DK - WOW! The Visual Encyclopedia of Everything

Every body movement, whether

it’s a leap in the air, a wink of the

eye, a rumbling stomach, or a

rapid heartbeat, is produced

by muscles. Skeletal muscles

are attached to bones of the

skeleton, which they pull to

move us around. Smooth

muscle moves food along the

intestine. Cardiac muscle keeps

the heart pumping. All muscles

are made of cells called fibres

that contract (get shorter) to

produce a pulling force.

MUSCLES

66

Deltoid muscle raises arm

sideways and swings it

backwards and forwards

SURFACE MUSCLES

Rectus abdominis muscle

pulls in the abdominal

wall and bends the

Body systems

Diaphragm muscle

separates the

thorax (chest) from

the abdomen and

aids breathing

Adductor longus

muscle pulls and

turns the thigh

inwards

(^1) SKELETAL MUSCLE
Long, cylindrical muscle fibres run
in parallel and can reach up to 30 cm
(1 ft) in length. They are bundled
together to form muscles that are
attached to bones by strong cords
called tendons. Skeletal muscles
move the body when instructed
by the nervous system.
(^2) SMOOTH MUSCLE
Tightly packed into layered sheets,
smooth muscle fibres are found
in the walls of hollow organs, such
as the small intestine, along which
they push food, and the bladder,
from which they expel urine. Smooth
muscle contracts slowly and cannot
be controlled voluntarily.
(^3) CARDIAC MUSCLE
Found solely in the wall of the heart,
cardiac muscle fibres form a branching
network that contracts automatically,
without stopping or tiring, to pump
blood around the body. Stimulation
by the nervous system increases or
decreases heart rate according to
the body’s demands.
FRONT MUSCLES
Skeletal muscles are arranged in overlapping
layers, with surface muscles covering those
deeper down. Muscles at the front of the
body produce facial expressions, move the
head forwards and to the side, move the
arms forwards and bend them at the elbow,
bend the body forwards and to the side,
bend the legs at the hip, straighten the
knees, and lift the feet upwards.
Quadriceps femoris is a
group of four muscles
that straightens the
leg at the knee
Tibialis
anterior
muscle lifts
the foot
Sartorius muscle bends
the thigh at the hip
and turns it inwards
DEEP MUSCLES
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