AIEM — ICSE Exam Prep

Locomotion and Movement

Movement is an essential feature of all living beings. A voluntary movement that changes an animal's place or location is called locomotion. All locomotions are movements, but all movements are not locomotions.

Types of movement

Cells of the human body show three main movements:

Amoeboid - by pseudopodia formed by streaming of protoplasm; uses microfilaments (e.g. macrophages, leucocytes).
Ciliary - in internal tubular organs lined by ciliated epithelium (e.g. trachea clears dust; oviduct moves ova).
Muscular - movement of limbs, jaws, tongue, etc.; used for locomotion and posture.

Muscle

Muscle is a specialised tissue of mesodermal origin, forming about 40-50% of body weight. Properties: excitability, contractility, extensibility, elasticity. By location there are three types - Skeletal (striated, voluntary), Visceral/smooth (nonstriated, involuntary) and Cardiac (striated, branched, involuntary).

Skeletal muscle structure

Muscle is made of bundles (fascicles) held by fascia; each fascicle has muscle fibres lined by sarcolemma enclosing sarcoplasm (a syncitium - many nuclei). The sarcoplasmic reticulum stores Ca++. Myofibrils show alternating dark A bands (myosin, thick filaments) and light I bands (actin, thin filaments). The Z line bisects the I band; the M line holds thick filaments; the H zone is the thin-filament-free centre of the A band. A sarcomere (between two Z lines) is the functional unit.

Mechanism (sliding filament theory)

Contraction occurs by thin filaments sliding over thick filaments. A motor neuron releases acetylcholine at the neuromuscular junction, generating an action potential that releases Ca++. Ca++ binds troponin, unmasking actin's active sites; the myosin head (an ATPase) binds actin forming a cross bridge, pulling actin inward and shortening the sarcomere (I band reduced, A band unchanged). Ca++ is then pumped back, masking actin and causing relaxation. Fatigue is due to lactic acid from anaerobic glycogen breakdown. Red fibres (high myoglobin, many mitochondria) are aerobic; white fibres (low myoglobin, high sarcoplasmic reticulum) are anaerobic.

Skeletal system

206 bones, grouped into axial (80 bones - skull, vertebral column, sternum, ribs) and appendicular (limb bones and girdles). Skull = 22 bones (8 cranial + 14 facial); hyoid is U-shaped; ear ossicles are malleus, incus, stapes. Vertebral column = 26 vertebrae (cervical 7, thoracic 12, lumbar 5, sacral 1 fused, coccygeal 1 fused); first vertebra is the atlas. 12 pairs of ribs: true (1-7), vertebrochondral/false (8-10), floating (11-12).

Joints and disorders

Joints are fibrous (no movement, e.g. skull sutures), cartilaginous (limited, e.g. between vertebrae) and synovial (considerable, fluid-filled cavity). Disorders: myasthenia gravis (autoimmune, neuromuscular junction), muscular dystrophy (genetic muscle degeneration), tetany (low Ca++), arthritis (joint inflammation), osteoporosis (decreased bone mass, low estrogen), gout (uric acid crystals in joints).