Locomotion and Movement

The One Thing

Human locomotion results from the coordinated action of the nervous system, ATP-powered muscle contraction, and the mechanical interaction of bones and joints. Muscles produce movement by contracting and pulling bones across joints; they cannot push.

Reactions, Processes and Experiments

Key Terms

• Movement: A change in position of the whole body or any body part.
• Locomotion: Movement that carries an organism from one place to another, such as walking, running, or swimming.
• Ciliary movement: Movement produced by the beating of cilia, such as the movement of particles in the respiratory tract.
• Flagellar movement: Movement produced by flagella, as seen in the movement of sperm.
• Amoeboid movement: Movement using temporary cytoplasmic projections called pseudopodia, as in Amoeba and certain white blood cells.
• Muscular movement: Movement produced by the contraction and relaxation of muscles.
• Human skeleton: The framework of bones and cartilage that supports the body, protects organs, and provides attachment for muscles.
• Axial skeleton: The skeleton along the central axis of the body, including the skull, vertebral column, ribs, and sternum.
• Appendicular skeleton: The skeleton of the limbs and the girdles that attach them to the axial skeleton.
• Bone: A hard connective tissue containing mineral salts and collagen; it provides strength, support, and protection.
• Cartilage: A flexible connective tissue found at joints, in the nose, ear, trachea, and other regions.
• Joint: A region where two or more bones meet.
• Fibrous joint: An immovable joint in which bones are connected by dense connective tissue, as in skull sutures.
• Cartilaginous joint: A slightly movable joint in which bones are joined by cartilage, as between adjacent vertebrae.
• Synovial joint: A freely movable joint containing a fluid-filled cavity, such as the knee, elbow, or shoulder.
• Ball-and-socket joint: A joint allowing movement in several directions, such as the shoulder and hip.
• Hinge joint: A joint that mainly permits movement in one plane, such as the elbow and knee.
• Pivot joint: A joint allowing rotation around an axis, such as the joint between the first two vertebrae.
• Skeletal muscle: A voluntary, striated muscle attached to bones and responsible for body movement.
• Smooth muscle: An involuntary, non-striated muscle found in organs such as the intestine and blood vessels.
• Cardiac muscle: An involuntary, striated muscle found only in the heart.
• Muscle fibre: A long, cylindrical cell of skeletal muscle containing many myofibrils.
• Myofibril: A contractile structure inside a muscle fibre made of repeating units called sarcomeres.
• Sarcomere: The basic functional unit of a striated muscle, extending from one Z-line to the next.
• Actin: A thin contractile protein filament in a sarcomere.
• Myosin: A thick contractile protein filament with heads that bind to actin and produce force.
• Sliding filament theory: The theory that muscle contracts when actin filaments slide inward over myosin filaments, shortening the sarcomere.
• Neuromuscular junction: The connection between a motor neuron and a muscle fibre where a nerve signal initiates contraction.
• Acetylcholine: A neurotransmitter released at the neuromuscular junction that stimulates a muscle fibre.
• Calcium ions: Ions released inside muscle fibres that expose binding sites on actin and allow contraction.
• ATP: The immediate energy source used by myosin heads during muscle contraction.
• Motor unit: A motor neuron and all the muscle fibres controlled by it.
• Antagonistic muscles: A pair of muscles that work in opposite directions, such as the biceps and triceps.
• Muscle fatigue: A temporary decline in the ability of a muscle to contract effectively after prolonged activity.
• Myasthenia gravis: An autoimmune disorder affecting neuromuscular transmission and causing muscle weakness.
• Muscular dystrophy: A group of inherited disorders involving progressive weakening and degeneration of skeletal muscles.
• Arthritis: A condition involving inflammation or degeneration of joints, often causing pain and restricted movement.
• Osteoporosis: A condition in which bones become weak and porous, increasing the risk of fractures.
• Gout: A painful joint disorder caused by deposition of uric acid crystals.

Easily Confused

• Movement vs locomotion: Movement is any change in position of the body or a body part; locomotion specifically changes the organism’s place.
• Tendon vs ligament: A tendon connects muscle to bone; a ligament connects bone to bone.
• Axial vs appendicular skeleton: The axial skeleton forms the central axis; the appendicular skeleton consists of the limbs and their girdles.
• Bone vs cartilage: Bone is hard and mineralised; cartilage is flexible connective tissue.
• Fibrous vs cartilaginous joint: A fibrous joint is immovable; a cartilaginous joint is slightly movable.
• Cartilaginous vs synovial joint: A cartilaginous joint is joined by cartilage; a synovial joint has a fluid-filled cavity and is freely movable.
• Skeletal vs smooth muscle: Skeletal muscle is generally voluntary and striated; smooth muscle is involuntary and non-striated.
• Skeletal vs cardiac muscle: Both are striated, but skeletal muscle is generally voluntary whereas cardiac muscle is involuntary and found only in the heart.
• Actin vs myosin: Actin is the thin filament; myosin is the thick filament with heads that bind to actin.
• Muscle fibre vs myofibril: A muscle fibre is a skeletal muscle cell; a myofibril is a contractile structure inside the fibre.
• Myofibril vs sarcomere: Myofibrils contain repeating sarcomeres; a sarcomere extends from one Z-line to the next.
• Sliding filament theory vs filament shortening: The theory states that actin and myosin slide relative to one another; their lengths remain essentially unchanged.
• Biceps vs triceps: Biceps contraction flexes the elbow; triceps contraction extends it.
• Aerobic vs anaerobic respiration: Aerobic respiration supplies much of the ATP during sustained activity; anaerobic respiration provides ATP briefly when oxygen is insufficient.
• Myasthenia gravis vs muscular dystrophy: Myasthenia gravis affects neuromuscular transmission; muscular dystrophy involves inherited progressive weakening and degeneration of skeletal muscles.
• Arthritis vs gout: Arthritis involves inflammation or degeneration of joints; gout is caused by deposition of uric acid crystals.
• Arthritis vs osteoporosis: Arthritis primarily affects joints; osteoporosis makes bones weak and porous.

What Gets Asked

• Definitions and distinctions: Questions may ask for the meanings of movement, locomotion, ciliary movement, flagellar movement, amoeboid movement, and muscular movement. Marks are lost by treating all movement as locomotion.
• Skeleton structure and functions: Questions may require the total number of adult bones, the division into 80 axial and 126 appendicular bones, or the protective roles of the skull, vertebral column, and rib cage. Marks are lost by confusing axial and appendicular skeletons.
• Joint classification: Questions may ask for examples and movement ranges of fibrous, cartilaginous, synovial, ball-and-socket, hinge, and pivot joints. Marks are lost by assigning the wrong movement type or example to a joint.
• Muscle contraction: Questions may require the sequence from nerve impulse to sarcomere shortening, including acetylcholine, calcium ions, actin, myosin, and ATP. Marks are lost by omitting calcium release or ATP-dependent myosin detachment.
• Sliding filament evidence: Questions may ask what happens to the Z-lines, I-band, H-zone, and A-band during contraction. Marks are lost by stating that actin and myosin filaments shorten; their overlap increases while their lengths remain essentially unchanged.
• Antagonistic muscles and energy supply: Questions may ask how biceps and triceps produce opposing movements or how aerobic and anaerobic respiration support contraction. Marks are lost by reversing flexion and extension or by failing to distinguish sustained aerobic supply from brief anaerobic supply.