Origins and insertions Muscles are often said to have an origin at one end and an insertion at the other. The origin (the one that moves least on contraction) is often proximal, the insertion distal. Often a muscle arises from more than one place: it is then said to have two or more heads (biceps, triceps). In some circumstances origin and insertion can be interchanged, so it is easier to talk of attachments. Forms of muscles Wide functional variation in terms of size and shape according to job done. The size of the functional component, the muscle fibre varies from 10-60*m in diameter, and mm to 15-30 cm in length. Diameter, length and arrangement of fascicles (bundles of fibres) varies from muscle to muscle: fine bundles in precision muscles, coarse ones in power muscles. Fascicles may be parallel, or oblique or spiral according to position of attachments. Lets look at some variants and see if we can explain them. The simplest is probably the
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