In human and zoological anatomy 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.
The anatomical position holds more relevant information on relations and terms of location for human anatomy.
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 end; the tail end is the caudal end. Within the head itself, rostral refers to the direction toward the end of the nose, and caudal is still used to refer to the tail direction.
The surface or side of the body normally oriented upwards, away from the pull of gravity, 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: in vertebrates, the spine or nerve chord is located on the dorsal side of the organism. A cow's udder is on the ventral side. A dolphin's dorsal fin is, unsurprisingly, on the dorsal side.
On the limbs or other appendages, a point closer to the main body is "proximal"; a point farther away is "distal".
The anatomical position is a schematic convention for describing the relative morphology of the human body. All terms in the study of anatomy refer to when the body is in this position.
The person is oriented
In an erect standing position
Eyes and head facing forward
Feet forward and perpendicular to the body
Arms close to the sides and palms of the hands facing forward with fingers extended.
*It should be noted that this is not the normal position that arms rest in.
Median and Sagittal planes
The body in anatomical position may be divided conceptually by planes. The median plane passes from the top to the bottom of the body and separates the left and the right sides of the body in equal halves.
Positions toward the median plane are called medial, and positions away from the median plane are called lateral. Hence ipsilateral refers to things on the same side, contralateral to something on the opposite side and bilateral to both sides.
A sagittal plane is any plane parallel to the median and hence the median plane is also called the midsagittal plane. A sagittal slice or section that is not on the median plane is also referred to as a parasagittal section.
The frontal or coronal plane essentially separates the body into the forward half and the back half. This plane is perpendicular to the median and also passes from the top to the bottom along the long axis of the body. The term posterior refers to objects on the back half of the body, behind the coronal plane and the term anterior refers to objects in front of this plane.
The horizontal or transverse plane is perpendicular to both of these planes and is the plane, which divides the body into an upper and a lower half. Positions above the transverse plane are called superior, and positions below the transverse plane are called inferior. In comparative anatomy, superior may be called the rostral (beak) or cranial (head) end. Inferior may be referred to as the caudal or (tail) ends.
Planes in between these three are known as oblique planes.
All acts of movement are considered to be a mixture or a single contribution of the following movement terms:
Flexion - where there is a reduction in the angle between bones or parts of the body. This term applies only to movement along the sagittal or median plane. An example of arms flexing is lifting a dinner plate. When applied to the trunk of the body, this term means bowing forwards.
Extension - is the opposite of flexion, and there is an increase in the angle. This term applies only to movement along the sagittal or median plane. With the trunk of the body, this movement is bowing backwards.
Adduction - where there is a reduction in the angle between bones or parts of the body. This only applies to movement along the coronal plane. An example of this is where extending arms outwards as if to fly.
Abduction - the exact opposite, with an increase in the angle. Also only applies to movement along the coronal plane.
Rotation - is rotation of an entire limb clockwise (laterally) or anti-clockwise (medially).
Pronation - this is the rotation of the hand so that the palm faces posteriorly. This is not medial rotation as this must be performed when the arm is half flexed. Prone means the hand is facing posteriorly.
Supination - the rotation of the hand so that the palm faces anteriorly. The hand is supine (facing anteriorly) in the anatomical position.
Protrusion - is the anterior movement of an object. This term is often applied to the jaw.
Retrusion - the opposite of protrusion.
Elevation - superior movement. This term is often applied to the shoulders (Eg. shrugging shoulders is elevation)
Depression - inferior movement, opposite of elevation.
Circumduction - is a special case of movement involving adduction, flexion, extension and abduction. The resulting movement creates a circular path of movement. The only joint in the human body capable of circumduction is the shoulder.
There are several cases where the meaning of these planes are slightly different. Hence new definitions for movement applies. This is apparent in the foot, the tongue, the hand, the penis, the brain and sometimes and the perineum.
Foot and Hand
Since the foot is discontiguous with the coronal plane, it is described by analogy and with embryological considerations, with the hand.
The palm (adj palmar) of the hand corresponds to the sole (adj plantar) of the foot, and the dorsum (back) of the hand corresponds to the dorsum (top) of the foot.
From this, the term dorsiflexion means to flex upwards (true flexion) and the term plantarflexion, meaning to extend downwards (true extension) are derived.
The term volar, used mainly in orthopaedics, is synonymous with palmar and plantar.
The foot is also capable of movement along another axis due to the flexibility of the ankle joint. These movements are
Eversion - the movement of the sole of the foot away from the median plane.
Inversion - the movement of the sole towards the median plane. (same as when an ankle is twisted.)
The position of the hand in anatomical position is considered supine, such that rotation of the hand so that the palm faces backwards is called pronation and the reverse action, supination.
In the anatomical position, the penis is considered to be erect and pointing upwards, i.e. the dorsal side of the penis is what one would normally call its topside.
The tongue has a dorsal side, which is facing upwards (the side that tastes and licks).
The perineum is a special place for obstetricians and gynecologists. The professions regard the perineal body in the perineum to be the center of everything and an important landmark. A lot of anatomy is based on relations to this body and so the terminology is affected.
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. Ipsilateral means on the same side, contralateral means on the other side and bilateral means on both sides.
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 be used relatively to organs, for example the proximal end of the urethra is attached to the bladder.
Structures on or closer to the body surface are superficial (or external) and those further inside are profound or deep (or internal).
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 Directions in the Limbs
In the limbs of most animals, the terms cranial and caudal are used in the regions proximal to the carpus (the wrist, in the forelimb) and the tarsus (the ankle in the hindlimb). Objects and surfaces closer to or facing towards the head are cranial; those facing away or further from the head are caudal. This usage is not common in human anatomy, however.
Distal to the carpal joint, the term dorsal replaces cranial and palmar replaces caudal. Similarly, distal to the tarsal joint the term dorsal replaces cranial and plantar replaces caudal. For example, the top of a dog's paw is its dorsal surface; the underside, either the palmar (on the forelimb) or the plantar (on the hindlimb) surface.
The sides of the forearm are named after its bones: Structures closer to the radius are radial, and structures closer to the ulna are ulnar. Similarly, in the lower leg, structures near the tibia (shinbone) are tibial and structures near the fibula are fibular (or peroneal).
Volar, a term which refers to both the palm and the sole, is sometimes used as a synonym for "palmar".
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