Bones and Movement

Skull :

·                The cranium protects the brain.

·                The cranium is made of many small bones fused together.

·                Jaw bones have sockets for teeth, needed to chew food.

·                Jaw bone has hinge joint with cranium to allow chewing action of teeth.

·                Ridges on bones provide for attachment of muscles

·                Nasal cavity allows for passage of air

·                Orbits for eyes and ear sockets allow skull bones to protect the sense organs.

Ribs :

·                Ribs articulate with the thoracic vertebrae behind and the sternum in front. 

·                These structures together protect the lungs and the heart from physical damage.

·                Ribs are hollow and contain bone marrow.

·                These cavities act as the site of formation of red blood cells

·                Ribs provide attachment to intercostal muscles linked to breathing to bring about changes in the volume of the thorax, causing air to flow into and out of the lungs

Pelvis :

·                The pelvis is the last part of the vertebral column (sacrum), which is attached to and fused with the pelvic girdles.

·                The pelvic girdle provides sockets for attachment to the head of the femur, which is rounded to form a ball and socket joint.

·                The femur makes hinge joint with at the knee with the tibia and the fibula.

·                The pelvis provides attachment to the muscles which operate the legs.

·                The pelvis protects the uterus and the fetus in females.

·                It supports the upper part of the body / muscles that keep the body upright.

·                The femur and all other bones of the legs are strong and light for walking and for support.

Note : The ligament at the front of the pelvic girdle loosens during the late stage of pregnancy to allow the head of the baby to pass through.

Pectoral girdle :

·                It provides attachment to arm muscles.

·                It provides attachment to humerus.

·                It provides attachment to breathing muscles.

·                It supports the head upright.

Functions of the human skeleton:

·                It protects internal organs from mechanical injury. The cranium protects the brain, the orbits protect the eyes. The ribcage protects the heart and lungs. The spinal cord is protected by the vertebral column.

·                Bones, such as, humerus, provide attachment to voluntary muscles, such as, the biceps and triceps. Contraction of muscles pulls on bones producing movement at joints. Bones act as levers.

·                The skeleton supports the body by keeping it upright and maintains body shape. For example – vertebral column supports the skull. Pelvic girdle

·                The skeleton has girdles for limb attachment.

·                Bones are the site of formation of red and white blood cells. Red blood cells are produced in cavities of long bones, such as, in the bone marrow of the pelvis and the ribs.

·                Ribcage provides attachment to breathing muscles.

Diet for bone formation : A balanced diet is needed that contains all required nutrients (listed below) in the right amounts :

·                Bone formation requires calcium salts and phosphates to form bone tissue, that contains calcium phosphate. Lack of calcium or phosphate leads to osteoporosis, where the bones become brittle.

·                Minerals are needed to make bones hard.

·                Vitamin D in dairy products is needed for bones to absorption / uptake of calcium. Lack of vitamin D causes rickets

·                Proteins, found in meat, beans, milk, fish are needed by bones to form cytoplasm of new cells. Lack of protein leads to stunted growth.

Joints : Friction is reduced at joints in the following ways:

·                Synovial fluid present at joints lubricates them.

·                Bones are shaped to articulate with one another.

Note : Jaw joints are flexible and loose, allowing sideways movement (left to right or right to left movement)

Features of a Synovial Joint :

·                Cartilage : Cartilage is tough, smooth and slippery. It covers the end of bones. It acts as a shock absorber, and allows friction free movement.

If cartilage is worn away, increased friction causes bones to ‘scrape’ against one another.  The previously smooth surfaces become rough. Movement becomes painful and may become almost impossible / impaired.

Cartilage allows bone shaft to grow by increasing in length.

·                Ligaments : They are strong and inelastic. They join bone to bone and prevent dislocation.

·                Bones are shaped to articulate with one another.

·                Synovial Fluid : Synovial fluid acts as a lubricant by preventing contact between cartilage. It reduces friction and stops bones from rubbing against one another. It acts as a shock absorber and cushions joint. It allows smooth movement at joints by reducing friction. It is secreted by synovial membrane into the space between bones.

If synovial membrane is torn, fluid leakage causes swelling of joint and pain on movement. Loss of lubrication. So, bones may rub against each other, increasing friction.

·                Tendons : Tendons attach muscle to bone and transmit the pull of muscle contractions to bone. They are strong and inelastic. They allow muscles to move at joints.

If tendons are damaged, muscles are unable to pull on bone. So, bones cannot be moved.

Hinge Joint : Hinge joints are present at the elbow and at the knee. It prevents movement through more than 180°, that is, in one plane only, due to the presence of the olecranon process – a structure at the end of the ulna.

Ball and Socket Joint : The joints at the shoulder and the hip are ball and socket joints. They are universal as they allow movement in three planes around 360°.

Raising of the forearm at the elbow joint :

·                The biceps muscle is attached to the scapula, at the top of the humerus and to the radius via tendons.

·                The triceps muscle is attached to the humerus and to the back of the ulna via tendons.

·                When the biceps muscle contracts, tendons transmit the pull to the radius and the elbow acts as a hinge / pivot, thus raising the lower arm at the partially movable hinge joint.

·                The biceps muscle acts as a flexor.

·                The triceps muscle is stretched / relaxed.

·                The biceps and triceps muscles work in antagonistic pairs.

·                When the triceps contract, the biceps are stretched / relaxed.

·                This straightens the arm.

Differences between the cardiac and skeletal muscle :

CARDIAC	SKELETAL
Not attached to bone	Attached to bone
Muscle cells are interconnected	Not interconnected – they occur as separate fibres that bundle to form muscles
No antagonistic action	They work in antagonistic pairs
Not fatigued	Fatigued
Continuous contraction as it acts as a pump / rhythmic contraction	Contraction is not continuous / one – off
Moves fluid	Doesn’t move fluid
It does not normally operate anaerobically. So no lactic acid is accumulated.	It respires anaerobically if oxygen is short in supply in case of burst activities. Lactic acid accumulation can cause muscle cramp, fatigue and pain.

Differences between cartilage and bone :

CARTILAGE	BONE
Light and flexible as it bends	Heavy, hard, strong and rigid
No solid matrix of chondrin – it has no calcium salts	Solid impervious matrix of calcium salts
Cells are scattered	Cells in regular pattern around blood vessel
External blood vessels – no blood vessel within matrix	There are (internal) blood vessels within the matrix
Reduces friction at joints by acting as a shock absorber	Provides rigid support for muscle attachment
Contains no marrow	Contains marrow
Not attached to muscle	Attached to muscle

Differences between tendons and ligaments :

Tendons	Ligaments
Inelastic	Elastic
White fibres	More yellow fibres
Link muscle to bone	Link bone to bone