Pelvic Innervation

Pelvic Plexuses Overview - Neural Networks

• Somatic Plexuses: Formed by anterior rami of spinal nerves.
  • Sacral Plexus: Roots L4-S4. Innervates pelvis, perineum, gluteal region, lower limb.
  • Coccygeal Plexus: Roots S4-Co1 & coccygeal nerve. Supplies anococcygeal region.
• Autonomic Plexuses: Intricate networks regulating pelvic visceral functions.
  • Superior Hypogastric Plexus (SHP):
    • Sympathetic fibers; anterior to L5 vertebra, below aortic bifurcation.
    • Continues aortic plexus; carries sympathetic fibers from lumbar splanchnics.
  • Inferior Hypogastric Plexus (IHP) / Pelvic Plexus:
    • Paired; situated beside pelvic viscera. Main pelvic autonomic distribution center.
    • Receives:
      • Sympathetic: from SHP (hypogastric nerves) & sacral sympathetic trunk.
      • Parasympathetic: from Pelvic Splanchnic Nerves (S2-S4, nervi erigentes).

⭐ The inferior hypogastric plexus (pelvic plexus) is the main neurovascular gateway to pelvic viscera, containing both sympathetic and parasympathetic fibers.

Somatic Innervation Details - Voluntary Volts

Sacral Plexus (L4-S4): Key for pelvic somatic supply.

• Pudendal Nerve (S2,S3,S4): Chief perineal nerve. 📌 S2,3,4 keeps pelvis off the floor.
  • Course: Exits greater sciatic foramen, enters lesser sciatic foramen, pudendal canal (Alcock's).
  • Branches:
    • Inferior rectal n.: External anal sphincter, perianal skin.
    • Perineal n.: Urogenital triangle muscles, scrotal/labial skin.
    • Dorsal n. of penis/clitoris: Penile/clitoral sensation.

  ⭐ The pudendal nerve (S2, S3, S4) is the primary somatic nerve of the perineum, essential for fecal/urinary continence and sexual sensation.

• Sciatic Nerve (L4-S3): Leaves pelvis via greater sciatic foramen. (Largest nerve).
• Superior Gluteal Nerve (L4-S1): Gluteus medius, minimus, TFL.
• Inferior Gluteal Nerve (L5-S2): Gluteus maximus.
• Nerve to Obturator Internus (L5-S2): Obturator internus, sup. gemellus.
• Nerve to Piriformis (S1,S2): Piriformis m.
• Nerves to Levator Ani & Coccygeus (S3,S4): Pelvic diaphragm.

Coccygeal Plexus (S4,S5,Co1):

• Anococcygeal Nerve: Skin over coccyx.

Autonomic Innervation Pathways - Auto Pilots

Controls involuntary visceral functions.

• Sympathetic System (L1-L2 origin): "Fight or Flight"
  • Sacral sympathetic trunk: Descends, ends at ganglion impar.
  • Sacral splanchnic nerves: Arise from L1-L2, join plexuses.
  • Superior Hypogastric Plexus ("presacral nerve"): Below aortic bifurcation, gives rise to...
  • Hypogastric nerves (R & L): Connect to Inferior Hypogastric Plexus.
• Parasympathetic System (S2, S3, S4 origin): "Rest and Digest"
  • Pelvic splanchnic nerves (Nervi Erigentes): From S2,S3,S4. 📌 Remember: S2,3,4 for Pelvic Parasympathetic.
• Inferior Hypogastric Plexus (Pelvic Plexus):
  • Mixed autonomic plexus (sympathetic + parasympathetic).
  • Formation: Hypogastric nerves + Pelvic splanchnic nerves.
  • Distribution: Supplies bladder, rectum, reproductive organs.
• Key Functions:
  • Micturition (sympathetic for storage, parasympathetic for voiding).
  • Defecation.
  • Erection (parasympathetic).
  • Ejaculation (sympathetic).

⭐ Pelvic splanchnic nerves (S2-S4), also known as nervi erigentes, provide parasympathetic innervation crucial for erection and stimulating bladder contraction.

Clinical Correlates & Injuries - Pelvic Pains

• Pudendal Nerve Block:
  • Approaches: Transvaginal, perineal.
  • Landmark: Ischial spine.

  ⭐ The ischial spine is the key palpable bony landmark for administering a pudendal nerve block, targeting the nerve as it enters the pudendal canal.

• Nerve Injuries & Causes:
  • Childbirth: Pudendal nerve, levator ani nerves.
  • Pelvic Surgery: Obturator, sciatic, hypogastric plexuses.
• Symptoms:
  • Chronic pelvic pain.
  • Fecal/urinary incontinence.
  • Sexual dysfunction.
• Specific Conditions:
  • Referred Pain: Obturator nerve injury → medial thigh pain.
  • Alcock's Canal Syndrome: Pudendal neuralgia (pain, numbness, dysfunction in pudendal nerve area).

High‑Yield Points - ⚡ Biggest Takeaways

• Pudendal nerve (S2-S4): Key for perineal sensation, sphincter control; vulnerable in childbirth.
• Pelvic splanchnic nerves (S2-S4): Drive parasympathetic functions in pelvis, crucial for erection.
• Inferior hypogastric plexus: Major autonomic control center for pelvic organs; damage causes widespread dysfunction.
• Obturator nerve (L2-L4): Injury causes thigh adductor weakness and medial thigh sensory loss.
• Sacral plexus (L4-S4): Origin of sciatic and pudendal nerves, vital for lower limb and perineum.
• Superior hypogastric plexus: Transmits sympathetic signals for ejaculation and pelvic vasoconstriction.