Anatomical terms of location: Difference between revisions

In anatomy and biology, several terms are used to describe the location of organs and other structures in the body of bilateral animals. These terms are listed and explained here. For some specific details of human anatomy, see anatomical position.

Directions

Animals typically have one end with a head and mouth, with the opposite end often having the anus and tail. The head end is the cranial (or rostral) end; the tail end is the caudal end.

When the animal is in its normal position of motion, the front end is anterior and the back end is posterior. In most animals (but not in humans) "cranial" or "rostral" is therefore synonymous with "anterior", while "caudal" is synonymous with "posterior".

The side of animals with the spine or nerve chord is the dorsal side; the opposite side, typically the one closest to the ground when walking on all legs, swimming or flying, is the ventral side. For example: a cow's udder is on the ventral side. A dolphin's dorsal fin is, unsurprisingly, on the dorsal side.

In human anatomy, because of the erect posture of humans, the terms are used as follows. One pictures a standing human and uses the terms upper (superior) and lower (inferior) accordingly. The anterior side is the front with the nipples and navel; the posterior side is the back. The terms "anterior" and "ventral" are therefore synonymous in human anatomy, as are the terms "posterior" and "dorsal".

Planes

Sometimes the orientation of certain planes need to be distinguished, for instance in medical imaging techniques such as CT scans, MRI scans or PET scans. One imagines a human in anatomical position (standing, arms hanging down with palms to the front) and an X-Y-Z coordinate system with the X-Y plane parallel to the ground, the X-axis going from left to right, the Y-axis passing from front to back, and the Z-axis going up and down.

• A transverse or axial plane is an X-Y plane, parallel to the ground, which (in humans) separates the superior from the inferior, or put another way, the head from the feet.
• A coronal or frontal plane is an X-Z plane, perpendicular to the ground, which (in humans) separates the anterior from the posterior, the front from the back, the ventral from the dorsal.
• A sagittal plane is a Y-Z plane, perpendicular to the ground and to the coronal plane, which separates left from right. The midsagittal plane is the specific sagittal plane that is exactly in the middle of the body.

Relative directions

Structures near the midline are called medial and those near the sides of animals are called lateral. Therefore, medial structures are closer to the midsagittal plane, lateral structures are further from the midsagittal plane. Structures in the midline of the body are median. For example, your cheeks are lateral to your nose and the tip of the nose is in the median line.

Structures that are close to the center of the body are proximal or central, while ones far removed are distal or peripheral. For example, the hands are at the distal end of the arms, while the shoulders are at the proximal ends. These terms can also used relatively to organs, for example the proximal end of the urethra is attached to the bladder.

Structures on or close to the body´s surface are superficial and those further inside are profound or deep.

When speaking of inner organs, visceral means close to or attached to the organ, while parietal is more distant. For example, the visceral pleura is attached to the lung and the parietal pleura is attached to the chest wall.

Relative Motions

Flexion means approximating adjacent parts of the body (usually at a joint) and extension means separating them. For example, the legs are are flexed at the knee joints when sitting down, and extended when standing up. Generally, flexion produces an acute angle between adjacent parts, with its vertex at the joint, and extension produces an obtuse angle.

Adduction means moving a part of the body toward or past its median line or toward the long axis of a limb. Abduction means moving a part of the body away from its median line or away from the long axis of a limb. For example, adducting the thighs brings the legs together, and abducting the thighs spreads the legs apart. Similarly, adducting the fingers brings them into contact with one another, and abducting the fingers spreads them apart.

Rotation means moving a part about its long axis, for example turning the neck. Pronation means rotating a part to the opposite direction of its anatomical position. Supination means rotating a part back to its anatomical position. For example, the hand can be pronated and supinated at the wrist.

An anterograde motion is in the normal direction of flow, while retrograde means reversed flow. For example, passage of food from the mouth to the stomach is in an anterograde direction, and gastric reflux is in a retrograde direction.