Locomotion and Movement
Welcome to HSLC Guru! In this article, we present a complete English-medium study guide for Class 11 Biology Chapter 20 — Locomotion and Movement, prepared strictly according to the ASSEB (Assam State School Education Board) syllabus. This chapter explores how organisms move, the various types of movements exhibited by animals, the structure and function of muscles, the human skeletal system, types of joints, and common disorders associated with the muscular and skeletal systems. The notes are designed to help students master the chapter through clear summaries, comprehensive question-answers, MCQs, fill-in-the-blanks, true/false statements, and a useful glossary.
Summary
Movement is one of the fundamental characteristics of all living organisms. The voluntary movement that results in change of place or position of the entire body is called locomotion. Animals exhibit three major types of movements — amoeboid movement (seen in macrophages and leucocytes by formation of pseudopodia), ciliary movement (seen in tracheal epithelium and fallopian tubes due to action of cilia), and muscular movement (in limbs, jaws, tongue, etc., requiring contraction of muscles). In humans, locomotion and movement are made possible by the coordinated action of the muscular system, skeletal system, and nervous system.
Muscles are specialised contractile tissues classified into three types: skeletal muscles (striated, voluntary, attached to bones), smooth muscles (non-striated, involuntary, found in inner walls of hollow organs), and cardiac muscles (striated, involuntary, found in the heart). A skeletal muscle is composed of bundles called fascicles, each containing many muscle fibres (cells). Each muscle fibre contains numerous myofibrils, which show alternating dark A-bands (containing thick myosin filaments) and light I-bands (containing thin actin filaments). The functional unit of a myofibril is the sarcomere, located between two Z-lines, with an H-zone in the centre of the A-band where actin filaments are absent.
Muscle contraction is explained by the sliding filament theory proposed by H.E. Huxley and A.F. Huxley. According to this theory, contraction occurs when the thin actin filaments slide over the thick myosin filaments, shortening the sarcomere. The mechanism begins when a nerve impulse reaches the motor end plate, releasing acetylcholine which triggers the release of Ca²⁺ from the sarcoplasmic reticulum. Calcium ions bind to troponin on the actin filament, exposing the active sites, allowing myosin heads (cross-bridges) to attach. Using ATP, the cross-bridges pull the actin filaments inward, causing the I-band and H-zone to shrink while the A-band remains constant. Relaxation occurs when Ca²⁺ is pumped back, breaking cross-bridges.
The human skeletal system consists of 206 bones, divided into the axial skeleton (80 bones — skull, vertebral column, sternum, ribs) and the appendicular skeleton (126 bones — pectoral and pelvic girdles, and bones of the limbs). Joints are points of contact between bones and are of three main types — fibrous (immovable, e.g., skull sutures), cartilaginous (slightly movable, e.g., between vertebrae), and synovial (freely movable, e.g., ball-and-socket joint at shoulder, hinge joint at knee, pivot joint between atlas and axis, gliding joint between carpals, saddle joint at thumb). Common disorders affecting these systems include myasthenia gravis (autoimmune fatigue of muscles), muscular dystrophy (progressive degeneration), tetany (rapid spasms due to low Ca²⁺), arthritis (joint inflammation), osteoporosis (decreased bone mass), and gout (inflammation due to uric acid crystal accumulation).
Very Short Answer Type Questions (1 Mark)
Q1. Define locomotion.
Answer: Locomotion is the voluntary movement of an organism resulting in a change of place or position of the entire body.
Q2. Name the structural and functional unit of a myofibril.
Answer: Sarcomere is the structural and functional unit of a myofibril.
Q3. What is the protein component of thick filaments?
Answer: The thick filament is composed of the protein myosin.
Q4. Name the joint between the atlas and axis vertebrae.
Answer: It is a pivot joint.
Q5. Which ion is essential for muscle contraction?
Answer: Calcium ion (Ca²⁺) is essential for muscle contraction.
Q6. What is the total number of bones in the adult human skeleton?
Answer: The adult human skeleton has 206 bones.
Q7. Name the disorder caused by decreased bone mass in old age.
