Keeping Your Body Healthy
-The Nervous SystemLesson 19
Health Stats This graph compares bicycle-helmet use and seatbelt use among teens.
Why do you think many more teens wear seat belts than bicycle helmets?
Goals/Objectives
• Identify parts and functions of the nervous
system.
• Identify behaviors to keep your nervous
system healthy.
Key Terms
• Nervous System
• Central Nervous System
• Peripheral Nervous System
The Nervous System
• The body system that carries messages to and
from the brain and spinal cord and all other
parts of the body is the nervous system.
• Composed of 2 divisions:
– Central nervous system
– Peripheral nervous system
Central Nervous System
Peripheral Nervous System
• The central nervous system
consists of the brain and
spinal cord.
• Relays responses to these
messages to your muscles
and glands as your body
responds to changes in your
environment.
• The peripheral nervous
system is made up of
nerves that branch out from
the central nervous system
to muscles, skin, internal
organs, and glands.
• Sense organs continually
send messages, such as
odors, sights, or tastes, to
your brain.
The Brain
• The mass of nerve tissue that acts as the control center
of the body is called the brain.
• Human brain weighs about 3 lbs.
• Can store more information that all the libraries in the
world put together
• Creates ideas and controls thinking, reasoning,
movement, and emotions
• The brain has 3 major parts:
– The cerebrum
– The cerebellum
– The brain stem
The Cerebrum
• The cerebrum is the largest part of the brain and
controls the ability to memorize, think, and learn.
• Determines a person’s intelligence and
personality
• Consists of two halves, called hemispheres
– The right hemisphere controls the left side of the body
– The left hemisphere controls the right side of the body
The Cerebellum & Brain Stem
• The cerebellum is the part of the brain that
controls and coordinates muscle activity.
• Helps you maintain your balance
• You’re ability to catch a ball is a function of
your cerebellum.
• The brain stem is the part of the brain that
controls the functions of the internal organs.
Spinal Cord
• The column of nerve cells that extends
downward from the brain is the spinal cord.
• Carries messages to and from your brain and
all parts of your body.
• Keeps your brain informed of changes in your
body and in your environment
• Protected by your vertebrae
Nerve Cells
• The nervous system is composed of cells
called neurons.
– A neuron is a nerve cell that is the structural and
functional unit of the nervous system.
• A neuron consists of a cell body, and axon, and
dendrites.
Parts of a Neuron
• A cell body is the main body of the neuron.
• An axon is an elongated fiber that carries
impulses away from the cell body to the
dendrites of another neuron.
• Dendrites are branching fibers that receive
impulses and carry them to the cell body.
Dendrite
Dendrites carry nerve
impulses toward a
neuron’s cell body.
Neuron Structure
Cell Body
The cell body controls
the cell’s basic functions.
Axon
Impulses travel along
axons toward other cells.
Myelin Sheath
Some axons are covered
by a myelin sheath
that increases the speed
of an impulse.
Synapse
The junction between
an axon and another
cell is a synapse.
Chemicals called
neurotransmitters pass
the impulse from the
sending neuron to the
receiving cell.
Sensory & Motor Neurons
• Sensory and motor neurons work together to
help you respond to your environment.
• Sensory neurons carry impulses from the
sense organs to the spinal cord and brain.
• Motor neurons carry responding impulses to
muscles and glands from the brain and spinal
cord.
– Cause responses in muscles and glands
Mixed Messages
Test how well your brain can handle conflicting messages.
Material
watch or clock with second hand
Try This
Read the list of words while your partner times how long it
takes you.
Notice that the words in the list are written in different
colors. This time you should say the color of each word as
your partner times you. Do not read the words, rather,
identify their colors.
Mixed Messages
Mixed
Messages
Think and Discuss
Did it take you more time to read the words or say the colors?
Describe the experience of saying the colors.
Which part of your brain most likely works hardest during this
activity? Which task is your brain better at—reading the words or
identifying their colors?
Once people master basic skills such as tying shoes or reading, they
perform them with little thought. How do you think this fact
affected your results in this activity?
What do you think would happen if you asked a young child who has
just learned to read to do this activity? Explain.
Reflex Action
• A reflex action is an involuntary action in which a message
is sent to the spinal cord, is interpreted, and is responded
to immediately.
• Do not take a conscious thought and take only a fraction of
a second.
– i.e. touching a hot stove and quickly pulling your hand away
• Sensory neurons carry the message that you touched
something hot to your spinal cord and brain
• Your brain interprets the message.
• Motor neurons carry the message back to your muscles.
• You respond by moving your hand.
A Reflex Action
Sensory neurons in your
hand send impulses
to your spinal cord.
Neurons in your spinal
cord process the
information and send
commands directly
to motor neurons that
control muscles in your
arm and hand.
Your muscles contract and
you quickly withdraw your hand.
Meanwhile, messages of pain travel
to the brain. Shortly after your arm
moves, you feel pain.
FYI – Sensory Signals
• Sensory signals are the only signals that travel
inward from the peripheral nervous system to
the central nervous system, and are sensitive
to light, temperature, chemicals, and pressure.
• Motor signals travel outward from the central
nervous system to the peripheral nervous
system.
How to Keep Your
Nervous System Healthy
• Wear a protective
helmet for sports.
• Avoid diving into the
shallow water or water
of unknown depth.
• Follow directions for
taking any medications
that affect the nervous
system.
• Use a safety belt.
• Avoid drinking alcohol
and using other drugs
that impair the
functions of the brain.
• Follow directions for
using household
products that contain
chemicals that may
affect the nervous
system.
Avoiding Head Injuries
•A bruiselike injury to the brain is known as a concussion.
•A coma is a prolonged period of deep unconsciousness.
•Head injuries can be avoided.
•Wear a helmet when you play contact sports.
•Fasten your seat belt.
•Before diving into water be sure that it is deep enough
and that there are no underwater hazards.
•Avoid drugs and alcohol.
Avoiding Nerve Injuries
•Individual peripheral nerves also can be injured.
•To help prevent carpal tunnel syndrome and similar nerve
injuries, it is important to take breaks from repetitive
motions and to maintain good posture.
Preventing Infections
•Nervous system infections are rare because its tissues are
well protected.
•Meningitis causes inflammation of the membranes
surrounding the brain and spinal cord.
•The most serious form of meningitis can be prevented
with a vaccine.
•A bite from an infected animal can transmit rabies, an
infection of the central nervous system.
•Avoid contact with animals that act sick or behave
strangely.
Living with Epilepsy
•Sudden, uncontrolled nerve impulses in the brain can lead
to a seizure.
•People with a disorder called epilepsy are prone to
seizures.
•Epileptic seizures include facial twitching, loss of
awareness, and muscle spasms.
Preventing Headaches
•The most common problem of the nervous system that
people experience are headaches.
•Proper diet, exercise, and sleep can help prevent
headaches.
•If you can identify certain foods or odors that trigger
headaches, you may be able to avoid those triggers.
Questions
1. What parts make up your nervous system?
2. What is the difference between the central nervous
system and the peripheral nervous system?
3. What is the difference between sensory neurons
and motor neurons?
4. What is a reflex action, and how to they help
protect the body?
5. Which part of the brain controls the ability to read?
6. Why is it so important to protect your nervous
system from injury?