Medicine

Muscle tissue is characterized by properties that allow movement. Muscle cells are excitable; they respond to a stimulus. They are contractile, meaning they can shorten and generate a pulling force. When attached between two movable objects, in other words, bones, contractions of the muscles cause the bones to move. Some muscle movement is voluntary, which means it is under conscious control. For example, a person decides to open a book and read a chapter on anatomy. Other movements are involuntary, meaning they are not under conscious control, such as the contraction of your pupil in bright light. Muscle tissue is classified into three types according to structure and function: skeletal, cardiac, and smooth.

The zygomatic [os zygomaticum] or malar bone forms the prominence known as the cheek and joins the zygomatic process of the temporal with the maxilla. It is quadrangular in form with the angles directed vertically and horizontally. The malar (or external) surface is convex and presents one or two small orifices for the transmission of the zygomatico-facial nerves and vessels. It is largely covered by the orbicularis oculi and near the middle is slightly ele- vated to form the malar tuberosity, which gives origin to the zygomaticus and zygomatic head of quadrate muscle of upper lip.

The defining characteristic of the somatic nervous system is that it controls skeletal muscles. Somatic senses inform the nervous system about the external environment, but the response to that is through voluntary muscle movement. The term “voluntary” suggests that there is a conscious decision to make a movement. However, some aspects of the somatic system use voluntary muscles without conscious control. One example is the ability of our breathing to switch to unconscious control while we are focused on another task. However, the muscles that are responsible for the basic process of breathing are also utilized for speech, which is entirely voluntary.

The mandible [mandibula] or lower jaw-bone is the largest and strongest bone of the face. It supports the mandibular teeth, and by means of a pair of condyles, moves on the skull at the mandibular fossae of the temporal bones. It consists of a horizontal portion — the body —  strongly curved, so as to somewhat resemble in shape a horseshoe, from the ends of which two branches or rami ascend almost at right angles.

The maxillae are two hollow irregular cuboidal bones with two prominent processes. They form a large portion of the facial skeleton.

The oral cavity is the first portion of the entire digestive tract. It is an irregularly shaped, elongated cavity, situated in the lower portion of the face, and its boundaries are partly bony and partly musculocutaneous. It is divided by the two rows of teeth into two incompletely separated spaces, the vestibulum oris and the oral cavity proper.

The spleen is a large blood-vascular organ closely associated with the lymphatic system.

The stomach is a sac-like dilatation of the digestive tube intervening between the oesophagus and the intestine.

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