Anatomical terminology

Anatomists and health care providers use anatomical terminology and medical terminology intermittently. These languages can be bewildering to the uninitiated, however the purpose of this language is not to confuse, but rather to increase precision and reduce medical errors. For example, is a scar “above the wrist” located on the forearm two or three inches away from the hand? Or is it at the base of the hand? Is it on the palm-side or back-side? By using precise anatomical terminology, ambiguity is eliminated. Anatomical terms derive from ancient Greek and Latin words, and because these languages are no longer used in everyday conversation, the meaning of their words does not change.

Anatomical vocabulary
Anatomical terms are made up of roots, prefixes, and suffixes. The root of a term often refers to an organ, tissue, or condition, whereas the prefix or suffix often describes the root. For example, in the disorder hypertension, the prefix “hyper-” means “high” or “over,” and the root word “tension” refers to pressure, so the word “hypertension” refers to abnormally high blood pressure. The roots, prefixes and suffixes are often derived from Greek or Latin, and often quite dissimilar from their English-language variants.

Latin names of structures such as musculus biceps brachii can be split up and refer to, musculus for muscle, biceps for "two-headed", brachii as in the brachial region of the arm.

The first word tells us what we are speaking about, the second describes it, and the third points to location.

Relative location


Anatomical terminology is often chosen to highlight the relative location of body structures. For instance, an anatomist might describe one band of tissue as “inferior to” another or a physician might describe a tumor as “superficial to” a deeper body structure. Terms are used to define the relative location of body structures in a body that is positioned in the anatomical position, which is standing, feet apace, with palms forward and thumbs facing outwards.

To further increase precision, anatomists standardize the way in which they view the body. Just as maps are normally oriented with north at the top, the standard body “map,” or anatomical position, is that of the body standing upright, with the feet at shoulder width and parallel, toes forward. The upper limbs are held out to each side, and the palms of the hands face forward. Using the standard anatomical position reduces confusion. It does not matter how the body being described is oriented, the terms are used as if it is in anatomical position. For example, a scar in the “anterior (front) carpal (wrist) region” would be present on the palm side of the wrist. The term “anterior” would be used even if the hand were palm down on a table.

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 of the body is on the observer’s right, and vice versa.

These standardized terms avoid confusion. Examples of terms include:


 * Anterior and posterior, which describe structures at the front (anterior) and back (posterior) of the body. For example, the toes are anterior to the heel, and the popliteus is posterior to the patella.
 * Superior and inferior, which describe a position above (superior) or below (inferior) another part of the body. For example, the orbits are superior to the oris, and the pelvis is inferior to the abdomen.
 * Proximal and distal, which describe a position that is closer (proximal) or further (distal) from the trunk of the body. For example, the shoulder is proximal to the arm, and the foot is distal to the knee.
 * Superficial and deep, which describe structures that are closer to (superficial) or further from (deep) the surface of the body. For example, the skin is superficial to the bones, and the brain is deep to the skull. Sometimes profound is used synonymously with deep.
 * Medial and lateral, which describe a position that is closer to (medial) or further from (lateral) the midline of the body. For example, the nose is medial to the eyes, and the thumb is lateral to the other fingers.
 * Ventral and Dorsal, which describe structures derived from the front (ventral) and back (dorsal) of the embryo, before limb rotation.
 * Cranial and caudal, which describe structures close to the top of the skull (cranial), and towards the bottom of the body (caudal).
 * Occasionally, sinister for left, and dexter for right are used.



Skull and brain
Different terms are used when it comes to the skull in compliance with its embryonic origin and its tilted position compared to in other animals.
 * Rostral refers to proximity to the front of the nose, and is particularly used when describing the skull.

Arm
When speaking of the arm different terminology is often used, so as to take account of the supination action the arm can perform. Therefor the terms ventral for anterior and dorsal for posterior are used preferentially. Aside from this additional terms are employed:
 * Radial referring to the radius bone, seen laterally in the anatomical position.
 * Ulnar referring to the ulna bone, medially positioned when in the anatomical position.

