Pelvic Floor Muscles: Anatomy and Function

• The pelvic floor muscles are essential for supporting pelvic organs, urinary and fecal continence, and overall function and quality of life.
• Physiotherapy assessment and training can improve pelvic floor muscle function and address related issues.
• Proper consent and client motivation are important aspects of pelvic floor muscle training.

Layers of the Pelvic Floor Muscles

• The pelvic floor muscles have multiple layers.

Anatomy of the Pelvic Floor Muscles

• The pelvic floor consists of muscles supporting pelvic organs and aiding urinary/fecal continence.
• This system works with other bodily structures.

The Perineum

• The perineum is divided into two triangles: the urogenital triangle (anterior) and the anal triangle (posterior).
• The perineal body, or central tendon of the perineum, is a fibromuscular structure in the midline where the anus and urogenital triangle meet.

Urogenital Triangle

• It is the anterior half of the perineum, bounded by the pubic symphysis, ischiopubic rami, and a line between the ischial tuberosities.
• It contains structures of the urogenital system like external genitalia and urethra.
• Several muscles in the urogenital triangle are important for sexual function and urinary control.

Bulbospongiosus (Bulbocavernosus)

• Assists with voiding and ejaculation.
• Acts as a vaginal sphincter.
• Assists in erection of the clitoris or penis.
• Contributes to orgasm contractions.
• In women, it originates at the perineum and inserts at the body of the clitoris and the bulb of the vestibule.
• In men, it originates at the perineum and the midline raphe and inserts at the body of the penis (corpus cavernosum).

Ischiocavernosus

• Extends between the ischium and the crura of the penis or clitoris.
• Stabilizes the erect penis in males and assists in clitoral erection in females.

Superficial Transverse Perineal

• Reinforces the deep transverse perineal muscle to stabilize the perineal body.
• Originates at the ischial tuberosity and meets at the perineal body.

External Anal Sphincter

• Provides voluntary control of defecation.
• Prevents defecation until appropriate.
• Originates on the skin/fascia surrounding the anal canal and inserts into the perineal body.
• It is continuous with puborectalis.
• Innervated by the inferior anal/rectal branch of the pudendal nerve (S2-4).

Intermediate Layer (Urogenital Diaphragm/Perineal Membrane)

• A muscular membrane between the symphysis pubis and ischial tuberosities.
• Works with the external urethral sphincter.
• It contains:
  • Urethral sphincter (sphincter urethrae).
  • Compressor urethrae.
  • Sphincter urethral vaginalis.
  • Deep transverse perineal.
  • Perineal membrane.

Levator Ani (Pelvic Diaphragm)

• A muscular layer forming the inferior border of the abdominopelvic cavity.
• It extends from the symphysis pubis to the coccyx.
• Attaches to the pubic bones anteriorly, ischial spines posteriorly, and the obturator internus muscle.
• Supports pelvic viscera, assists continence, aids sexual function, and positions the fetal head during childbirth.
• Supplied by sacral roots (S2-4) and the perineal branch of the pudendal nerve.
• Consists of three paired striated muscles: puborectalis, pubococcygeus, and iliococcygeus.

Puborectalis

• A thick, narrow muscle forming a U-shaped sling around the rectum.
• Arises from the symphysis pubis and urogenital diaphragm.
• Supports pelvic organs, regulates defecation, and is the primary muscle of anal continence.
• Active during respiration.
• Supplied by the nerve to the levator ani (S4) and the pudendal nerve (S2-4).

Pubococcygeus

• A wider, thinner part of the levator ani with attachments to the perineal body, anal canal, and vaginal wall.
• Arises from the obturator fascia and the posterior aspect of the pubis.
• Lifts and draws forward.
• Compresses the urethra, vagina, and anus.
• Elevates the recto-anal junction.
• Supports pelvic viscera.
• Active during inspiration.
• Supplied by the pudendal nerve (S2,3) and sacral ventral rami (S2,3).

Iliococcygeus

• A thin sheet of muscle.
• Arises from the ischial spine and obturator fascia.
• Inserts on the sacrum and anococcygeal raphe.
• Lifts upwards and forwards.
• Works with transverse abdominus.
• Presses the urethra and vagina against the pubis.
• Elevates the recto-anal junction.
• Supports pelvic viscera.
• Active during inspiration.
• Supplied by the pudendal nerve (S2,3) and sacral ventral rami (S2,3).

Anal Triangle

• It is the posterior part of the perineum.
• Lacks fascial components and is mainly skeletal muscle (external anal sphincter).
• Contains the anal canal, anus, and external anal sphincter.
• Formed by the coccyx, sacrotuberous ligaments, and a line between the ischial tuberosities.
• Contains the anal canal and ischiorectal fossae.
• The levator ani is the superior boundary.

Clinical Significance

• Pelvic floor muscles are important in pelvic floor dysfunction, urinary incontinence, pelvic organ prolapse, and sexual dysfunction.
• Understanding the anatomy and function helps with accurate assessment and treatment.
• Physiotherapy interventions include exercises, manual techniques, and biofeedback.

Characteristics of Pelvic Floor Muscles

• Operate under conscious control and have reflex actions.
• Composed of type 1 (slow twitch) and type 2 (fast twitch) fibers.
• Possess strength, power, endurance, speed, agility, and tone.
• Can contract and relax through a range of motion.
• Can become overactive and tight.
• Voluntary contractions are needed for training, even though they work tonically and reflexively.

Type 1 Fibers

• Slow twitch fibers that makes up 70%-80% of fibres
• Small motor neurons
• Low power producers
• Aerobic
• Work for hours

Type 2 Fibers

• Fast twitch fibers that makes up 20-30% of fibres
• Large motor neurons
• High power producers
• Anaerobic
• Work for 1 min- 30 min

Other Muscles Impacting Pelvic Health

• Obturator internus: Influences pelvic floor muscle function due to fascial attachments.
• Piriformis: Abducts and externally rotates the hip, stabilizes the hip, and assists in pelvic tilting.