CSEC PE Lecture | The human skeletal system (Part Two)
Last week, we looked at bone growth and formation, functions and types of bone in the human skeleton. We continue this week's lesson by looking on the bones of the vertebral column and the types of joints.
THE VERTEBRAL COLUMN
The vertebral column, spine or backbone consists of 33 specialised bones called vertebrae. Between each vertebra, there is a disc of cartilage that allows a small amount of movement and act as shock absorber. The vertebral column can be divided into five sections.
- Cervical vertebrae - This is the neck region and consists of seven vertebrae. They provide attachment for neck muscles and support the head and neck. The top vertebra (atlas) fits into the skull and allows nodding of the head. The second vertebra (axis) allows rotation of the head.
- Thoracic vertebrae - These are 12 vertebrae that support the ribcage and forms part of the chest area. They allow slight bending, forward, backwards and sideways.
- Lumber vertebrae - These are the five largest bones of the spine. The muscles of the back are attached to them. They allow large range of bending forward, backwards and sideways. This region can be easily injured.
- Sacral vertebrae - These five vertebrae are fused together and form a very strong base that supports the weight of the body and passes force from the legs and hip to upper body.
- Coccyx - These are five fused vertebrae. They have no special function other than for muscle attachment.
FUNCTIONS OF THE VERTEBRAL COLUMN
The vertebral column is important in all sporting movements, it is flexible, strong and allows bending and stretching into many different positions. It is also vulnerable to injury if preventative care is not taken. The vertebral column:
- Protects the spinal cord
- Supports the upper body
- Give a wide range of movement
- Is important for posture
- Passes force to the body parts
Disorders of the spine:
- Scoliosis - a sideway curvature of the spine that affects posture, causing difficulty in standing straight.
- Kypsosis - a forward bending of the spine that makes the person appear to be leaning forward.
TYPES OF JOINTS
A joint is where two or more bones meet (articulate). There are over 100 joints in the body. Joints are divided into three types based on the amount of movement they allow.
- Fixed or immovable joints (fibrous)
In these, bones are fused together by tough fibres. These types of joints are found in areas requiring strength. Examples are the joints between the plates of the cranium (skull) and the fused joints in the sacrum.
- Slightly movable joints (cartilaginous)
In these, a small amount of movement can occur. The bones are linked by cartilage. Cartilage is a tough, but flexible cushion of tissue that stops the bones from knocking together (friction) and can also compress a little to allow slight movement. Slightly movable joints are found between most of the vertebrae in the vertebral column and the joint between the ribs and sternum.
- Freely movable joints (synovial)
All freely movable joints share features which prevent friction between moving bones. One of the main features is the presence of synovial fluid between the moving bones. The bones are held together by slightly elastic fibres called ligaments, which allows the bones to move; any damage to the ligament results in the joint losing some of its strength and stability.
There are six basic types of synovial joints (freely movable):
- Ball and socket - These moves freely in all direction. Ligaments are often used to keep the joint stable. This type is only the hip and shoulders.
- Hinge - The movement of this type works like a hinged door. The movement allowed is flexion and extension. This type of joint is formed at the elbows and knee.
- Pivot - These joints allow only rotation because of its 'ring on a peg' structure. This is found between the atlas and axis vertebrae in the neck and between radius and ulna, below the elbow.
- Saddle joints - These allow movement in several planes, back, forward and side to side. Bones are shaped like saddle and fit neatly together. Example the thumb.
- Gliding - These allow slight movement in all direction, however, ligaments limit another. Examples are the carpal bones of the hand vertebrae.
- Condyloid - These allow movement in several planes, back and forward and sideways. A ligament prevents rotation. The rounded end of bones fit into the hollow of another. Examples are the wrist and ankles.
Joints work smoothly together when we perform sporting activities. They must be capable of their full range of movement in order to work well. The demands of sport puts severe stress on joints. Therefore, it is essential to warm up before an activity and cool down after the activity. Joints can be injured as a result of impact, internal forces or a mixture of both. Examples sprains, torn ligaments and dislocation.