Pelvic floor muscles

Pelvic Floor Overview - The Body's Basement

A funnel-shaped muscular sling supporting pelvic organs, crucial for urinary/fecal continence and childbirth. Composed of two main diaphragms:

• Pelvic Diaphragm: Deeper, larger layer.
  • Levator Ani: Forms the bulk of the floor. Comprised of three muscles:
    • Puborectalis
    • Pubococcygeus
    • Iliococcygeus
  • Coccygeus (Ischiococcygeus): Posterior muscle.
• Urogenital (UG) Diaphragm: Superficial to the pelvic diaphragm.

⭐ The puborectalis muscle forms a U-shaped sling around the anorectal junction. Its tonic contraction is vital for fecal continence; relaxation permits defecation.

Pelvic Diaphragm - The Main Sling

• A broad, funnel-shaped muscular sheet forming the majority of the pelvic floor, separating the pelvic cavity from the perineum below.
• Components:
  • Levator Ani:
    • Pubococcygeus
    • Puborectalis
    • Iliococcygeus
    • 📌 Mnemonic: "PIP" - Pubococcygeus, Iliococcygeus, Puborectalis.
  • Coccygeus (Ischiococcygeus): Smaller, posterior triangular muscle.
• Innervation: Nerve to levator ani (branches of S3-S4) and direct branches from S4.
• Functions: Supports pelvic viscera, resists ↑ intra-abdominal pressure, crucial for urinary/fecal continence.

⭐ The Puborectalis muscle forms a "puborectal sling" that kinks the anorectal junction. Relaxation of this sling is required to straighten the anorectal angle, allowing for defecation. Its tonic contraction is vital for fecal continence.

Urogenital Diaphragm - The Lower Deck

• Aka the Perineal Membrane; inferior to the main pelvic diaphragm.
• Stretches between the ischiopubic rami, filling the anterior gap of the levator ani.
• Contents (Deep Perineal Pouch):
  • Deep Transverse Perineal m.
  • External Urethral Sphincter
  • Bulbourethral (Cowper's) glands in males.
  • Innervation: Pudendal nerve (S2-S4).

⭐ The Perineal Body is a central fibromuscular mass. It anchors the bulbospongiosus, external anal sphincter, and transverse perineal muscles. Damage during childbirth is a common cause of pelvic organ prolapse.

Innervation & Vasculature - Power & Pipes

• Innervation:

  • Pudendal Nerve (S2-S4): Main somatic (motor and sensory) nerve to the perineum. Innervates the external urethral and anal sphincters.
  • Direct sacral branches (S3-S4): Directly supply the levator ani muscle superiorly.

• Vasculature:

  • Internal Pudendal Artery: Branch of the internal iliac artery; the primary blood supply.

⭐ The pudendal nerve can be anesthetized (pudendal nerve block) for obstetric procedures by injecting near the ischial spine.

📌 Mnemonic: "S2, S3, S4 keeps the pelvis off the floor."

Clinical Correlates - When the Floor Fails

• Pelvic Organ Prolapse (POP): Descent of pelvic organs (bladder, uterus, rectum) into the vagina. Results from damage to the levator ani and perineal body, often from childbirth (pudendal nerve injury).
  • Cystocele: Bladder prolapse.
  • Rectocele: Rectum prolapse.
• Incontinence:
  • Stress Urinary: Leakage with ↑ abdominal pressure (cough, sneeze). Due to weak urethral sphincter & pelvic floor.
  • Fecal: Damage to external anal sphincter & puborectalis.

⭐ Kegel exercises, which strengthen the pubococcygeus muscle, are a first-line treatment for stress urinary incontinence.

High‑Yield Points - ⚡ Biggest Takeaways

• The levator ani (puborectalis, pubococcygeus, iliococcygeus) and coccygeus muscles form the pelvic diaphragm.
• The puborectalis muscle creates the anorectal angle, essential for maintaining fecal continence.
• Innervation is primarily from the pudendal nerve (S2-S4).
• Injury, often during childbirth, can lead to pelvic organ prolapse (cystocele, rectocele) and stress urinary incontinence.
• Kegel exercises are designed to strengthen the pelvic floor muscles.