Locomotion and Movement Class 11 Notes

Movement ranges from gross movement of the whole body to extremely small movements such as those of the eye. NCERT recognises three main modes of movement, all of them ultimately driven by the contraction and relaxation of muscle cells.

The skeletal system is made of bone and cartilage, both of which are types of specialised connective tissue. It performs a fixed set of functions that should be memorised together, because they are asked directly.

• Support — gives the body shape and holds the body upright.
• Protection — the cranium guards the brain, the rib cage guards the heart and lungs, the vertebral column guards the spinal cord.
• Locomotion — the limbs act as levers, with muscles supplying the force.
• Storage — mineral reservoir for calcium and phosphate; the bone marrow is the site of blood cell production.

Bone is a dynamic, living tissue. The cells of cartilage are chondrocytes, and the matrix of cartilage contains chondroitin sulphate. The cells of bone are osteocytes, which lie in small spaces called lacunae and are connected by canaliculi. The matrix is organic, made of collagen protein, and mineralised with hydroxyapatite, which is what gives bone its hardness.

• Long bones — humerus, radius, ulna, femur, tibia, fibula; act as levers.
• Short bones — carpals in the wrist and tarsals in the ankle; provide stability and fine movement.
• Flat bones — ribs, sternum, clavicle; protect organs and provide muscle attachment.
• Irregular bones — hip bone, sacrum, and the bones of the face; have an irregular shape.

The axial skeleton has 80 bones and forms the body axis. The appendicular skeleton has 126 bones and includes the limb bones together with the pectoral and pelvic girdles that anchor them.

The cranium has 8 bones: one frontal, two parietal, one occipital, two temporal, one sphenoid and one ethmoid. The face has 14 bones: two maxilla, two zygomatic, two nasal, two lacrimal, two palatine, two inferior nasal concha, one vomer and one mandible. The hyoid is the only bone in the body that does not articulate with any other bone.

The pectoral girdle is made of two clavicles and two scapulae. Each upper limb then contains a humerus, a radius, an ulna, eight carpals, five metacarpals and fourteen phalanges, giving 30 bones. The pelvic girdle is made of two innominate or coxal bones, and each lower limb contains a femur, a patella, a tibia, a fibula, seven tarsals, five metatarsals and fourteen phalanges, again 30 bones.

The vertebral column is dorsally placed and is formed of 33 vertebrae. In adults the five sacral vertebrae fuse to form the sacrum and the four coccygeal vertebrae fuse to form the coccyx, so 26 vertebrae remain separate.

• Cervical vertebrae, 7 — the atlas and axis are special; the first cervical vertebra is the atlas, the second the axis, and the axis permits the nodding of the head.
• Thoracic vertebrae, 12 — each articulates with a pair of ribs, and most carry costal facets on the body and on the transverse processes.
• Lumbar vertebrae, 5 — the stoutest, with a massive body suited to bearing load, and no costal facets.
• Sacrum, fused — formed by 5 fused vertebrae, articulating with the pelvic girdle at the sacroiliac joint.
• Coccyx, fused — formed by 4 fused vertebrae, the vestigial tail.

There are 12 pairs of ribs. Ribs one to seven are true or vertebrosternal ribs, joined directly to the sternum by their own costal cartilages. Ribs eight to ten are false or vertebrochondral, joining the sternum only through the cartilage of the rib above. Ribs eleven and twelve are floating ribs, attached only to the vertebral column and carrying no sternal connection.

The sternum is a flat bone, ventral to the heart, and has three parts: the manubrium, the body, and the xiphoid process.

A joint is the region where two bones meet. Joints are classified by the tissue present between the articulating bones and by the degree of movement they permit, giving three groups.

There are three types of muscle tissue, distinguished by the presence of striations, the control of their activity, and the shape and number of their nuclei. Learn this table by heart, since almost every question compares these three.

• Skeletal muscle — striated and voluntary; long, unbranched, cylindrical, multinucleate; attached to bones; rich in sarcoplasmic reticulum; myoglobin present; fatigues readily.
• Smooth muscle — non-striated and involuntary; spindle-shaped, unbranched, uninucleate; found in the walls of the gut, the blood vessels, the bronchi, the iris and the ureters; drives peristalsis; does not fatigue.
• Cardiac muscle — striated but involuntary; cylindrical, branched and uninucleate; has intercalated discs; present only in the heart; contracts rhythmically at about 70 to 75 beats per minute from an intrinsic myogenic rhythm.

Muscles are named according to their site of action. The name is prefixed by the origin, suffixed by the insertion, and additionally by the number of heads, the orientation and the region. Biceps brachii means a muscle with two heads, placed in the arm region.

