Skeletal and Muscular Systems: Joints, Movements and Muscles

Skeletal System

The skeletal system provides support, protection, movement, storage for minerals and lipids, blood cell production, and energy storage.
The skeletal system is composed of bones, cartilage, ligaments and tendons.
The human skeleton is typically made up of 206 bones which can be classified as either axial (80 bones) or appendicular (126 bones).
Axial skeleton consists of the skull, vertebral column, ribs and sternum while the appendicular skeleton involves the limbs and pelvic girdle.
Bones are either categorised as long, such as the femur, short, such as the carpals, flat, such as the scapula, or irregular, such as the vertebrae.

A joint, also known as an articulation, refers to any point where two bones meet.
Joints can provide varying degrees of movement and can be functionally classified as synarthroses (immovable), amphiarthroses (slightly movable), or diarthroses (freely movable).
They can also be structurally categorised into fibrous (joined by dense connective tissue), cartilaginous (joined by cartilage), or synovial (not directly joined).
Synovial joints are enclosed by a fibrous articular capsule lined with synovial membrane and contain synovial fluid to lubricate the joint. These include hinge, pivot, saddle, plane, condyloid, and ball and socket joints.

Flexion and extension refer to decreases/increases in the angle between articulating bones, respectively.
Abduction is the motion of a structure away from the midline while adduction refers to motion towards the centre of the body.
Rotation can refer to the movement of a body part around its own axis. Rotation can be internal (toward the centre of the body) or external (away from the centre of the body).
Circumduction is the movement of a body segment in a circle.
Pronation and supination refer to rotations of the forearm, with pronation turning the hand to face downwards, while supination turns the hand to face upwards.

The muscular system is responsible for producing movement, maintaining posture, stabilising joints, and generating heat.
Muscles can be classified into three types: skeletal, cardiac, and smooth muscles.
Skeletal muscles are voluntary muscles, which contract and relax to move bones, while cardiac muscles and smooth muscles are involuntary.
Muscles work in pairs known as agonists and antagonists. The agonist is the primary muscle responsible for movement, while the antagonist opposes the agonist to provide balance.
Basic components of a muscle include muscle fibres, myofibrils, actin and myosin filaments, sarcoplasmic reticulum, and sarcolemma. These are all critical in the process of muscular contraction.