Class 11 Biology NCERT Notes- Chapter 17: Movement and Locomotion

Detailed Study Notes – Chapter 17: Movement and Locomotion (Class 11 Biology, Notes, PDFs, Quizzes, MCQs)

1. Introduction to Movement and Locomotion

Movement is a fundamental characteristic of all living beings, from the streaming of protoplasm in unicellular organisms like Amoeba to the complex actions of multicellular animals. Locomotion is a specific type of voluntary movement that results in a change of place or location, such as walking, running, swimming, or flying.

• Relationship: All forms of locomotion are movements, but not all movements result in locomotion. For example, humans can move their limbs, jaws, and tongue to change body posture without changing their location.
• Integrated Function: In many organisms, structures used for locomotion also serve other purposes. For instance, in Paramoecium, cilia facilitate both locomotion and the movement of food. In Hydra, tentacles are used for both capturing prey and locomotion.
• Purpose of Locomotion: Animals generally perform locomotion for essential life activities, including the search for food, shelter, mates, suitable breeding grounds, and favourable climatic conditions, as well as to escape from predators.

2. Types of Movement in the Human Body

The cells of the human body exhibit three primary types of movement:

1. Amoeboid Movement: This movement is effected by pseudopodia, which are formed by the streaming of protoplasm. It involves cytoskeletal elements like microfilaments.
   • Examples: Macrophages and leucocytes (white blood cells) in the blood.
2. Ciliary Movement: This occurs in internal tubular organs lined with ciliated epithelium. It involves the coordinated movement of cilia.
   • Examples: Removing dust and foreign particles from the trachea; facilitating the passage of ova through the female reproductive tract.
3. Muscular Movement: This is essential for most forms of locomotion and other complex movements. It relies on the contractile property of muscles.
   • Examples: Movement of limbs, jaws, and tongue.
   • Coordination: Effective locomotion requires the perfect coordinated activity of the muscular, skeletal, and neural systems.

Flagellar movement, an outgrowth of the cell membrane, is also noted for its role in the swimming of spermatozoa, maintaining water current in sponges, and locomotion in protists like Euglena.

3. The Muscular System

Muscles are specialised tissues of mesodermal origin that constitute about 40-50% of the body weight in a human adult. They possess unique properties: excitability, contractility, extensibility, and elasticity.

3.1. Classification of Muscles

Muscles are classified based on location, appearance, and the nature of regulation.

Feature	Skeletal Muscle	Visceral (Smooth) Muscle	Cardiac Muscle
Location	Associated with skeletal components.	Inner walls of hollow visceral organs (e.g., alimentary canal, reproductive tract).	Heart.
Appearance	Striated (striped).	Non-striated (smooth).	Striated, branching pattern.
Control	Voluntary (under conscious control of the nervous system).	Involuntary (not under conscious control).	Involuntary.
Primary Function	Locomotory actions and changes in body posture.	Transportation of food, gametes, etc., through tracts.	Pumping of blood.

3.2. Structure of Skeletal Muscle

• Organisation: An organised skeletal muscle consists of multiple muscle bundles (fascicles) held together by a collagenous connective tissue layer called fascia.
• Muscle Fibre: Each fascicle contains numerous muscle fibres (muscle cells).
  • Sarcolemma: The plasma membrane of a muscle fibre.
  • Sarcoplasm: The cytoplasm of a muscle fibre, which contains many nuclei (a syncitium).
  • Sarcoplasmic Reticulum: The endoplasmic reticulum of a muscle fibre, which serves as a storehouse for calcium ions (Ca++).
  • Myofibrils/Myofilaments: A large number of parallelly arranged filaments within the sarcoplasm.

3.3. The Sarcomere: The Functional Unit of Contraction

Each myofibril exhibits alternate dark and light bands, which give skeletal muscle its striated appearance. This pattern is due to the arrangement of two key proteins: actin and myosin.

• I-Band (Isotropic Band): The light band, containing thin actin filaments.
• A-Band (Anisotropic Band): The dark band, containing thick myosin filaments. It also contains overlapping portions of actin filaments.
• Z-Line: An elastic fibre that bisects the centre of each I-Band. Thin actin filaments are firmly attached to the Z-line.
• Sarcomere: The portion of the myofibril between two successive Z-lines. It is the functional unit of muscle contraction.
• H-Zone: The central part of the thick filament (A-band) that is not overlapped by thin filaments in a resting muscle.
• M-Line: A thin fibrous membrane in the middle of the A-band that holds the thick filaments together.

