Major Muscles and Muscle Groups

Facial Muscles
The muscles used in facial expression are unique in that they are attached to various parts of the facial skin. They surround and radiate from the vital orifice of the face; the mouth, nostrils, eyes and ears. Some muscles open these orifices write, others narrow or close them.

Muscles of Mastication
Four large muscles on each side move the jaw. The temporal (in the temple) and the masseter (on the side of the jaw) can be felt when a person bites forcibly. The other muscle help provide the motions needed for grinding food between the molars.

Tongue, Swallowing, and Speech Muscles
The tongue is almost all muscle, and it is capable of very precise, complicated, and elaborate movements. In eating, the tongue moves food around, in swallowing, it pushes food into the throat, and in taking, it articulates the sounds coming from the larynx. Once food enters the pharynx (the throat) it is moved down into the esophagus by waves of muscle contraction. Special sets of muscles guard the larynx. Others alter the tension and position of the vocal cords.

Respiratory Muscles
Deep in the neck and between the ribs are muscles that lift and regulate the ribs during inspiration, they relax completely during expiration. Even more important to breathing is a dome shaped horizontal partition, the diaphragm, below the lungs and above the abdominal cavity. Its contraction greatly enlarges the chest and draws air into the lungs with each inspiration.

Abdominal Wall Muscles
Layer of muscle enclose and can greatly compress the contents of the abdomen. This forceful, the contents of the colon and rectum during bowel movements, and the baby from a woman's uterus. In each each of this cases, smooth muscle in the walls of the hollow organs also take part in the expulsion of the contents. Further, each of the outlets is guarded by a ring of striated (voluntary) muscle that can be trained to prevent uncontrolled expulsions.

Back Muscles
The vertebral column has a great number of muscle bundles that help to position and move it. When cough off guard, these muscles can be strained, causing spasms and pain.

Shoulder and Hip Muscles
The scapula (shoulder blade) must be kept constantly in a proper position so that the upper limb and hand may be used. Large muscles radiate from it to the chest wall, spinal column, and skull. The shoulder joint is capable of many movements, because it has flexors, extensors, abductors, adductors, and rotators.

The hip bones are much less mobile, the huge muscles at the top are concerned mostly with moving and stabilizing the hip joint. This joint also requires a complete complement of muscles, the larges of which is a gluteus maximus, which is important in climbing and running.

Limb Muscles
Emphasis in the arms and legs is on opposing groups of flexors and extensor muscles on the front and back of each limb. Almost all the muscles act on the joints just below them, some go on into the hand or foot to act as flexors and extensors of the digits. In addition, the digits have many small local muscles that produce fine movements.

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