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The Nervous System:
Coach Book Pgs. 62-65
The Main Idea
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Your body carries out many complex activities to keep you alive and healthy.
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These activities must be controlled to keep the body working properly.
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Most of the body functions are controlled and coordinated by your nervous system.
Importance of Nervous System
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You could not move without your nervous system, or think, feel pain, or taste any of your
favorite foods.
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You could not move without your nervous system, or think, feel pain, or taste any of your
favorite foods.
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Any internal or external change that causes a response is called a stimulus. (plural stimuli)
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The nervous system controls the body’s functions and its responses to stimuli.
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The nervous system is composed of three main structures: the brain, the spinal cord, and the
many nerves throughout your body.
The Central and Peripheral Nervous System
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The central nervous system is made up of the brain and the spinal cord.
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The peripheral nervous system consists of the many nerves that communicate between the
central nervous system and the rest of the body.
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Both parts of the nervous system are involved in both voluntary and involuntary
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actions.
Neurons
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Your nervous system is like a giant computer, with wires and electrical circuits sending and
receiving messages.
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Nerve cells, or neurons, branch out from the brain and the spinal cord.
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Many neurons form bundles of fibers called nerves.
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These nerves form a network through which messages in the form of electrical signals can travel
to all parts of the body.
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The electrical signals carried by neurons are called impulses.
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Notice that the neuron is made up of three main PARTS: dendrites, a cell body, and an axon.
Structure of a typical nerve cell:
Label the 3 main parts
• Impulses travel through neurons in only one direction.
• An impulse is transmitted from the axon of the one neuron to the dendrite
of another.
• The dendrite carries the impulse to the cell body.
• The axon then carries the impulse away from the cell body to the next
neuron.
Types of Neurons
• There are 3 main TYPES: sensory neurons, motor neurons, and
interneurons.
1. Sensory neurons - carry impulses from the sense organs to the spinal cord
and brain.
– Sense organs are parts of your body that take in information from
the external world.
– Most of your sense organs are centralized in your head. (eyes, ears,
nose, & taste buds)
– Your body’s largest sense organ is your skin.
– Once information is sent to the brain to process, your brain decides
how the body will respond.
2. Motor neurons carry impulses from the brain and spinal to the
muscles and glands.
3. Interneurons, carry impulses between sensory neurons and motor
neurons.
Central Nervous System
• The central nervous system is the control center of the body. It includes the
brain and spinal cord.
• The thick column of nerve tissue that links the brain to most of the nerves is
the spinal cord.
• The brain controls most functions in the body.
• The brain is located in the head and is protected by the skull.
Protecting the Brain
• 3 layers of connective tissue cover the brain.
• The space between the middle layer and inner layer is filled with a watery
fluid that helps protect it.
• The skull also protects the brain.
Parts of the brain
1. Cerebrum - largest part of the brain.
-Interprets input from the senses, controls movement, and carries out
complex mental processes like learning.
- Certain areas of it are associated with smell, touch, taste, hearing, and
vision.
-Other areas control movement, speech, written language and abstract
thought.
2. Cerebellum - 2nd largest part of brain.—
-Coordinates the actions of your muscles and helps you keep your balance.
3. The brain stem controls your involuntary actions like breathing and your
heartbeat.
The Spinal Cord
• The spinal cord is a bundle of nerves that links the peripheral nerves and
the brain.
• The spinal cord runs down the center of your back and is protected inside a
column of bones, the vertebrae.
Central Nervous System continued…
• The brain and the spinal cord are connected by the brain stem.
• The brain stem is the part of your nervous system that controls your body’s
involuntary responses.
• Involuntary responses are those that are not under your conscious control
and happen automatically. (ex. Heartbeat)
Reflexes
• Most responses are controlled by the brain.
• However, a reflex is controlled by the spinal cord.
• A reflex is a rapid, involuntary response to a stimulus.
• An example, if you touch a really hot object with your hand. The impulse is
sent to the spinal cord immediately. The spinal cord responds by sending
impulses to your arm muscles to cause you to quickly pull away your hand.