Structure: The Body’s Muscles

Muscles consist of tissue that can contract powerfully to move the body, maintain its posture, and work the various internal organs, including the heart and blood vessels. These functions are performed by three different types of muscle, of which skeletal muscle makes up the greatest bulk. (Many of the body’s skeletal muscles are identified, image here.) Usually each end of a skeletal muscle is attached to a bone by a tendon, a flexible cord of fibrous tissue. The skeletal muscles may be controlled consciously to produce movement.

Muscle

Muscle fibres

Myofibril

Structure of skeletal muscle

Bundles of closely packed muscle fibres form skeletal muscle. Each muscle fibre is made up of smaller units called myofibrils. Within each myofibril are strands of thick and thin myofilaments. When stimulated by nerve impulses, these elastic filaments slide in between each other, like interlacing fingers, causing the contraction of each myofibril and, ultimately, of the whole muscle.

Types of muscle

The three types of muscle are skeletal muscle, which covers and moves the skeleton; cardiac (heart) muscle, which pumps blood around the body; and smooth muscle, which is found in the walls of the digestive tract, blood vessels, and the genital and urinary tracts. Smooth muscle performs the unconscious actions of the body, such as propelling food along the digestive tract.

Skeletal muscle

This type of muscle is formed of long, strong, parallel fibres, which are able to contract quickly and powerfully, but can do so only for short periods of time.

Cardiac muscle

Short, branching, interlinked fibres form a network within the wall of the heart. Cardiac muscle contracts rhythmically and continually without tiring.

Smooth muscle

These fibres are short, spindle-shaped, and thinner than skeletal muscle fibres. Smooth muscle cells form sheets of muscle that can contract for prolonged periods.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

Back to top