Dermatomes and Myotomes

Dermatomes are areas on the surface of the skin that are control by specific nerve roots from the spinal cord

Myotomes correspond to muscles that are controlled by specific nerve roots from the spinal cord

  • Cranial Nerves branch out off the brain (12)
  • Nerve Roots branch out off the spinal cord (31)

info.med.yale.edu/ caim/cnerves/ lowback/dclmlama.htm

These nerve roots branch out to form a plexus which is a network of intersecting nerves which travel to different parts of the body, they are both motor and sensory

  • Cervical Plexus1 C1-C4 nerve roots innervate the diaphragm, shoulder and neck.
  • Brachial Plexus2 C5-T1 nerve roots innervate the upper limbs
  • Lumbosacral Plexus3L1- L5, S2 nerve roots innervate the lower extremity

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3. "LifeART (and/or) MediClip image copyright (2005) Lippincott Williams & Wilkins. All rights reserv

  • Skin (sensation) is innervated by a single nerve roots called the dermatomes
  • Muscles (movement) are innervated by singe nerve roots called myotomes
  • Nerves and nerve roots are typically injured by compression or stretching forces
  • When a nerve root is damaged a deficit may occur in the corresponding limb
  • The evaluation of nerve root damage can be done by testing dermatomes and myotomes
  • Nerve root trauma should always be inspected by a physician

Dermatomes

  • Test for abnormalities in sensitivity by using a pinwheel, paper clip or finger nail
  • The athlete should close his/her eyes and give the therapist feedback with regards to various stimuli
  • All tests should be compared bilaterally

Nerve RootDermatome Patterns

Upper Extremity

C1Top of head

C2Temporal & occipital regions of head

C3Neck and posterior cheek

C4Superior shoulder and clavicle

C5Deltoid patch & lateral arm

C6Lateral forearm, thumb and index finger

C7Posterior lateral forearm & middle finger

C8Medial forearm, ulna border & ring/little fingers

T1Medial side of forearm & upper arm

Lower Extremity

L1Back, hip and groin

L2Anterior superior thigh, medial thigh above knee

L3Back, anterior thigh and medial knee

L4Lateral thigh/knee, anterior medial lower leg to medial aspect of big toe

L5Lateral knee and lateral lower leg and top of foot

S1Buttocks, posterior lateral thigh and lateral plantar surface of foot

S2Buttocks, posterior medial thigh and medial plantar surface of foot

Figure 24-4 Dermatome distribution of the spinal nerves.From Thibodeau GA, Patton KT: Anatomy and Physiology,ed 6, St. Louis, 2006, Mosby.

(Cameron, Michelle H.. Physical Rehabilitation: Evidence-Based Examination, Evaluation, and Intervention. W.B. Saunders Company, 032007.).

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Myotomes

  • Test with resistive exercises
  • The clinician will check for weakness in strength
  • All tests should be compared bilaterally

Upper Extremity

Nerve Root MuscleTest

C4 Upper trapstested with resisted shoulder shrugs/elevation

C5 Deltoids, Bicepstested with resisted shoulder abduction

C6 Biceps, Wrist Exttested with resisted elbow flexion, wrist extension

C7 Wrist Flexors, Elbow Exttested with resisted wrist flexion, elbow extension

C8 Thumb Ext, Flexorstested with resisted thumb extension

T1 Hand Intrinsicsfingers abduction & adduction

Lower Extremity

Nerve Routes MuscleTest

L1-L2 Iliopsoas, hip adductorstested with resisted hip flexion

L3 Quadricepstested with resisted knee extension

L4Anterior Tibialis, tested with resisted foot dorsiflexion

L5 Extensor Hallucis, Glut Mediustested with resisted great toe extension

S1/S2 Gastrocneniustested with plantar flexion