Can you create a table of the spinal nerve roots and the regions they innervate?

Spinal Nerve Roots and Their Innervation Territories

The spinal nerve roots are organized into cervical (C1-C8), thoracic (T1-T12), lumbar (L1-L5), and sacral (S1-S5) segments, each providing motor and sensory innervation to specific body regions through their ventral and dorsal rami.

Cervical Nerve Roots (C1-C8)

Upper Cervical Roots

• C1 (Suboccipital nerve): Composed of ventral roots (and sometimes dorsal roots with or without a ganglion), providing motor innervation to suboccipital muscles; minimal to no cutaneous sensory distribution 1
• C2: Supplies the posterior scalp and upper posterior neck region through the greater occipital nerve 2
• C3: Innervates the lower posterior neck and supraclavicular region 3, 2
• C4: Provides sensory innervation to the lower neck and shoulder region, with contributions to diaphragmatic innervation via the phrenic nerve (C3-C5) 3, 4

Lower Cervical Roots

• C5: Innervates the lateral shoulder and upper lateral arm; motor supply to deltoid and biceps muscles 3, 4
• C6: Supplies the lateral forearm, thumb, and index finger; motor innervation to wrist extensors 3, 4
• C7: Innervates the middle finger and posterior forearm; motor supply to triceps and wrist/finger extensors 3, 4
• C8: Supplies the medial forearm, ring finger, and little finger; motor innervation to hand intrinsic muscles 3, 4

Important Clinical Considerations for Cervical Roots

• The cutaneous branches from lower cervical dorsal rami (C5-C7) are frequently absent, with continuous absence occurring in 87% of cases 2
• Symptom distribution from cervical nerve root irritation (dynatomal maps) differs significantly from classic sensory dermatomal maps, with symptoms frequently extending beyond traditional dermatome boundaries 4
• The brachial plexus is formed from C5-T1 ventral rami (occasionally including C4 and/or T2), providing all motor and sensory innervation to the upper extremity 3

Thoracic Nerve Roots (T1-T12)

• T1: Supplies the medial arm and contributes to brachial plexus innervation of the hand 3
• T2-T12: Each thoracic nerve root provides sensory innervation to a horizontal band (dermatome) around the trunk in a sequential pattern from upper chest to lower abdomen 2
• T4: Corresponds approximately to the nipple line
• T10: Corresponds approximately to the umbilicus
• T12: Supplies the region just above the inguinal ligament

Lumbar Nerve Roots (L1-L5)

Lumbar Plexus Formation

• L1-L4 ventral rami form the lumbar plexus, with terminal branches supplying the obturator and femoral nerve territories 3

Individual Root Distributions

• L1: Innervates the inguinal region and upper anterior thigh
• L2: Supplies the anterior and medial thigh 3
• L3: Innervates the anterior thigh and medial knee; motor supply to quadriceps 3
• L4: Supplies the medial leg and medial foot; motor innervation to anterior tibialis and quadriceps 3, 5
• L5: Innervates the lateral leg, dorsum of foot, and great toe; motor supply to foot dorsiflexors and toe extensors 3, 5

Sacral Nerve Roots (S1-S5)

Sacral Plexus Formation

• L4-S4 ventral rami form the sacral plexus (connected via the lumbosacral trunk at L4-L5), with terminal branches supplying gluteal, peroneal, and tibial nerve territories 3

Individual Root Distributions

• S1: Supplies the posterior leg, lateral foot, and small toe; motor innervation to gastrocnemius, hamstrings, and gluteal muscles 3, 5
• S2: Innervates the posterior thigh and leg 3
• S3-S4: Provide sensory innervation to the perineum and motor innervation to pelvic floor muscles 3
• S5: Supplies the perianal region 3

Critical Anatomical Variations

Lumbosacral Transitional Vertebrae

• In patients with a sacralized L5, the L4 nerve root assumes the typical function of the L5 nerve root, altering both motor and sensory distributions 5
• In patients with a lumbarized S1 (creating an "L6"), the nerve root distribution remains similar to a normal S1 pattern 5
• These variations occur in a significant proportion of the population and can create diagnostic confusion during nerve root blocks 5

Clinical Pitfalls and Caveats

• Dermatomal maps represent sensory deficits from nerve injury, while dynatomal maps (pain referral patterns) often extend well beyond classic dermatome boundaries 4
• The absence of cutaneous branches from lower cervical dorsal rami means that posterior neck sensation may not reliably localize to specific cervical levels 2
• Transitional vertebrae at the lumbosacral junction require careful radiographic correlation before performing selective nerve root procedures 5
• The cervical nerve roots exit above their corresponding vertebrae (C5 root exits above C5 vertebra), while thoracic and lumbar roots exit below their corresponding vertebrae 6