Movement & Its Types | Science & Technology for UPSC CSE PDF Download

Body Movement

Movement is a change in the position of a body part with respect to the whole body or with respect to an external reference. Movement is a defining feature of living organisms. Examples include blinking of the eyes, breathing, eating and walking. In multicellular animals such as humans, movements become more refined during growth - for example, infants crawl, then learn to walk and run.

Most body movements are produced by the coordinated action of skeleton, joints, muscles and the nervous system. Joints are the points where two or more bones meet and they permit or restrict motion in particular directions. Muscles contract and relax to pull on bones across joints, producing movement. The nervous system controls the timing and strength of muscle contractions so that movement is smooth and purposeful.

Skeleton, Bones and Joints

Basic features

• Skeleton - a framework formed by bones that gives shape to the body and protects internal organs.
• Skull - formed by several bones fused together; it protects the brain.
• Vertebral column - made of small, disc-like bones called vertebrae (about 33 vertebrae in humans); it supports the trunk and protects the spinal cord.
• Rib cage - formed by ribs and the sternum; the ribs (12 pairs) protect thoracic organs such as the heart and lungs.
• Appendicular bones - shoulder (pectoral) bones, pelvic bones and limb bones enable locomotion and manipulation.
• Cartilage - a softer, flexible connective tissue that occurs at many joints (for example, at the tip of the nose and between ribs and sternum) and reduces friction between bones.
• Muscles - work in antagonistic pairs (one muscle contracts while the other relaxes) to move bones at joints.

Types of joints (overview)

Joints differ in structure and the type/amount of movement they allow. Major types include:

• Fibrous joints - bones joined by fibrous tissue; little or no movement (e.g., sutures of the skull).
• Cartilaginous joints - bones joined by cartilage; allow limited movement (e.g., intervertebral discs).
• Synovial joints - freely movable joints with a synovial cavity, articular cartilage and synovial fluid (e.g., shoulder, knee, hip).

Locomotion

Locomotion refers to movements that result in a change of place. Examples include walking, running, swimming and flying. Locomotion allows organisms to find food, shelter, mates and to escape predators. Different animals use different structures for locomotion:

• In unicellular organisms, cilia, flagella or pseudopodia provide propulsion.
• Invertebrates may use waves of muscle contractions, jointed appendages, bristles or a hydrostatic skeleton.
• Vertebrates use limbs, fins or wings that are supported by bones and moved by muscles.

Amoeboid and Ciliary Movements

Amoeboid movement

Amoeboid movement is a crawling-type motion produced by extension of cytoplasm as pseudopodia (false feet). It occurs in amoeba, some white blood cells (leucocytes) and other cells that migrate within tissues. The movement depends on the cytoskeleton (actin microfilaments) and coordinated polymerisation/depolymerisation of actin filaments.

Ciliary movement

Some cells and tissues show movement produced by rhythmic beating of cilia. Examples in humans include the ciliated epithelium of the trachea (which moves mucus and trapped particles out of the respiratory tract) and the fallopian tube (where ciliary action helps move the ovum). Ciliary movement also occurs in many protists (e.g., Paramecium) and in the larval stages of many invertebrates.

Cilia

Definition: Cilia are minute, hair-like projections on the surface of many eukaryotic cells.

What are cilia? Cilia are slender, membrane-bound projections built from microtubules. They may occur singly or, more commonly, in large numbers on a cell surface. Cells bearing cilia are called ciliates in the context of protists. In animals, cilia have roles in locomotion, moving fluid over cell surfaces and sensory reception.

Cilia

Flagella

Definition: Flagella are long, whip-like cellular appendages used primarily for locomotion. The word flagellum means "whip". Flagella occur in bacteria, archaea and eukaryotes, but their structure and molecular composition differ between these domains.

In eukaryotes, flagella (and cilia) have a microtubular core made of tubulin and show bending movements driven by dynein motor proteins. In bacteria, flagella are helical filaments made of the protein flagellin and are rotated by a basal motor embedded in the cell envelope.

The diagram of a sperm representing Flagella Structure at the posterior end

Bacterial flagellum - key features

• Filament - the long helical external part composed of flagellin.
• Hook - a short curved region that connects the filament to the basal body and functions as a universal joint.
• Basal body - anchors the flagellum to the cell envelopes and contains the rotary motor and rings that pass through cell wall layers.

Functions of flagella

1. Enable motility and chemotaxis - movement toward or away from chemical stimuli.
2. Act as sensory structures in some organisms, detecting environmental cues such as pH and temperature.
3. In some eukaryotes, flagella are involved in reproduction (e.g., sperm cells) and in secretory roles (for example, flagella of Chlamydomonas have been shown to participate in signalling and secretion).

