The Skeletal System
Cervical region – the main function of the cervical spine is to support the weight of the head
Thoracic region –the main function of the thoracic spine is to protect the organs of the chest by providing attachment for the rib cage.
Lumbar region –the main function of the lumbar spine is to bear the weight of the body.
Sacral region –the main function of the sacrum is to provide attachment for the iliac (hip) bones and protect the pelvic organs.
Coccyx region –the four fused bones of the coccyx or tailbone don’t really have a function. It is an embryology remnant of a tail from our primate ancestors.
Types of Bones
Long Bones – These have a greater length than width, with growth plates (epiphysis) at either end, having a hard outer surface of compact bone and a spongy inner known as cancellous bone containing bone marrow. Examples of long bones would be: Tibia, Fibula, Femur, Humerus. But even some of the smallest bones in the body such as: Metacarpals, Metatarsals and Phalanges are long bones.
Short Bones – These are approximately as wide as they are long. The primary function of short bones is to provide support and stability with little movement. They consist of cancellous (spongy) bone surrounded in a thin layer of compact bone. Examples of short bones include: Tarsals and Carpals.
Flat Bones – These have a spongy middle between two layers of compact bone. They are found in areas which need protection and also in parts where broad muscle attachment is needed. In adults, the highest numbers of red blood cells are formed in flat bones. Examples of flat bones would include: Scapula, Sternum and Cranium. The Pelvis and Ribs are also classed as flat bones.
Irregular Bones – These bones do not fit into any category. They have lots of projections and grooves from which lots of muscles and ligaments attach. They primarily consist of cancellous (spongy) bone, with a thin outer layer of compact bone. Examples of Irregular bones would consist of: the Vertebrae, Sacrum and Mandible.
Sesamoid Bones – These resemble the shape of a sesame seed. They are small bones wrapped in tendons and give extra protection to joints. Examples of sesamoid bones would be the Patella and the base of the thumb.
Function of Skeletal System
1. Support - The skeleton is the framework of the body, it supports the softer tissues and provides points of attachment for most skeletal muscles.
2. Protection - The skeleton provides mechanical protection for many of the body's internal organs, reducing risk of injury to them. For example, cranial bones protect the brain, vertebrae protect the spinal cord, and the ribcage protects the heart and lungs.
3. Movement - Skeletal muscles are attached to bones, therefore when the associated muscles contract they cause bones to move.
4. Storage of Minerals - Bone tissues store several minerals, including calcium (Ca) and phosphorus (P). When required, bone releases minerals into the blood - facilitating the balance of minerals in the body.
5. Production of Blood Cells - Blood cells are made in the bone marrow by 'stem' cells. The bone marrow is the soft 'spongy' material in the centre of bones. The large flat bones such as the Pelvis and Sternum contain the most bone marrow.
6. Storage of Chemical Energy - With increasing age some bone marrow changes from 'red bone marrow' to 'yellow bone marrow'. Yellow bone marrow consists mainly of adipose cells, and a few blood cells. It is an important chemical energy reserve.
The skeleton of a newborn baby is made up of more than 300 parts, most of which are made of cartilage. Over time, most of this cartilage turns into bone, in a process called ossification. As the baby grows, some of its bones fuse together to form bigger bones. By adulthood, your skeleton contains just 206 bones. A long bone, such as your femur, grows in length at either end in regions called epiphyseal plates (growth plates) by a process that is similar to endochondral ossification (Endochondral ossification involves the replacement of hyaline cartilage with bony tissue. Most of the bones of the skeleton are formed this way). Growth occurs when cartilage cells divide and increase in number in these growth plates. These new cartilage cells push older, larger cartilage cells towards the middle of a bone. Eventually, these older cartilage cells die and the space they occupied is replaced with bone. When a bone has reached its full size, its growth plates are converted into bone. Long bone growth comes to an end around the end of puberty. When long bone growth stops, you stop getting taller.
The Axial and Appendicular Skeleton
The axial skeleton and the appendicular skeleton together form the complete skeleton.
The Axial Skeleton
The axial skeleton consists of the 80 bones along the central axis of the human body. It is composed of six parts; the human skull, the ossicles of the middle ear, the hyoid bone of the throat, the rib cage, sternum and the vertebral column.
The word "Axial" is taken from the word "axis" and refers to the fact that the bones are located close to or along the central axis of the body.
The Appendicular Skeleton
The appendicular skeleton is made of 126 bones in the human body. The word appendicular is the adjective of the noun appendage, which itself means a part that is joined to something larger. Functionally it is involved in locomotion (Lower limbs) of the axial skeleton and manipulation of objects in the environment (Upper limbs).
Fixed Joints - Some of your joints are fixed and don't allow any movement. A good example of this is your Cranium. The bones in your Cranium are held together with fibrous connective tissue.
Slightly Movable Joints - Other joints, such as those between the vertebrae, which are connected to each other by pads of cartilage, can only move a small amount.
Synovial Joints - Most of your joints are synovial joints. They are movable joints containing a lubricating liquid called synovial fluid. Synovial joints are predominant in your limbs where mobility is important. Ligaments help provide their stability and muscles contract to produce movement. The most common synovial joints are: * Gliding Joint – Allows one bone to slide over another. Gliding joints occur between the surfaces of two flat bones that are held together by ligaments. Some of the bones in your wrists and ankles move by gliding against each other.
* Hinge Joint – Allows movement similar to a hinge. It has a convex and concave surface and allows movement in one plane about a single axis. It allows the movements of flexion and extension. The knee and elbow joints are good examples of hinge joints.
* Ball & Socket - Ball and socket joints are the most mobile type of joint in the human body. It allows flexion, extension, rotation, abduction, adduction and circumduction. Good examples of the ball & socket joint are the hip and shoulder. Hip bone
* Condyloid – This allows movement in two planes and can produce flexion, extension, abduction and adduction movements. The wrist is a clondyloid joint.
* Transverse ligament
Pivot – This joint allows rotation and movement in one plane about one axis. An example of this joint can be found between the atlas and axis of the neck.
* Saddle – This joint allows movement in one plane and one axis. A limited amount of rotation and sliding can occur. The thumb is an example of a saddle joint.