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Muscle Contraction

Structure of skeletal muscle
There are three types of muscle in the body:

Cardiac muscle which is found exclusively in the heart
Smooth muscle
which is found in the walls of blood vessels and the gut
Skeletal muscleis attached to bone and acts under voluntary, conscious control.


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At the centre of each A band is a lighter coloured region
called the H zone and at the centre of each I band is a line
called the Z line. The distance between adjacent Z lines is
called a sarcomere . When a muscle contracts, these
sarcomeres shorten and…

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with the presynaptic membrane an release their acetylcholine. The acetylcholine diffuses to the
postsynaptic membrane, altering its permeability to sodium ions, which enter rapidly, depolarising
the membrane.

The acetylcholine is broken down by acetylcholinesterase to ensure that the muscle is not
over-stimulated. The resulting choline and ethanoic acid (acetyl) diffuse…

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The myosin then reattaches itself further along the actin filament and the cycle is repeated as
long as nervous stimulation of the muscle continues.


When nervous stimulation ceases, calcium ions are actively transported back into the
sarcoplasmic reticulum, using energy from the hydrolysis of ATP.
This reabsorption of the…


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