Page 29 - ASOP ROT Study Guide

5 . 2 Skeletal Muscles

Muscles produce forces which maintain posture as well as producing movement from place to
place (locomotion). Muscles also produce heat when they are active and this is used to maintain
body temperature.

A muscle causes movement when it contracts and shortens, pulling on the bones to which it is
attached. This pull results in movement at the joint between the bones. The muscles that
produce movement at a joint are connected to the bones on either side of the joint - they are said
to cross the joint. Some muscles cross more than one joint so contraction of these muscles can
cause movement at both joints. In most cases the body of the muscle itself does not lie across
the joint. It is usually on the proximal side of the joint and is connected to the distal bone by a
long narrow structure known as a tendon. The tendon consists of tough fibrous tissue. If the
attachment of a muscle to bone is by a short, wide, sheet-like fibrous tissue structure, the
attachment is called an aponeurosis).

One end of a muscle's attachment to bone is called the origin and the other end the insertion.
The origin is always on the less mobile bone and the insertion is always on the more mobile
bone. For the limbs this means that the origin of a muscle is always proximal and the insertion
distal.

The movement of any of the major joints involves the coordinated action of many muscles.
Those involved in producing the movement are called agonists while those opposing the
movement (causing the opposite movement) are called antagonists. The most powerful
muscle causing movement in a particular direction is called the prime mover.