• Number of heads — biceps, triceps, quadriceps.
• Orientation — rectus means straight, oblique means slanting, transversus means across.
• Region — brachii for the arm, glutei for the gluteal region, pectoralis for the chest.

A muscle is supplied by a motor nerve, and a motor unit consists of one motor neuron together with all the muscle fibres that it innervates. At the neuromuscular junction the nerve releases the neurotransmitter acetylcholine, which depolarises the sarcolemma. Calcium is then released from the sarcoplasmic reticulum and the contraction cycle begins.

A muscle cell contains many myofibrils running along its length. Each myofibril is built of repeating units called sarcomeres, delimited by Z lines. The sarcomere is the contractile unit, and the sliding filament theory explains how it shortens.

A sarcomere contains thin filaments of actin, with tropomyosin and troponin distributed on them, and thick filaments of myosin. The thin filaments attach to the Z line, the thick filaments lie in the centre of the sarcomere, and the M line holds the thick filaments together. The I band contains only thin filaments, the A band contains the thick filaments, and the H zone contains only thick filaments.

• ATP binds to the myosin head and energises it, releasing ADP and inorganic phosphate.
• The energised head attaches to actin, forming a cross bridge, and then pulls the actin towards the centre.
• The head releases the actin only when a fresh ATP binds to it, so rigor mortis follows ATP depletion.
• Calcium released from the sarcoplasmic reticulum binds troponin, which shifts tropomyosin off the myosin binding sites on actin.

During vigorous exercise the muscle faces an oxygen debt, because the rate of energy demand far exceeds the rate of aerobic supply. Extra glucose is broken down anaerobically to lactic acid, which causes muscle fatigue. When oxygen becomes available again the lactic acid is reconverted to glucose in the liver, which is then taken up by the muscle, and this recycling is called the Cori cycle.

The disorders listed here are all caused by a fault in the muscle, the joint, the nerve supply or the metabolism, and each is named in NCERT as a candidate for a one-mark question.

• Muscular dystrophy — a genetic progressive wasting of the muscle, with the replacement of muscle fibres by fibrous tissue, so the muscle weakens continuously.
• Parkinson's disease — degeneration of the basal ganglia of the brain, producing tremor, a shuffling gait, a masked expression and rigidity.
• Tetany — rapid involuntary contraction of the muscles caused by a fall in blood calcium, often following an upset in the calcium and phosphate balance.
• Arthritis — inflammation of the joints, with swelling, pain and stiffness, so that the joint becomes difficult to move.
• Osteoporosis — a loss of bone mass, with the bones becoming porous and brittle and therefore prone to fracture, especially in elderly women.

Exercises (NCERT Q1–Q10)

• 1) Draw the diagram of a sarcomere of skeletal muscle showing different regions.
• 2) Define sliding filament theory of muscle contraction.
• 3) Describe the important steps in muscle contraction.
• 4) Write true or false. If false change the statement so that it is true. (a) Actin is present in thin filament (b) H-zone of striated muscle fibre represents both thick and thin filaments. (c) Human skeleton has 206 bones. (d) There are 11 pairs of ribs in man. (e) Sternum is present on the ventral side of the body.
• 5) Write the difference between : (a) Actin and Myosin (b) Red and White muscles (c) Pectoral and Pelvic girdle
• 6) Match Column I with Column II : (a) Smooth muscle (i) Myoglobin (b) Tropomyosin (ii) Thin filament (c) Red muscle (iii) Sutures (d) Skull (iv) Involuntary
• 7) What are the different types of movements exhibited by the cells of human body?
• 8) How do you distinguish between a skeletal muscle and a cardiac muscle?
• 9) Name the type of joint between the following:- (a) atlas/axis (b) carpal/metacarpal of thumb (c) between phalanges (d) femur/acetabulum (e) between cranial bones (f) between pubic bones in the pelvic girdle
• 10) Fill in the blank spaces: (a) All mammals (except a few) have __________ cervical vertebra. (b) The number of phalanges in each limb of human is __________ (c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely __________ and __________. (d) In a muscle fibre Ca²⁺ is stored in __________ (e) __________ and __________ pairs of ribs are called floating ribs. (f) The human cranium is made of __________ bones.

