Skeletal and Muscular Systems

• The skeletal and muscular systems are interlinked, relating to movement, structure, and function.

Skeletal System

• Provides the body's framework, protects organs, and facilitates movement.
• Adult skeletons consist of 206 bones.
• Functions include support, protection, movement, mineral storage (calcium and phosphorus), and blood cell production (hematopoiesis in bone marrow).
• The axial skeleton includes the skull, vertebral column, ribs, and sternum.
• The appendicular skeleton includes the limbs (humerus, femur, etc.) and pelvis.

Muscular System

• Enables movement through contraction, pulling on bones.
• Comprises over 600 muscles classified as skeletal, smooth, and cardiac.
• Functions include voluntary and involuntary movements, posture maintenance, and heat production.

Major Bones and Synovial Joints

• Major bones include the skull, vertebrae, ribs, humerus, femur, tibia, and fibula.
• Synovial joints, such as the knee, elbow, shoulder, and hip joints, allow a wide range of motion.

Synovial Joint Structure

• Synovial membrane secretes synovial fluid for lubrication, reducing friction due to articular cartilage covering bone surfaces.

Joint Actions

• Flexion: Decreases the angle at a joint (e.g., bending the knee or elbow).
• Extension: Increases the angle at a joint (e.g., straightening the knee or elbow).
• Abduction: Movement away from the midline (e.g., raising arms sideways).
• Adduction: Movement toward the midline (e.g., lowering arms back).
• Rotation: Twisting movement around an axis (e.g., turning the head).

Types of Joints

• Hinge Joints: Allow flexion and extension (e.g., elbow, knee).
• Ball-and-Socket Joints: Allow multi-directional movement (e.g., shoulder, hip).
• Pivot Joints: Allow rotation (e.g., neck).
• Gliding Joints: Allow sliding movements (e.g., wrist).

Characteristics and Functions of Muscle Fibres

• Slow Twitch Muscle Fibres (Type I): Endurance-oriented, fatigue-resistant, efficient in using oxygen, rich in mitochondria and myoglobin, ideal for prolonged activities like marathon running.
• Fast Twitch Muscle Fibres (Type II): Power-oriented, quick to fatigue, generate more force, fewer mitochondria, suited for short bursts of power like sprinting or weightlifting.

Types of Muscle Contractions

• Isotonic Contractions:
  • Concentric: Muscle shortens while generating force (e.g., lifting a weight).
  • Eccentric: Muscle lengthens while controlling force (e.g., lowering a weight).
• Isometric Contractions: Muscle generates force without changing length (e.g., holding a weight steady or pushing against a wall).

Muscle Relationships

• Agonist: The primary muscle responsible for movement (e.g., biceps during elbow flexion).
• Antagonist: The muscle that opposes the agonist (e.g., triceps during elbow flexion).
• Stabiliser: Muscles that stabilise a joint during movement (e.g., rotator cuff muscles).

Motion

• Linear Motion: Movement along a straight line (e.g., running).
• Angular Motion: Movement around an axis (e.g., a gymnast rotating).
• General Motion: Combination of linear and angular motion (e.g., cycling).

Velocity, Speed, Acceleration and Momentum

• Velocity: The rate of change of displacement; includes direction (vector quantity).
• Speed: Distance covered per unit time (scalar quantity).
• Acceleration: The rate of change of velocity.
• Momentum: The product of mass and velocity (momentum = mass × velocity).

Balance and Stability

• Centre of Gravity: The point where the body's mass is concentrated; affects balance and varies with body position.
• Line of Gravity: An imaginary vertical line that passes through the centre of gravity; affects stability and should fall within the base of support for optimal balance.
• Base of Support: The area beneath an object that includes all points of contact with the ground; a larger base increases stability.