Dermatome
Dermatome: (derma = skin, tome = cutting)
· A specific area of skin that is
innervated by single spinal nerve
· There are 8 cervical nerves ( with
the exception of c1 as it has no dermatome)
· 12 thoracic , 5 lumber and 5 sacral
nerves
· During embryonic development , the
dermatome arises from 1 of the 3 somites of mesoderm which is the middle layer
of embryonic tissue
· Dermatomes and their spinal nerves
are assessed using pain, temperature and light touch
· Dermatome map is a diagram that
identifies dermatome
Clinical importance of dermatome:
· Useful to help localize neurological
level particularly in rediculopathy
· Viruses that infect spinal nerve such
as herpes zoster reveal their origin by showing up as a painful dermatomic area
Important dermatomes
and anatomical landmarks:
C1: vertex of the skull
C2: one cm lateral to occipital protuberance i-e a point at
least 3 cm behind the ear, Forehead occipit
C3: neck, temporal area
C4: shoulder area, clavicle, upper scapula
C5: deltoid, anterior arm till base of the thumb
C6: Ant arm, red side of hand to thumb and index finger
C7: lat arm and forearm to index, long and ring fingers
C8: medial arm and forearm to long, ring and little finger
T1: medial side of forearm to the base of little finger
T2: med side of upper arm to med elbow, pectoral and
midscapular area
T3: to T6: upper thorax
T5 T6 T7: coastal margin
T10: umbilicus
T8 to T12: abdomen and lumber region
L1: back, over trochanter and groin
L2: back, front of thigh and knee
L3: back, upper buttock, and thigh and knee, med lower leg
L4: medical buttock, lateral thigh, med leg, dorsum of foot, big toe
L5: buttock, post and lateral thigh, lateral aspect of leg , dorsum of
foot med half of sole, first, second and third toes
S1: buttock, thigh and post leg
S2: same as S1
S3: groin, med thigh to knee
S4: perineum, genital, lower sacrum
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