NEET Physics: Waves – NCERT Masterclass & 100 MCQ Quiz

LOCOMOTION AND MOVEMENT

NCERT Masterclass & NEET Biology Study Module

1. Types of Movement

All locomotions are movements but all movements are not locomotions. Cells of the human body exhibit three main types of movements:

• Amoeboid: Macrophages and leucocytes in blood move using pseudopodia. Cytoskeletal elements like microfilaments are also involved.
• Ciliary: Occurs in most of our internal tubular organs lined by ciliated epithelium. E.g., removing dust from trachea and passage of ova through the female reproductive tract.
• Muscular: Movement of our limbs, jaws, tongue, etc., relies on the contractile property of muscles.

2. Muscle Anatomy & Structure

Muscle is a specialized tissue of mesodermal origin. Properties include excitability, contractility, extensibility, and elasticity. Types: Skeletal (striated, voluntary), Visceral (smooth, non-striated, involuntary), and Cardiac (striated, involuntary, branching with intercalated discs).

Structure of Skeletal Muscle:

• Muscle $\rightarrow$ Muscle Bundles (Fascicles) held by Fascia $\rightarrow$ Muscle Fibres (Cells).
• Muscle Fibre: Lined by plasma membrane called Sarcolemma enclosing the Sarcoplasm. It is a syncytium (multinucleated). The endoplasmic reticulum (Sarcoplasmic Reticulum) is the storehouse of Calcium ions ($Ca^{2+}$).
• Myofibrils: Contain alternate dark and light bands.

Contractile Proteins:
Actin (Thin filament): Made of two 'F' (filamentous) actins helically wound. Has two filaments of Tropomyosin running along its length. Troponin is distributed at regular intervals, masking the active binding sites for myosin.
Myosin (Thick filament): A polymer of Meromyosins. Each meromyosin has two parts: a globular head with a short arm (HMM - Heavy Meromyosin) and a tail (LMM - Light Meromyosin). The head has ATP binding sites and Actin binding sites, acting as an ATPase enzyme.

3. Mechanism of Muscle Contraction

Best explained by the Sliding Filament Theory: Contraction of a muscle fibre occurs by the sliding of the thin filaments (Actin) over the thick filaments (Myosin).

1. Signal sent by CNS via motor neuron reaches the Neuromuscular junction (Motor end plate).
2. Neurotransmitter (Acetylcholine) is released, generating an action potential in the sarcolemma.
3. This causes the release of Calcium ions ($Ca^{2+}$) from the sarcoplasmic reticulum into the sarcoplasm.
4. $Ca^{2+}$ binds to a subunit of Troponin on actin filaments, removing the masking of active sites for myosin.
5. Using energy from ATP hydrolysis, the myosin head binds to the exposed active sites on actin to form a Cross-bridge.
6. This pulls the attached actin filaments towards the centre of 'A' band. The 'Z' line attached to these actins is pulled inwards, causing a shortening of the sarcomere (contraction). (I-bands shorten, A-bands retain their length).

4. Skeletal System

Consists of a framework of bones and a few cartilages. Total bones in adult human: 206. Divided into Axial and Appendicular skeletons.

A. Axial Skeleton (80 bones):

• Skull (22 bones): Cranial (8 bones) + Facial (14 bones). A U-shaped bone called Hyoid is present at the base of the buccal cavity. Each middle ear has 3 tiny bones (Malleus, Incus, Stapes) called Ear Ossicles. Skull articulates with the vertebral column via two occipital condyles (Dicondylic skull).
• Vertebral Column (26 bones): Cervical (7), Thoracic (12), Lumbar (5), Sacral (1-fused), Coccygeal (1-fused). First vertebra is Atlas.
• Sternum (1 bone): Breast bone on the ventral midline.
• Ribs (12 pairs): True ribs (1st to 7th pairs - attached to sternum). False/Vertebrochondral ribs (8th, 9th, 10th - attach to 7th rib). Floating ribs (11th, 12th - not connected ventrally).

B. Appendicular Skeleton (126 bones):

• Forelimbs (30 bones each): Humerus, Radius & Ulna, Carpals (8 wrist bones), Metacarpals (5 palm bones), Phalanges (14 digits).
• Hindlimbs (30 bones each): Femur (longest bone), Tibia & Fibula, Tarsals (7 ankle bones), Metatarsals (5), Phalanges (14), Patella (1 knee cap).
• Pectoral Girdle: Clavicle (collar bone) and Scapula. Scapula has a depression called Glenoid cavity which articulates with the head of the humerus.
• Pelvic Girdle: Two coxal bones. Each formed by fusion of Ilium, Ischium, and Pubis. The cavity for thigh bone articulation is the Acetabulum. The two halves meet ventrally to form the Pubic symphysis (contains fibrous cartilage).

5. Joints & Disorders

• Fibrous Joints: Do not allow any movement. E.g., Sutures in the flat skull bones.
• Cartilaginous Joints: Bones joined together with the help of cartilages. Permits limited movement. E.g., Joints between adjacent vertebrae.
• Synovial Joints: Fluid-filled synovial cavity between articulating surfaces. Considerable movement.
  - Ball and socket: Humerus and pectoral girdle.
  - Hinge joint: Knee joint.
  - Pivot joint: Between atlas and axis.
  - Gliding joint: Between the carpals.
  - Saddle joint: Between carpal and metacarpal of thumb.

Disorders:
- Myasthenia gravis: Autoimmune disorder affecting neuromuscular junction leading to fatigue, weakening and paralysis of skeletal muscle.
- Muscular dystrophy: Progressive genetic degeneration of skeletal muscle.
- Tetany: Rapid spasms (wild contractions) in muscle due to low $Ca^{2+}$ in body fluid.
- Arthritis: Inflammation of joints.
- Osteoporosis: Age-related disorder characterized by decreased bone mass and increased chances of fractures. Decreased levels of estrogen is a common cause.
- Gout: Inflammation of joints due to accumulation of uric acid crystals.

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🚀 NEET LOCOMOTION MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Muscles, Bones, Joints, and Disorders.

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