Locomotion and Movement — Revision Notes

⚡ 30-Second Revision

Movement: — Change in position of body part. Locomotion: Change in entire organism's location.
Muscle Types: — Skeletal (voluntary, striated), Smooth (involuntary, non-striated), Cardiac (involuntary, striated, intercalated discs).
Sarcomere: — Functional unit of muscle contraction, between two Z-lines.
Sliding Filament Theory: — Actin slides over myosin. A-band constant, I-band shortens, H-zone shortens/disappears.
Key Players: — $Ca^{2+}$ (binds troponin, exposes actin sites), ATP (energy for myosin head movement & detachment).
Joints: — Fibrous (immovable, e.g., sutures), Cartilaginous (slightly movable, e.g., pubic symphysis), Synovial (freely movable, e.g., hinge, ball-and-socket).
Disorders: — Myasthenia Gravis (autoimmune, neuromuscular junction), Muscular Dystrophy (genetic, muscle degeneration), Osteoporosis (decreased bone mass), Gout (uric acid in joints).

2-Minute Revision

Locomotion is the movement of the entire body, while movement is any change in position. Organisms exhibit amoeboid, ciliary, flagellar, and muscular movements. The muscular system has three types: skeletal (voluntary, striated, attached to bones), smooth (involuntary, non-striated, in viscera), and cardiac (involuntary, striated, in heart).

Skeletal muscle contraction follows the Sliding Filament Theory: actin filaments slide over myosin filaments, shortening the sarcomere. This process requires ATP for myosin head movement and detachment, and $Ca^{2+}$ ions to expose the actin binding sites by interacting with troponin and tropomyosin.

The skeletal system provides support, protection, and leverage. Joints are classified as fibrous (immovable), cartilaginous (slightly movable), and synovial (freely movable). Synovial joints include ball-and-socket (shoulder), hinge (elbow), and pivot (atlas-axis) joints, each allowing specific movements.

Common disorders include Myasthenia Gravis (autoimmune, neuromuscular junction), Muscular Dystrophy (genetic, muscle degeneration), Osteoporosis (bone mass loss), and Gout (uric acid in joints).

5-Minute Revision

Start by differentiating movement and locomotion. Movement is any change in position, while locomotion is a change in the organism's entire location. Recall the four types of movement: amoeboid (pseudopodia, e.

g., macrophages), ciliary (cilia, e.g., Paramecium, tracheal lining), flagellar (flagella, e.g., sperm), and muscular (most higher animals). Focus on the three muscle types: Skeletal (voluntary, striated, multinucleated, rapid contraction, attached to bones), Smooth (involuntary, non-striated, uninucleated, slow sustained contraction, in visceral organs), and Cardiac (involuntary, striated, uninucleated, branched, intercalated discs, rhythmic contraction, only in heart).

Deep dive into skeletal muscle contraction: the Sarcomere is the functional unit. The Sliding Filament Theory explains how actin (thin) filaments slide past myosin (thick) filaments. Remember the changes: A-band length is constant, I-band shortens, H-zone shortens/disappears.

The process begins with a neural signal releasing acetylcholine at the neuromuscular junction. This triggers $Ca^{2+}$ release from the sarcoplasmic reticulum. $Ca^{2+}$ binds to troponin, moving tropomyosin to expose myosin-binding sites on actin.

Myosin heads, energized by ATP hydrolysis (ATP $\rightarrow$ ADP + Pi), form cross-bridges with actin. The release of ADP+Pi causes the power stroke, pulling actin. A new ATP binds, detaching myosin. This cycle continues as long as $Ca^{2+}$ and ATP are present.

Relaxation occurs when $Ca^{2+}$ is pumped back into the sarcoplasmic reticulum.

Review the skeletal system: Axial (skull, vertebral column, ribs, sternum) and Appendicular (limbs, girdles). Understand bone functions: support, protection, movement, mineral storage, hematopoiesis. Master joint classification: Fibrous (immovable, e.

g., skull sutures), Cartilaginous (slightly movable, e.g., pubic symphysis, intervertebral discs), and Synovial (freely movable, with synovial fluid). Know the six types of synovial joints and their examples: Ball-and-socket (shoulder, hip), Hinge (elbow, knee), Pivot (atlas-axis), Gliding (carpals), Condyloid (wrist), Saddle (thumb carpometacarpal).

Finally, quickly revise the key features of musculoskeletal disorders: Myasthenia Gravis (autoimmune, ACh receptors), Muscular Dystrophy (genetic, dystrophin), Tetany (low $Ca^{2+}$), Arthritis (joint inflammation), Osteoporosis (bone mass loss), Gout (uric acid crystals).

