MUSCLES – TYPES, LOCATIONS AND FUNCTION

There are three types of muscles, located at various parts of the body. In order to function all use energy in form of ATP. These include smooth, skeletal and cardiac muscles.

Smooth Muscle (Involuntary Muscles)

These are spindle-shaped and contain filaments with myofibrils. Each muscle is bound by plasma membrane. They are found lining internal organs such as alimentary canal, bladder, and blood vessels. They are controlled by involuntary part of the nervous system.

They are concerned with movement of materials along the organs and tubes. They contract slowly and fatigue slowly.

Skeletal Muscle (striated or voluntary muscle)

1. Skeletal muscles are striated and have several nuclei.
2. They are long fibres each containing myofibrils and many mitochondria.
3. They have cross-striations or stripes.
4. They are also called voluntary muscles because the contraction is controlled by voluntary nervous system.
5. They are surrounded by connective tissue and are attached to bones by tendons.
6. Their contraction brings about movement of bone, resulting in locomotion.
7. They contract quickly and fatigue quickly.

Cardiac Muscle

1. Consist of a network of striated muscle fibres connected by bridges.
2. Are short cells with numerous mitochondria and uninucleate.
3. They are found exclusively in the heart.
4. Contractions of cardiac muscles are generated from within the muscles and are rhythmic and continuous hence they are myogenic.
5. They do not tire or fatigue.
6. The rate can be modified by involuntary nervous system.
7. Their contractions result in the heart pumping blood.

Role of muscles in movement of the human arm

Muscles that bring about movement are antagonistic, i.e. when one set contracts the other relaxes.

Antagonistic muscles of human forelimb

1. The biceps muscles of the forelimb act as flexors while the triceps muscles act as extensors.
2. The biceps has its point of origin on the scapula and the point of insertion on the radius.
3. The triceps has its points of origin on the scapula and humerus and is inserted on the ulna.
4. When the muscles contract, the limb acts as a lever with the pivot at the joint.
5. Contraction of biceps muscles bends (flexes) the arm while contractions of triceps extend the arm.