Planes


Anatomy is often described in planes, referring to two-dimensional sections of the body. A section is a two-dimensional surface of a three-dimensional structure that has been cut. A plane is an imaginary two-dimensional surface that passes through the body. Three planes are commonly referred to in anatomy and medicine:
 * The sagittal plane is the plane that divides the body or an organ vertically into right and left sides. If this vertical plane runs directly down the middle of the body, it is called the midsagittal or median plane. If it divides the body into unequal right and left sides, it is called a parasagittal plane, or less commonly a longitudinal section.
 * The frontal plane is the plane that divides the body or an organ into an anterior (front) portion and a posterior (rear) portion. The frontal plane is often referred to as a coronal plane, following Latin corona, which means "crown".
 * The transverse plane is the plane that divides the body or organ horizontally into upper and lower portions. Transverse planes produce images referred to as cross sections.

Functional state
Anatomical terms may be used to describe the functional state of an organ:
 * Anastamoses refers to the connection between two structures previously branched out, such as blood vessels or leaf veins.
 * Patent, meaning a structure such as an artery or vein that abnormally remains open, such as a patent ductus arteriosus, referring to the ductus arteriosus which normally becomes ligamentum arteriosum within three weeks of birth.
 * Visceral and parietal' describe structures that relate to an organ (visceral), or the wall of the cavity that the organ is in (parietal). For example, the parietal peritoneum surrounds the abdominal cavity.
 * Paired, referring to a structure that is present on both sides of the body. For example, the hands are paired structures.

Regions
A body that is lying down is described as either prone or supine. Prone describes a face-down orientation, and supine describes a face up orientation. These terms are sometimes used in describing the position of the body during specific physical examinations or surgical procedures.



The human body’s numerous regions have specific terms to help increase precision. Notice that the term “brachium” or “arm” is reserved for the “upper arm” and “antebrachium” or “forearm” is used rather than “lower arm.” Similarly, “femur” or “thigh” is correct, and “leg” or “crus” is reserved for the portion of the lower limb between the knee and the ankle.

Landmarks
When describing the position of anatomical structures, landmarks may be used to describe location. These landmarks may include structures, such as the umbilicus or sternum, or anatomical lines, such as the midclavicular line from the centre of the clavicle.

Body cavities


Anatomical structures are often described in terms of the cavity in which they reside. The body maintains its internal organization by means of membranes, sheaths, and other structures that separate compartments. The dorsal (posterior) cavity and the ventral (anterior) cavity are the largest body compartments. These cavities contain and protect delicate internal organs, and the ventral cavity allows for significant changes in the size and shape of the organs as they perform their functions. The lungs, heart, stomach, and intestines, for example, can expand and contract without distorting other tissues or disrupting the activity of nearby organs.

The ventral cavity includes the thoracic and abdominopelvic cavities and their subdivisions. The dorsal cavity includes the cranial and spinal cavities. This illustration shows a lateral and anterior view of the body and highlights the body cavities with different colors. Together the cranial cavity and vertebral cavity can be referred to as the dorsal body cavity. In the posterior (dorsal) cavity, the cranial cavity houses the brain, and the spinal cavity (or vertebral cavity) encloses the spinal cord. Just as the brain and spinal cord make up a continuous, uninterrupted structure, the cranial and spinal cavities that house them are also continuous. The brain and spinal cord are protected by the bones of the skull and vertebral column and by cerebrospinal fluid, a colorless fluid produced by the brain, which cushions the brain and spinal cord within the posterior (dorsal) cavity.
 * The cranial cavity is a large, bean-shaped cavity filling most of the upper skull where the brain is located.
 * The vertebral cavity is a very narrow, thread-like cavity running from the cranial cavity down the entire length of the spinal cord.