Prelims Revision Notes

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Movement vs. Locomotion: — Movement is general change in position of body parts; Locomotion is specific change in entire organism's location.
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Types of Movement:

* Amoeboid: Pseudopodia (e.g., Amoeba, macrophages, leukocytes). Actin polymerization/depolymerization. * Ciliary: Cilia (e.g., Paramecium, tracheal lining, oviducts). Coordinated beating, ATP-dependent. * Flagellar: Flagella (e.g., sperm, Euglena). Whip-like motion, ATP-dependent. * Muscular: Contractile proteins (actin, myosin) in muscle cells.

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Muscle Types:

* Skeletal: Voluntary, striated, multinucleated, cylindrical, rapid contraction, attached to bones. Responsible for locomotion and posture. * Smooth: Involuntary, non-striated, uninucleated, spindle-shaped, slow sustained contraction, in walls of visceral organs (e.g., gut, blood vessels). * Cardiac: Involuntary, striated, uninucleated, branched, intercalated discs (for rapid communication), rhythmic contraction, only in heart.

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Skeletal Muscle Structure:

* Muscle $\rightarrow$ Fascicles $\rightarrow$ Muscle fibers (cells) $\rightarrow$ Myofibrils. * Sarcolemma: Muscle cell membrane. Sarcoplasm: Cytoplasm. Sarcoplasmic Reticulum: Stores $Ca^{2+}$. * Myofibrils: Contain myofilaments (actin and myosin). * Sarcomere: Functional unit, between two Z-lines. Contains A-band (myosin + overlapping actin), I-band (actin only), H-zone (myosin only, within A-band), M-line (center of A-band).

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Sliding Filament Theory of Muscle Contraction:

* Neural signal: ACh released at neuromuscular junction $\rightarrow$ action potential in sarcolemma $\rightarrow$ T-tubules. * **$Ca^{2+}$ release:** Action potential triggers $Ca^{2+}$ release from sarcoplasmic reticulum.

* Binding: $Ca^{2+}$ binds to troponin $\rightarrow$ moves tropomyosin $\rightarrow$ exposes active sites on actin. * Cross-bridge formation: Myosin head (energized by ATP hydrolysis: ATP $\rightarrow$ ADP + Pi) binds to actin.

* Power stroke: ADP + Pi released $\rightarrow$ myosin head pivots $\rightarrow$ pulls actin towards M-line. * Detachment: New ATP binds to myosin $\rightarrow$ myosin detaches from actin. * Re-cocking: ATP hydrolyzed $\rightarrow$ myosin head re-energized.

* Sarcomere changes: A-band length constant. I-band shortens. H-zone shortens/disappears. Z-lines move closer. * Relaxation: $Ca^{2+}$ pumped back into SR (requires ATP) $\rightarrow$ tropomyosin covers actin sites.

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Skeletal System:

* Axial: Skull, vertebral column (26 vertebrae), sternum, ribs (12 pairs). * Appendicular: Limb bones (30 each limb), Pectoral girdle (clavicle, scapula), Pelvic girdle (coxal bones). * Bone functions: Support, protection, movement, mineral storage ($Ca^{2+}$, $PO_4^{3-}$), hematopoiesis.

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Joints (Articulations):

* Fibrous: Immovable (e.g., sutures of skull). * Cartilaginous: Slightly movable (e.g., pubic symphysis, intervertebral discs). * Synovial: Freely movable, synovial cavity with fluid. * Ball-and-socket: Shoulder, hip (multi-axial).

* Hinge: Elbow, knee (uni-axial: flexion/extension). * Pivot: Atlas-axis (rotation). * Gliding: Carpals (sliding). * Condyloid: Wrist (biaxial: flexion/extension, abduction/adduction).

* Saddle: Thumb carpometacarpal (modified condyloid).

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Disorders:

* Myasthenia Gravis: Autoimmune, affects neuromuscular junction (ACh receptors), muscle weakness. * Muscular Dystrophy: Genetic, progressive muscle degeneration (e.g., dystrophin defect). * Tetany: Rapid muscle spasms due to low $Ca^{2+}$ in body fluids.

* Arthritis: Joint inflammation (e.g., Osteoarthritis, Rheumatoid Arthritis). * Osteoporosis: Decreased bone mass, brittle bones (common in older women due to estrogen deficiency). * Gout: Accumulation of uric acid crystals in joints, inflammatory arthritis.

Vyyuha Quick Recall

To remember the key events of muscle contraction (Sliding Filament Theory):

Calm Tigers Always Move Precisely During Reaching

Calcium release
Troponin binds $Ca^{2+}$
Actin sites exposed
Myosin binds actin (cross-bridge)
Power stroke (pulls actin)
Detachment (new ATP binds)
Re-cocking (ATP hydrolysis)