Answer: Osteoporosis.
Q8. Which protein covers the active sites on actin filaments?
Answer: Tropomyosin (along with troponin) covers the active sites of actin filaments.
Q9. What type of joint is found at the shoulder?
Answer: Ball-and-socket joint.
Q10. Name the autoimmune disorder that causes muscle fatigue.
Answer: Myasthenia gravis.
Short Answer Type Questions (2-3 Marks)
Q1. Differentiate between movement and locomotion.
Answer: Movement is the change in position of any part of the body, while locomotion is the change of place or position of the entire body. All locomotion involves movement, but not all movements result in locomotion. For example, the beating of cilia is a movement but not locomotion, whereas walking and swimming are forms of locomotion.
Q2. What are the three types of muscles? Mention one feature of each.
Answer: The three types of muscles are: (i) Skeletal muscles — striated, voluntary, attached to bones, responsible for body movement; (ii) Smooth muscles — non-striated, involuntary, found in walls of internal organs like the stomach and intestines; (iii) Cardiac muscles — striated, involuntary, branched, found exclusively in the wall of the heart.
Q3. Describe the structure of a sarcomere.
Answer: A sarcomere is the portion of a myofibril located between two successive Z-lines. It contains a central A-band (dark band, with thick myosin filaments) and two halves of I-bands (light bands, with thin actin filaments) on either side. The H-zone is the central region of the A-band where only myosin filaments are present. The M-line bisects the H-zone.
Q4. What is the sliding filament theory?
Answer: The sliding filament theory states that during muscle contraction, the thin actin filaments slide over the thick myosin filaments, causing the sarcomere to shorten. The lengths of actin and myosin filaments do not change; only the I-band and H-zone shrink, while the A-band remains constant. This theory was proposed by H.E. Huxley and A.F. Huxley.
Q5. Distinguish between the axial and appendicular skeleton.
Answer: The axial skeleton consists of 80 bones forming the main axis of the body — skull, vertebral column, sternum, and ribs. The appendicular skeleton consists of 126 bones — bones of the limbs and the girdles (pectoral and pelvic) that connect the limbs to the axial skeleton.
Q6. Briefly describe synovial joints and give two examples.
Answer: Synovial joints are freely movable joints characterised by the presence of a fluid-filled synovial cavity between the articulating bones. The synovial fluid lubricates the joint and reduces friction. Examples include the ball-and-socket joint at the shoulder and hip, and the hinge joint at the knee and elbow.
Long Answer Type Questions (5-7 Marks)
Q1. Describe the structure of a skeletal muscle in detail.
Answer: Skeletal muscles are voluntary muscles attached to bones by tendons. Each muscle is composed of a number of bundles called fascicles, held together by a tough connective tissue covering called the perimysium. The entire muscle is enclosed by an outer covering called epimysium. Each fascicle contains numerous parallel muscle fibres (muscle cells). A muscle fibre is a long, cylindrical, multinucleated cell surrounded by a plasma membrane called the sarcolemma. The cytoplasm, called sarcoplasm, contains numerous parallel myofibrils embedded in it. Each myofibril shows alternating dark A-bands (anisotropic) and light I-bands (isotropic). The A-band contains thick filaments composed of the protein myosin. The I-band contains thin filaments composed of the protein actin (along with troponin and tropomyosin). The dark line bisecting the I-band is called the Z-line, and the portion of the myofibril between two successive Z-lines is the sarcomere — the functional unit of contraction. The central H-zone within the A-band contains only myosin filaments and is bisected by the M-line. The sarcoplasmic reticulum, an extensive network of membranes, surrounds the myofibrils and stores Ca²⁺ ions, which are essential for contraction.
Q2. Explain the mechanism of muscle contraction in detail.