The thoracic cavity consists of three cavities that fill the interior area of the chest. The diaphragm divides the thoracic and the abdominal cavities. The abdominal cavity occupies the entire lower half of the trunk, anterior to the spine. Just under the abdominal cavity, anterior to the buttocks, is the pelvic cavity. The pelvic cavity is funnel shaped and is located inferior and anterior to the abdominal cavity. Together the abdominal and pelvic cavity can be referred to as the abdominopelvic cavity while the thoracic, abdominal, and pelvic cavities together can be referred to as the ventral body cavity. Subdivisions of the Posterior (Dorsal) and Anterior (Ventral) Cavities The anterior (ventral) cavity has two main subdivisions: the thoracic cavity and the abdominopelvic cavity. The thoracic cavity is the more superior subdivision of the anterior cavity, and it is enclosed by the rib cage. The thoracic cavity contains the lungs and the heart, which is located in the mediastinum. The diaphragm forms the floor of the thoracic cavity and separates it from the more inferior abdominopelvic cavity. The abdominopelvic cavity is the largest cavity in the body. Although no membrane physically divides the abdominopelvic cavity, it can be useful to distinguish between the abdominal cavity, the division that houses the digestive organs, and the pelvic cavity, the division that houses the organs of reproduction.
 * The two pleural cavities are situated on both sides of the body, anterior to the spine and lateral to the breastbone.
 * The superior mediastinum is a wedge-shaped cavity located between the superior regions of the two thoracic cavities.
 * The pericardial cavity within the mediastinum is located at the center of the chest below the superior mediastinum. The pericardial cavity roughly outlines the shape of the heart.

Abdomen


To promote clear communication, for instance about the location of a patient’s abdominal pain or a suspicious mass, health care providers typically divide up the cavity into either nine regions or four quadrants.

Quadrants
The abdomen may be divided into four quadrants, more commonly used in medicine, subdivides the cavity with one horizontal and one vertical line that intersect at the patient’s umbilicus (navel).. The right upper quadrant (RUQ) includes the lower right ribs, right side of the liver, and right side of the transverse colon. The left upper quadrant (LUQ) includes the lower left ribs, stomach, spleen, and upper left area of the transverse colon. The right lower quadrant (RLQ) includes the right half of the small intestines, ascending colon, right pelvic bone and upper right area of the bladder. The left lower quadrant (LLQ) contains the left half of the small intestine and left pelvic bone.

Regions
The more detailed regional approach subdivides the cavity with one horizontal line immediately inferior to the ribs and one immediately superior to the pelvis, and two vertical lines drawn as if dropped from the midpoint of each clavicle, resulting in nine regions. The upper right square is the right hypochondriac region and contains the base of the right ribs. The upper left square is the left hypochondriac region and contains the base of the left ribs. The epigastric region is the upper central square and contains the bottom edge of the liver as well as the upper areas of the stomach. The diaphragm curves like an upside down U over these three regions. The central right region is called the right lumbar region and contains the ascending colon and the right edge of the small intestines. The central square contains the transverse colon and the upper regions of the small intestines. The left lumbar region contains the left edge of the transverse colon and the left edge of the small intestine. The lower right square is the right iliac region and contains the right pelvic bones and the ascending colon. The lower left square is the left iliac region and contains the left pelvic bone and the lower left regions of the small intestine. The lower central square contains the bottom of the pubic bones, upper regions of the bladder and the lower region of the small intestine.

Membranes


A serous membrane (also referred to as a serosa) is a thin membrane that covers the walls of organs in the thoracic and abdominal cavities. The serous membranes have two layers; parietal and visceral, surrounding a fluid filled space. The visceral layer of the membrane covers the organ (the viscera), and the parietal layer lines the walls of the body cavity (pariet- refers to a cavity wall). . Between the parietal and visceral layers is a very thin, fluid-filled serous space, or cavity. An example of a serous cavities include the pericardium, which surrounds the heart.

Movement


Joints, especially synovial joints allow the body a tremendous range of movements. Each movement at a synovial joint results from the contraction or relaxation of the muscles that are attached to the bones on either side of the articulation. The type of movement that can be produced at a synovial joint is determined by its structural type.

Movement types are generally paired, with one being the opposite of the other. Body movements are always described in relation to the anatomical position of the body: upright stance, with upper limbs to the side of body and palms facing forward.

General motion
Terms describing motion in general include:
 * Flexion and Extension, which refer to a movement that decreases (flexion) or increases (extension) the angle between body parts. For example, when standing up, the knees are extended.
 * Abduction and adduction refers to a motion that pulls a structure away from (abduction) or towards (adduction) the midline of the body or limb. For example, a star jump requires the legs to be abducted.
 * Internal rotation (or medial rotation) and External rotation (or lateral rotation) refers to rotation towards (internal) or away from (external) the center of the body. For example, the asana posture in yoga requires the legs to be externally rotated.
 * Elevation and Depression refers to movement in a superior (elevation) or inferior (depression) direction. For example, a person saluting must elevate their arm.