3.4. Structure of Contractile Proteins

1. Actin (Thin Filament):
   • Composed of two helically wound ‘F’ (filamentous) actins.
   • Each ‘F’ actin is a polymer of monomeric ‘G’ (Globular) actins.
   • Tropomyosin: Two filaments of this protein run along the length of the ‘F’ actins.
   • Troponin: A complex protein distributed at regular intervals on the tropomyosin. In a resting state, a subunit of troponin masks the active binding sites for myosin on the actin filaments.
2. Myosin (Thick Filament):
   • A polymerised protein made of many monomeric units called Meromyosin.
   • Each meromyosin has two parts:
     • Heavy Meromyosin (HMM): A globular head with a short arm. This component projects outwards from the filament and is known as the cross arm. The head is an active ATPase enzyme and has binding sites for both ATP and actin.
     • Light Meromyosin (LMM): A tail portion.

3.5. Mechanism of Muscle Contraction (Sliding Filament Theory)

The sliding filament theory states that muscle contraction occurs by the sliding of the thin filaments (actin) over the thick filaments (myosin).

Steps of Contraction:

1. Signal Initiation: The Central Nervous System (CNS) sends a signal via a motor neuron. A motor neuron and the muscle fibres it connects to form a motor unit.
2. Neuromuscular Junction: The signal reaches the neuromuscular junction (motor-end plate), the synapse between the motor neuron and the sarcolemma.
3. Neurotransmitter Release: The neuron releases the neurotransmitter acetylcholine, which generates an action potential in the sarcolemma.
4. Calcium Ion Release: The action potential spreads through the muscle fibre, causing the sarcoplasmic reticulum to release calcium ions (Ca++) into the sarcoplasm.
5. Activation of Actin: The increased Ca++ level leads to calcium binding with a subunit of troponin. This binding removes the masking of the active sites on actin.
6. Cross-Bridge Formation: Using energy from ATP hydrolysis (ATP → ADP + Pi), the myosin head binds to the now-exposed active sites on the actin, forming a cross-bridge.
7. Power Stroke: The myosin head pulls the attached actin filaments towards the centre of the A-band. The Z-lines attached to the actins are also pulled inward, causing the sarcomere to shorten (contract).
8. Changes during Contraction: The I-bands are reduced in length, and the H-zone disappears, while the A-bands retain their length.
9. Cross-Bridge Detachment: The myosin releases the ADP and Pi and returns to its relaxed state. A new ATP molecule binds to the myosin head, causing the cross-bridge to break.
10. Re-cocking and Repetition: The ATP is again hydrolysed by the myosin head, and the cycle of cross-bridge formation and sliding repeats as long as Ca++ and ATP are present.

Relaxation: When the neural signal stops, Ca++ ions are pumped back into the sarcoplasmic reticulum. This causes the troponin to re-mask the actin filaments, preventing cross-bridge formation. The Z-lines return to their original position, and the muscle relaxes.

3.6. Muscle Fatigue and Fibre Types

• Fatigue: Repeated activation of muscles can lead to the accumulation of lactic acid due to the anaerobic breakdown of glycogen, causing fatigue.
• Red Fibres:
  • contains a high content of myoglobin, a red-colored oxygen-storing pigment.
  • Possess plenty of mitochondria for aerobic ATP production.
  • Also called aerobic muscles.
• White Fibres:
  • contains very little myoglobin, appearing pale or whitish.
  • Have fewer mitochondria but a high amount of sarcoplasmic reticulum.
  • Depend on anaerobic processes for energy.

4. The Skeletal System

The skeletal system, composed of 206 bones and a few cartilages in an adult human, provides a framework for the body and plays a significant role in movement. Bone is a hard connective tissue due to calcium salts, while cartilage is a slightly pliable connective tissue due to chondroitin salts.

4.1. Divisions of the Skeleton

1. Axial Skeleton (80 bones): Comprises bones along the main axis of the body.
2. Appendicular Skeleton: Consists of the bones of the limbs and their girdles.