Answer: Muscle contraction occurs in the following stages: (i) A nerve impulse from a motor neuron reaches the neuromuscular junction (motor end plate), releasing the neurotransmitter acetylcholine. (ii) Acetylcholine generates an action potential in the sarcolemma, which spreads through the T-tubules to the sarcoplasmic reticulum. (iii) This stimulates the sarcoplasmic reticulum to release Ca²⁺ ions into the sarcoplasm. (iv) Ca²⁺ binds to troponin on the actin filament, causing tropomyosin to shift and exposing the active sites for myosin. (v) The myosin head (cross-bridge), activated by ATP, binds to the active site on actin, forming an actin-myosin cross-bridge. (vi) The cross-bridge tilts inward, pulling the actin filament toward the centre of the sarcomere. This is the power stroke. (vii) ATP binds to the myosin head, releasing it from actin. The myosin head re-cocks for another power stroke. (viii) The cycle repeats as long as Ca²⁺ and ATP are available. (ix) During relaxation, Ca²⁺ is actively pumped back into the sarcoplasmic reticulum, troponin-tropomyosin complex covers the active sites again, and the muscle relaxes. As a result of contraction, the sarcomere shortens, the I-band and H-zone shrink, while the A-band remains constant.
Q3. Describe the various types of joints in the human body with examples.
Answer: Joints are the points where two or more bones meet. They are classified into three main types: (i) Fibrous joints — These are immovable joints where bones are held together by dense fibrous connective tissue. Example: sutures in the skull. (ii) Cartilaginous joints — These joints permit limited movement and the bones are connected by cartilage. Example: joints between adjacent vertebrae of the vertebral column. (iii) Synovial joints — These are freely movable joints characterised by a fluid-filled synovial cavity. They are further classified into: (a) Ball-and-socket joint — between humerus and pectoral girdle (shoulder); (b) Hinge joint — knee and elbow; (c) Pivot joint — between atlas and axis vertebrae; (d) Gliding joint — between carpals; (e) Saddle joint — between carpal and metacarpal of thumb. Synovial joints provide great mobility, essential for locomotion and limb movements.
Q4. Describe briefly the major disorders of the muscular and skeletal system.
Answer: Common disorders of the muscular and skeletal system include: (i) Myasthenia gravis — An autoimmune disorder affecting the neuromuscular junction, leading to fatigue, weakness, and paralysis of skeletal muscles. (ii) Muscular dystrophy — A genetic disorder characterised by progressive degeneration of skeletal muscles. (iii) Tetany — Rapid spasms (wild contractions) in muscles due to low Ca²⁺ levels in body fluids. (iv) Arthritis — Inflammation of joints, causing pain and stiffness. (v) Osteoporosis — Age-related disorder characterised by decreased bone mass and increased risk of fractures, due to lowered levels of estrogen. (vi) Gout — Inflammation of joints due to accumulation of uric acid crystals.
Q5. Describe the human axial skeleton.
Answer: The axial skeleton consists of 80 bones forming the longitudinal axis of the body. It includes: (i) Skull — formed of 22 bones, divided into the cranial bones (8) which protect the brain, and facial bones (14). The skull articulates with the vertebral column through the occipital condyle. (ii) Vertebral column — composed of 26 vertebrae, divided into 7 cervical, 12 thoracic, 5 lumbar, 1 sacrum (formed by 5 fused vertebrae), and 1 coccyx (formed by 4 fused vertebrae). It encloses the spinal cord and supports the head. (iii) Sternum — a flat bone in the centre of the thorax, formed of three parts (manubrium, body, and xiphoid process). (iv) Ribs — 12 pairs of thin, flat bones forming the rib cage; the first 7 pairs are true ribs (attached directly to sternum), pairs 8-10 are false ribs (attached indirectly), and pairs 11-12 are floating ribs (not attached to sternum). The axial skeleton protects vital organs such as the brain, spinal cord, heart, and lungs.
Multiple Choice Questions (MCQs)
Q1. The functional unit of a myofibril is:
(a) Sarcolemma (b) Sarcomere (c) Sarcoplasm (d) Sarcoplasmic reticulum
Answer: (b) Sarcomere
Q2. The thick filament of a sarcomere is made up of:
(a) Actin (b) Tropomyosin (c) Troponin (d) Myosin
Answer: (d) Myosin
Q3. The total number of bones in the adult human skeleton is:
(a) 200 (b) 204 (c) 206 (d) 210
Answer: (c) 206
Q4. The joint between atlas and axis is:
(a) Hinge (b) Pivot (c) Ball-and-socket (d) Saddle
Answer: (b) Pivot
Q5. Which of the following is an autoimmune disorder?
