This article explains the dermatomes and myotomes of the human body, with an included dermatome map. Examining myotomes and dermatomes is a vital part of a thorough neurological examination, particularly when a patient has a spinal cord injury.
Dermatomes and myotomes both arise from somites, which are divisions of the body of an embryo. Somites are paired structures which run cephalocaudally (along the head to toe axis of the body).
In the developing human embryo, somites form dermatomes and myotomes, as well as tendons, cartilage and sclerotomes (which form bone).
Definition: “An area of skin supplied by a single spinal nerve”
If you imagine the human body as a map, each dermatome represents the sensory innervation of a particular spinal nerve.
It is important to bear in mind that the dermatomes of the head are supplied by branches V1, V2 and V3 of the trigeminal nerve.
The list below details nerve roots and the approximate area of skin that they provide innervation to:
Cranial nerve 5 (trigeminal)
V1 – ophthalmic branch – top of the head
V2 – maxillary branch – nares to the top lip
V3 – mandibular branch – bottom lip to jaw
C2 – occipital protuberance
C3 – supraclavicular fossa
C4 – acromioclavicular joint
C5 – lateral antecubital fossa
C6 – thumb
C7 – middle finger
C8 – little finger
T1 – medial antecubital fossa
T2 – the apex of the axilla
T3-T12 – bands down the torso
L1 – upper anterior thigh
L2 – mid anterior thigh
L3 – medial femoral condyle
L4 – medial malleolus
L5 – dorsum of 3rd metatarsal phalangeal joint
S1 – lateral heel
S2 – popliteal fossa
S3 – ischial tuberosity
S4-5 – perianal area
Light touch sensation
Assesses dorsal/posterior columns and spinothalamic tracts.
1. The patient’s eyes should be closed for this assessment
2. Touch the patient’s sternum with the cotton wool wisp to confirm they can feel it
3. Ask the patient to say “yes” when they are touched
4. Using a wisp of cotton wool, gently touch the skin (don’t stroke)
5. Assess each of the dermatomes
6. Compare left to right, by asking the patient if it feels the same on both sides
Assesses spinothalamic tracts.
Repeat the previous assessment steps, but this time using the sharp end of a neurotip.
This information can also be found as part of the Geeky Medics guides to upper and lower limb neurological examinations.
Definition: “A group of muscles innervated by a single spinal nerve”
This list details some important myotomes’ nerve roots and the actions that their associated muscles produce:
C4 – shoulder shrugs
C5 – shoulder abduction and external rotation; elbow flexion
C6 – wrist extension
C7 – elbow extension and wrist flexion
C8 – thumb extension and finger flexion
T1 – finger abduction
L2 – hip flexion
L3 – knee extension
L4 – ankle dorsiflexion
L5 – great toe extension
S1 – ankle plantarflexion
S4 – bladder and rectum motor supply
For information about examining myotomes, see the motor sections of the Geeky Medics upper and lower limb neurological examination guides.
We can classify groups of nerves into plexuses.
Cervical plexus (C1-C4) – innervates the diaphragm, shoulders and neck
Brachial plexus (C5 – T1) – innervates the upper limbs
Lumbosacral plexus (L2-S1) – innervates the lower extremities