Locomotion and Movement: NEET notes

1. Movement and locomotion

NCERT §17 (opening)

• Movement is a key feature of living things. Amoeba moves by streaming of its protoplasm; many organisms move cilia, flagella or tentacles; humans move limbs, jaws, eyelids and tongue.
• When a voluntary movement takes the organism to a new place it is locomotion. Walking, running, climbing, flying and swimming all count.
• The same structure can serve both purposes: Paramoecium's cilia move food through the cytopharynx and also move the animal, and Hydra's tentacles catch prey and help it move.
• So every locomotion is a movement, but not every movement is a locomotion.
• Animals move from place to place to find food, shelter, mates, breeding grounds or a better climate, and to escape enemies or predators.

2. Types of movement

NCERT §17.1

• Cells of the human body show three main kinds of movement: amoeboid, ciliary and muscular.
• Amoeboid movement is seen in specialised cells such as macrophages and leucocytes. Pseudopodia form by streaming of protoplasm, as in Amoeba, and microfilaments of the cytoskeleton are involved.
• Ciliary movement happens in most internal tubular organs lined by ciliated epithelium. Cilia in the trachea sweep out dust and foreign particles breathed in, and cilia help move ova along the female reproductive tract.
• Muscular movement moves limbs, jaws and tongue. Locomotion needs perfectly coordinated work by the muscular, skeletal and neural systems.
• Flagella drive the swimming of sperm, keep water flowing through the canal system of sponges and move protists such as Euglena.

3. Types of muscle

NCERT §17.2

• Muscle is a specialised tissue of mesodermal origin and makes up about 40–50 per cent of an adult human's body weight.
• Muscles show excitability, contractility, extensibility and elasticity.
• By location there are three types: skeletal, visceral and cardiac.
• Skeletal muscles are attached to the skeleton, look striped under a microscope (striated) and are under voluntary control; they bring about locomotion and changes of posture.
• Visceral muscles line the inner walls of hollow organs such as the alimentary canal and reproductive tract. They are unstriped (smooth) and involuntary, and they move food along the gut and gametes along the genital tract.
• Cardiac muscle is the muscle of the heart. Its cells join in a branching pattern; it is striated but involuntary, since the nervous system does not directly control it.

4. Structure of skeletal muscle

NCERT §17.2

• A skeletal muscle is made of many bundles, or fascicles, held together by a common layer of collagenous connective tissue called fascia; each bundle contains many muscle fibres.
• Each fibre is covered by a plasma membrane, the sarcolemma, around the sarcoplasm. The fibre is a syncytium, because its sarcoplasm holds many nuclei.
• The sarcoplasmic reticulum, the fibre's endoplasmic reticulum, stores calcium ions.
• The sarcoplasm is packed with many parallel myofibrils (myofilaments), each showing alternate dark and light bands. The stripes come from the arrangement of two proteins, actin and myosin.
• The light I band (isotropic) holds actin, the thin filaments; the dark A band (anisotropic) holds myosin, the thick filaments. Both run parallel to each other and to the fibre's long axis.
• An elastic Z line bisects each I band, and the thin filaments are anchored to it. A thin fibrous M line holds the thick filaments together at the middle of the A band.
• The stretch of myofibril between two successive Z lines is the sarcomere, the functional unit of contraction.
• At rest the ends of the thin filaments partly overlap the free ends of the thick filaments; the central part of the thick filaments left without overlap is the H zone.

5. Structure of contractile proteins

NCERT §17.2.1

• Each thin (actin) filament is made of two F (filamentous) actins twisted round each other in a helix; each F actin is a polymer of G (globular) actin monomers.
• Two filaments of tropomyosin run close to the F actins along the whole length.
• Troponin, a complex protein, sits at regular intervals on the tropomyosin. At rest one subunit of troponin covers the sites on actin where myosin would bind.
• Each thick (myosin) filament is a polymer of many monomers called meromyosins.
• A meromyosin has a globular head with a short arm, the heavy meromyosin (HMM), and a tail, the light meromyosin (LMM).
• The heads and short arms stick out from the thick filament at regular distances and angles as cross arms.
• The globular head is an active ATPase enzyme, with binding sites for ATP and active sites for actin.