(a) Tetany (b) Gout (c) Myasthenia gravis (d) Osteoporosis
Answer: (c) Myasthenia gravis
Q6. The human vertebral column has how many vertebrae?
(a) 24 (b) 26 (c) 30 (d) 33
Answer: (b) 26
Q7. During muscle contraction, which band shortens?
(a) A-band (b) I-band (c) M-line (d) Z-line
Answer: (b) I-band
Q8. Cardiac muscles are:
(a) Striated and voluntary (b) Non-striated and voluntary (c) Striated and involuntary (d) Non-striated and involuntary
Answer: (c) Striated and involuntary
Q9. Tetany is caused by deficiency of:
(a) Sodium (b) Potassium (c) Calcium (d) Iron
Answer: (c) Calcium
Q10. Which type of movement is exhibited by macrophages?
(a) Ciliary (b) Amoeboid (c) Muscular (d) Flagellar
Answer: (b) Amoeboid
Fill in the Blanks
Q1. The functional unit of a myofibril is the __________.
Answer: sarcomere
Q2. The thin filament of a muscle fibre is made up of __________.
Answer: actin
Q3. The neurotransmitter released at the neuromuscular junction is __________.
Answer: acetylcholine
Q4. The joint at the shoulder is a __________ joint.
Answer: ball-and-socket
Q5. __________ is an age-related disorder caused by decreased bone mass.
Answer: Osteoporosis
True or False
Q1. Skeletal muscles are involuntary in nature.
Answer: False (Skeletal muscles are voluntary.)
Q2. The A-band of a sarcomere shortens during muscle contraction.
Answer: False (The A-band remains constant; only I-band and H-zone shorten.)
Q3. The pivot joint is found between atlas and axis.
Answer: True
Q4. Gout is caused by accumulation of uric acid crystals in the joints.
Answer: True
Q5. The human skull contains 32 bones.
Answer: False (The human skull contains 22 bones.)
Glossary
| Term | Definition |
|---|---|
| Locomotion | Voluntary movement of an organism resulting in change of place. |
| Sarcomere | Functional unit of a myofibril, located between two Z-lines. |
| Myofibril | Contractile filament within a muscle fibre. |
| Actin | Protein forming the thin filament of muscle fibres. |
| Myosin | Protein forming the thick filament of muscle fibres. |
| Sarcolemma | Plasma membrane of a muscle fibre. |
| Sarcoplasm | Cytoplasm of a muscle fibre. |
| A-band | Dark band of a sarcomere containing myosin filaments. |
| I-band | Light band of a sarcomere containing actin filaments. |
| H-zone | Central region of A-band containing only myosin. |
| Z-line | Dark line bisecting the I-band; boundary of a sarcomere. |
| Cross-bridge | Myosin head that binds to actin during contraction. |
| Acetylcholine | Neurotransmitter released at the neuromuscular junction. |
| Axial skeleton | Bones of skull, vertebral column, sternum, and ribs (80 bones). |
| Appendicular skeleton | Bones of limbs and girdles (126 bones). |
| Synovial joint | Freely movable joint with a fluid-filled cavity. |
| Pivot joint | Joint allowing rotational movement (e.g., atlas-axis). |
| Hinge joint | Joint allowing movement in one plane (e.g., knee). |
| Myasthenia gravis | Autoimmune disorder causing skeletal muscle fatigue. |
| Tetany | Wild muscle spasms due to low Ca²⁺ levels. |
| Arthritis | Inflammation of joints causing pain and stiffness. |
| Osteoporosis | Decreased bone mass leading to fragile bones. |
| Gout | Inflammation of joints due to uric acid crystal deposits. |
| Muscular dystrophy | Progressive genetic degeneration of skeletal muscles. |