Muscles

Locomotion in Humans

In all higher organisms (specially animals) movement is generated by contraction of muscles. Some muscles move skeleton while others move visceral organs and heart. Accordingly there are 3 types of muscles which constitute 40-50% of the total body weight. Muscles have properties like excitability, contractility, extensibility and elasticity.

Types of Muscles

• Skeletal muscle,
• Cardiac muscle,
•  Smooth muscle

Skeletal muscle :

These generate external movement associated with skeleton, remain attached to bones through tendon, under conscious control hence also termed as voluntary muscle. In lower magnification these have transverse stripes hence also called as striped or striated muscle.

Cardiac muscle

This is also striated muscle but under involuntary control, hence has rhythmic pattern of contraction with varying frequency. This is untiring muscle (no fatigue) and keeps on acting life long.

Being striated it is structurally similar to skeletal muscle except the presence of

• Cross fibres, besides parallel fibres
• Intercalated discs — which represent the joints of two myoblasts.

Contraction pattern is rhythmic and also fast controlled by autonomic nervous system (ANS).

Untiring muscle (no fatigue), works ceaselessly throughout the life.

Generates impulse like nerve (i.e. myogenic heart of vertebrates).

Smooth Muscle:

Unstriped; hence structurally different from above two types.

Muscle cell spindle-shaped (not cylindrical), uninucleated each formed of single myoblast.

Actin filaments remain attached, to dense bodies in the cytoplasm.

Actin and Myosin filaments not arranged in any pattern hence no striations.

Involuntary muscle, under ANS control is found in visceral organs (visceral muscle). Contraction, termed as peristalsis, is rhythmic, slow and prolonged.