the job of a neuron?
How do neurons do their jobs?

Neurons are cells that transmit signals to/from
the CNS
Parts of the neuron

Dendrite - receives information or stimuli


Cell Body - responds to information received by
dendrites


Produces the action potential- an electrical output signal of
a neuron
Axon - transmits signal to end of the neuron



Ex: pain, pressure
Nerves are bundles of axons
May be surrounded by myelin for rapid relay of signals
Synapse (synaptic terminal) - transmits signals to
other neurons, found at the terminus of the axon

A neurotransmitter is released in response to the action
potential
Action Potentials: How neurons
transmit signals
A.
B.
C.
D.
Dendrites pick up
chemical signals
The cell body converts
the chemical to an
electrical signal
The axon carries the
electrical signal to the
terminal buttons
The terminal buttons
release a chemical
(neurotransmitter) to
dendrites on the next
neuron
Chemical  Electrical  Chemical
Action Potentials: How neurons
transmit signals

A neuron is a CELL


Has a semi-permeable cell membrane
Neurons are like a French Fry:

High K+ on the inside, high Na+ on the outside
Na+ Na+ K+ Na+
Na+ Na+ Na+ K+ Na+
Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+ K+ K+
Na+ Na+ Na+ Na+
Na+ K+ Na+ Na+
Action Potentials: How neurons
transmit signals

The cell membrane contains ion channels




Allow only certain ions to pass through
Sodium channels allow Na+ to enter neuron
Potassium channels allow K+ to exit neuron
Na+/K+ pumps restore the neuron back to normal by
pumping Na+ back out of and K+ back into the neuron
Na+ Na+ K+ Na+
Na+ Na+ Na+ K+ Na+
Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+ K+ K+
Na+ Na+ Na+ Na+
Na+ K+ Na+ Na+
1. Dendrite receives neurotransmitter signal
Neurotransmitter (NT):
A chemical messenger that
is released from neurons.
* If the neuron does not
get enough NT, it will not
produce an Action Potential
dendrites
2. Cell body relays signal to axon
axon
cell body
3. Na+ channels open and Na+ rushes inside
Na+
Na+
Na+
Na+
Na+
K+
K+
axon
K+
K+
Na+
K+
K+
K+
4. K+ channels open and K+ rushes out
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+ Na+
axon
K+
K+
K+
K+
Na+
K+
K+
K+
5. Other Na+ channels open, like a chain reaction
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+ K+
K+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
6. Action potential reaches synaptic terminals
7. NT is released and goes to dendrite of next
neuron
axon
Dendrite
of next
neuron
NT
receptor
on
dendrite
Neurotransmitter
molecules
8. Na+/K+ pumps move ions back to their
starting points
K+
Na+
K+
K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
8. Na+/K+ pumps move ions back to their
starting points
K+
K+
K+
K+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
Na+
Na+
K+
K+
K+
K+
Na+
K+
Na+
Na+
Na+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
8. Na+/K+ pumps move ions back to their
starting points
Na+
Na+
Na+
Na+
Na+
K+
K+
axon
K+
K+
Na+
K+
K+
K+
Steps of the Action Potential
1.
2.
3.
4.
5.
Dendrite receives neurotransmitter signal
Cell body relays signal to axon
Na+ channels open and Na+ rushes inside
K+ channels open to let K+ out
Causes other Na+ channels to open, like a chain
reaction
6. Action potential reaches synaptic terminals
7. Neurotransmitter is released and goes to
dendrite of next neuron
8. Na+/K+ pumps move ions back to their starting
points ***requires ATP***
REVIEW!!!
1.
2.
3.
4.
5.
What is homeostasis?
What is the nervous system?
What is the cell type that transmits
signals in the nervous system?
What is the role of a dendrite?
Which part of the neuron relays the
electrical signal?
REVIEW!!!
6.
7.
8.
9.
10.
In what order are signals relayed from
one neuron to the next?
What feature of the NS allows your body
to rapidly respond to the environment?
What 3 neurons are involved in the
process from #7 above?
What is an action potential?
What is the name of the chemical that is
released from synaptic terminals of
neurons?
Action Potentials: How neurons
transmit signals
http://www.youtube.com/watch?v=YwN9aCobCy8


Write a narration to go with this YouTube
clip
Be prepared to share your narration with
the class