Human anatomical terms

Human anatomical terms make up a distinct nomenclature to describe areas of the body, to provide orientation when describing parts of human anatomy, and to distinguish different movements of the body. An understanding of these terms is necessary to study the human body in depth. Many of these terms are also applicable in animal anatomy (zootomy).

Origin of terms
Many English anatomical terms originate from Latin and Greek and were even in use 2000 years ago. It is helpful to know that Latin words change their endings to pluralize words. Common conversions include words singular words ending in –us change to –i, -um to –a, and –a to –ae. Occasionally, newer terms have been introduced and are used alongside older terms. Some terms are also eponymous, but many of these have been replaced with more descriptive words and phrases.

Anatomical body position
The anatomical position is the position that provides a reference point for describing the structures of the body. In this position, the body is erect and the face forward. The feet are together, flat on the floor and the toes pointing forward. The arms are down at the sides with the palms turned forward with the thumb side of the hand away from the body. When the body lying face down in the anatomical position, this is the prone position. When the body is lying face up, this is the supine position.

Body landmarks
Anatomists use specific terms to indicate visible areas of the body. The cephalon or cephalic region refers to the head. This area is further differentiated into the cranium (skull), facies (face), frons (forehead), oculus (eye area), auris (ear), bucca (cheek), nausus (nose), oris (mouth), and mentis (chin). The neck area is called the cervicis or cervical region.

On the trunk of the body, the chest is referred to as the thoracic area. The shoulder in general is the acromial, while the curve of the shoulder is the deltoid. The back as a general area is the dorsum or dorsal area, and the lower back as the lumbus or lumbar region. The shoulderblades are the scapular area and the breastbone is the sternal region. The abdominal area is the region between the chest and the pelvis. The breast is called the mamma or mammary, the armpit as the axilla and axillary, and the navel as the umbilicus and umbilical. The pelvis is the lower torso, between the abdomen and the thighs. The groins, where the thigh joins the trunk, are the inguen and inguinal area.

The entire arm is referred to as the brachium and brachial, the front of the elbow as the antecubitis and antecubital, the back of the elbow as the olecranon or olecranal, the forearm as the antebrachium and antebrachial, the wrist as the carpus and carpal area, the hand as the manus and manual, the palm as the palma and palmar, the thumb as the pollex, and the fingers as the digits, phalanges, and phalangeal. The buttocks are the gluteus or gluteal region and the pubic area is the pubis.

Anatomists divide the lower limb into the thigh, the part of the limb between the hip and the knee, and the leg, which refers only to the area of the limb between the knee and the ankle. The thigh is the femur and the femoral region. The kneecap is the patella and patellar while the back of the knee is the popliteus and popliteal area. The leg (between the knee and the ankle) is the crus and crural area, the outside of the leg is the peroneal area, and the calf is the sura and sural region. The ankle is the tarsus and tarsal, and the heel is the calcaneus or calcaneal. The foot is the pes and pedal region, and the sole of the foot the planta and plantar. As with the fingers, the toes are also called the digits, phalanges, and phalangeal area. The big toe is referred to as the hallux.

Use of the terms right and left
When anatomists refer to the right and left of the body, it is in reference to the right and left of the subject, not the right and left of the observer. When observing a body in the anatomical position, the left body is on the observer’s left and vice versa.

Regions of the abdomen and pelvis
Anatomists and medical personnel divide the 'Abdomen Proper' into smaller regions to facilitate study and discussion. The two most common schemes are division into four quadrants and also into nine areas.

The abdominopelvic quadrants evenly divide the space of the torso below the diaphragm into four. They are referred to simply by location: the right upper quadrant, right lower quadrant, left upper quadrant, and left lower quadrant. The right upper quadrant contains the right portion of the liver, the gallbladder, right kidney, a small portion of the stomach, portions of the ascending and transverse colon and parts of small intestine. The left upper quadrant is the location of the left portion of the liver, the larger portion of the stomach, the pancreas, left kidney, spleen, portions of the transverse and descending colon and parts of the small intestine. In the right lower quadrant sits the cecum, appendix, part of the small intestines, the right reproductive organs, and the right ureter. The left lower quadrant houses the majority of the small intestine, some of the large intestine, the left reproductive organs and the left ureter.

