How the Brain Works The Facts Visually Explained by DK (z-lib.org)

Brain Anatomy

The brain is a complex mass of soft tissue composed

almost entirely of neurons, glial cells (see

p.21), and blood vessels, which are

grouped into an outer layer, the cortex,

and other specialized structures.

Divisions of the brain

The brain is divided into three

unequal parts: the forebrain,

midbrain, and hindbrain. These

divisions are based on how they

develop in the embryonic brain,

but they also reflect differences

in function. In the human brain,

the forebrain dominates, making

up nearly 90 percent of the brain

by weight. It is associated with

sensory perception and higher

executive functions. The midbrain

and hindbrain below it are more

involved with the basic bodily

functions that determine survival,

such as sleep and alertness.

Cervical

nerves

Thoracic

nerves

Sacral

nerves

Lumbar

nerves

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Hindbrain

Made up of the cerebellum at the lower

rear of the brain and the brain stem, which

connects to the spinal cord, the hindbrain

is the most primitive part of the brain.

The genes that control its development

evolved around 560 million years ago.

Midbrain

The smallest brain section, this is associated with

the sleep-wake cycle, thermoregulation (control

of body temperature), and visual reflexes, such

as the rapid eye movements that scan complex

scenes automatically. The substantia nigra,

which is a region associated with planning

smooth muscle control, is in the midbrain.

There are 31 pairs of spinal nerves

that branch out from the spinal cord

above each vertebral bone, named

after the parts of the spine to which

they connect. They relay signals

between the brain and sensory

organs, muscles, and glands.

SPINAL NERVES

Direct connections

to all three sections

of brain are carried

in spinal cord

Surface layer of forebrain,

known as gray matter, is made

from unsheathed neurons

Tracts of white

matter—neurons

sheathed with

fatty myelin

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US_028-029_Brain_Anatomy.indd 28 20/09/2019 12:31