Muscle System & Functions of Muscles in Human Body

When you are awake the muscles in your neck and back hold you and your head upright. When you nod off, those muscles relax and your head falls to one side. Muscles do more than just support you – by pulling your bones they produce every movement from lilting a pen to running a marathon.

Major muscles of our body

muscular system of human body
muscular system of human body

Orbicularis oculi: Closes the eye.

Deltoid: Raises the arm sideways and swings it backwards and forwards.

Pectoralis major: Pulls the arm forwards and towards the body.

External oblique: Bends and twists the upper body.

Quadriceps femoris: Bends the thigh at the hip and straightens the knee.

Muscles cannot attach directly to bones. instead, tendons, which are like tough cords, connect muscles with bones. Look at the back of your hand and wiggle your fingers and you will see tendons moving. Those particular ones extend all the way from muscles in the forearm to your finger bones.

Latissimus dorsi:
Pulls the arm downwards, inwards, and backwards.

Triceps brachii:
Straightens the arm from the elbow.

Gluteus maximus:
Straightens the hip by pulling the thigh back.

Straighten the thigh at the hip and bend the knee.

Pulls the Achilles tendon to point the foot downwards.

Achilles tendon

Three types on muscles

Skeletal muscle
Pulls on bones so you can move your body.

Smooth muscle
Found in the walls of hollow organs, such as the bladder.

Cardiac muscle
Found in the wall of the heart. it constantly contracts to pump blood.

What about you?

Stretch before exercise to prevent cramp, which is when a muscle stays contracted when it should have relaxed and causes pain.

Three types of fitness


Measures how efficiently your heart pumps blood.

man carrying weight

Measures how strong your muscles are.

body flexibility

Measures how flexible your joints, tendons, and muscles are.

How to: straighten and bend your arm

01. Straighten your arm with triceps muscle, which will pull your forearm downwards.

02. To bend your arm, contract (shorten) your biceps so it pulls your forearm upwards.

03. As your biceps keep contracting (feel the bulge!), relax your triceps muscle to enable your arm to keep bending from the elbow.

04. Your biceps is now fully contracted and your arm bent… time to straighten it again?

In numbers

The number of skeletal muscles in the human body.

50 cm
(20 in) The length of the longest muscle in your body, the sartorius, which is a thigh muscle.

40 – 50%
The proportion of the male body’s weight that is made up by muscles.

The proportion of the female body’s weight that is made up by muscles.

0.5 cm
(0.25 in) The length of the shortest muscle in your body, the stapedius, which is located in your ear.

Inside a muscle

inside a muscle

Muscles are made up of long cylindrical cells called fibres.

Nerve fibres:
Carry signals from the brain that make the muscle fibres contract.

Blood vessels:
Carry oxygen and food to the muscle fibres.

muscle contracts to pull bones.

bundle of parallel muscle fibres.

Five facial expressions

fear facical expression

Muscles pull the lower jaw downwards to open the mouth wide.

anger facial expression

Muscles pull the eyebrows downwards, making them wrinkle.

joy facial expression

Muscles pull and lift the corners of the mouth.

surprise facial expression

Muscles raise the eyebrows and make the forehead wrinkle.

sadness facial expression

Muscles pull the corners of the mouth downwards