Quick Revision Notes: Class 11 Biology

Chapter: Locomotion and Movement (गमन एवं संचलन)

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1. Introduction

• Locomotion (गमन): Voluntary movements resulting in a change of place or location (e.g., walking, running, swimming). All locomotions are movements, but all movements are not locomotions.
• Movement (संचलन): A positional change of body parts without changing the overall place (e.g., breathing, beating of heart, tongue movement).

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2. Types of Movement in Humans

1. Amoeboid Movement (अमीबीय गति): Exhibited by macrophages and leucocytes (WBCs) using pseudopodia (formed by cytoplasmic streaming).
2. Ciliary Movement (पक्षाभिकीय गति): Occurs in internal tubular organs lined by cilia, e.g., trachea, fallopian tubes.
3. Muscular Movement (पेशीय गति): Exhibited by limbs, jaws, tongue, etc., utilizing the contractile property of muscles.

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3. Types of Muscles

Muscles are specialized tissues of mesodermal origin.

Feature	Skeletal Muscle (कंकाल पेशी)	Smooth Muscle (चिकनी पेशी)	Cardiac Muscle (हृदय पेशी)
Location	Attached to bones (Skeletal system)	Walls of internal organs (Visceral)	Walls of the heart
Appearance	Striated (धारदार) / Striped	Non-striated / Smooth	Faintly striated with intercalated discs
Control	Voluntary (ऐच्छिक)	Involuntary (अनऐच्छिक)	Involuntary (अनऐच्छिक)
Function	Body posture, locomotion	Transport of food, gametes	Pumping blood

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4. Structure of Skeletal Muscle (Macroscopic to Microscopic)

• Muscle Bundle / Fascicle: Each skeletal muscle has many parallel muscle bundles held together by collagenous connective tissue called fascia.
• Muscle Fibre (Muscle Cell): Covered by a plasma membrane called sarcolemma, enclosing the sarcoplasm. It is a syncytium (multinucleated).
• Myofibrils: Numerous parallel filamentous structures in the sarcoplasm containing alternating dark and light bands:
  • A-Band (Anisotropic / Dark Band): Contains Myosin protein.
  • I-Band (Isotropic / Light Band): Contains Actin protein.
  • Z-Line: An elastic line that bisects each I-band.
  • Sarcomere: The functional unit of muscle contraction, defined as the region between two successive Z-lines (Z to Z).

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5. Structure of Contractile Proteins (Myofilaments)

A. Thin Filament (Actin)

• Made of two 'F' (filamentous) actins helically wound to each other.
• Each 'F' actin is a polymer of monomeric 'G' (globular) actins.
• Two filaments of Tropomyosin run close to the 'F' actins throughout its length.
• Troponin is distributed at regular intervals on the tropomyosin to mask the active binding sites for myosin.

B. Thick Filament (Myosin)

• Polymerized protein where each monomer is called a Meromyosin.
• Each meromyosin has two important parts:
  • A globular head with a short arm (forms the Heavy Meromyosin - HMM).
  • A tail (forms the Light Meromyosin - LMM).
• The head has active sites for ATP binding and actin-binding sites.

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6. Mechanism of Muscle Contraction: Sliding Filament Theory

Proposed by H.E. Huxley and J.5. Hanson. Contraction occurs when thin filaments slide over thick filaments.

• Step 1: Central Nervous System (CNS) sends a signal via a motor neuron.

• Step 2: Neuron meets sarcolemma at the Neuromuscular Junction (Motor End Plate), releasing a neurotransmitter (Acetylcholine) which generates an action potential in the sarcolemma.

• Step 3: Action potential triggers the release of Calcium ions ($Ca^{2+}$) from the sarcoplasmic reticulum into the sarcoplasm.

• Step 4: $Ca^{2+}$ binds to troponin on actin filaments, exposing the active binding sites for myosin.

• Step 5: Myosin heads bind to these sites using energy from ATP hydrolysis to form Cross-bridges.

• Step 6: Myosin pulls the attached actin filaments towards the center of the A-band (H-zone shortens/disappears).

• Step 7: Sarcomere shortens (Muscle contracts).

