MUSCULAR TISSUE | MOTION OF THE WORLD | Medicoze

This is a contractile tissue. There are skeletal, smooth and cardiac muscles.

Skeletal (striated, voluntary) muscle

This acts mainly on the bony skeleton or as a diaphragm, but it is also found around the pharynx and larynx, and forms some sphincters. It is composed of unbranched fibres of sarcoplasm limited by a membrane, the sarcolemma, and contains many nuclei. Each fibre has a motor endplate and contains many contractile units, the myofibrils, which have

alternating dark (A) and light (I) bands. A dark line (the Z disc) crosses the middle of the I band. The bands of adjacent myofibrils coincide, giving the muscle fibre its striated appearance.Each fibre is enveloped and attached to its neighbour by a fibrous endomysium, and bundles of fibres are enclosed by a fibrous perimysium. A muscle composed of many bundles is

surrounded by an epimysium.The motor nerve supply of the muscle comes from the anterior horn cells of the spinal cord and the motor nuclei of the brainstem. The sensory supply arises in the more specialized spindles and tendon organs as well as the simpler touch

and pain endings. Impulses from the sensory endings pass into the posterior horn of the spinal cord.Skeletal muscles are formed by voluntary fibres. The muscles are usually attached at each end to bone, by the periosteum,either directly or through tendons and aponeuroses,and cross one or more joints. Occasionally two muscles meet

at a common stretchable union known as a raphe. Muscles have a very rich blood supply.

Muscle fibres are arranged either parallel

to the direction of the action (sartorius), or obliquely to it.

aponeurosis  is a flat, thin tendinous expansion

providing a wide attachment, as seen in the abdominal wall muscles. When a movement occurs at a joint, the muscles concerned

in producing it are known as the prime movers

or agonists and those opposing it as antagonists. Muscles contracting to steady the joint across which movement is occurring are known as synergists. A further type of action is known as the action of paradox, in which a muscle gradually relaxes against the pull of gravity, e.g. bending forwards produced by relaxing the back muscles.