Exhaustive Keyword List with Brief Descriptions
SECTION 1: TYPES OF MOVEMENT
Locomotion: Voluntary movement that results in a change of place or location. Examples: walking, running, climbing, flying, swimming. All locomotions are movements, but not all movements are locomotions.
Movement A significant feature of all living beings. Includes a broad range of activities — from protoplasmic streaming in unicellular organisms to limb movement in humans.
Amoeboid Movement is effected by pseudopodia formed by streaming of protoplasm. Seen in Amoeba, macrophages, and leucocytes. Cytoskeletal elements like microfilaments are involved.
Ciliary Movement Coordinated movement of cilia lining internal tubular organs (e.g., trachea). Helps remove dust and foreign particles; it also facilitates the passage of ova through the female reproductive tract.
Muscular Movement: Movement of limbs, jaws, tongue, etc., requiring muscular contraction. Locomotion requires coordinated activity of muscular, skeletal, and neural systems.
Flagellar Movement: Movement produced by flagella. Helps in the swimming of spermatozoa, the maintenance of water current in sponges, and locomotion in protists like Euglena.
Pseudopodia: Temporary cytoplasmic projections in amoeboid cells used for movement and engulfing prey/particles.
SECTION 2: MUSCLE TYPES
Muscle A specialised tissue of mesodermal origin contributing 40–50% of adult body weight. Properties: excitability, contractility, extensibility, elasticity.
Skeletal Muscle Attached to skeletal components. Striated in appearance; voluntary (under nervous system control). Involved in locomotion and body posture changes.
Striated Muscle Another name for skeletal muscle, referring to its striped microscopic appearance due to alternating actin and myosin bands.
Visceral muscle is located in the walls of hollow visceral organs (the alimentary canal, reproductive tract). Non-striated (smooth), involuntary. Assists in food transport through the digestive and genital tracts.
Smooth Muscle (Non-striated Muscle). Alternative name for visceral muscle. No visible striation; not under voluntary control.
Cardiac Muscle: the muscle of the heart. Striated in appearance but involuntary. Cells branch and assemble in a branching pattern, not directly controlled by the nervous system.
Voluntary Muscles: Muscles under conscious control of the nervous system — skeletal muscles.
Involuntary Muscles: Muscles not under conscious control — visceral (smooth) and cardiac muscles.
SECTION 3: STRUCTURE OF SKELETAL MUSCLE
Muscle Bundle / Fascicle A group of muscle fibres held together by a connective tissue layer. Multiple fascicles make up a muscle.
Fascia: A common collagenous connective tissue layer that holds muscle bundles together to form an organized skeletal muscle.
Muscle Fiber (Muscle Cell): The individual cell unit of muscle. Lined by the sarcolemma, it is a syncytium containing many nuclei.
Sarcolemma: The plasma membrane lining each muscle fiber. Conducts action potentials across the muscle cell.
Sarcoplasm: The cytoplasm of the muscle fiber. Contains myofibrils, nuclei, and sarcoplasmic reticulum.
Sarcoplasmic Reticulum: The endoplasmic reticulum of the muscle fiber. Serves as a store house of calcium ions (Ca²⁺), essential for muscle contraction.
Myofibrils / Myofilaments: Parallelly arranged filaments in the sarcoplasm. Each myofibril contains alternating dark (A) and light (I) bands and is made of actin and myosin proteins.
Sarcomere: The functional unit of muscle contraction. The portion of a myofibril between two successive Z lines. Contains one A band and two half I bands.
A Band (Anisotropic Band): The dark band of the sarcomere. Contains thick myosin filaments (and overlapping actin). Retains its length during contraction.
I Band (Isotropic Band): The light band of the sarcomere. Contains only thin actin filaments. Shortens during contraction.
Z line: An elastic fiber that bisects the I band. Thin actin filaments are firmly attached to it. The distance between two Z lines defines one sarcomere.
M Line: A thin fibrous membrane in the middle of the A band that holds the thick myosin filaments together.
H Zone: The central region of the A band, not overlapped by thin actin filaments, in a resting state. Disappears during full contraction.
SECTION 4: CONTRACTILE PROTEINS
Actin: a thin filament protein. Two 'F' (filamentous) actins are helically wound to form one thin filament. F-actin is a polymer of monomeric 'G' (globular) actin.
Myosin A thick filament protein. Made of polymerized monomeric units called meromyosins. Contains ATPase activity and has binding sites for both ATP and actin.
Tropomyosin A regulatory protein running close to the F-actin throughout its length. In the resting state, it covers the active binding sites on actin.
Troponin A complex protein distributed at regular intervals on tropomyosin. A subunit of troponin masks the active sites on actin for myosin in resting state. Ca²⁺ binding removes this masking.
Meromyosin: The monomeric subunit of myosin. Each meromyosin has a globular head and a tail. Two types: Heavy Meromyosin (HMM) and Light Meromyosin (LMM).
Heavy Meromyosin (HMM): The head and short arm of meromyosin. Projects outwards from the myosin filament as a cross-arm. The globular head is an active ATPase enzyme.
