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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)

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info.med.yale.edu/ caim/cnerves/ options/ 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 Plexus3 L1- L5, S2 nerve roots innervate the lower extremity

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2. .../Brachial_Plexus.jpg

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 Root Dermatome Patterns

Upper Extremity

C1 Top of head

C2 Temporal & occipital regions of head

C3 Neck and posterior cheek

C4 Superior shoulder and clavicle

C5 Deltoid patch & lateral arm

C6 Lateral forearm, thumb and index finger

C7 Posterior lateral forearm & middle finger

C8 Medial forearm, ulna border & ring/little fingers

T1 Medial side of forearm & upper arm

Lower Extremity

L1 Back, hip and groin

L2 Anterior superior thigh, medial thigh above knee

L3 Back, anterior thigh and medial knee

L4 Lateral thigh/knee, anterior medial lower leg to medial aspect of big toe

L5 Lateral knee and lateral lower leg and top of foot

S1 Buttocks, posterior lateral thigh and lateral plantar surface of foot

S2 Buttocks, posterior medial thigh and medial plantar surface of foot

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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.).

Myotomes

• Test with resistive exercises

• The clinician will check for weakness in strength

• All tests should be compared bilaterally

Upper Extremity

Nerve Root Muscle Test

C4 Upper traps tested with resisted shoulder shrugs/elevation

C5 Deltoids, Biceps tested with resisted shoulder abduction

C6 Biceps, Wrist Ext tested with resisted elbow flexion, wrist extension

C7 Wrist Flexors, Elbow Ext tested with resisted wrist flexion, elbow extension

C8 Thumb Ext, Flexors tested with resisted thumb extension

T1 Hand Intrinsics fingers abduction & adduction

Lower Extremity

Nerve Routes Muscle Test

L1-L2 Iliopsoas, hip adductors tested with resisted hip flexion

L3 Quadriceps tested with resisted knee extension

L4 Anterior Tibialis, tested with resisted foot dorsiflexion

L5 Extensor Hallucis, Glut Medius tested with resisted great toe extension

S1/S2 Gastrocnenius tested with plantar flexion

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