Peripheral Nerve Anatomy

Authors: Flaherty, Alice W.; Rost, Natalia S.

Title: Massachusetts General Hospital Handbook of Neurology, The, 2nd Edition

Copyright 2007 Lippincott Williams & Wilkins

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Peripheral Nerve Anatomy

A. See also

Peripheral Neuropathy p. 93.

B. Spinal level by disc

Table 23. Symptoms of disc herniation.

Disc	Root	Motor	Sensory	Reflex
C5-6	C6	Biceps, wrist ext.	Med. arm and hand	Biceps
C6-7*	C7	Triceps, wrist flex.	Middle finger	Triceps
C7-T1	C8	Finger flex.	Lat. hand	Finger
L3-4	L4	Quadriceps	Med. calf	Knee
L4-5*	L5	Dorsiflexors	Med. foot
L5-S1	S1	Plantar flexors	Lat. foot	Ankle
*Most common syndromes.

Figure 10. Dermatomes and peripheral nerve territories. (From Patton HD, et al. Introduction to Basic Neurology. Philadelphia: Saunders; 1976, with permission.)

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C. Spinal level by function

• 1. Movement:

  • a. Neck: C1-4.

  • b. Diaphragm: C3-5.

  • c. Shoulder: Abduction and lateral rotation are C5. Adduction and medial rotation are C6-8.

  • d. Elbow: Flexion is C5-6. Extension is C6-8.

  • e. Wrist: C6-8. Extension = radial n. Flexion = median + ulnar n.

  • f. Hand: Finger abduction and adduction are ulnar nerve (C8-T1). Grip is median nerve. Finger extension is radial nerve.

  • g. Thumb test: Can tell radial, median, and ulnar nerve lesions by thumb movements. Mnemonic is RUM: Radial extends, Ulnar adducts, and Median abducts. Flexion + extension = in plane of the palm; abduction + adduction = at right angles to the palm.

  • h. Intercostals: T2-9.

  • i. Abdominals: Upper is T9-10. Lower is T11-12.

  • j. Hip: Flexion is L2-4, adduction is L3-4, abduction is L5-S1.

  • k. Knee: Extension is L2-4; flexion is L4-S1.

  • l. Foot: Dorsiflexion is L4-S1; plantar flexion is S1-2.

  • m. Bladder, anal sphincter: S2-4.

• 2. Sensation:

  • a. Arm: Shoulders: C4; inner forearm: C6; outer forearm: T1; thumb: C6; fifth finger: C8.

  • b. Leg: Front of thigh: L2; medial calf: L4; lateral calf: L5; fifth toe: S1; midline buttocks: S3.

D. Spinal level by nerve

• 1. See also: p. 95 for sx of common entrapment syndromes.

  

  Figure 11. The brachial plexus. (From Warwick R, Williams P. Gray's Anatomy. 35th ed. London: Churchill Livingstone; 1973, with permission.)

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• 2. Brachial plexus: C5-T1.

  • a. Plexi:

    • 1) Upper plexus: C5-6. Deltoids, biceps, supra- + infraspinatus.

    • 2) Middle plexus: C7.

    • 3) Lower plexus: C8-T1.

  • b. Cords: Upper-mid-lower plexi recombine to form three cords; lateral and medial cord then recombine to form median nerve.

    • 1) Lateral cord (from upper + middle plexus) forms musculocutaneous nerve, lateral anterior thoracic nerve, median nerve.

    • 2) Posterior cord (from upper, middle, and lower plexus) forms radial nerve, axillary nerve, and subscapular nerve.

    • 3) Medial cord (from lower plexus) forms ulnar nerve, medial cutaneous nerve, median nerve.

• 3. Nerves of arm: Note that any weakness of both flexors and extensors or of all intrinsic hand muscles implies that the lesion cannot be a mononeuropathy.

  • a. Long thoracic nerve: C5-7. Serratus anterior. Test: scapula wings when pt presses arm forward against a wall.

  • b. Axillary nerve: C5-6. Deltoid, etc. Test: abduct arm >90 degrees.

  • c. Musculocutaneous nerve: C5-6. Biceps.

  • d. Radial nerve: C5-8, esp. C7. Extensors (triceps, wrist, and finger), supinator, brachioradialis.

  • e. Median nerve: C6-T1. Flexors except ulnar: most forearm flexors, flex. dig. superior; all pronators. Hand: LOAF muscles (Lumbricals 1 and 2, Opp. pollicis, Abd. poll. brev., Flex. poll. brev.).

  • f. Ulnar nerve: C8-T1. Flexor digitorum profundus 3 and 4, flexor carpi ulnaris. Most of intrinsic hand (except LOAF muscles above): thumb adductors and flexors, interossei, lumbricals 3 and 4, hypothenar muscles.

• 4. Leg:

  • a. Femoral nerve: L2-4.

    • 1) Function: Extend knee.

    • 2) Muscles: Iliopsoas, quadriceps, sartorius, rectus femoris.

  • b. Obturator nerve: L2-4.

    • 1) Function: Adduct leg.

    • 2) Muscles: Adductor longus, brevis, and magnus; gracilis, pectineus .

  • c. Sciatic nerve (tibial and peroneal nerve): L4-S2.

    • 1) Function: Extend and abduct hip, flex knee, all foot mvts.

      • a) Deep peroneal nerve: Extends toes and ankle.

      • b) Superficial peroneal nerve: Everts foot.

      • c) Tibial nerve: Superficial tibial flexes foot; deep tibial flexes toes.

    • 2) Muscles: Semitendinosus and semimembranosus, biceps femoris, gastrocnemius, soleus, foot muscles .

E. Spinal level by reflex

• 1. Cervical: Biceps is C5-6. Supinator is C5-6. Triceps is C6-8.

• 2. Thoracic: Scratch towards navel. Contraction with scratching above navel is T8-10; below navel is T10-12.

• 3. Lumbar: Knee is L2-4. Ankle is S1-2. Babinski is L4-S2.