6. Mechanism of muscle contraction

NCERT §17.2.2

• The sliding filament theory explains contraction: a muscle fibre shortens because the thin filaments slide over the thick filaments.
• The CNS starts contraction by sending a signal along a motor neuron. A motor neuron with the muscle fibres it supplies is a motor unit.
• The junction between a motor neuron and the sarcolemma is the neuromuscular junction, or motor end plate. There the signal releases the neurotransmitter acetylcholine, which sets up an action potential in the sarcolemma.
• The action potential spreads through the fibre and causes calcium ions to be released into the sarcoplasm.
• Ca²⁺ binds a subunit of troponin, which uncovers the active sites for myosin on actin.
• Using energy from ATP hydrolysis, the myosin head binds the exposed sites to form a cross bridge, and pulls the attached actin filaments towards the centre of the A band.
• The Z lines attached to those actins are pulled inwards too, so the sarcomere shortens. During contraction the I bands shorten while the A bands keep their length.
• The myosin head releases ADP and Pi and returns to its relaxed state; a fresh ATP binds and the cross bridge breaks. The ATP is hydrolysed again and the cycle of making and breaking cross bridges repeats, sliding the filaments further.
• This goes on until Ca²⁺ is pumped back into the sarcoplasmic cisternae, the actin sites are covered again, and the Z lines return to their original place: relaxation.

7. Red and white fibres

NCERT §17.2.2

• Reaction time varies between muscles.
• Repeated activation can build up lactic acid from the anaerobic breakdown of glycogen, which causes fatigue.
• Muscle contains myoglobin, a red pigment that stores oxygen. Muscles rich in myoglobin look reddish and are called red fibres.
• Red fibres also have plenty of mitochondria that use their stored oxygen to make ATP, so they are called aerobic muscles.
• White fibres have very little myoglobin and look pale. They have few mitochondria but a lot of sarcoplasmic reticulum, and depend on anaerobic processes for energy.

8. Axial skeleton

NCERT §17.3

• The skeletal system is a framework of bones and a few cartilages. Bone has a very hard matrix because of calcium salts; cartilage has a slightly pliable matrix because of chondroitin salts.
• The human skeleton has 206 bones and a few cartilages, grouped into the axial and the appendicular skeleton.
• The axial skeleton has 80 bones lying along the body's central axis: those of the skull, the vertebral column, the sternum and the ribs.
• The skull has 22 bones: 8 cranial bones that form the cranium around the brain, and 14 facial bones at the front. A single U-shaped hyoid lies at the base of the buccal cavity, and each middle ear has three ossicles: malleus, incus and stapes.
• The skull joins the top of the vertebral column by two occipital condyles, so it is called dicondylic.
• The vertebral column is built from 26 vertebrae on the dorsal side. Counting down from the skull: 7 cervical, 12 thoracic, 5 lumbar, then one fused sacral and one fused coccygeal. Almost all mammals, humans included, have seven cervical vertebrae.
• Each vertebra has a central neural canal for the spinal cord. The first vertebra, the atlas, articulates with the occipital condyles. The column protects the spinal cord, supports the head and gives attachment to the ribs and back muscles.
• The sternum, or breastbone, is a flat bone lying in the midline on the front (ventral) side of the thorax.
• Humans have 12 pairs of ribs. Every rib is a thin, flat bone; at the back it joins the vertebral column and at the front the sternum. Its dorsal end carries two articular surfaces, so it is called bicephalic.
• The first 7 pairs are true ribs, joined to the sternum by hyaline cartilage. Pairs 8, 9 and 10 join the seventh rib through hyaline cartilage instead of the sternum: vertebrochondral or false ribs. Pairs 11 and 12 have no ventral connection: floating ribs.
• The thoracic vertebrae, the ribs and the sternum make up the rib cage between them.

