Childrens Illustrated Encyclopedia

The brain and oTher parTs of the nervous system—the spinal

cord and nerves—are made from billions of interconnected nerve

cells called neurons that transmit millions of high-speed nerve

signals, or impulses, every second. When signals reach the brain, it

processes them and sends out instructions to the body. The spinal

cord that runs from the brain down the back, relays signals between

spinal nerves and the brain and also controls many reflexes. Cablelike

nerves contain bundles of neurons: sensory neurons carry signals from

receptors in the skin and sense organs to the spinal cord and brain, enabling

us to sense and respond to our surroundings; motor neurons carry signals

from the brain and spinal cord to muscles, telling them to move the body in

a smooth, coordinated fashion.

Cerebellum processes

and coordinates

signals going out

to muscles from

the hemispheres.

Hypothalamus has

overall control of

the internal organs

and is linked to the

pituitary gland and the

hormonal system.

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Meninges are membranes

that surround and cushion

the brain within the skull.

Brain stem

Spinal cord

Area associated

with touch

Area that controls the

muscles, which make

body movements

Area associated

with coordination

and balance

Area that controls

breathing and

blood pressure

White matter

Cerebral cortex

Neuron cell body

Nerve

fiber

(axon)

nerve Cells

each neuron has a main cell body

with fine, spidery connections called

dendrites and a long, wirelike fiber

called the axon. The dendrites and

axon connect the neuron to

thousands of other neurons, creating

millions of pathways for nerve signals.

sleep

When we sleep,

the body rests but the brain

is still working, controlling

our breathing and heartbeat.

We remember some of our

night thoughts as dreams.

Area involved with

consciousness, creativity,

and personality

Cerebral hemispheres

The largest parts of the brain are the two folded cerebral hemispheres.

our thoughts are based in these hemispheres. The outer layer of the brain

is called the cerebral cortex. it is rich in nerve cell bodies. The inner layer is

called the white matter. it consists mainly of nerve fibers. if the two hemispheres

were spread out, they would cover an area the size of a pillowcase.

Skull

White

matter

Nerve reflex

When you prick your

finger, sensory neurons

carry signals to the

spinal cord. here

they pass through relay

neurons and then

straight back along

motor neurons to the

muscles. This is called

a reflex—an automatic

reaction that we make

without thinking.

Brain and nerves

Pituitary gland

Area that

controls vision

Area that

controls

hearing, smell,

and taste

heart and blood

human body

muscles and movement

Brain

Signals pass along arm

through sensory neuron

Relay neuron

in spinal cord

Motor neuron

carries signals to

muscles in upper arm

Pain receptor in hand

Sensory neuron carries nerve

signals to the spinal cord from

pain receptors in the skin.

Spinal cord

Muscles pull

arm away

Thorn touches skin

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