Answers at a glance

1. 1
   Q1 → One sarcomere runs Z line to Z line (about 2.0–2.5 µm) and contains, at each end, an I band made of thin actin filaments only, and centrally a dark A band whose middle portion is the H zone containing thick myosin filaments only. A labelled sketch should also show that the A band equals the full length of a myosin filament and that the I band contains no myosin.
2. 2
   Q2 → Sliding filament theory states that muscle contraction is caused by the thin (actin) filaments sliding over the thick (myosin) filaments so that their degree of overlap increases. The filaments do not shorten; the I band and H zone narrow while the A band remains constant, and the Z lines are pulled toward one another, shortening the sarcomere.
3. 3
   Q3 → A nerve impulse depolarises the sarcolemma; the sarcoplasmic reticulum releases Ca²⁺, which binds troponin and shifts tropomyosin to expose the myosin-binding sites on actin. Myosin heads then form cross-bridges, ATP hydrolysis energises each head, and the power stroke pulls the thin filaments toward the centre of the sarcomere, narrowing the I band and H zone while the A band stays constant. New ATP detaches each cross-bridge, and relaxation follows when Ca²⁺ is pumped back into the sarcoplasmic reticulum.
4. 4
   Q4 → (a) True. (b) False — the H-zone contains thick filaments only. (c) True. (d) False — man has 12 pairs of ribs. (e) True.
5. 5
   Q5 → (a) Actin is the thin, track-forming filament of the I band; myosin is the thick filament of the A band and is the motor protein with ATPase activity that forms cross-bridges. (b) Red muscle is myoglobin-rich, aerobic, slow and fatigue-resistant; white muscle is anaerobic, fast and fatigable. (c) The pectoral girdle is made of two scapulae and two clavicles, lies dorsally, articulates with the forelimbs and is present in all vertebrates; the pelvic girdle is made of two innominate bones, lies ventrally, articulates with the hind limbs and is present from amphibians onwards.
6. 6
   Q6 → (a) — (iv) Involuntary; (b) — (ii) Thin filament; (c) — (i) Myoglobin; (d) — (iii) Sutures.
7. 7
   Q7 → Amoeboid movement, by cytoplasmic streaming and pseudopodia (macrophages, leucocytes); ciliary movement, by the beating of cilia (movement of the ovum in the fallopian tube, clearing mucus from the trachea); and muscular movement, by contraction of muscle cells (limbs, tongue, jaws and the heart).
8. 8
   Q8 → A skeletal muscle is voluntary, attached to bones, multinucleate, striated, has no intercalated discs, stores much glycogen and is fatigable. A cardiac muscle is involuntary, occurs only in the heart wall, has one central nucleus, has intercalated discs, depends on aerobic respiration with many mitochondria, and is non-fatigable.
9. 9
   Q9 → (a) Pivot joint; (b) Saddle joint; (c) Hinge joint; (d) Ball and socket joint; (e) Suture (a fibrous, immovable joint); (f) Pubic symphysis, a secondary cartilaginous joint.
10. 10
    Q10 → (a) one; (b) 14; (c) troponin and tropomyosin; (d) sarcoplasmic reticulum; (e) 11th and 12th; (f) 8.

MCQ Questions

1 Mark Questions

1. 1
   What is the central calcium-storing organelle of a muscle fibre? (Ans: sarcoplasmic reticulum)
2. 2
   Which joints allow free (synovial) movement? (Ans: ball-and-socket, hinge, pivot, gliding joints)
3. 3
   Name the protein that forms the Z-discs of the sarcomere. (Ans: actin filaments anchored; also actinin — the Z-line)
4. 4
   Define a sarcomere. (Ans: the segment between two successive Z-lines, the functional unit of striated muscle)

2 Mark Questions

1. 1
   Differentiate between voluntary (skeletal) and involuntary (smooth and cardiac) muscles.
2. 2
   What is the sliding filament theory of contraction? (Ans: thin actin filaments slide over thick myosin filaments, shortening the sarcomere without shortening the filaments)
3. 3
   Write two disorders of the muscular system. (Ans: muscular dystrophy, tetany, myasthenia gravis, spasm)

3 Mark Questions

1. 1
   Describe the ultrastructure of the sarcomere, naming the I-band, A-band, H-zone, M-line and Z-line.
2. 2
   Explain the mechanism of muscle contraction, including the roles of Ca²⁺, troponin and tropomyosin.
3. 3
   Describe the structure of the axial and appendicular skeleton with the number of bones in each. (Ans: axial 80, appendicular 126)

5 Mark Questions

1. 1
   Discuss the sliding filament theory in detail and explain the steps of excitation–contraction coupling from the motor neuron impulse to relaxation.
2. 2
   Give a comparative account of the three types of muscles (skeletal, smooth, cardiac) and the types of joints found in the human skeleton, classifying skeletal bones into axial and appendicular. (Ans: striated vs non-striated; voluntary/involuntary; myogenic/neurogenic)