4.2. The Axial Skeleton

• Skull (22 bones):
  • Cranial Bones (8): Form the cranium, the protective covering for the brain.
  • Facial Bones (14): Form the front part of the skull.
  • Hyoid Bone: A single U-shaped bone at the base of the buccal cavity.
  • Ear Ossicles (3 in each middle ear): Malleus, Incus, and Stapes.
  • The skull articulates with the vertebral column via two occipital condyles (a dicondylic skull).
• Vertebral Column (26 vertebrae):
  • Extends from the base of the skull, forming the main framework of the trunk.
  • Protects the spinal cord, which passes through the neural canal of each vertebra.
  • Regions:
    • Cervical (7 vertebrae) – The first is the atlas.
    • Thoracic (12 vertebrae)
    • Lumbar (5 vertebrae)
    • Sacral (1, fused from multiple vertebrae)
    • Coccygeal (1, fused from multiple vertebrae)
• Sternum and Ribs:
  • Sternum: A flat bone on the ventral midline of the thorax.
  • Ribs (12 pairs): Thin, flat bones. Each is bicephalic, having two articulation surfaces on its dorsal end to connect to the vertebral column.
    • True Ribs (Pairs 1-7): Attach dorsally to thoracic vertebrae and ventrally to the sternum via hyaline cartilage.
    • Vertebrochondral (False) Ribs (Pairs 8-10): Do not connect directly to the sternum but join the 7th rib.
    • Floating Ribs (Pairs 11-12): Not connected ventrally.
  • Rib Cage: Formed by the thoracic vertebrae, ribs, and sternum.

4.3. The Appendicular Skeleton

Each limb is made of 30 bones.

• Bones of the Fore Limb (Hand):
  • Humerus (upper arm)
  • Radius and Ulna (forearm)
  • Carpals (wrist – 8 bones)
  • Metacarpals (palm – 5 bones)
  • Phalanges (digits – 14 bones)
• Bones of the Hind Limb (Leg):
  • Femur (thigh – longest bone)
  • Tibia and Fibula (lower leg)
  • Tarsals (ankle – 7 bones)
  • Metatarsals (foot – 5 bones)
  • Phalanges (digits – 14 bones)
  • Patella: A cup-shaped bone (kneecap) covering the knee ventrally.
• Girdles: Connect the limbs to the axial skeleton.
  • Pectoral (Shoulder) Girdle:
    • Each half consists of a clavicle (collar bone) and a scapula.
    • The scapula is a large, triangular flat bone with a ridge (spine) that projects as the acromion.
    • The glenoid cavity, a depression below the acromion, articulates with the head of the humerus to form the shoulder joint.
  • Pelvic (Hip) Girdle:
    • Consists of two coxal bones.
    • Each coxal bone is formed by the fusion of three bones: ilium, ischium, and pubis.
    • The acetabulum is a cavity at the point of fusion where the femur articulates.
    • The two halves meet ventrally to form the pubic symphysis, which contains fibrous cartilage.

5. Joints

Joints are points of contact between bones, or between bones and cartilages. They act as a fulcrum for movements carried out by muscle-generated force.

5.1. Types of Joints

1. Fibrous Joints:
   • Do not allow any movement.
   • Bones are fused end-to-end by dense fibrous connective tissues.
   • Example: Sutures between the flat skull bones forming the cranium.
2. Cartilaginous Joints:
   • Permit limited movement.
   • Bones are joined together by cartilages.
   • Example: Joints between adjacent vertebrae in the vertebral column.
3. Synovial Joints:
   • Allow considerable movement.
   • Characterised by a fluid-filled synovial cavity between the articulating surfaces of the bones.
   • Examples:
     • Ball and Socket Joint: Between the humerus and pectoral girdle.
     • Hinge Joint: Knee joint.
     • Pivot Joint: Between the atlas and the axis vertebrae.
     • Gliding Joint: Between the carpals.
     • Saddle Joint: Between the carpal and metacarpal of the thumb.

6. Disorders of the Muscular and Skeletal System

• Myasthenia gravis: An autoimmune disorder affecting the neuromuscular junction, leading to fatigue, weakening, and paralysis of skeletal muscle.
• Muscular dystrophy: Progressive degeneration of skeletal muscle, mostly due to genetic disorders.
• Tetany: Rapid spasms (wild contractions) in the muscle due to low Ca++ levels in body fluid.
• Arthritis: Inflammation of joints.
• Osteoporosis: An age-related disorder characterised by decreased bone mass and increased fracture risk, commonly caused by decreased estrogen levels.
• Gout: Inflammation of joints caused by the accumulation of uric acid crystals.

