← Nerve roots

Spinal nerve root

S2

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.

Inferior gluteal nerve

  • Gluteus maximus

Nerve to piriformis

  • Piriformis

Sciatic nerve → tibial division · thigh

  • Semitendinosus
  • Semimembranosus
  • Biceps femoris (long head)

Sciatic nerve → common fibular division · thigh

  • Biceps femoris (short head)

Tibial nerve · leg

  • Gastrocnemius
  • Soleus
  • Plantaris
  • Flexor digitorum longus
  • Flexor hallucis longus

Tibial → medial plantar nerve

  • Abductor hallucis
  • Flexor digitorum brevis
  • Flexor hallucis brevis
  • First lumbrical

Tibial → lateral plantar nerve

  • 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)

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
Root contributions and variation

An S2 contribution to obturator internus and superior gemellus is source-dependent. Direct levator ani supply may include S2, but S3–S4 is the usual core range. Pudendal muscle entries reflect shared segmental supply; an S2–S4 nerve origin does not establish equal contributions to every target. Foot-root assignments are variable. Pelvic autonomic smooth muscle is not part of this skeletal-muscle list.

References