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

BRAIN FUNCTIONS AND THE SENSES

Making a Move

SPINAL CORD

Making a MoveOnce our brain has planned a movement (see pp.96–97), it sends signals to the appropriate muscles in the body, via the nervous system, to turn intention into action.From brain to spineSignals from the motor and parietal areas of the cortex are sent along the axons of neurons, through the brain stem, to communicate with motor neurons in the spinal cord. Most of the axons form part of a bundle called the lateral corticospinal tract, which crosses over at the base of the brain stem so that axons from one brain hemisphere connect to motor nerves for the opposite side of the body. Other nerve tracts originate in different parts of the midbrain and perform specific movement functions.

A motor homunculus shows which areas of the motor cortex control which areas of the body. Areas for adjacent body parts—such as the arm and hand—are generally grouped together. The body parts are shown in proportion; those areas that make complex movements, such as the face and the hand, take up more space in the cortex than those making simple movements, such as the foot.

MOTOR HOMUNCULUS

SIMPLE AND COMPLEX MOVEMENTS

Nerve tractsThe axons of

the lateral corticospinal

tract send signals to

muscles that connect to

the skeleton to produce voluntary limb movements. Other groups of axons are responsible for the body’s involuntary responses, such as balance, as well as for fine-tuning movements.

Vestibulospinal tract

KEY

Axons cross to opposite side

of body in midbrain

MIDBRAIN

CEREBELLUM

Most signals originate in

primary

motor area

1

PS

NI

LA

T

R

A

C

T

S

L

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F

T

S

ID

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F

B

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IN

Axons collect in

midbrain and join

spinal cord

Lateral corticospinal tract begins in cortex and runs through thalamus

Axons cross

over to opposite side of body

just below

Rubrospinal tract aids fine motor control brain stem

Vestibulospinal tract,

which originates in

brain stem, helps regulate balance

and body

orientation

Neurons from brain (upper

motor neurons) pass

signals down spinal cord

Reticulospinal tract helps coordinate movement

PARIETAL CORTEX

PRIMARY MOTOR

AREA

Red Reticular formation

nucleus

Lateral corticospinal tractRubrospinal tractReticulospinal

tractMotor-nerve axon

SP

INA

L^ COR

AHT D

AL

UM

S

PONS

PR

IM

AR

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MO

TO

R^ AR

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