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A dermatome is an area of
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...
that is mainly supplied by afferent nerve fibres from the
dorsal root The dorsal root of spinal nerve (or posterior root of spinal nerve or sensory root) is one of two "roots" which emerge from the spinal cord. It emerges directly from the spinal cord, and travels to the dorsal root ganglion. Nerve fibres with the ve ...
of any given
spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
. There are 8 cervical nerves (C1 being an exception with no dermatome), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Each of these nerves relays sensation (including pain) from a particular region of skin to the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
. The term is also used to refer to a part of an embryonic
somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide ...
. Along the
thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the c ...
and
abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...
the dermatomes are like a stack of discs forming a human, each supplied by a different spinal nerve. Along the arms and the legs, the pattern is different: the dermatomes run longitudinally along the limbs. Although the general pattern is similar in all people, the precise areas of innervation are as unique to an individual as fingerprints. An area of skin innervated by a single
nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
is called a peripheral nerve field. The word ''dermatome'' is formed from
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...
δέρμα 'skin, hide' and τέμνω 'cut'.


Clinical significance

A dermatome is an area of skin supplied by sensory neurons that arise from a spinal nerve ganglion. Symptoms that follow a dermatome (e.g. like pain or a rash) may indicate a pathology that involves the related nerve root. Examples include somatic dysfunction of the spine or viral infection. Certain skin problems tend to orient the lesions in the dermatomal direction. In referred pain, sensory nerve fibers such as that from dermatomes may come together at the same
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
level as the general visceral afferent fibers such as that from the
heart The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...
. When the general visceral sensory fiber is simulated, the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
does not clearly discern whether the
pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...
is coming from the body wall or from the
viscera In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a f ...
, so it perceives the pain as coming from somewhere on the body wall, e.g. left arm/hand pain, jaw pain. So the pain is "referred to" the related dermatomes of the same spinal segment. Viruses that lie dormant in nerve ganglia (e.g.
varicella zoster virus Varicella-zoster virus (VZV), also known as human herpesvirus 3 (HHV-3, HHV3) or ''Human alphaherpesvirus 3'' (taxonomically), is one of nine known herpes viruses that can infect humans. It causes chickenpox (varicella) commonly affecting chil ...
, which causes both
chickenpox Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab ...
and
herpes zoster Shingles, also known as zoster or herpes zoster, is a viral disease characterized by a painful skin rash with blisters in a localized area. Typically the rash occurs in a single, wide mark either on the left or right side of the body or fac ...
commonly
shingles Shingles, also known as zoster or herpes zoster, is a viral disease characterized by a painful skin rash with blisters in a localized area. Typically the rash occurs in a single, wide mark either on the left or right side of the body or fac ...
), often cause either pain, rash or both in a pattern defined by a dermatome (a zosteriform pattern). However, the symptoms may not appear across the entire dermatome.