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Q&A Section

Short-Answer Questions (Answer in 2-3 sentences)

1. Differentiate between movement and locomotion.
2. What are the three main types of cellular movement exhibited in the human body? Provide one example for each.
3. Explain the role of cilia in the trachea and the female reproductive tract.
4. What are the four special properties of muscle tissue?
5. Compare skeletal muscles and visceral muscles based on their appearance and control mechanisms.
6. Describe the composition of a muscle bundle, also known as a fascicle.
7. What is a sarcomere, and why is it considered the functional unit of muscle?
8. Identify the proteins that constitute the thick and thin filaments of a myofibril.
9. What is the role of the sarcoplasmic reticulum in muscle contraction?
10. Describe the structure of a myosin monomer (meromyosin).
11. What is the function of troponin and tropomyosin in a resting muscle fibre?
12. What is a motor unit?
13. Explain the function of acetylcholine at the neuromuscular junction.
14. According to the sliding filament theory, what happens to the I-bands and A-bands during muscle contraction?
15. What causes muscle fatigue after repeated activation?
16. Differentiate between red and white muscle fibres based on their myoglobin content and primary energy source.
17. Name the two principal divisions of the human skeletal system and list the main components of the axial skeleton.
18. How many bones are in the human skull, and what are its two main sets of bones?
19. Describe the structure of the human vertebral column, listing its five regions and the number of vertebrae in each.
20. What are true ribs, false ribs, and floating ribs?
21. List the bones of the human fore limb, starting from the shoulder joint.
22. What three bones fuse to form a coxal bone of the pelvic girdle?
23. What is a synovial joint, and what is its key characteristic?
24. Provide an example of a hinge joint and a ball and socket joint.
25. What is osteoporosis, and what is a common cause of this disorder?

Multiple-Choice Questions (MCQs)

1. Which of the following is a voluntary movement that results in a change of place? A) Streaming of protoplasm B) Movement of cilia C) Locomotion D) Peristalsis
2. The contractile property of muscles is used for locomotion by: A) Only human beings B) Majority of multicellular organisms C) Only unicellular organisms D) Only vertebrates
3. The plasma membrane of a muscle fibre is called the: A) Sarcoplasm B) Sarcomere C) Sarcolemma D) Sarcoplasmic reticulum
4. The dark band in a myofibril, which contains myosin, is known as the: A) I-band B) Z-line C) H-zone D) A-band
5. The functional unit of muscle contraction is the portion of the myofibril between two successive: A) M-lines B) Z-lines C) H-zones D) A-bands
6. In a resting muscle fibre, the active binding sites for myosin on actin are masked by: A) Tropomyosin B) Meromyosin C) Troponin D) Myoglobin
7. The globular head of a myosin molecule is an active: A) Acetylcholine enzyme B) ATPase enzyme C) Calcium channel D) Actinase enzyme
8. Muscle contraction is initiated by a signal from the: A) Central Nervous System (CNS) B) Sarcoplasmic Reticulum C) Heart D) Skeletal bones
9. The release of which ion into the sarcoplasm triggers muscle contraction? A) Sodium (Na+) B) Potassium (K+) C) Calcium (Ca++) D) Chloride (Cl-)
10. During muscle contraction, which of the following occurs? A) The A-bands get reduced. B) The I-bands get reduced. C) The A-bands expand. D) The Z-lines move further apart.
11. The accumulation of which substance causes muscle fatigue? A) Uric acid B) Acetylcholine C) Lactic acid D) Carbon dioxide
12. The human axial skeleton consists of how many bones? A) 206 B) 120 C) 80 D) 26
13. The vertebral column is differentiated into how many regions? A) 3 B) 4 C) 5 D) 7
14. The 8th, 9th, and 10th pairs of ribs are known as: A) True ribs B) Floating ribs C) Vertebrochondral ribs D) Bicephalic ribs
15. The longest bone in the human body is the: A) Humerus B) Tibia C) Sternum D) Femur
16. The glenoid cavity articulates with the head of the humerus to form the: A) Knee joint B) Elbow joint C) Shoulder joint D) Hip joint
17. Which type of joint does not allow any movement? A) Synovial joint B) Cartilaginous joint C) Fibrous joint D) Hinge joint
18. The joint between the atlas and axis vertebrae is an example of a: A) Saddle joint B) Pivot joint C) Gliding joint D) Ball and socket joint
19. Gout is an inflammation of joints due to the accumulation of: A) Lactic acid crystals B) Uric acid crystals C) Calcium salts D) Synovial fluid
20. Myasthenia gravis is an autoimmune disorder that affects the: A) Neuromuscular junction B) Synovial membrane C) Bone marrow D) Sarcoplasmic reticulum

Essay Questions

1. Explain the complete process of muscle contraction as described by the sliding filament theory, starting from the neural signal and ending with muscle relaxation.
2. Describe the detailed structure of a skeletal muscle fibre, including the arrangement of myofilaments that creates the striated appearance.
3. Compare and contrast the three types of muscle tissue found in the human body (skeletal, visceral, and cardiac) in terms of their location, structure, function, and mode of control.
4. Outline the composition of the human axial skeleton, detailing the bones of the skull, vertebral column, and rib cage.
5. Describe the structure of the appendicular skeleton, including the bones of the forelimbs, hindlimbs, pectoral girdle, and pelvic girdle.
6. Explain the structure and function of the two contractile proteins, actin and myosin, detailing all their component parts.
7. Classify the three major types of joints found in the human body, providing examples and describing the degree of movement each allows.
8. Discuss the roles of ATP and Calcium ions (Ca++) in the mechanism of muscle contraction and relaxation.
9. Differentiate between red muscle fibres and white muscle fibres based on their biochemical and structural characteristics and explain how these differences relate to their function.
10. Describe five different disorders of the muscular and skeletal system, explaining the cause and primary symptoms of each.