Cilia and Flagella - Comparison

A comparative diagram of Cilia and Flagella

Important differences and similarities:

• Occurrence: Cilia are numerous and shorter; flagella are longer and fewer per cell.
• Structure: Eukaryotic cilia and flagella share the same microtubule arrangement (the 9+2 axoneme) and dynein motors; bacterial flagella are structurally and evolutionarily distinct, made of flagellin and rotated by a basal motor.
• Motion: Cilia typically beat in coordinated waves; eukaryotic flagella produce undulating or whip-like movements; bacterial flagella rotate to propel the cell.
• Number and placement: Cilia often cover much of a cell surface and may fuse into specialized structures (e.g., cirri); flagella are usually one or a few and often polar (at one or both ends of the cell) in eukaryotes, while bacteria may be monotrichous, lophotrichous, amphitrichous or peritrichous.

Muscular System

What is the muscular system? The muscular system is the organ system whose primary function is to produce movement of the body and to maintain posture and heat production. Humans have roughly 600-700 named muscles which, together with bones and joints, enable a wide range of movements. Muscle tissue occurs in the heart, walls of hollow organs, blood vessels and attached to the skeleton.

Types of muscle tissue

1. Cardiac muscle: Found only in the heart. It is involuntary (not under conscious control) and has a striated appearance due to organised protein filaments. Cardiac muscle cells are connected by intercalated discs which allow rapid coordinated contraction to pump blood.
2. Smooth (visceral) muscle: Found in the walls of internal organs (intestine, blood vessels, stomach, iris). It is involuntary and non-striated (smooth) in appearance. Smooth muscle contractions move contents through organs and regulate vessel diameter.
3. Skeletal muscle: Attached to bones by tendons; responsible for voluntary movements such as walking, grasping and facial expressions. Skeletal muscle fibres are long, multinucleated and striated; they contract in response to signals from motor neurons.

Types of Body Movements (names from NCERT lists)

The following movement terms describe directions or specific joint actions commonly used in anatomy and physiology. Brief definitions are given for clarity.

• Flexion - decreasing the angle between two bones (e.g., bending the elbow).
• Lateral flexion - bending of the trunk or neck to the side.
• Dorsiflexion - upward movement of the foot at the ankle joint (toes toward shin).
• Plantarflexion - downward movement of the foot at the ankle (pointing toes away from shin).
• Extension - increasing the angle between two bones (e.g., straightening the elbow).
• Hyperextension - extension beyond the normal anatomical position.
• Abduction - movement of a limb away from the midline of the body.
• Adduction - movement of a limb toward the midline.
• Transverse abduction - abduction movement in the transverse (horizontal) plane.
• Transverse adduction - adduction movement in the transverse plane.
• Rotation / Lateral rotation - turning of a bone around its own long axis away from the midline.
• Medial rotation - rotation of a bone toward the midline.
• Supination - rotation of the forearm so the palm faces anteriorly (or upward).
• Pronation - rotation of the forearm so the palm faces posteriorly (or downward).
• Protraction - moving a part of the body forward in the horizontal plane (e.g., protruding the jaw).
• Retraction - moving a part of the body backward (e.g., pulling the shoulder blades together).
• Elevation - lifting a body part superiorly (e.g., shrugging the shoulders).
• Depression - lowering a body part (e.g., dropping the shoulders).
• Inversion (reversion) - turning the sole of the foot inward.
• Eversion - turning the sole of the foot outward.
• Opposition - movement of the thumb to touch other fingers (important for grasping).

Body Movement in Other Animals

1. Earthworm

• Earthworms lack bones; their body is segmented into rings (segments) called metameres.
• Locomotion occurs by alternating contraction and relaxation of circular and longitudinal muscles.
• Hydrostatic pressure of fluid in the coelomic cavity combined with muscular waves permits extension and shortening of segments, producing forward movement.
• Earthworms secrete mucus that helps them move through soil.
• They possess tiny bristles called setae on each segment that anchor the worm during locomotion.

2. Snail

Snails have an external shell (an exoskeleton of calcium carbonate) that protects the soft body but does not aid locomotion. Locomotion is performed by a muscular foot. The foot makes slow wavelike contractions and produces a gliding motion, aided by mucus secretion.

3. Cockroach

• Cockroaches have a hard external exoskeleton made of chitin and are segmented.
• They possess three pairs of jointed legs and typically two pairs of wings; coordinated action of muscles attached to the exoskeleton enables walking, climbing and flying.

4. Fish

Fish have a streamlined body shape that reduces resistance while swimming. Propulsion is mainly produced by lateral undulations of the trunk and tail (caudal fin), and paired fins and dorsal/anal fins help with steering and stability.