Special motions of the hands and feet
These terms refer to movements that are regarded as unique to the hands and feet:
 * Dorsiflexion and Plantarflexion refers to flexion (dorsiflexion) or extension of the foot at the ankle. For example, dorsiflexion occurs when pressing the brake pedal of a car.
 * Palmarflexion and dorsiflexion refer to movement of the flexion (palmarflexion) or extension (dorsiflexion) of the hand at the wrist. For example, prayer is often conducted with the hands dorsiflexed.
 * Pronation and Supination refer to rotation of the forearm or foot so that in the anatomical position the palm or sole is facing anteriorly (supination) or posteriorly (pronation) rotation of the forearm. For example, a person skiing must pronate their arms in order to grasp the skis.
 * Eversion and Inversion refer to movements that tilt the sole of the foot away from (eversion) or towards (inversion) the midline of the body.

Other special motions
Other terms include:
 * Anterograde and Retrograde flow, refers to movement of blood or other fluids in a normal (anterograde) or abnormal (retrograde) direction.
 * Protraction and Retraction refer to an anterior (protraction) or posterior (retraction) movement of the arm at the shoulders.
 * Circumduction refers to the circular (or, more precisely, conical) movement of a body part, such as a ball-and-socket joint or the eye. It consists of a combination of flexion, extension, adduction, and abduction. "Windmilling" the arms or rotating the hand from the wrist are examples of circumductive movement.
 * Opposition – A motion involving a grasping of the thumb and fingers.
 * Reposition – To release an object by spreading the fingers and thumb.
 * Reciprocal motion of a joint – Alternating motion in opposing directions, such as the elbow alternating between flexion and extension.
 * Protrusion and Retrusion are sometimes used to describe the anterior (protrusion) and posterior (retrusion) movement of the jaw.

Muscles


Muscle action that moves the axial skeleton work over a joint with an origin and insertion of the muscle on respective side. The insertion is on the bone deemed to move towards the origin during muscle contraction. Muscles are often present that engage in several actions of the joint; able to perform for example both flexion and extension of the forearm as in the biceps and triceps respectively. This is not only to be able to revert actions of muscles, but also brings on stability of the actions though muscle coactivation.

Agonist and antagonist muscles
The muscle performing an action is the agonist, while the muscle which contraction brings about an opposite action is the antagonist. For example an extension of the lower arm is performed by the triceps as the agonist and the biceps as the antagonist (which contraction will perform flexion over the same joint). Muscles that work together to perform the same action are called synergists. In the above example synergists to the biceps can be the brachioradialis and the brachialis muscle.

Skeletal and smooth muscle
The gross anatomy of a muscle is the most important indicator of its role in the body. One particularly important aspect of gross anatomy of muscles is pennation or lack thereof. In most muscles, all the fibers are oriented in the same direction, running in a line from the origin to the insertion. In pennate muscles, the individual fibers are oriented at an angle relative to the line of action, attaching to the origin and insertion tendons at each end. Because the contracting fibers are pulling at an angle to the overall action of the muscle, the change in length is smaller, but this same orientation allows for more fibers (thus more force) in a muscle of a given size. Pennate muscles are usually found where their length change is less important than maximum force, such as the rectus femoris.

Skeletal muscle is arranged in discrete muscles, an example of which is the biceps brachii. The tough, fibrous epimysium of skeletal muscle is both connected to and continuous with the tendons. In turn, the tendons connect to the periosteum layer surrounding the bones, permitting the transfer of force from the muscles to the skeleton. Together, these fibrous layers, along with tendons and ligaments, constitute the deep fascia of the body.

Joints
Movement is not limited to only synovial joints, although they allow for most freedom. Muscles also run over symphysis, which allow for movement in for example the vertebral column by compression of the intervertebral discs. Additionally, synovial joints can be divided into different types, depending on their axis of movement.

Systemic 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 as a thing in itself. 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.

Anatomical variation
The term anatomical variation is used to refer to a difference in anatomical structures that is not regarded as a disease. Many structures vary slightly between people, for example muscles that attach in slightly different places. For example, the presence or absence of the palmaris longus tendon. Anatomical variation is unlike congenital anomalies, which are considered a disorder.