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Answer Key

Short-Answer Questions

1. Movement is a general term for a change in position of any body part, and it is a significant feature of all living beings. Locomotion is a specific type of voluntary movement that results in the entire organism changing its location, such as walking or running.
2. The three main types of cellular movement are amoeboid (e.g., macrophages), ciliary (e.g., cells lining the trachea), and muscular (e.g., movement of limbs).
3. In the trachea, the coordinated movement of cilia helps remove inhaled dust particles and foreign substances. In the female reproductive tract, ciliary movement facilitates the passage of the ovum towards the uterus.
4. The four special properties of muscle tissue are excitability (ability to respond to a stimulus), contractility (ability to shorten forcefully), extensibility (ability to be stretched), and elasticity (ability to recoil to original resting length).
5. Skeletal muscles have a striated or striped appearance and are under voluntary control of the nervous system. Visceral muscles are smooth in appearance (non-striated) and are involuntary, meaning their activities are not under conscious control.
6. A muscle bundle, or fascicle, is a component of an organised skeletal muscle. It contains a number of individual muscle fibres (muscle cells) and is held together with other fascicles by a common connective tissue layer called fascia.
7. A sarcomere is the portion of a myofibril located between two successive Z-lines. It is considered the functional unit of muscle because its shortening, caused by the sliding of actin and myosin filaments, is the fundamental event that leads to the contraction of the entire muscle fibre.
8. The thick filaments are composed of the protein myosin. The thin filaments are primarily composed of the protein actin, along with two other regulatory proteins, tropomyosin and troponin.
9. The sarcoplasmic reticulum is the endoplasmic reticulum of a muscle fibre. It acts as a storage reservoir for calcium ions (Ca++), which it releases into the sarcoplasm to initiate muscle contraction upon receiving an action potential.
10. A myosin monomer (meromyosin) consists of two parts: a globular head with a short arm, called heavy meromyosin (HMM), and a tail, called light meromyosin (LMM). The head contains binding sites for ATP and actin and functions as an ATPase enzyme.
11. In a resting muscle, tropomyosin filaments run along the actin and physically cover the myosin-binding sites. Troponin is a complex protein that holds the tropomyosin in this blocking position, thus preventing the formation of cross-bridges.
12. A motor unit consists of a single motor neuron and all the skeletal muscle fibres it innervates. When the motor neuron fires, all the muscle fibres in its motor unit contract together.
13. Acetylcholine is a neurotransmitter released by a motor neuron at the neuromuscular junction. It binds to receptors on the sarcolemma, generating an action potential that spreads across the muscle fibre and triggers the release of calcium ions.
14. According to the sliding filament theory, during muscle contraction, the thin filaments slide over the thick filaments. This causes the I-bands to shorten and the H-zone to disappear, while the A-bands retain their original length.
15. Muscle fatigue is caused by the accumulation of lactic acid within the muscle. This occurs during repeated activation when the muscle breaks down glycogen anaerobically (without sufficient oxygen) to produce energy.
16. Red fibres have a high myoglobin content, giving them a reddish appearance, and rely on aerobic respiration for energy. White fibres have low myoglobin content and appear pale, relying on anaerobic processes for their energy.
17. The two principal divisions are the axial skeleton and the appendicular skeleton. The axial skeleton consists of the skull, vertebral column, sternum, and ribs.
18. The human skull is composed of a total of 22 bones. These are divided into two main sets: the cranial bones (8 in number) which protect the brain, and the facial bones (14 in number).
19. The human vertebral column consists of five regions: cervical (7 vertebrae), thoracic (12 vertebrae), lumbar (5 vertebrae), sacral (1 fused vertebra), and coccygeal (1 fused vertebra).
20. True ribs (pairs 1-7) connect directly to the sternum. False ribs (pairs 8-10) connect to the cartilage of the 7th rib instead of the sternum directly. Floating ribs (pairs 11-12) do not connect to the sternum at all.
21. The bones of the human fore limb are the humerus, radius, ulna, carpals (8), metacarpals (5), and phalanges (14).
22. Each coxal bone is formed by the fusion of three bones: the ilium, ischium, and pubis.
23. A synovial joint is characterised by the presence of a fluid-filled synovial cavity between the articulating surfaces of the two bones. This arrangement allows for considerable movement.
24. A hinge joint example is the knee joint. A ball and socket joint example is the joint between the humerus and the pectoral girdle (shoulder joint).
25. Osteoporosis is an age-related disorder characterised by decreased bone mass, making bones fragile and increasing the risk of fractures. A common cause is decreased levels of estrogen.