9. Appendicular skeleton

NCERT §17.3

• The appendicular skeleton is the bones of the limbs together with their girdles. Each limb has 30 bones.
• Fore limb: humerus, radius and ulna, 8 carpals (wrist), 5 metacarpals (palm) and 14 phalanges (digits).
• Hind limb: femur (the longest bone), tibia and fibula, 7 tarsals (ankle), 5 metatarsals and 14 phalanges. A cup-shaped patella, the knee cap, covers the knee on its ventral side.
• The pectoral and pelvic girdles join the upper and lower limbs to the axial skeleton; each girdle has two halves.
• Each half of the pectoral girdle has a clavicle and a scapula. The scapula is a large triangular flat bone on the dorsal thorax between the second and seventh ribs.
• The scapula's raised ridge, the spine, ends in a flat expanded acromion, with which the clavicle articulates. Just below the acromion lies the glenoid cavity; the humerus head fits into it, making the shoulder joint.
• The clavicle, or collar bone, is a long slender bone with two curves.
• The pelvic girdle has two coxal bones, each formed by fusion of the ilium, ischium and pubis. At the point of fusion is the acetabulum, the cavity into which the thigh bone fits.
• The two halves of the pelvic girdle meet ventrally at the pubic symphysis, which contains fibrous cartilage.

10. Joints

NCERT §17.4

• A joint is a place where two bones meet, or a bone meets a cartilage; no bony part of the body can move without one.
• Muscles generate the force, and the joint acts as the fulcrum for the movement.
• By structure there are three kinds: fibrous, cartilaginous and synovial.
• Fibrous joints allow no movement. Example: the sutures, dense fibrous tissue joining the flat skull bones end to end to form the cranium.
• In cartilaginous joints the bones are held together by cartilage. Example: the joints between adjacent vertebrae, which permit limited movement.
• Synovial joints have a fluid-filled synovial cavity between the two articulating surfaces and allow considerable movement, so they matter most for locomotion.
• Synovial joint examples: ball and socket (humerus and pectoral girdle), hinge (knee), pivot (atlas and axis), gliding (between the carpals) and saddle (carpal and metacarpal of the thumb).

11. Disorders of muscular and skeletal system

NCERT §17.5

• Myasthenia gravis: an autoimmune disorder of the neuromuscular junction, causing fatigue, weakening and paralysis of skeletal muscle.
• Muscular dystrophy: skeletal muscle wastes away progressively, in most cases because of a genetic disorder.
• Tetany: rapid spasms (wild contractions) of muscle caused by low Ca²⁺ in body fluid.
• Arthritis: inflammation of joints.
• Osteoporosis: an age-related disorder with reduced bone mass and higher chances of fractures; lower oestrogen is a common cause.
• Gout: inflammation of joints due to build-up of uric acid crystals.

