There are 2 divisions that make up the skeletal system. These are the axial skeleton and the appendicular skeleton. The axial skeleton consists of the cranium, ribs, sternum and the vertebrae. The appendicular skeleton consists of the upper limbs (arms), lower limbs (legs), pectoral girdle and pelvic girdle.
In our everyday life, the skeleton has 5 purposes:
- Protection: a rigid structure to protect vital organs on impact.
- Support: a rigid structure which tissue attaches onto and keeps the body in shape and upright.
- Cell production: bone marrow produces blood cells, mainly red blood cells.
- Movement: rigid structure with joints that act as levers and allow us to move.
- Mineral reserve: substances such as fats and minerals can be stored within the bones for later use.
There are 5 types of bones within the human body. These are:
- Long: longer than they are wide. (e.g. the femur and the humerous)
- Short: as wide as they are long (e.g. the carpals and tarsals)
- Flat: flat and protect another structure (e.g scapula and ribs)
- Irregular: no common characteristics (e.g the vertebrae)
- Sesamoid: contained within a tendon (e.g. the patella and in the sole of the foot)
Within these types of bones, there are also 2 types of boney material; these are called cancellous bone and compact bone. Cancellous bone is mainly for red cell production. It is soft and spongy with low density and a high surface area. Compact bone is strong and stops bone crumpling under pressure. It is hard and smooth, and has a high density.
Task Two
Each joint in the human body can be put into one of three categories; synovial, fibrous and cartilegenous. These 3 categories are all very different to each other:
Synovial - Most of the joints in the body are synovial joints. These joints are "freely moveable" and are characterised by being surrounded by an articular capsule which contains the synovial fluid. Synovial fluid lubricates the joints, supplies nutrients to the cartilage and it contains cells that remove microbes and debris within the joint cavity. Because of the larger range of movements of these joints, there is an increased risk of injury.
Fibrous - These joints are also called "fixed" or "immoveable" joints, because they do not move. These joints have no joint cavity and are connected via fibrous connective tissue.
Cartilegenous - These joints also have no joint cavity and the bones are connected tightly to each other with cartilage. These joints only allow a small amount of movement, so are also called "partly" or "slightly moveable" joints.
This table shows examples of the three joint categories:
The category of synovial joints has six different types:
- Ball and socket: This is a ball and a socket which allow bones to move freely in all directions. Ligaments are often used to keep the joint stable. (e.g. the shoulder and the hip)
- Ellipsoid: movement is avaible in two planes, the rounded end of one fits into the hollow end of another. It can move backwards/forwards, side to side, and can rotate. (e.g. in the wrist)
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Hinge: Movement in one plane only, which means it will open until it is straight. Movement is limited because of the shape of the bones and the position of kmmmmmmmmkkk ligaments. (e.g. the elbow and the knee)
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Pivot: this is two ‘discs’ on top of each other. Only rotation is possible because it has a ‘ring on a peg’ structure. (e.g. in the neck)
- Saddle: this joint is more versatile than the hinge joint and the gliding joint, it allows movement forwards, backwards and side-to-side. The saddle joint gives the thumb the ability to “cross over” the palm of the hand. (e.g. in the thumb)
- Gliding: One bone slides on top of another which means little movement is possible in all directions, ligaments limit the movement. (e.g. in the fingers)
Each of these groups of synovial joints have different types of joint movement. These are called flexion, extension, hyperextension, rotation, circumduction, plantar flexion, dorsiflexion, eversion, inversion, pronation, supination, adduction and abduction.
- Flexion is bending at a joint to decrease the angle.
- Extension is straightening at a joint to increase the angle.
- Hyperextension is extending beyond the anatomical position.
- Dorsiflextion is bending the foot upwards.
- Plantar flexion is bending the foot downwards.
- Abduction is moving a part of the body away from the midline.
- Adduction is moving a part of the body toward the midline.
- Rotation is moving a joint around an axis.
- Circumduction is moving a part of the body following a circular path.
- Supination is turning the palm upwards.
- Pronation is turning the palm of the hand downward.
- Eversion is turning the foot to face outward.
- Inversion is turning the foot to face inward.
The range of movement for each synovial joint are shown in this table: