17Class 11 Biology
Locomotion and Movement short notes
Short notes on muscle contraction and the human skeleton. Learn the bone counts and the sliding filament steps.
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Muscle
- Muscles are made of fascicles, fibres and myofibrils. The sarcomere runs between two Z lines.
- The I band has thin actin filaments, and the A band has thick myosin filaments. The H zone sits in the A band.
- In contraction, thin filaments slide over thick ones. The sarcomere and I band shorten, and the A band stays the same.
- Calcium binds troponin, exposing sites on actin, and myosin uses ATP to form cross bridges.
- Red fibres have much myoglobin and are aerobic. White fibres have less, and are anaerobic.
Skeleton (206 bones)
- Axial skeleton: 80 bones. Skull 22, vertebrae 26, sternum 1, ribs 24, hyoid 1, and ear ossicles 6.
- Appendicular skeleton: 126 bones.
- Vertebrae: cervical 7, thoracic 12, lumbar 5, sacral 1 and coccygeal 1.
- Ribs: true 7 pairs, false 3 pairs and floating 2 pairs.
- Each limb has 30 bones.
Joints and disorders
- Fibrous joints (skull) don't move, cartilaginous ones (vertebrae) move a little, and synovial ones (knee) move freely.
- Myasthenia gravis: an autoimmune disorder of the neuromuscular junction.
- Muscular dystrophy: progressive genetic muscle weakness.
- Arthritis affects joints, and osteoporosis lowers bone mass.
- Tetany: rapid spasms caused by low blood calcium.
Where students slip up
- Saying the A band shortens in contraction. It stays the same.
- Counting 33 vertebrae. An adult has 26, since some fuse.
- Mixing up actin (thin) and myosin (thick).
Try it on your weakest chapter.
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