The Skeletal System

The Skeletal System

The Skeletal System serves many important functions; it provides the shape and form for our bodies in addition to supporting, protecting, allowing bodily movement, producing blood for the body, and storing minerals such as calcium.

Functions

Its 206 bones form a rigid framework to which the softer tissues and organs of the body are attached. Skeletal bones provide the body with a protective framework and provides storage for calcium.

  • Vital organs are protected by the skeletal system. The brain is protected by the surrounding skull as the heart and lungs are encased by the sternum and rib cage.
  • Bodily movement is carried out by the interaction of the muscular and skeletal systems. For this reason, they are often grouped together as the muscular-skeletal system. Muscles are connected to bones by tendons. Bones are connected to each other by ligaments. Where bones meet one another is typically called a joint. Muscles which cause movement of a joint are connected to two different bones and contract to pull them together. An example would be the contraction of the biceps and a relaxation of the triceps. This produces a bend at the elbow. The contraction of the triceps and relaxation of the biceps produces the effect of straightening the arm.
  • Blood cells are produced by the marrow located in some bones. An average of 2.6 million red blood cells is produced each second by the bone marrow to replace those worn out and destroyed by the liver.
  • Bones serve as a storage area for minerals such as calcium and phosphorus. When an excess is present in the blood, build-up will occur within the bones. When the supply of these minerals within the blood is low, it will be withdrawn from the bones to replenish the supply.

The human skeleton is divided into two distinct parts:

The axial skeleton consists of bones that form the axis of the body and support and protect the organs of the head, neck, and trunk. These bones are:

The Skull, the Sternum, the Ribs and the Vertebral Column

The appendicular skeleton is composed of bones that anchor the appendages to the axial skeleton. These bones are:

The Upper and Lower Extremities, the Shoulder and Pelvic Girdle (the sacrum and coccyx are considered part of the vertebral column)

Types of Bone

The bones of the body fall into four general categories: long bones, short bones, flat bones, and irregular bones.

  • Long bones are longer than they are wide and work as levers. The bones of the upper and lower extremities (ex. humerus, tibia, femur, ulna, metacarpals, etc.) are of this type.
  • Short bones are short, cube-shaped, and found in the wrists and ankles.
  • Flat bones have broad surfaces for protection of organs and attachment of muscles (ex. ribs, cranial bones, bones of shoulder girdle).
  • Irregular bones are all others that do not fall into the previous categories. They have varied shapes, sizes, and surfaces features and include the bones of the vertebrae and a few in the skull.

Bone Composition

Bones are composed of tissue that may take one of two forms. Compact 0r dense bone, spongy or cancellous bone. Most bones contain both types.

  • Compact bone is dense, hard, and forms the protective exterior portion of all bones.
  • Spongy bone is inside the compact bone and is very porous (full of tiny holes like chocolate aero). Spongy bone occurs in most bones.

The following charts show the main bones that you will need to have a good knowledge of.

Bones of the Skull and Face

The adult skull is usually made up of 22 bones. You can find a fibrous joint in the sutures of the skull. Many of the 22 bones are small bones that make up larger ones. The most significant to you as a therapist are:-

NamePosition
FrontalMakes up your forehead and also the roof of your eye sockets. It joins with the parietal and temporal bones
ParietalForms the roof and sides of the cranium
OccipitalSituated at the back of the cranium
TemporalSituated on both sides of the cranium
SphenoidLocated at the front of the temples and contains a sinus cavity and houses the pituitary gland
EthmoidForms the roof of the nasal passage
NasalForms the bridge of the nose
LacrimalThe most fragile bone of the face and is part of the eye socket
MaxillaForms the upper jaw and is the largest facial bone
MandibleForms the lower jaw and is the strongest of the skull
ZygomaticForm the angle of the cheeks

Within the skull, the sinuses aim to lighten and improve the voice tone, and to secrete mucus to help with air filtration. They are to be found at the frontal, ethmoid, maxilla and sphenoid bones.

Bones of the Neck, Chest, Shoulder and Spine

NamePosition
Cervical versionThe neck
HyoidU-shaped bone at the front of the neck
ClavicleSlender long bones at the base of neck
ScapulaTriangular bones in the upper back
HumerusUpper arm
SternumBreast bone

We have 7 bones in the neck, which form the cervical vertebrae. Our shoulders have 4 bones. These are 2 clavicles (collar bones) and 2 scapulae (shoulder bones).

The sternum is a dagger shaped bone located in the centre of the chest. It helps protect the heart, along with the ribs, which are thin, flat curved bones. There are 24 bones which make up the ribs, and these are arranged in 12 pairs. The function of the ribcage is to allow for inspiration and expiration.

