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KEY WORDS KEY WORDS A2 Chapter 3 - MUSCLES
Skeletal muscle: the muscle that causes our bodies to move, also called striated muscle.
Myofibril: part of a muscle fibre, contains sarcomeres and the contractile proteins actin and myosin.
Sarcoplasmic reticulum: equivalent to the endoplasmic reticulum of cells. It forms a network of
channels that spread out over the surface of the myofibrils and acts as a store of calcium ions that
when released initiate muscle contraction.
Sarcoplasm: the equivalent of cytoplasm the liquid interior of a muscle fibre.
A band: the dark band in a myofibril.
I band: the light band in a myofibril.
H zone: the lighter region in the centre of the A band.
Z line: the darker region in the centre of the I band.
Sarcomere: the repeating unit of a myofibril, goes from one Z line to another.
Myosin: thick protein filament.
Actin: thin protein filament.
Troponin: globular protein on actin.
Tropomyosin: thread-like protein that winds around the surface of actin.
Transverse tubules: a network of folds/tubes from the membrane of a myofibril that provides
access for electrical activity to the inside of the myofibril.
Slow-twitch muscle fibres: contract up to 10 times as slowly as fast-twitch fibres but have greater
Fast twitch type IIa (FOG): characteristics are fast contraction, large force, fatigues easy.
Fast twitch type IIb (FG): characteristics are very rapid contractions, very large forces, fatigues very
Motor Unit: a motor neurone and its muscle fibres.
All of nothing law: muscles fibres either contract or do not contract; there is no such thing as a
Spatial summation: changes in strength of contraction are brought about by altering the number
and size of motor units involved.