The muscular system

The bones and joints provide leverage and form the framework of the body, they are incapable of movement themselves.

Motion results from the contraction and relaxation of muscles.

Muscle tissue constitutes about 40 - 50 % of total body weight.

Muscle characteristics

There are four principle characteristics

i. Excitability

The ability of muscle tissue to receive and respond to stimuli. A stimulus is a change in the internal or external environment strong enough to initiate an response

ii. Contractility

The ability of muscle tissue to actively contract

iii. Extensibility

The ability of the muscle tissue to be stretched. Many skeletal muscles are arranged in opposing pairs. While one is contracting the other is relaxed and undergoing extension.

iv. Elasticity

The ability to return to an original shape after contraction or extension

How muscles are named

Names of nearly 700 skeletal muscles are based on several types of characteristics

1. May indicate direction of the muscle fibres

Rectus usually parallel to midline

Oblique - diagonal to midline

2. May be named according to location -tibialis anterior

3. Size - maximus, medius, minimus, longus, brevis

4. Number of origins - biceps brachii, quadriceps femoris

5. Named on basis of shape - deltoid = triangular

6. After origin or insertion - Sternocleidomastoid

7. Their actions - flexor, extensor, rotator abductor

Structure of a skeletal muscle

Muscle tissue consists of fibres that are highly specialised for the active generation of the force of contraction.

Muscles are attached to bones via trendons

It is Striated i.e.

The fibres contain alternated light and dark bands, striations that are perpendicular to the long axis of the fibres.