The spine, technically called the vertebral column, consists of 33 irregular shaped bones, called vertebrae. Its main function is to house and protect the spinal cord. Arranged within 5 sections, these bones make up the 7 vertebrae of the cervical (neck) , the 12 vertebrae of the thoracic (chest), 5 lumbar (lower back), 5 that are fused to form the sacrum (back wall of pelvic girdle) and 4 coccygeal bones that form the coccyx (tail bone).

In between these vertebrae are vertebral discs which are made up of fibrous cartilage which acts as a shock absorber. Sometimes a disc may collapse. This is called a “slipped disc” and can cause intense pain as the disc presses on a nerve root. Massage may be of a great benefit if this happens.

Bones of the Arm and Hand

The forearm is made up of two bones called the Radius and Ulna, with the ulna being the larger of these two bones. The radius and ulna on the forearm form a hinge with the upper arm bone called the Humerus and this enables the arm to flex and extend.

The wrist is made up of eight individual bones called the Carpals.

The palm of the hand is made up of bones called the Metacarpals and the finger bones are called the Phalanges. The fingers are made up of three bones except for the thumb which has two.

Bones of the Leg and Foot

The tibia and the fibula are the bones that make up the lower leg. (The tibia is normally called the shinbone) the fibula forms part of the ankle joint.

Seven bones all with individual names make up the tarsals they are named Calcaneum, Talus, Cuboid, Outer Cuneiform, Middle Cuneiform, Inner cuneiform and Navicular and five Metatarsals together support the major arches of the foot.

The toes are made of phalanges like the fingers. Big toes have two phalanges and the others have three.

Joints

A joint is formed where two or more bones meet and join each other. A joint will allow movement, for example the elbow and wrist. As we discovered earlier, the bones are joined to each other by ligaments.

There are three types of joints. They are fibrous (immoveable), cartilaginous (partially moveable) and synovial (freely moveable).

Fibrous joints are held together by only a ligament, for example the teeth are held to their bony sockets. These joints are immovable, and an example would be the sutures of the skull.

Cartilaginous joints occur where the connection between the bones is made up of cartilage. An example would be between the vertebrae in the spine, which allows for some movement.

Synovial joints are the commonest and are highly moveable. They consist of two or more bones held together by a synovial capsule which surrounds the entire joint. They also have a synovial membrane which secretes synovial fluid, which acts as a lubricant. There are five types of synovial joints which are classified by the shape of the joint and the movement available. They are the ball and socket, such as the hip and shoulder, the hinge, such as the knee, the double hinge, such as the wrist, the gliding joint where bones glide on each other and the pivot joint, where one bone turns on another.

Cartilage

Cartilage is a form of dense connective tissue that covers the surface of joints and acts as a shock absorber. It is found in many areas of the body, including the knees, ribs, the nose, ear and bronchial tubes.

Growth and Repair of Bones

Bone is continually going through a system of growth and repair called ossification. There are two stages of ossification, with the first stage consisting of the cartilage being covered with a layer of Osteoblasts, which are cells that are constantly forming new bone, using calcium and other minerals. Further cells called osteoclasts then break down the calcium to prevent the bones becoming too dense whilst the bones get larger. There are also old bone cells called osteocytes which are mature cells that store the calcium of the body.

Pathologies of the Skeletal System

Postural DefectsMeaning
KyphosisExcessive curvature at the top of the spine.
ScoliosisCurvature of the spine to one side.
LordosisInward curve of the lower back.
Cervical SpondylitisArthritis of the spine in the neck.
FracturesMeaning
SimpleFracture causing little damage to the surrounding tissue. The skin remains intact.
CompoundThe bone is sticking through the skin.
ComminutedThe bone breaks into several pieces.
GreenstickThe bone is bent and broken on only one side.
ImpactedOne broken fragment is impacted into the end of another.
ComplicatedWhen the broken bone causes damage to other organs.
Skeletal DiseaseMeaning
GoutType of arthritis in one or more joints, usually the big toe.
Paget’sNormal cycle of bone renewal and repair is disrupted.
OsteoarthritisArthritis where bony spurs grow.
OsteoporosisWeak and fragile bones.
Rheumatoid arthritisArthritis that attacks the cells that line the joints.
RicketsSoftening and weakening of bones that can cause bow legs.
SclerodermaTargets the connective tissue of skin, muscles and organs.
SynovitisInflammation of the synovial membrane.
Ankylosing SpondilitisA form of inflammatory arthritis, affecting the joints of the lower back.
Systemic Lupus ErythematosusAn autoimmune disorder that can affect many parts of the body including the joints