The nine divisions (sometimes also called nine quadrants, though the word 'quadrant' itself means division into four equal parts) of the abdominopelvic region are smaller than the four abdominopelvic quadrants and allow more detailed discussion of the area. These are the right hypochondriac, right lumbar, right inguinal (or right iliac), epigastric, umbilical, hypogastric (or pubic), left hypochondriac, left lumbar, and left inguinal (or left iliac). The right and left hypochondriac regions are the outer and uppermost segments. The epigastric lies between these two. The outer middle sections are the right lumbar and left lumbar regions, with the umbilical region between them. The lowest portions are the right and left iliac region with the hypogastric between these.

The Perineum is considered to be the 10th division.

Anatomical directions
Anatomists use specific directional terms to describe structures of the body. These terms always use anatomical position as a point of reference, even if the structure or body described is in another position. Some terms have different connotations in veterinary anatomy.

Anterior and ventral both mean toward the front of the body, while posterior and dorsal mean the back of the body. These terms are almost always used in pairs, with anterior pairing with posterior and ventral pairing with dorsal. The nose is on the anterior (ventral) surface of the head. The spine is on the posterior (dorsal) side of the body. (In veterinary anatomy, ventral is abdominal side of the animal and dorsal is the backside, while anterior means toward the head while posterior means toward the tail.)

The terms superior, cranial, and cephalic all mean toward the head or the upper part of a structure while inferior and caudal</B> refer to the lower part of a structure or away from the head. For example, the shoulder is superior (cranial) to the elbow and the elbow is inferior (caudal) to the shoulder. These terms are also used in their respective pairs: superior with inferior and cranial or cephalic with caudal. (The terms superior and inferior are not used in veterinary anatomy.)

Proximal</B> means closer to the trunk (torso) while distal</B> is away from the trunk. The statement “the knee is proximal to the foot” means the knee is closer to the torso than the foot. Conversely, the foot is distal to the knee.

Medial</B> describes a structure toward the midline of the body and lateral</B> away from that midline. Intermediate describes a structure between a medial and a lateral structure. The nose is medial to the ears while the ears are lateral to the nose. The cheeks are intermediate between the nose and the ears.

Superficial</B> means close to the surface of the body while deep</B> means away from the surface. The brain is deep to the skull while the skull is superficial to the brain.

Planes of the body
Anatomists also divide the body into planes to facilitate discussion. These are the coronal or frontal plane, the sagittal, midsagittal or median sagittal, and the transverse or horizontal plane. These planes are defined using the anatomical position as a reference point. The coronal or frontal section divides the body lengthwise from anterior to posterior and side to side. When the body is divided into the coronal plane, the anterior of the face, trunk and legs would be separated from the posterior. The sagittal plane bisects the left and right sides of the body longitudinally. This plane runs down the center of the head, torso, and between the legs and feet. A midsagittal or median sagittal section evenly divides the body along the midline, while a parasagittal division is parallel to a midsagittal division. The transverse or horizontal plane runs perpendicularly to the longitudinal axis of the body, dividing it into upper and lower sections.

Body cavities
The body is contains two main cavities, dorsal and ventral, that house and protect the internal organs. These cavities are subdivided to further distinguish location.

The dorsal body cavity is the space within the cranium (skull) and the spinal canal, which is surrounded by the vertebrae. The fluid filled space inside the cranium is called is the cranial cavity, and it contains the brain. The spinal cavity is the space that encloses the spinal cord and extends from the cranial cavity to the base of the spine.

The ventral body cavity contains the organs in the chest and abdomen. It is further divided by the diaphragm into the superior thoracic cavity and the inferior abdominopelvic cavity.

