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The Nervous System
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When you wave to a friend, what causes the muscles in your hand to
move? What makes your heart beat day and night every day of your life?
How can you tell when something is burning? Your ability to perform these
actions, and sense changes in your environment is all thanks to your
nervous system.
The brain is the center of the nervous system and coordinates all of the
body’s activities. It is the most complex organ in the human body. The
brain is made up of approximately 100 billion nerve cells (neurons). The
three major parts of the brain are the cerebrum, cerebellum, and brain
stem.
Surrounding and protecting the brain are membranes, a fluid layer, and
the skull.
How do messages from your brain reach all parts of your body? How do
messages from all parts of your body reach your brain? Nerve cells, called
neurons, transport impulses from your body to your brain and from your
brain to all parts of your body. The messages are carried through
electrical and chemical signals.
Neurons are made up of three main parts, the cell body, axons, and
dendrites.
Axons and dendrites branch out to messages to be sent and received to
all parts of the body.
The spinal cord is the long bundle of nerves that runs down the middle of
your back. It serves as the main pathway for messages between the brain
and the body. In men the spinal cord is about 45 centimeters long. In
women it is about 43 centimeters long. Your backbone protects the spinal
cord from damage.
The organs of the nervous system - brain, neurons, and spinal cord - all
work together to control and coordinate all the activities of the body.
Information is transferred throughout your body by electrical and chemical
impulses. Your nervous system helps your body act and react to this
information.
Use the colored diagram to Label each part of the brain and explain what
each part does.
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Draw and label the neuron from the Holt textbook page 657
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