Multiple-Choice Questions (MCQs) Key

Question	Answer
1	C
2	B
3	C
4	D
5	B
6	C
7	B
8	A
9	C
10	B
11	C
12	C
13	C
14	C
15	D
16	C
17	C
18	B
19	B
20	A

Essay Question Answers

1. Sliding Filament Theory: The process begins when a neural signal from the CNS arrives at the neuromuscular junction via a motor neuron, releasing acetylcholine. This generates an action potential in the sarcolemma, which travels into the muscle fibre and triggers the sarcoplasmic reticulum to release Ca++ ions into the sarcoplasm. The Ca++ ions bind to a subunit of troponin on the actin filaments, causing a conformational change that moves tropomyosin, exposing the active sites on actin. The myosin head, energised by the hydrolysis of ATP into ADP and Pi, binds to these exposed sites, forming a cross-bridge. The myosin head then pivots (the “power stroke”), pulling the actin filament toward the centre of the sarcomere, which shortens. A new ATP molecule binds to the myosin head, causing it to detach from actin. The cycle repeats as long as Ca++ and ATP are available. Relaxation occurs when the neural signal ceases, Ca++ is pumped back into the sarcoplasmic reticulum, troponin re-masks the actin sites, and the muscle returns to its original length.
2. Skeletal Muscle Fibre Structure: A skeletal muscle fibre is a long, cylindrical cell enclosed by a plasma membrane called the sarcolemma. Its cytoplasm, the sarcoplasm, contains multiple nuclei (syncitium) and a specialised endoplasmic reticulum called the sarcoplasmic reticulum, which stores calcium. The fibre is packed with parallel myofibrils, which are composed of contractile myofilaments. These myofilaments are arranged into repeating functional units called sarcomeres. The striated appearance is due to the alternating dark ‘A’ bands (containing thick myosin filaments) and light ‘I’ bands (containing thin actin filaments). Each ‘I’ band is bisected by a ‘Z’ line, and a sarcomere extends from one ‘Z’ line to the next. The central region of the ‘A’ band, where thin filaments do not overlap in a resting muscle, is the ‘H’ zone, which is bisected by an ‘M’ line that holds myosin filaments in place.
3. Comparison of Muscle Tissues:
   • Skeletal Muscle: Attached to bones. It is striated and voluntary. Its primary function is locomotion and changing body posture.
   • Visceral (Smooth) Muscle: Found in the walls of hollow internal organs. It is non-striated (smooth) and involuntary. It functions to move substances through tracts, like food in the digestive system.
   • Cardiac Muscle: Found only in the heart. It is striated, branched, and involuntary. Its sole function is to pump blood throughout the body continuously. While both skeletal and cardiac muscle are striated, cardiac muscle cells assemble in a branching pattern and their control is not under the direct command of the central nervous system.
4. Axial Skeleton: The axial skeleton comprises 80 bones along the body’s main axis. The Skull contains 22 bones (8 cranial, 14 facial), plus the hyoid bone and 6 ear ossicles. The Vertebral Column is formed by 26 vertebrae arranged into 5 regions: cervical (7), thoracic (12), lumbar (5), sacral (1 fused), and coccygeal (1 fused). It protects the spinal cord. The Rib Cage is formed by the sternum (a flat bone on the ventral midline) and 12 pairs of ribs. These include 7 pairs of true ribs, 3 pairs of false ribs, and 2 pairs of floating ribs, which all articulate with the thoracic vertebrae dorsally.
5. Appendicular Skeleton: This division includes the limbs and girdles. Each of the four limbs contains 30 bones. The fore limb consists of the humerus, radius, ulna, 8 carpals, 5 metacarpals, and 14 phalanges. The hind limb consists of the femur, patella, tibia, fibula, 7 tarsals, 5 metatarsals, and 14 phalanges. The Pectoral Girdle connects the forelimbs and consists of two halves, each with a clavicle and a scapula. The scapula’s glenoid cavity forms the shoulder joint with the humerus. The Pelvic Girdle connects the hind limbs and consists of two coxal bones, each formed by the fusion of the ilium, ischium, and pubis. The acetabulum cavity forms the hip joint with the femur.
