Skeletal System

THE STRUCTURE OF THE SKELETON

There are four major classifications of bone in the human skeleton.

Long bones: Bones that are longer than they are wide, like a femur. These play a key part in leverage and movement.

Short bones: Bones that are box-like in shape, like tarsals. These are designed to be weight bearing.

Flat bones: Thin, plate bones that act like a shell, such as the cranium. They provide protection and a large surface to which muscles can attach.

Irregular bones: Unusually shaped bones for a unique purpose, like vertebrae. These also provide protection and a large surface to which muscles can attach.

THE FUNCTIONs OF THE SKELETON

Protection

The skeleton protects vital organs. The ribs protect the lungs & heart while the cranium protects the brain. In an exam question you would need to link this to a sports example such as a rugby player may receive a knock to the head and the cranium would protect the brain from injury and allow them to continue playing.

Blood cell production

Platelets, red & white blood cells are formed in the bone marrow. In exam questions you may need to discuss the importance of these in a sporting activity. As red blood cells carry oxygen this is the cell you need to focus on as this has an immediate effect on physical activity. Platelets and white blood cells would not be immediate but would help recover from an injury such as an abrasion.

Muscle Attachment

The skeleton offers a surface for muscles to attach to. A muscle is joined to a bone by a tendon. When a muscle is contracted it pulls on a bone to create movement.

Joints for movement:

Movement in the skeleton can only take place at a joint. A joint is where bones meet. Any sporting example is likely to require movement.

Mineral Storage:

The skeletal system stores minerals such as calcium in the bones. Minerals are essential for many functions in the human body. Calcium is particular important when contracting a muscle and phosphorus (also stored in bones) is used in energy production.

joints

A joint is a place where two or more bones meet and is also called an articulation.

The role of joints and connective tissue

Connective tissues consist of ligaments, cartilage and tendons.
A joint is held together by ligaments which give the joints their stability.
Cartilage is found at the ends of bones and where joints meet.
Tendons attach muscles to the skeleton.

Synovial joints

Synovial joints (freely movable joints) allow us the free movement to perform skills and techniques during physical activity.

Synovial joints have synovial fluid in the joint cavity that lubricates or 'oils' the joint so it moves smoothly. Synovial fluid is made by the synovial membrane.

In synovial joints, the ends of the bones are covered with cartilage (called articular cartilage) which cushions the joint and prevents friction and wear and tear between the bone ends. Cartilage is a soft, spongy connective tissue. The articular capsule prevents wear and tear on the bones.

The bones in a synovial joint are connected by ligaments, which:

are a type of connective tissue and are tough, fibrous and slightly elastic
connect bone to bone and help keep the joint together
stabilise the joints during movement and prevent dislocation by restricting actions outside the normal joint range
can absorb shock because of their elasticity, which protects the joint
help maintain correct posture and movement

The movement at a synovial joint is caused by the muscles attached across the joint. Muscles are attached to bone by tendons. Tendons are very strong, inelastic connective tissues that allow a muscle to pull on a bone to move it.

Types of synovial joints

Four of the synovial joint types are responsible for a range of sporting techniques.

Hinge - these can be found in the elbow, knee and ankle. Hinge joints are like the hinges on a door, and allow you to move the elbow and knee in only one direction. They allow flexion and extension of a joint. At the ankle, different terms are used. When the toes are pointed downwards, it is plantar flexion and when the toes are pointed upwards it is dorsiflexion.
Ball and socket - these types of joint can be found at the shoulder and hip and allow movement in almost every direction. A ball and socket joint is made up of a round end of one bone that fits into a small cup-like area of another bone.
Pivot - this joint can be found in the neck between the top two vertebrae. It allows only rotational movement such as moving your head from side to side as if you were saying 'no'.
Condyloid - this type of joint is found at the wrist. It allows you to flex and extend the joint, and move it from side to side.

Types of joint movement in the skeletal system

The different types of movement that are permitted at each joint are described below.

Flexion – bending a joint. This occurs when the angle of a joint decreases. For example, the elbow flexes when performing a biceps curl.

Extension – straightening a joint. This occurs when the angle of a joint increases, for example, at the elbow when putting a shot.

Abduction – movement away from the midline of the body. This occurs at the hip and shoulder joints during a jumping jack movement.

Adduction – movement towards the midline of the body. This occurs at the hip and shoulder, returning the arms and legs back to their original position from a jumping jack movement.

Circumduction – this is where the limb moves in a circle. This occurs at the shoulder joint during an overarm tennis serve.

Rotation – this is where the limb moves in a circular movement around a fixed joint towards or away from the midline of the body. This occurs in the hip in golf while performing a drive shot.

Plantar flexion – pointing the toes – this movement only occurs at the ankle, for example, pointing the toes in ballet.

Dorsiflexion – the foot moves towards the shin as if you are pulling your toes up. This movement only occurs at the ankle.

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