Important dermatomes and anatomical landmarks

Following is a list of
spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
s and points that are characteristically belonging to the dermatome of each nerve: * C2 – At least one cm lateral to the occipital protuberance at the
base of the skull The base of skull, also known as the cranial base or the cranial floor, is the most inferior area of the skull. It is composed of the endocranium and the lower parts of the calvaria. Structure Structures found at the base of the skull are for ...
. Alternately, a point at least 3 cm behind the ear. * C3 – In the
supraclavicular fossa The Supraclavicular fossa is an indentation (fossa) immediately above the clavicle. In terminologia anatomica, it is divided into ''fossa supraclavicularis major'' and ''fossa supraclavicularis minor'' Fullness in the supraclavicular fossa can be ...
, at the midclavicular line. * C4 – Over the acromioclavicular joint. * C5 – On the lateral (radial) side of the
antecubital fossa The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical positio ...
, just proximally to the elbow. * C6 – On the dorsal surface of the proximal phalanx of the
thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...
. * C7 – On the dorsal surface of the proximal phalanx of the
middle finger The middle finger, long finger, second finger, third finger, toll finger or tall man is the third digit of the human hand, located between the index finger and the ring finger. It is typically the longest digit. In anatomy, it is also calle ...
. * C8 – On the dorsal surface of the proximal phalanx of the
little finger The little finger, or pinkie, also known as the baby finger, fifth digit, or pinky finger, is the most ulnar and smallest digit of the human hand, and next to the ring finger. Etymology The word "pinkie" is derived from the Dutch word ''p ...
. * T1 – On the medial (ulnar) side of the
antecubital fossa The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical positio ...
, just proximally to the
medial epicondyle of the humerus The medial epicondyle of the humerus is an epicondyle of the humerus bone of the upper arm in humans. It is larger and more prominent than the lateral epicondyle and is directed slightly more posteriorly in the anatomical position. In birds, whe ...
. * T2 – At the apex of the
axilla The axilla (also, armpit, underarm or oxter) is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm and the thoracic cage, bounded superior ...
. * T3
Intersection In mathematics, the intersection of two or more objects is another object consisting of everything that is contained in all of the objects simultaneously. For example, in Euclidean geometry, when two lines in a plane are not parallel, thei ...
of the midclavicular line and the third intercostal space * T4 – Intersection of the midclavicular line and the fourth intercostal space, located at the level of the nipples. * T5 – Intersection of the midclavicular line and the fifth intercostal space, horizontally located midway between the level of the nipples and the level of the xiphoid process. * T6 – Intersection of the midclavicular line and the horizontal level of the xiphoid process. * T7 – Intersection of the midclavicular line and the horizontal level at one quarter the distance between the level of the xiphoid process and the level of the umbilicus. * T8 – Intersection of the midclavicular line and the horizontal level at one half the distance between the level of the xiphoid process and the level of the umbilicus. * T9 – Intersection of the midclavicular line and the horizontal level at three quarters of the distance between the level of the xiphoid process and the level of the umbilicus. * T10 – Intersection of the midclavicular line, at the horizontal level of the umbilicus. * T11 – Intersection of the midclavicular line, at the horizontal level midway between the level of the umbilicus and the
inguinal ligament The inguinal ligament (), also known as Poupart's ligament or groin ligament, is a band running from the pubic tubercle to the anterior superior iliac spine. It forms the base of the inguinal canal through which an indirect inguinal hernia may ...
. * T12 – Intersection of the midclavicular line and the midpoint of the inguinal ligament. * L1 – Midway between the key sensory points for T12 and L2. * L2 – On the anterior medial thigh, at the midpoint of a line connecting the midpoint of the inguinal ligament and the medial epicondyle of the femur. * L3 – At the medial epicondyle of the femur. * L4 – Over the
medial malleolus A malleolus is the bony prominence on each side of the human ankle. Each leg is supported by two bones, the tibia on the inner side (medial) of the leg and the fibula on the outer side (lateral) of the leg. The medial malleolus is the promi ...
. * L5 – On the dorsum of the foot at the third
metatarsophalangeal joint The metatarsophalangeal joints (MTP joints), also informally known as toe knuckles, are the joints between the metatarsal bones of the foot and the proximal bones ( proximal phalanges) of the toes. They are condyloid joints, meaning that an elli ...
. * S1 – On the lateral aspect of the
calcaneus In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. ...
. * S2 – At the midpoint of the
popliteal fossa The popliteal fossa (also referred to as hough, .html" ;"title="/sup>">/sup> or kneepit in analogy to the cubital fossa) is a shallow depression located at the back of the knee joint. The bones of the popliteal fossa are the femur and the tibia ...
. * S3 – Over the
tuberosity of the ischium The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large swelling posteriorly on the superior ramus of the ischium. It marks ...
or infragluteal fold * S4 and S5 – In the
perianal The anus ( Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...
area, less than one cm lateral to the
mucocutaneous zone A mucocutaneous junction, or mucocutaneous boundary, is a region of the body in which mucosa transitions to skin. Mucocutaneous zones occur in animals, at the body orifices. In humans, mucocutaneous junctions are found at the lips, nostrils, conjun ...
Following is a list
cranial nerves Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...
responsible for sensation from the face: * V1 (1st division of the Trigeminal nerve) - associated with Herpes zoster ophthalmicus * V2 (2nd division of the Trigeminal nerve) * V3 (3rd division of the Trigeminal nerve)


Additional images

File:Gray812and814.svg, Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. File:Gray826and831.svg, Lower limb. File:Gray834.svg, Foot. File:Dermatomes and cutaneous nerves - anterior.svg, Major dermatomes and cutaneous nerves (anterior view). File:Dermatomes and cutaneous nerves - posterior.svg, Major dermatomes and cutaneous nerves. (posterior view).


See also

* Cutaneous innervation *
Dorsal root The dorsal root of spinal nerve (or posterior root of spinal nerve or sensory root) is one of two "roots" which emerge from the spinal cord. It emerges directly from the spinal cord, and travels to the dorsal root ganglion. Nerve fibres with the ve ...
* Peripheral nerve field


References


External links


3D Dermatomes Web App
''Instamedic'' *

''The New York Times'' {{DEFAULTSORT:Dermatome (Anatomy) somatosensory system Neurology Skin anatomy