Must-know facts

1. All locomotions are movements, but not all movements are locomotions.
2. Three cell movements in humans: amoeboid (macrophages, leucocytes), ciliary (trachea, oviduct), muscular.
3. Muscle is mesodermal and about 40–50 per cent of adult body weight.
4. Skeletal: striated, voluntary. Visceral: smooth, involuntary. Cardiac: striated, branched, involuntary.
5. Muscle → fascicles (held by fascia) → muscle fibres (sarcolemma, syncytium) → myofibrils → sarcomeres.
6. Sarcoplasmic reticulum stores Ca²⁺.
7. I band: actin (thin), light. A band: myosin (thick), dark. Z line bisects I band; M line in middle of A band; H zone is thick filament not overlapped.
8. Sarcomere = Z line to Z line, the functional unit of contraction.
9. Thin filament: 2 F actins (polymers of G actin) + 2 tropomyosin filaments + troponin at intervals.
10. Meromyosin: HMM (head + short arm) and LMM (tail). Head is an ATPase with ATP binding sites and actin sites.
11. Contraction order: motor neuron → acetylcholine at motor end plate → action potential → Ca²⁺ released → Ca²⁺ binds troponin → actin sites exposed → cross bridge (ATP energy) → actin pulled to centre of A band → sarcomere shortens.
12. During contraction I band and H zone shorten; A band length stays the same.
13. Relaxation: Ca²⁺ pumped back into sarcoplasmic cisternae, actin sites masked, Z lines return.
14. Red fibres: much myoglobin, many mitochondria, aerobic. White fibres: little myoglobin, few mitochondria, much sarcoplasmic reticulum, anaerobic.
15. 206 bones: axial 80, appendicular 126 (limbs 120 + girdles 6).
16. Skull 22 (8 cranial + 14 facial); plus 1 hyoid and 3 ossicles per ear.
17. Vertebrae 26: cervical 7, thoracic 12, lumbar 5, sacral 1, coccygeal 1.
18. Ribs: 12 pairs; 7 true, 3 false (vertebrochondral), 2 floating; bicephalic.
19. Each limb 30 bones. Hand: 1+1+1+8+5+14. Leg: 1+1+1+7+5+14+patella.
20. Coxal bone = ilium + ischium + pubis; acetabulum takes the femur. Glenoid cavity takes the humerus.
21. Joints: fibrous (sutures, no movement), cartilaginous (vertebrae, limited), synovial (considerable).
22. Synovial: ball and socket (shoulder), hinge (knee), pivot (atlas/axis), gliding (carpals), saddle (thumb carpal–metacarpal).

Common traps

Key terms

Locomotion

A voluntary movement that changes the organism's place.

Amoeboid movement

Movement by pseudopodia formed by protoplasmic streaming, as in macrophages and leucocytes.

Ciliary movement

Coordinated beating of cilia in tubular organs such as the trachea and oviduct.

Fascicle

A bundle of muscle fibres inside a skeletal muscle.

Fascia

Collagenous connective tissue layer holding the fascicles of a muscle together.

Sarcolemma

The plasma membrane of a muscle fibre.

Syncytium

A cell mass with many nuclei in one cytoplasm, as in a muscle fibre.

Sarcoplasmic reticulum

The endoplasmic reticulum of a muscle fibre; stores calcium ions.

Sarcomere

The part of a myofibril between two Z lines; the functional unit of contraction.

I band

Light, isotropic band containing thin actin filaments; shortens on contraction.

A band

Dark, anisotropic band containing thick myosin filaments; keeps its length on contraction.

H zone

Central part of the thick filaments not overlapped by thin filaments.

Tropomyosin

Protein running in two filaments along the F actins of a thin filament.

Troponin

Complex protein on tropomyosin whose subunit masks actin's myosin binding sites at rest.

Meromyosin

The monomer of the thick filament, with a head and short arm (HMM) and a tail (LMM).

Cross bridge

The link formed when a myosin head binds an exposed active site on actin.

Motor unit

A motor neuron together with the muscle fibres it supplies.

Neuromuscular junction

Motor end plate: where a motor neuron meets the sarcolemma.

Myoglobin

Red oxygen-storing pigment of muscle, abundant in red fibres.

Dicondylic skull

A skull that joins the vertebral column by two occipital condyles.

Bicephalic rib

A rib with two articular surfaces at its dorsal end.

Acetabulum

Cavity in the coxal bone where the femur articulates.

Glenoid cavity

Depression below the acromion of the scapula where the humerus articulates.

Synovial joint

A joint with a fluid-filled cavity between the bones, allowing considerable movement.

Tetany

Rapid muscle spasms caused by low Ca²⁺ in body fluid.

Osteoporosis

Age-related loss of bone mass with more fractures; low oestrogen is a common cause.