6. Contractile Proteins:
   • Actin (Thin Filament): It is made of two ‘F’ (filamentous) actins helically wound together. Each ‘F’ actin is a polymer of ‘G’ (globular) actin monomers. Two other proteins are present: Tropomyosin, which runs along the ‘F’ actin and covers the myosin-binding sites in a resting state, and Troponin, a complex protein that sits on tropomyosin and has a binding site for Ca++, controlling tropomyosin’s position.
   • Myosin (Thick Filament): It is a polymer of meromyosin proteins. Each meromyosin has a tail (Light Meromyosin, LMM) and a globular head with a short arm (Heavy Meromyosin, HMM). The HMM projects outwards to form a cross-arm, which contains an active ATPase enzyme, a binding site for ATP, and an active site for binding to actin.
7. Joint Classification:
   • Fibrous Joints: These joints are immovable. The bones are held together by dense fibrous connective tissue. An example is the sutures of the cranium.
   • Cartilaginous Joints: These joints allow for limited movement. The bones are joined together by cartilage. An example is the joint between adjacent vertebrae.
   • Synovial Joints: These joints allow for considerable movement and are crucial for locomotion. They are characterised by a fluid-filled synovial cavity between the bones. Examples include the ball and socket joint (shoulder), hinge joint (knee), pivot joint (atlas/axis), gliding joint (carpals), and saddle joint (thumb carpal/metacarpal).
8. Roles of ATP and Ca++: Calcium ions (Ca++) are the primary trigger for contraction. When released from the sarcoplasmic reticulum, Ca++ binds to troponin, causing it to move tropomyosin and expose the myosin-binding sites on actin. The removal of Ca++ (by pumping it back into the sarcoplasmic reticulum) causes the muscle to relax. ATP has two critical roles. First, its hydrolysis (ATP → ADP + Pi) by the myosin head provides the energy for the “power stroke” that pulls the actin filament. Second, the binding of a new ATP molecule to the myosin head is required for the cross-bridge to detach, allowing the muscle to relax or the contraction cycle to repeat.
9. Red vs. White Muscle Fibres:
   • Red Fibres: Appear red due to a high content of the oxygen-storing pigment myoglobin. They are rich in mitochondria and are adapted for aerobic respiration, which allows for sustained, slower contractions over long periods without fatigue. They are also called aerobic muscles.
   • White Fibres: Appear pale or whitish due to a low myoglobin content. They have fewer mitochondria but a large amount of sarcoplasmic reticulum. They rely on anaerobic glycolysis for rapid energy production, making them suitable for fast, powerful contractions of short duration, but they fatigue quickly.
10. Five Musculoskeletal Disorders:
    • Myasthenia gravis: An autoimmune disorder where the body’s immune system attacks receptors at the neuromuscular junction, impairing the transmission of nerve signals to muscles. This leads to fatigue, progressive weakening, and potential paralysis of skeletal muscles.
    • Muscular dystrophy: A group of genetic disorders characterised by the progressive degeneration and weakening of skeletal muscles.
    • Tetany: A condition causing rapid, involuntary muscle spasms (wild contractions) due to abnormally low levels of calcium ions (Ca++) in the body fluid, which increases the excitability of neurons.
    • Arthritis: Characterised by inflammation of one or more joints, causing pain and stiffness.
    • Gout: A form of arthritis caused by the accumulation of uric acid crystals in the joints, leading to severe inflammation and pain.

