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5.4 Locomotion and Movement
Structure of Skeletal Muscle
Muscle → Fascicles → Muscle Fibres → Myofibrils
Sarcomere:
The functional unit of a myofibril, between two Z-lines.
Myofilaments:
Actin (Thin Filament):
Contains troponin and tropomyosin.
Myosin (Thick Filament):
Has a head (cross-arm) with an ATPase site.
Sliding Filament Theory
Signal
from CNS releases
acetylcholine
at the neuromuscular junction.
Action potential causes
Ca²⁺ release
from the sarcoplasmic reticulum.
Ca²⁺ binds to
troponin
, exposing active sites on actin.
Myosin heads
bind to actin, forming a
cross-bridge
.
Myosin heads pull actin filaments towards the center of the sarcomere (
power stroke
).
ATP binds to myosin, breaking the cross-bridge.
The cycle repeats as long as Ca²⁺ and ATP are present.
Red vs. White Muscles
Feature
Red Muscles (Slow)
White Muscles (Fast)
Myoglobin
High
Low
Mitochondria
Numerous
Few
Contraction
Slow, sustained
Fast, short duration
Fatigue
Resistant
Prone to fatigue
The Skeleton
Axial Skeleton (80 bones):
Skull:
Cranium (8), Face (14)
Vertebral Column:
26 vertebrae
Sternum & Ribs:
12 pairs
Appendicular Skeleton (126 bones):
Girdles:
Pectoral (shoulder), Pelvic (hip)
Limbs:
Arms and Legs
Joints
Fibrous Joints:
Immovable (e.g., skull sutures).
Cartilaginous Joints:
Slightly movable (e.g., between vertebrae).
Synovial Joints:
Freely movable, contain synovial fluid.
Types of Synovial Joints
Ball and Socket:
Shoulder, hip.
Hinge:
Knee, elbow.
Pivot:
Between atlas and axis vertebrae.
Gliding:
Between carpals (wrist bones).
Saddle:
Between carpal and metacarpal of the thumb.
Muscular & Skeletal Disorders
Myasthenia Gravis:
Autoimmune, affects neuromuscular junction.
Muscular Dystrophy:
Genetic degeneration of muscle.
Tetany:
Muscle spasms due to low Ca²⁺.
Arthritis:
Inflammation of joints.
Osteoporosis:
Decreased bone mass.
Gout:
Uric acid crystal accumulation in joints.