Human Anatomy Health Article

Definition

Human anatomy is the study of the structure of the human body and the relationship between its parts.

Anatomic position

Discussions on the subject of human anatomy assume that the person is standing erect, feet slightly apart, arms by the side with palms facing forward, thumbs pointing away from the body. This is referred to as the anatomic position and acts as a common reference point for anatomists (an expert or student of anatomy). If the body is lying face up, it is referred to as supine, if it is lying face down, the body is in a prone position.

Various structures can be described in relation to any number of imaginary flat surfaces or planes that bisect the body. The median sagittal plane is a vertical plane that passes through the center of the body, dividing it into right and left sides. The coronal plane, on the other hand, is a vertical plane that is perpendicular to the sagittal plane and divides the body into front and back halves. A paramedian plane passes vertically through the body at any point parallel to the median sagittal plane, while a horizontal or transverse plane is perpendicular to both the sagittal and coronal planes. A plane on an angle to the transverse plane is called an oblique plane.

A number of terms can be used to describe the location of body structures in relation to the above planes. One structure that is closer to the sagittal plane than another is said to be medial, while one that is farther from the sagittal plane is lateral (e.g. the heart is medial to the left lung). Structures found on the same side of the median sagittal plane are referred to as ipsilateral, while those on opposite sides of the body are called contralateral. A structure is anterior or ventral if it is before or in front of

another structure, and posterior or dorsal if it found after or behind (e.g. the trachea or windpipe is anterior to the esophagus). Superior or cranial structures are found closer to the top or crown of the head than inferior or caudal structures (e.g. the heart is superior to the stomach). It is important to remember that the terms left and right are used from the perspective of the person being viewed, not the observer; for instance, the right lung would be on the left hand side of a body as viewed by an observer.

The head, neck, and trunk (the main axis) make up the axial portion of the body while the appendages or limbs compose the appendicular portion. To describe the limbs, the term proximal refers to a structure that is closer to the limb origin; a distal structure is farther from the limb origin (e.g. the wrist is distal to the elbow). The hand has a palmar surface (the anterior side) and a dorsal surface (the posterior side). The upper surface of the foot is called the dorsal surface, while the bottom side is called the plantar surface. Superficial structures are located nearer to the surface of the body; those found farther from the surface are referred to as deep structures (e.g. the skin is superficial to the skeletal muscles). Internal structures are found inside of an organ or cavity, in contrast to external surfaces which are found outside (e.g. alveoli are internal to the lungs).

Terms of movement

A joint is a site where two or more bones come together. Some joints allow no movement between bones(e.g. the bones of the skull); others allow only slight movement (e.g. the joints between bones of the vertebral column). Still other joints allow free movement (e.g. the hip joint). There are subsequently numerous terms to describe the various movements that joints can make.

Flexion is the bending of a joint, typically in the anterior direction; an example is the bending of the arm at the elbow. In contrast, the term extension describes the straightening of a joint; an example is the straightening of the leg at the knee. Abduction is the movement of a joint away from the midline along the coronal plane, while adduction is the movement toward the midline along the same plane; the arm, for example, abducts at the shoulder if it moves away from the torso in the same plane. Rotation occurs when a body part moves around its axis; medial rotation results in the anterior surface facing medially and lateral rotation results in the anterior surface facing laterally. The term pronation describes movement of the hand so that it faces posteriorly; supination causes the hand to face anteriorly. Circumduction is a movement that combines flexion, extension, abduction, and adduction; circling the arm around the shoulder joint is an example.

The term protraction describes a motion forward and retraction a motion backward; these describe the movement of the mandible (jaw) at the temporomandibular joints. Inversion occurs when the sole of the foot is turned to face the median (this would happen if you tried to stand on the outer side of your foot); eversion is movement that causes the sole of the foot to face laterally.