Download 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
K+
K+
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K+
• Defined: Neuron at rest
• Neuron exterior is positive
in charge
– Due to abundance of Na+
outside
K+
K+
Interior
K+
K+
• 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.
impulse
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impulse
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Kimpulse
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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
Na+
Na+
Na+
Vesicle exits the
cell and dissolves
imp
ulse+
K
imp
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K+
imp
ulse+
K
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
se
Neurotransmitters
cause Na+
channels to
open… creating
new impulse
Na+
Na+
imp
ulse
K
Terminal end
of one cell
Na+
imp
ulse
K
Dendrite of
another cell
K
imp
ulse
Brain
impulse
neurotransmitters
impulse
neurotransmitters
impulse
neurotransmitters
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.