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The Nervous System and
Neurons
Is this even possible? Why or why not?
• Network of connected cells, tissue, and organs
• Controls thoughts, movement, life processes
• Quick responses– Ex: Sunny day pupils
shrinking
Nervous System
CNS and PNS
• AKA: Highly specialized nerve cells– Transfer electrical impulses to/from the brain
• 4 Main Parts1) Cell body: contains nucleus and organelles2) Dendrites: branches that receive messages from neighboring cells3) Axon: extension that carries messages away from the cell body4) Axon Terminal: End of neuron
Neurons
Three Types of Neurons:
1) Sensory– Detect stimuli and
transmit signals to/from the brain
– Detect sense (sight, smell, sound, taste, touch)
2) Interneuron– Located in the brain– Receive signals from the sensory neurons
Three Types of Neurons:
3) Motor– Pass messages to other tissue– Ex: Nerve attached to muscle
• Muscle reacts by contracting and stretching
Three Types of Neurons:
Resting Potential
• Defined: Neuron at rest• Neuron Exterior is positive in
charge – Due to abundance of Na+
outside
• Neuron Interior is negative– Due to abundance of
proteins and…– Some K+ inside the cell
K+
K+K+
K+K+
K+
K+
K+
K+
Interior
Action Potential• Defined: The electrical
impulse that is triggered & moves quickly down an axon
• Generating the Impulse– Na channels in the
membrane open and allow Na+ to diffuse into the cell
– Area becomes positively charged (impulse)
• After the Impulse– K channels open to allow K+
to exit the cell– Area returns to negative
charge• Process continues down the
axon
impulse
Na+ Na+
Na+Na+
Na+
Na+
Na+Na+
Na+
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impulseimpulse impulse
Cleaning Up the Mess
• Who?– Na/K pump
• What?– Na is pumped back out of
the cell…– K is pumped back into the
cell• When?
– After the impulse has passed
• Where?– Located in cell membrane
• Why?– To restore the initial charge
inside & outside the cell• How?
– Active transport (REQUIRES ATP)
Na+ Na+
Na+
Na+
Na+
Na+
Na+
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Na+
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Na+
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Synapse• Defined: Gap between
neurons• Problem: Impulse cannot
cross the gap• Solution: Neurotransmitter
proteins are sent from one neuron to another
• Steps:1) Impulse reaches axon
terminal (end)2) Vesicle releases
neurotransmitters, which attach to receptors on neighbor
3) Channels open on dendrite of neighboring cell…new impulse created
Neuro
transm
itter
pro
tein
s
Impulse reaches the axon terminal
Vesicle exits the cell and dissolves
Terminal end of one cell
Dendrite of another cell
Na
impulseK
NaNa
impulse
impulseK K
impulse
Neurotransmitters diffuse across the synapse and attach to receptors of a neighboring neuron
Neurotransmitters cause Na channels to open… creating new impulse
Terminal end of one cell
Dendrite of another cell
Na
Na
K Kimpulse
impulse
Na
impulse
K
Feet
Brain
….
….
….
….
impulse
impulse
impulse
impulse
impulse
neurotransmitters
neurotransmitters
neurotransmitters
neurotransmitters
and causes MOVEMENT!
Impulses eventually reach the muscles…
1. What is the function of the nervous system?2. List the 4 main parts and describe the purpose of the 4 main parts of
a neuron.3. The nervous system is divided into 2 parts. What are they and what
do they include?4. Describe the internal and external environment of a neuron in resting
potential. How is resting potential reached?5. What is a synapse and why is it a problem for neurons?6. To what part of the nervous system do motor neurons, interneurons,
and sensory neurons belong?7. When an impulse is within a neuron it is electrical. When the signal
moves to the next neuron it is _________________. What is the specific name for this?
8. Describe how an action potential moves down a neuron.
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