Interactive Anatomy
The Sciatic Nerve Pathway
Select a nerve root to see where it originates and what symptoms compression causes
Full Pathway
L4 Root
L5 Root
S1 Root
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L4 root
L5 root
S1 root
Origin
L4 – S3 nerve roots
Nerve diameter
~2 cm — largest in body
Pathway
Gluteal space → posterior thigh → foot
L4 Root — L3/L4 disc
Dermatome
Anterior thigh, inner knee, medial shin
Reflex
Patellar (knee jerk)
Motor test
Walk on heels (tibialis anterior)
L5 Root — L4/L5 disc (most common)
Dermatome
Outer calf, top of foot, big toe
Reflex
None reliable — motor exam critical
Motor test
Great toe extension (EHL strength)
S1 Root — L5/S1 disc
Dermatome
Posterior calf, heel, outer foot
Reflex
Achilles (ankle jerk)
Motor test
Single-leg calf raise (gastrocnemius)