Myotomes and dermatomes connect spinal nerve roots to movement and sensation. A myotome is the group of muscles or movement predominantly supplied by one spinal nerve root. A dermatome is an area of skin predominantly supplied by one dorsal root. Because neighbouring roots overlap, clinical examination looks for patterns rather than a single isolated point.
Add your labelled myotome and dermatome maps here.
Root patterns versus peripheral-nerve patterns
A C7 radiculopathy may weaken several muscles supplied by different peripheral nerves but sharing C7 fibres; a radial-nerve lesion weakens muscles supplied by the radial nerve across one or more roots. Similarly, a dermatome follows a root while a named cutaneous nerve follows a peripheral pathway. Always interpret motor, sensory, reflex and functional findings together.
Learning outcomes
- Define myotome, dermatome, spinal nerve root, peripheral nerve and reflex arc.
- State the clinically tested upper-limb myotomes from C4 to T1.
- Locate key upper-limb dermatome points from C4 to T2.
- Use reflexes and pattern recognition to distinguish root from peripheral-nerve involvement.
- Perform and document a safe neurological screen for physiotherapy referral.
1. Myotomes
Myotomes are best tested with resisted movements that isolate a root as much as possible. No movement is supplied by only one root; use a dominant root value as a clinical shorthand.
| Root | Key movement/myotome | Useful muscles | Important peripheral nerves |
|---|---|---|---|
| C4 | Scapular elevation/shoulder shrug and diaphragmatic contribution. | Trapezius/diaphragm (with C3–5). | Spinal accessory plus cervical/phrenic contributions. |
| C5 | Shoulder abduction; some shoulder external rotation. | Deltoid, supraspinatus, infraspinatus. | Axillary and suprascapular. |
| C6 | Elbow flexion and wrist extension; forearm supination. | Biceps, brachioradialis, wrist extensors. | Musculocutaneous and radial. |
| C7 | Elbow extension; wrist/finger extension; some wrist flexion. | Triceps, extensor digitorum, wrist flexors/extensors. | Radial, median and ulnar contributions. |
| C8 | Finger flexion, thumb extension and grip. | FDP, FPL, finger extensors. | Median, ulnar and radial. |
| T1 | Finger abduction/adduction and intrinsic hand control. | Dorsal/palmar interossei, adductor pollicis. | Deep ulnar. |
| T2 | Upper medial arm/axillary sensory transition; no single standard limb movement. | Intercostal/axillary-region muscles. | Intercostobrachial and thoracic contributions. |
1.1 How to test a myotome
- Explain the test, position the patient and stabilise the adjacent segment.
- Demonstrate the movement and test active range before resistance.
- Apply gradual resistance in a safe direction; compare sides and note pain, tremor and fatigue.
- Test a second muscle supplied by the same root but a different peripheral nerve.
- Document position, resistance, side, grade/quality, pain and sensory/reflex findings.
2. Dermatomes
Dermatome maps differ slightly between references because roots overlap and individuals vary. Use standard key points and compare sides. A single normal sensation does not exclude radiculopathy; a pattern across multiple points is more meaningful.
| Root | Key dermatome area | Practical sensory point |
|---|---|---|
| C4 | Lower neck and top of shoulder. | Skin over the acromioclavicular/shoulder-tip region. |
| C5 | Lateral upper arm. | Skin over the deltoid region above the elbow. |
| C6 | Lateral forearm and thumb side of hand. | Thumb pulp or radial forearm. |
| C7 | Middle of the hand and posterior central arm/forearm. | Middle-finger pulp. |
| C8 | Medial forearm and little-finger side of hand. | Little-finger pulp. |
| T1 | Medial forearm to medial upper arm. | Medial forearm above the elbow. |
| T2 | Axilla and upper medial arm. | Axillary fold/upper medial arm, with sensitivity and privacy. |
2.1 Sensory examination principles
- Explain the stimulus and ask the patient to close the eyes only after consent.
- Compare left and right at corresponding points; test light touch first and stronger modalities only when appropriate.
- Map the border of altered sensation rather than recording “numb arm.”
- Protect an insensate limb from heat, pressure, sharp edges and prolonged loading.
- Consider peripheral nerve territories, dermatomes, central lesions, diabetic neuropathy and non-organic patterns.
