Transcript The Nervous System and Neurons

The Nervous System
and
Neurons
Nervous System
• Network of connected
cells, tissue, and organs
• Controls thoughts,
movement, life
processes
• Quick responses
– Ex: Sunny day  pupils
shrinking
CNS and PNS
Neurons
• AKA: Highly specialized nerve cells
– Transfer electrical impulses to and from the brain
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4 Main Parts
Cell body: contains nucleus and organelles
Dendrites: branches that receive messages from neighboring cells
Axon: extension that carries messages away from the cell body
Axon Terminal: End of neuron
Three Types of Neurons:
1) Sensory
– Detect stimuli and
transmit signals to/from
the brain
– Detect sense (sight, smell,
sound, taste, touch)
Three Types of Neurons:
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
Resting Potential
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• Defined: Neuron at rest
• Neuron exterior is positive
in charge
– Due to abundance of Na+
outside
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• Neuron interior is negative
– Due to abundance of
proteins (neg charge)
– Some K+ inside the cell
Action Potential
• Defined: neuron at work
• 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
• Na+/K+ pumps work to restore
initial charge.
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Synapse
• Defined: Gap between neurons
• Problem: Impulse cannot cross
the gap
• Solution: Neurotransmitters
(chemical signals) are sent from
one neuron to another
• Steps:
1) Impulse reaches axon
terminal (end)
2) Vesicle releases
neurotransmitters into
synapse, which attach to
receptors on neighboring
neuron
3) Na+ Channels open on
dendrite of neighboring
neuron… creates new impulse
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Vesicle exits the
cell and dissolves
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Impulse reaches the
axon terminal
Terminal end
of one cell
Dendrite of
another cell
Neurotransmitters
diffuse across the
synapse and attach to
receptors of a
neighboring neuron
impul
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Neurotransmitters
cause Na+
channels to
open… creating
new impulse
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Terminal end
of one cell
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Dendrite of
another cell
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Brain
impulse
neurotransmitters
impulse
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impulse
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impulse
neurotransmitters
impulse
Feet
Impulses eventually reach the muscles…
and causes MOVEMENT!
Review
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 signal?
8. Describe how an action potential moves down a neuron.