Light Meromyosin (LMM): The tail portion of meromyosin. Forms the backbone of the thick myosin filament.
Cross Arm / Cross Bridge: The HMM component projecting from the myosin filament surface. Attaches to exposed active sites on actin to initiate contraction.
SECTION 5: MECHANISM OF MUSCLE CONTRACTION
Sliding Filament Theory: The accepted mechanism of muscle contraction. States that contraction of a muscle fibre takes place by the sliding of thin actin filaments over the thick myosin filaments.
Motor Neuron: A nerve cell that carries the signal from the CNS to the muscle. Along with the muscle fibers it connects, it constitutes a motor unit.
Motor Unit A motor neuron along with all the muscle fibres it innervates.
Neuromuscular Junction (Motor End Plate) The junction between a motor neuron and the sarcolemma of a muscle fibre. The site where neural signals are converted into muscle action.
Acetylcholine is the neurotransmitter released at the neuromuscular junction. Generates an action potential in the sarcolemma of the muscle fiber.
Action Potential: The electrical signal that travels across the sarcolemma into the muscle fiber, triggering Ca²⁺ release from the sarcoplasmic reticulum.
Calcium Ions (Ca²⁺) Released from sarcoplasmic reticulum upon action potential. Binds to troponin, removing masking of active sites on actin and enabling cross bridge formation.
Cross Bridge Cycle The cyclical process of cross bridge formation, rotation (power stroke), breakage, and re-cocking using ATP energy, which drives the sliding of filaments.
ATPase Enzyme activity of the myosin head. Hydrolyses ATP to ADP + Pi to provide energy for cross bridge formation and head rotation.
Muscle Relaxation Occurs when Ca²⁺ ions are pumped back into sarcoplasmic reticulum, causing re-masking of actin sites by troponin, breaking of cross bridges, and return of Z lines to original position.
Muscle Fatigue Results from repeated stimulation of muscles. Caused by accumulation of lactic acid due to anaerobic breakdown of glycogen.
Lactic Acid By-product of anaerobic glycogen breakdown in fatigued muscles, leading to a decrease in muscle performance.
Myoglobin Red-coloured oxygen-storing pigment in muscles. High content gives the muscle a reddish colour (Red fibres/aerobic muscles).
Red Fibers (Aerobic Muscles) Muscles with high myoglobin content and many mitochondria. Rely on aerobic respiration for ATP; resistant to fatigue.
White Fibres (Anaerobic Muscles) Muscles with less myoglobin, pale appearance, and fewer mitochondria. High sarcoplasmic reticulum; depend on anaerobic metabolism for energy.
SECTION 6: SKELETAL SYSTEM
Skeletal System A framework of 206 bones and a few cartilages. Significant role in body movement; divided into axial and appendicular skeletons.
Bone A specialised connective tissue with a very hard matrix due to calcium salts. Provides structural support and attachment for muscles.
Cartilage A specialised connective tissue with a slightly pliable matrix due to chondroitin salts. Found at joints and in structures like ribs.
Axial Skeleton: The 80 bones along the main axis of the body: skull, vertebral column, sternum, and ribs.
Appendicular Skeleton: Bones of the limbs and their girdles (pectoral and pelvic). Each limb is made of 30 bones.
SECTION 7: SKULL
Skull is composed of 22 bones, divided into cranial bones (8) and facial bones (14).
Cranium: The hard protective outer covering of the brain formed by 8 cranial bones.
Cranial Bones: 8 bones: Frontal, Parietal (2), Temporal (2), Occipital, Sphenoid, Ethmoid.
Facial Bones: 14 skeletal elements forming the front part of the skull, including the maxilla, Mandible, Zygomatic, Nasal, Lacrimal, etc.
Hyoid: A single U-shaped bone at the base of the buccal cavity. Not directly connected to any other bone.
Ear Ossicles: Three tiny bones in the middle ear: Malleus, Incus, and Stapes. Involved in sound transmission.
Malleus: The hammer-shaped ear ossicle connected to the eardrum.
Incus: The anvil-shaped middle ear ossicle.
Stapes The stirrup-shaped ear ossicle connecting to the oval window of the inner ear.
SECTION 8: VERTEBRAL COLUMN
Vertebral Column Formed by 26 serially arranged vertebrae. Extends from the base of the skull; protects the spinal cord, supports the head, and serves as attachment for ribs.
Vertebra Each unit of the vertebral column with a central hollow neural canal for the spinal cord.
Atlas The first cervical vertebra. Articulates with the occipital condyles of the skull (dicondylic skull).
Cervical Vertebrae 7 vertebrae in the neck region. Found in almost all mammals.
Thoracic Vertebrae 12 vertebrae in the chest region. Articulate with the ribs.
Lumbar Vertebrae 5 vertebrae in the lower back. Largest and strongest vertebrae.
Sacrum 1 fused vertebra forming the posterior wall of the pelvis.
Coccyx 1 fused vertebra at the base of the vertebral column (tailbone).