5. Birds

Birds have adaptations for flight: lightweight hollow bones, strong flight muscles (especially the pectoralis major for the downstroke), feathers that form aerodynamic surfaces and a keeled sternum for muscle attachment. Wing flapping generates lift and thrust.

Types of Cilia

1. Motile cilia - occur in large numbers on the cell surface and beat rhythmically to move fluid or the cell itself. In humans they are present in the respiratory tract, where coordinated beating moves mucus and trapped particles out of the lungs.
2. Non-motile cilia (primary cilia) - usually a single, immotile cilium per cell that acts as a sensory antenna. Primary cilia coordinate many cellular signalling pathways and are important in development and organ function (for example, they sense fluid flow in kidney tubules and are involved in photoreceptor function in the retina).

Cilia - Structure

Cilia are membrane-bound projections whose core is formed by microtubules arranged as an axoneme. The typical motile axoneme has a 9+2 arrangement: nine peripheral doublets of microtubules surrounding two central singlet microtubules. Motor proteins called dyneins attached to the outer doublets produce sliding forces between microtubules, converted into bending.

The cilium is anchored in the cell by a basal body (also called a kinetosome), which has nine triplets of microtubules arranged similarly to a centriole. Typical cilia range from about 0.25 μm in diameter up to lengths of several micrometres.

Cilia - Functions

• Motile cilia move fluid and particles along epithelial surfaces (e.g., mucus clearance in airways, moving ovum in fallopian tubes).
• Primary cilia function as sensory organelles and signalling hubs that detect chemical and mechanical cues (e.g., sensing urine flow in kidney tubules, photoreception in retinal cells).
• Cilia are involved in embryonic development, cell cycle regulation and tissue homeostasis.

Cilia Disorders

• Ciliopathies - a group of genetic disorders caused by defects in cilia structure or function (basal bodies, axonemal components or associated proteins), which can affect multiple organ systems.
• Primary ciliary dyskinesia (PCD) - most commonly an autosomal recessive condition in which motile cilia beat abnormally or not at all. Consequences include impaired mucus clearance from the lungs, recurrent respiratory infections, chronic sinusitis and sometimes situs inversus (abnormal organ positioning).

Cilia - Quick facts

• Cilia are organelles present in eukaryotic cells.
• They occur in two functional types: motile cilia and non-motile (primary) cilia.
• Primary cilia act as sensory organelles.
• Cilia and eukaryotic flagella share the same basic 9+2 microtubular structure and are homologous.
• Many protists (for example, Paramecium) use cilia for locomotion and feeding.

Bacterial Flagellum - Structure in more detail

The bacterial flagellum is a helical filament driven by a rotary motor in the cell envelope. Its main parts are:

• Filament - composed of repeating units of the protein flagellin; it is the long external propeller.
• Hook - a short, curved structure that links the filament to the basal body and transmits torque while allowing the filament to act at different angles.
• Basal body - a complex of rings and a rotor-stator motor that span the cell membrane(s) and cell wall and rotate the filament. The specific rings present depend on whether the bacterium is Gram-negative or Gram-positive.

Basal body rings and location

• L-ring - found in Gram-negative bacteria; located in the outer membrane or lipopolysaccharide (LPS) layer and absent in Gram-positive bacteria (which lack an outer membrane).
• P-ring - embedded in the peptidoglycan (cell wall) layer.
• MS-ring - located in the cytoplasmic (inner) membrane and forms part of the rotor.
• C-ring - located on the cytoplasmic side; involved in switching the direction of rotation and in coupling to the motor proteins.

Types of bacterial flagellar arrangement

1. Monotrichous - a single flagellum at one pole of the cell. Reversal of rotation reverses direction of movement.
2. Peritrichous - many flagella distributed over the entire cell surface. When multiple flagella rotate counter-clockwise (CCW), they form a bundle that propels the cell forward (a run); when some flagella rotate clockwise (CW), the bundle falls apart and the cell tumbles, changing direction.
3. Lophotrichous - a cluster of flagella at one or both poles (several flagella at the same pole); reversal of rotation changes swimming direction.
4. Amphitrichous - a single flagellum at each pole; the bacterium can reverse direction by switching the rotation of the appropriate flagellum.

Summary (optional)

Movement in living organisms ranges from cellular amoeboid motion and ciliary beating to whole-body locomotion produced by coordinated interaction of bones, joints, muscles and nerves. Cilia and flagella are specialised organelles for locomotion and sensing. Muscles are specialised tissues that convert chemical energy into mechanical work, classified as cardiac, smooth and skeletal. Understanding the structures and mechanisms of movement provides a foundation for physiology, anatomy and microbiology topics relevant to life sciences and allied examinations.