3. Reflexes supporting root localisation
| Reflex | Spinal levels | Peripheral nerve/muscle | Technique and interpretation |
|---|---|---|---|
| Biceps | C5–C6, mainly C5 | Musculocutaneous; biceps | Tap tendon in cubital fossa while elbow is relaxed; compare sides. |
| Brachioradialis | C5–C6, mainly C6 | Radial; brachioradialis | Tap tendon near radial styloid; observe elbow flexion/supination response. |
| Triceps | C6–C8, mainly C7 | Radial; triceps | Tap tendon above olecranon with arm supported. |
Reflexes can be reduced by root/nerve/peripheral lesions and increased by upper motor-neuron lesions. Temperature, anxiety, medication, age and technique affect responses; interpret with the complete neurological examination.
4. Root, plexus and peripheral-nerve comparison
| Pattern | Motor findings | Sensory findings | Clue |
|---|---|---|---|
| Radiculopathy | Several muscles from the same root, possibly different peripheral nerves. | Dermatomal, often with neck pain/radiation. | Reflex change and spinal provocation may support root involvement. |
| Plexopathy | Mixed peripheral-nerve distribution from a plexus region. | Overlapping root/nerve territories. | Traction, tumour, surgery or thoracic-outlet mechanism. |
| Mononeuropathy | Muscles supplied by one named nerve. | Named-nerve cutaneous area; roots may span several levels. | Entrapment or local trauma along nerve course. |
| Polyneuropathy | Often bilateral distal weakness. | Stocking/glove or length-dependent pattern. | Systemic/metabolic disease; refer for medical assessment. |
| Central lesion | Pattern may not respect one root/nerve; tone/reflexes may change. | Higher cortical or tract pattern. | Associated speech, face, leg or coordination findings. |
5. Physiotherapy application
- Use myotomes and dermatomes to identify the likely level of impairment, not to make a diagnosis in isolation.
- Protect skin and joints when sensation or motor control is reduced.
- Choose strengthening and motor-retraining tasks that are safe for the involved root/nerve and tissue stage.
- Use visual feedback, graded sensory input and task practice when proprioception or cutaneous sensation is impaired.
- Document functional consequences: dropping objects, difficulty dressing, loss of pinch, altered gait with an arm problem or inability to use an assistive device.
Scenario: cervical radiculopathy pattern
A patient reports neck pain radiating to the thumb, weak elbow flexion and reduced biceps reflex. Test cervical movement cautiously, compare C5–C6 myotomes, examine the radial and median nerve territories, assess red flags and document the pattern. Severe progressive weakness, gait change, bowel/bladder symptoms, trauma, fever or systemic illness requires urgent referral.
6. Common pitfalls
- Calling the thumb “C7” because the patient describes hand numbness without mapping the area.
- Using one muscle to represent a whole root when the muscle has dual or multiple root supply.
- Confusing radial-nerve sensory loss with C7 dermatome loss.
- Ignoring pain inhibition, limited joint range or effort when interpreting weakness.
- Assuming a normal light-touch point excludes a root lesion because dermatomes overlap.
7. Examination points and revision questions
High-yield points
- C5: shoulder abduction; C6: elbow flexion/wrist extension; C7: elbow extension; C8: finger flexion; T1: finger abduction/adduction.
- C5 is lateral upper arm, C6 thumb/radial forearm, C7 middle finger, C8 little finger/medial hand, T1 medial forearm.
- Biceps reflex is mainly C5–6, brachioradialis C6 and triceps C7.
- Root and peripheral nerve maps overlap; localise using multiple findings.
- Define a myotome and a dermatome.
- List the key upper-limb movements for C5–T1.
- Map C4–T2 sensory key points.
- Compare a C7 radiculopathy with a radial-nerve lesion.
- Explain the role of biceps, brachioradialis and triceps reflexes.
- Describe a safe neurological screen for a patient with neck-to-arm pain.
References for further study
- TeachMeAnatomy: Myotomes
- TeachMeAnatomy: Dermatomes
- NCBI Bookshelf: Cutaneous innervation
- UAMS: Upper-limb nerve tables
- AAFP: Peripheral nerve injury patterns
Educational note: Neurological testing should be supervised and interpreted with the history, full examination and local referral protocols.