Intervertebral Disc Cartilaginous cushion between vertebrae allowing limited movement and shock absorption.
Neural Canal The hollow central portion of each vertebra through which the spinal cord passes.
SECTION 9: RIBS AND STERNUM
Sternum A flat bone on the ventral midline of the thorax. Articulates with ribs ventrally.
Ribs 12 pairs of thin flat bones connecting the thoracic vertebrae to the sternum. Each rib is bicephalic (two articulation surfaces).
True Ribs (1st–7th pairs) Directly connected to the sternum via hyaline cartilage ventrally and to thoracic vertebrae dorsally.
False Ribs / Vertebrochondral Ribs (8th–10th pairs) Do not directly articulate with sternum; join the 7th rib via hyaline cartilage.
Floating Ribs (11th–12th pairs) Not connected ventrally; free-ending.
Rib Cage Formed by thoracic vertebrae, ribs, and sternum together. Protects the thoracic organs.
SECTION 10: LIMB BONES
Humerus The single bone of the upper arm; articulates with pectoral girdle at the shoulder joint.
Radius One of two bones of the forearm (lateral side).
Ulna One of two bones of the forearm (medial side).
Carpals 8 wrist bones.
Metacarpals 5 palm bones.
Phalanges 14 finger/toe bones (digits) in each limb.
Femur The thigh bone; longest bone in the human body. Articulates with pelvic girdle at the hip joint.
Tibia The larger shin bone of the lower leg.
Fibula The smaller shin bone of the lower leg (lateral side).
Tarsals 7 ankle bones.
Metatarsals 5 foot bones.
Patella A cup-shaped bone (kneecap) covering the knee ventrally.
SECTION 11: GIRDLES
Pectoral Girdle Connects the upper limbs to the axial skeleton. Each half consists of a clavicle and a scapula.
Clavicle (Collar Bone) A long slender bone with two curvatures. Articulates with the acromion of the scapula.
Scapula A large triangular flat bone in the dorsal part of the thorax (between 2nd and 7th ribs). Has a ridge called the spine ending in the acromion.
Acromion A flat expanded process at the end of the spine of the scapula. Articulates with the clavicle.
Glenoid Cavity A depression below the acromion on the scapula. Articulates with the head of the humerus to form the shoulder joint.
Pelvic Girdle Connects the lower limbs to the axial skeleton. Consists of two coxal bones.
Coxal Bone Formed by fusion of three bones: ilium, ischium, and pubis.
Ilium The large upper part of the coxal bone.
Ischium The lower and posterior part of the coxal bone.
Pubis The anterior part of the coxal bone.
Acetabulum The cavity at the point of fusion of ilium, ischium, and pubis. Articulates with the head of the femur (hip joint).
Pubic Symphysis The joint where the two halves of the pelvic girdle meet ventrally. Contains fibrous cartilage.
SECTION 12: JOINTS
Joint A point of contact between bones, or between bones and cartilages. Acts as a fulcrum for muscle-driven movement.
Fibrous Joint No movement permitted. Bones joined by dense fibrous connective tissue in the form of sutures. Example: flat skull bones forming the cranium.
Suture A type of fibrous joint found in the skull where flat bones are joined end-to-end by dense fibrous tissue.
Cartilaginous Joint Bones joined by cartilage; allows limited movement. Example: joints between adjacent vertebrae in the vertebral column.
Synovial Joint Characterized by a fluid-filled synovial cavity between articulating bone surfaces. Allows considerable movement; most important for locomotion.
Synovial Cavity The fluid-filled space in a synovial joint that reduces friction and enables free movement.
Ball and Socket Joint A synovial joint allowing movement in multiple planes. Example: humerus and pectoral girdle (shoulder), femur and acetabulum (hip).
Hinge Joint A synovial joint allowing movement in one plane only. Example: knee joint.
Pivot Joint A synovial joint allowing rotational movement. Example: between atlas and axis vertebrae.
Gliding Joint A synovial joint allowing sliding movements. Example: between carpals.
Saddle Joint A synovial joint allowing movement in two planes. Example: between carpal and metacarpal of the thumb.
SECTION 13: DISORDERS OF MUSCULAR AND SKELETAL SYSTEM
Myasthenia Gravis An autoimmune disorder affecting the neuromuscular junction. Leads to fatigue, weakening, and paralysis of skeletal muscles.
Muscular Dystrophy Progressive degeneration of skeletal muscle, mostly due to a genetic disorder.
Tetany Rapid, wild muscle spasms (cramps) caused by low calcium (Ca²⁺) levels in body fluids.
Arthritis Inflammation of joints, causing pain, swelling, and restricted movement.
Osteoporosis An age-related disorder characterised by decreased bone mass and increased risk of fractures. Decreased oestrogen levels are a common cause.
Gout Inflammation of joints due to accumulation of uric acid crystals in joint spaces.
QUICK REFERENCE: KEY NUMBERS
Source: NCERT Biology, Chapter 17 – Locomotion and Movement (Reprint 2025–26)