• Relaxation: $Ca^{2+}$ is pumped back into the sarcoplasmic reticulum, masking the actin filaments, causing the Z-lines to return to their original position.

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7. Human Skeletal System

Comprises 206 bones and a few cartilages. Divided into two principal divisions:

A. Axial Skeleton (अक्षीय कंकाल) – 80 Bones

1. Skull (कूपिका/खोपड़ी) – 29 bones:
   • Cranial bones (कपाल) = 8
   • Facial bones (चेहरा) = 14
   • Hyoid bone (ह्याइड) = 1 (at the base of buccal cavity)
   • Ear Ossicles (कर्ण अस्थियाँ) = 6 (Malleus, Incus, Stapes - 2 each)
2. Vertebral Column (कशेुक दंड) – 26 bones (derived from 33 embryonic vertebrae):
   • Cervical (ग्रीवा) = 7
   • Thoracic (वक्षीय) = 12
   • Lumbar (कटि) = 5
   • Sacral (त्रिक) = 1 (fused 5)
   • Coccygeal (अनुत्रिक) = 1 (fused 4)
3. Sternum (उरोस्थि) – 1 bone (flat bone on ventral midline of thorax).
4. Ribs (पसलियाँ) – 12 pairs (24 bones):
   • True Ribs (1st to 7th pairs): Attached dorsally to thoracic vertebrae and ventrally to the sternum via hyaline cartilage.
   • False Ribs / Vertebrochondral (8th, 9th, and 10th pairs): Do not articulate directly with the sternum; joined to the 7th rib.
   • Floating Ribs (11th and 12th pairs): Not connected ventrally.

B. Appendicular Skeleton (उपांगीय कंकाल) – 126 Bones

1. Limbs (पाद) – 120 bones (60 in each):
   • Forelimb (अग्रपाद): Humerus, Radius, Ulna, Carpals (8), Metacarpals (5), Phalanges (14). Total = 30.
   • Hindlimb (पश्चपाद): Femur (longest bone), Patella (knee cap), Tibia, Fibula, Tarsals (7), Metatarsals (5), Phalanges (14). Total = 30.
2. Girdles (मेखलाएँ) – 6 bones:
   • Pectoral Girdle (अंश मेखला): Clavicle (collar bone) and Scapula (shoulder blade) – 2 each.
   • Pelvic Girdle (श्रोणि मेखला): Two coxal bones (formed by fusion of Ilium, Ischium, and Pubis). Meets at the Pubic Symphysis.

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8. Joints (संधियाँ)

Joints are points of contact between bones, or between bones and cartilages.

1. Fibrous Joints (तंतुमय संधियाँ):
   • Immovable (Synarthroses).
   • Bones are fused end-to-end by dense connective tissue (e.g., Sutures in the flat skull bones).
2. Cartilaginous Joints (उपास्थिमय संधियाँ):
   • Slightly movable (Amphiarthroses).
   • Bones are joined together by cartilage (e.g., between adjacent vertebrae in the vertebral column, Pubic symphysis).
3. Synovial Joints (शाइनावियल संधियाँ):
   • Freely movable (Diarthroses).
   • Characterized by a fluid-filled synovial cavity between articulating surfaces.
   • Examples:
     • Ball and Socket Joint: Shoulder and Hip joints (allows movement in all directions).
     • Hinge Joint: Knee and Elbow joints (back-and-forth movement).
     • Pivot Joint: Between Atlas and Axis vertebrae (rotation).
     • Gliding Joint: Between carpals.
     • Saddle Joint: Between carpal and metacarpal of thumb.

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9. Disorders of Muscular and Skeletal System

• Myasthenia Gravis: Autoimmune disorder affecting neuromuscular junction leading to fatigue, weakening, and paralysis of skeletal muscle.
• Muscular Dystrophy: Progressive degeneration of skeletal muscle mostly due to genetic disorder.
• Tetany: Rapid spasms (wild contractions) in muscles due to low $Ca^{2+}$ in body fluid (hypocalcemia).
• Arthritis: Inflammation of joints.
• Osteoporosis: Age-related disorder characterized by decreased bone mass and increased chances of fractures (often due to estrogen deficiency in women).
• Gout: Inflammation of joints due to accumulation of uric acid crystals.