Download The Nervous System

The Nervous System
What is the Nervous System?
 The nervous system is the highway along
which your brain sends and receives
information about what is happening in
the body and around it. This highway is
made up of billions of nerve cells, or
neurons (say new-rons) which join
together to make nerves.
 A nerve is a fiber that sends impulses
through the body.
These fibers are covered by fatty
substance called myelin (my-e-lin).
Myelin helps the messages go fast
through the neurons.
Nerve cells work by a mixture of
chemical and electrical action.
The two main parts of the nervous
system are the central nervous system
and the peripheral (per-if-er-al) nervous
system.
Nerve cells – What is a neuron?
A neuron is a nerve cell. The brain is made up of
approximately 100 billion neurons.
Neurons are similar to other cells in the body in
some ways such as:
Neurons are surrounded by a membrane.
Neurons have a nucleus that contains genes.
Neurons contain cytoplasm, mitochondria
and other "organelles".
However, neurons differ from other cells in the
body in some ways such as:
Neurons have specialized projections
called dendrites and axons. Dendrites bring information
to the cell body and axons take information away from
the cell body.
Neurons communicate with each other through an
electrochemical process.
Neurons form specialized connections called
"synapses" and produce special chemicals called
"neurotransmitters" that are released at the synapse.
There are approximately 1 quadrillion synapses in
the human brain.
How nerve cells work
At the end of each nerve cell there is a
synaptic terminal (sin-ap-tik term-in-ul). This is
full of extremely tiny sacs which hold
neurotransmitter chemicals (new-ro-transmitta- kem-ik-als).
These chemicals transmit nerve impulses from
one nerve to another or from nerves to
muscle cells.
An electrical nerve impulse travels along the
neuron to these sacs which then release the
neurotransmitter chemicals.
The chemicals move along to the next
neuron sparking an electrical charge
which moves the nerve impulse forward.
This happens several times until the
message gets where it's going.
It's a bit like you running around the
house switching lights on. Pressing the
switch causes electricity to flow through
to the light bulb.
Parts of the Nervous System
Central Nervous System
Peripheral Nervous System
THE CENTRAL NERVOUS SYSTEM
 The brain and the spinal cord make up the
central nervous system.
 Your spinal cord is a long bundle of neurons that
goes down your back.
 The brain lies protected inside the skull and from
there controls all the body functions by sending
and receiving messages through nerves.
The brain
 The brain is the control center for your body and it sits in
your skull at the top of your spinal cord.
 The brain has three main parts.
 The cerebellum (say se-re-bell-um).
 The cerebrum (say se-re-brum), which has two parts, the left and
right cerebral hemispheres, (say se-re-brell hem-iss-fears).
 The brain stem, that controls a lot of the 'automatic' actions of
your body such as breathing and heart beat, and links the brain
to the spinal cord and the rest of the body.
 Your brain is wrapped in 3 layers of tissue and floats in a
special shock-proof fluid to stop it from getting bumped
on the inside of your skull as your body moves around.
THE PERIPHERAL NERVOUS SYSTEM
The peripheral nervous system carries
messages to and from the central
nervous system. It sends information
to the brain and carries out orders
from the brain.
Messages travel through the cranial
nerves, those which branch out from
the brain and go to many places in
the head such as the ears, eyes and
face.
Messages can also travel through the
spinal nerves which branch out from
the spinal cord.
Nerves
 Nerves are sort of like wires that carry communication signals
or impulses around the body. Inside each nerve is a bundle
of nerve fibers. Some nerves are really long, like the ones
that go all the way from your feet to your spinal cord. Nerve
cells are called neurons.
 There are two main types of nerves: motor nerves and sensory
nerves. Motor nerves
 - Motor nerves allow the brain to control our muscles. The brain sends
signals over the motor nerves to tell our muscles to expand or
contract so we can move. Sensory nerves
 - The second type of nerves are called sensory nerves. These nerves
carry signals to the brain to tell it about what is going on in the outside
world. They come from our skin (touch), nose (smell), eyes (sight),
tongue (taste), nose (smell), and ears (hear).
Parts to the peripheral nervous system
The somatic (say so-mat-ik) system:
 sends sensory information to the central nervous system through
peripheral nerve fibers. Sensory means that it sends the
information coming from all your senses, touch, vision, hearing,
taste, smell and position.
 sends messages to motor nerve fibers to get the muscles to
move the body.
The autonomic (say or-tow-nom-ik) system
 is responsible for making sure that all the automatic things that
your body needs to do to keep you going, like breathing,
digesting etc. continue working smoothly without your having to
think about them. (How hard would it be to have to keep
thinking, "Breathe in, breathe out," or "Start digesting the food
stomach!")
Helping the Nervous System
 You can help your nervous system work well and be
healthy by being active, having a healthy diet and
keeping yourself busy and happy.
 Exercise releases a chemical, called serotonin, in the
brain which makes you feel good, relaxes muscles and
gets rid of stress.
 Good food gives your body the vitamins and minerals
needed to build healthy nerves and tissue.
 Keeping busy and happy helps you to deal with life
when things go wrong.