Spinal nerve root
S3
Muscle contributions
Follow the branches from the spine toward their muscle targets. These are parallel pathways, not a chain in which one muscle innervates the next. Most muscles receive more than one root.
Direct nerve to levator ani
- Puborectalis
- Pubococcygeus
- Iliococcygeus
Pudendal → inferior rectal branch
- External anal sphincter
Pudendal → perineal branches
- Bulbospongiosus
- Ischiocavernosus
- Superficial transverse perineal
- Deep transverse perineal (where distinct)
- External urethral sphincter complex: sphincter urethrae; compressor urethrae and urethrovaginal sphincter where present
Sciatic → tibial → medial plantar nerve · reported foot contributors
- Abductor hallucis
- Flexor digitorum brevis
- First lumbrical
Sciatic → tibial → lateral plantar nerve · reported foot contributors
- Quadratus plantae
- Abductor digiti minimi
- Flexor digiti minimi brevis
- Adductor hallucis
- Lumbricals 2–4
- Plantar interossei (three)
- Dorsal interossei (four)
- Opponens digiti minimi (when distinguishable)
Root contributions and variation
The plantar-muscle entries reflect reported anatomical root ranges, not an isolated S3 clinical myotome; contributions vary by source and individual. Some references include S3 for coccygeus, while muscle-specific sources emphasize S4 with minor S5. Pudendal and direct pelvic branches overlap. Autonomic smooth muscle is excluded.