How do muscles contract?
Muscle fibres are long, thin, tapered cylindrical cells full of the mechanisms required to convert chemical energy into movement. Fibres are arranged parallel to each other and usually lengthways. A sheath of collagen surrounds individual fibres. Bundles of fibres and the whole muscle are surrounded by more connective tissue. Blood vessels, motor neurons (the sort of nerve that innervates muscle fibres) and other nerves wind in between the bundles.
The contractile apparatus in each muscle fibre is arranged in parallel long cylindrical strands, called myofibrils. Actin and myosin are the contractile protein polymers contained in myofibrils and they too are long and lie parallel and lengthways. Using energy derived from ATP, the actin and myosin "filaments" attach via cross bridges and slide past each other in opposite directions, thus causing a contraction.
Just like an oar in a rowing boat, it reaches out from the myosin filament (or rowing boat) and grabs on to the actin (or water), and pulls the actin towards it and then pushes it away. The cross-bridge oar is then recycled so it can grab on to another bit of actin (water) and so continue the contraction. This is the "sliding filament' and cross-bridge theories which explains how muscles shorten.
Sunday 29/11/09 NSC will be having a beach training session! Meet at Merewether baths at 12pm sharp.
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