Spinal nerve root
S4
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
Direct pelvic branches
- Coccygeus
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
- External anal sphincter (S4 perineal contribution)
Root contributions and variation
Levator ani receives direct sacral branches with possible pudendal contribution. The external anal sphincter has inferior rectal S2–S3 supply and an S4 perineal contribution in detailed descriptions. These pathways overlap rather than providing a single exclusive root per muscle. No routine lower-limb skeletal-muscle targets are assigned here.