The thoracic cavity contains the lungs, heart, the lower esophagus, the thymus gland, and other organs of the cardiovascular, respiratory, and lymphatic systems. This cavity is subdivided into the right pleural cavity of the right lung, the left pleural cavity of the left lung, and the mediastinum, between the pleural cavities, which houses the trachea, esophagus, thymus, heart, and vessels connected to the heart. The medistinum contains the pericardial cavity, which is the area surrounding the heart.

The abdominopelvic cavity is often divided into the superior abdominal and inferior pelvic cavities. The abdominal cavity contains the digestive organs and glands, namely the liver, gallbladder, spleen, kidneys, pancreas, stomach, small intestine and the majority of the large intestine. The pelvic cavity is surrounded by the pelvis and contains the inferior portion of the large intestine, bladder, uterine tubes, and reproductive organs.

Types of movement
The body has a wide variety of movements available to it, depending on the joint where the movement occurs. Movement occurs when a muscle or muscles contract over joints and is dependent on the joint’s mobility and the location of the muscle in relation to the joint. The different types of movement have specific terms, often in pairs to describe opposite movements.

Flexion occurs in the sagittal plane, when the angle of a joint decreased. It occurs in hinge joints and ball-and-socket joints. When the knee is bent, this is a form of flexion. Conversely, extension occurs when the angle is increased along the same plane. Straightening of the leg is extension. Hyperextension occurs when the extension is beyond 180°. The neck is hyperextended when the chin tilts up toward the ceiling. Some people with flexible ligaments and tendons can hyperextend the elbows and knees, which can cause injury in these joints. Flexion and extension of the ankle are dorsiflexion and plantar flexion, respectively.

Abduction</B> is the movement of a limb away from the median plane of the body. This occurs when someone jumps the arms legs apart, as in jumping jacks, and also when fanning the fingers and toes. Adduction is the reversal of this movement, bringing the limb back to the median plane.

Circumduction is a circular movement of the joint, such as drawing a circle with the arm and wrist straight. It is a combination of abduction, adduction, flexion and extension in a ball-and-socket joint.

A movement of the vertebrae in the coronal plane away from the midline is lateral flexion. The cervical and thoracic regions of the spine are most capable of this movement. It occurs when one moves the ear toward the shoulder with the nose facing forward.

Rotation is movement of a bone around the longitudinal axis of that bone. Lateral (or external) rotation occurs when the anterior aspect rotates outward and medial rotation occurs when it rotates inward. Turning the head to look to the side is lateral rotation, and bringing it back to the center is medial rotation. These movements occur across all ball-and-socket joints. Pronation and supination occur at the wrist to rotate the palm. Pronation is the turning of the palm from the anatomical position to face backward. Turning the palm forward is supination.

Inversion is a movement of the foot to turn the sole medially while eversion turns it laterally.

Gliding is the motion in any direction of two articulating surfaces sliding past one another. This minimum movement occurs in the carpal bones of the hands and tarsal bones of the feet and also between the clavicles and sternum.

Protraction is movement anteriorly in the transverse plane. Biting the upper lip with the lower teeth is protraction of the jaw, and moving the jaw back to its normal position is retraction.

Elevation is the motion of a limb superiorly, such as lifting the shoulders toward the ears. Depression is the opposite, inferior movement as in opening the mouth.

Opposition is a movement unique to the thumb when it moves toward a finger or the palm to grasp something

Systematic and regional approaches to anatomy
In the systematic approach to the study of anatomy, each system of the body, such as the digestive system, is studied in its continuity until every system has been examined. The regional approach observes all aspects of a particular region at one time. For example, each muscle, organ, bone, nerve and any other structure in the abdomen is studied together, then the student continues in this fashion with each region. The regional approach better facilitates study with dissection, while the systematic approach is appreciated for its comprehensive look at each system throughout the body.