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Glossary

Term	Definition
A-band	The dark band of a myofibril, which contains the entire length of the thick (myosin) filaments.
Acetabulum	A cavity in the pelvic girdle at the point of fusion of the ilium, ischium, and pubis, where the thigh bone (femur) articulates.
Acromion	A flat, expanded process on the scapula that projects from a slightly elevated ridge called the spine. The clavicle articulates with it.
Actin	A protein that forms the thin filaments in muscle fibres. It consists of ‘G’ (globular) actin monomers polymerised into ‘F’ (filamentous) actin.
Amoeboid Movement	A type of movement effected by pseudopodia, formed by the streaming of protoplasm. Exhibited by cells like macrophages and leucocytes.
Appendicular Skeleton	The division of the skeleton consisting of the bones of the limbs and their girdles.
Arthritis	Inflammation of joints.
Atlas	The first cervical vertebra, which articulates with the occipital condyles of the skull.
Axial Skeleton	The division of the skeleton comprising the bones along the main axis of the body: skull, vertebral column, sternum, and ribs.
Bicephalic	A term describing ribs, which have two articulation surfaces on their dorsal end for connecting to the vertebral column.
Cardiac Muscles	Striated, branched, and involuntary muscles of the heart.
Cartilaginous Joints	Joints where bones are joined by cartilage, permitting limited movement (e.g., between vertebrae).
Ciliary Movement	Movement caused by the coordinated beating of cilia, occurring in internal tubular organs.
Clavicle	A long, slender bone with two curvatures, commonly called the collar bone; part of the pectoral girdle.
Coxal bone	A bone of the pelvic girdle formed by the fusion of the ilium, ischium, and pubis.
Cross arm	The part of the myosin filament, consisting of the globular head and short arm (HMM), that projects outwards to interact with actin.
Fascia	A common collagenous connective tissue layer that holds muscle bundles (fascicles) together.
Fascicle	A bundle of muscle fibres within a skeletal muscle.
Femur	The thigh bone; the longest bone in the human body.
Fibrous Joints	Immovable joints where bones are fused end-to-end by dense fibrous connective tissues (e.g., sutures of the skull).
Glenoid Cavity	A depression in the scapula that articulates with the head of the humerus to form the shoulder joint.
Gout	Inflammation of joints due to the accumulation of uric acid crystals.
H-Zone	The central part of the thick filament (within the A-band) that is not overlapped by thin filaments in a resting muscle.
I-band	The light band of a myofibril, which contains only the thin (actin) filaments.
Locomotion	Voluntary movement that results in a change of place or location.
Meromyosin	The monomeric protein unit of a myosin (thick) filament, consisting of a head (HMM) and a tail (LMM).
Motor Unit	A motor neuron along with the muscle fibres it connects to.
Movement	One of the significant features of living beings, involving a change in position or posture of body parts.
Muscular dystrophy	Progressive degeneration of skeletal muscle, mostly due to a genetic disorder.
Myasthenia gravis	An autoimmune disorder affecting the neuromuscular junction, leading to fatigue, weakening, and paralysis of skeletal muscle.
Myofibril	A long, parallelly arranged filament in the sarcoplasm of a muscle fibre, composed of sarcomeres.
Myoglobin	A red-colored, oxygen-storing pigment found in muscle.
Myosin	A protein that forms the thick filaments in muscle fibres. Its head has ATPase activity and binds to actin.
Neuromuscular Junction	The junction (synapse) between a motor neuron and the sarcolemma of the muscle fibre; also called the motor-end plate.
Osteoporosis	The ventral joint where the two halves of the pelvic girdle meet, contains fibrous cartilage.
Pectoral Girdle	The shoulder girdle, which helps in the articulation of the upper limbs with the axial skeleton. Consists of the clavicle and scapula.
Pelvic Girdle	The hip girdle, which helps in the articulation of the lower limbs with the axial skeleton. Consists of two coxal bones.
Pubic Symphysis	The ventral joint where the two halves of the pelvic girdle meet, containing fibrous cartilage.
Red Fibres	Muscles with high myoglobin content, plenty of mitochondria, and a reddish appearance; also called aerobic muscles.
Rib Cage	Joints characterised by a fluid-filled synovial cavity between articulating bones, allowing for considerable movement.
Sarcolemma	The plasma membrane of a muscle fibre.
Sarcomere	The functional unit of muscle contraction; the portion of the myofibril between two successive Z-lines.
Sarcoplasm	The cytoplasm of a muscle fibre.
Sarcoplasmic Reticulum	The endoplasmic reticulum of muscle fibres, which is a storehouse of calcium ions.
Scapula	A large, triangular flat bone in the dorsal part of the thorax, part of the pectoral girdle.
Sliding Filament Theory	The theory explaining that muscle contraction occurs by the sliding of thin filaments over thick filaments.
Skeletal Muscles	Striated, voluntary muscles that are closely associated with the skeletal components of the body.
Synovial Joints	Joints characterised by a fluid-filled synovial cavity between articulating bones, allowing for considerable movement.
Tetany	A condition of rapid spasms (wild contractions) in muscle due to low Ca++ in body fluid.
Troponin	A complex protein on the thin filament that binds to calcium ions and regulates the position of tropomyosin.
Tropomyosin	A protein on the thin filament that masks the active binding sites for myosin on the actin filaments in a resting state.
Visceral Muscles	Non-striated, involuntary muscles located in the inner walls of hollow visceral organs.
White Fibres	Muscles with low myoglobin content and a pale appearance; they depend on anaerobic processes for energy.
Z-line	An elastic fibre that bisects the I-band and serves as an attachment point for thin filaments.