Anatomy 6: Anal Triangle and Innervation Flashcards Preview

Block I: Reproduction & Sexuality > Anatomy 6: Anal Triangle and Innervation > Flashcards

Flashcards in Anatomy 6: Anal Triangle and Innervation Deck (26):

Define the ischiorectal (ischioanal) fossa

Wedge-shaped regions on either side of the anus which hold two extensive fat pads. Continuous with the deep perineal pouch (green arrows)


Define the boundaries of the ischiorectal fossa (3)

  • Base = skin
  • Lateral = lower part of obturator internus
  • Medial = levator ani


Define the pectineate line

Dividing line between the endodern-derived hindgut (above) and ectoderm-derived anal pit (below).

NOTE: Internal hemorrhoids (above) are not painful, whereas external (below) are


Location of the external anal sphincter

Around the lower 2/3 of the anal canal


Location of the internal anal sphincter

Around the upper 2/3 of the anal canal


3 parts of the external anal sphincter

  • Deep
  • Superficial
  • Subcutaneous


4 vessels of the anal blood supply

  • Internal pudentary artery and vein (from and to internal iliac artery)
  • Inferior rectal artery and vein


Define the pudendal canl

A passageway within the obturator fascia on the lateral wall of the ischiorectal fossa for the internal pudental artery and vein, and the pudendal nerve


Describe the trajectory of the internal pudendal artery

  1. Leaves the pelvis through the greater sciatic foramen close to the ischial spine
  2. Enters the lesser sciatic foramen after wrapping around the ischial spine to gain access to the perineum


Artery that branches off the internal pudendal artery at the start of the canal and at the end of the canal

  • Start = inferior rectal artery
  • End = perineal branches that enter the deep and superficial perineal pouches


Distal branches of the internal pudendal artery

Dorsal artery of the penis/clitoris


7 branches of the lumbar plexus (somatic)

  • Iliohypogastric nerve
  • Ilioinguinal nerve
  • Genitofemoral nerve
  • Lateral cutaneous nerve of the thigh
  • Femoral nerve
  • Obturator nerve
  • Nerve branching to the lumbosacral trunk (L4+L5)


Somatic branches of the sacral plexus (3)

  • Lumbosacral trunk (L4, L5)
  • Pudendal nerve (S2, S3, S4)
  • Sciatic (L4, L5, S1, S2, S3)


Trajectory of the lumbosacral trunk

Travels over the pelvic brim to join the sciatic nerve


Trajectory of the pudendal nerve (S2, S3, S4)

Out the greater and in the lesser sciatic foramen to the perineum


Trajectory of the sciatic nerve (L4, L5, S1, S2, S3)

Out the greater sciatic foramen inferior to piriformis


Parasympathetic innervation for the pelvis

  • Pelvic splanchnic nerve


Describe the trajectory of the pelvic splanchnic nerves

  1. Arise from the ventral rami of S2-S4
  2. Travel from each side of the pelvis to the corresponding inferior hypogastric plexus
  3. Travel to the distal 1/3 of the transverse colon, sigmoid colon, rectum, bladder and genitalie
  4. Preganglionic parasympathetic fibers synapse in the walls of the organs


Location of inferior hypogastric plexus

Bilaterally on the walls of the rectum


2 sympathetic ganglions of the pelvis

Superior hypogastric

Inferior hypogastric


Autonomic plexus in the abdomen and pelvis

Sacral planchnic


Trajectory of the sacral splanchnic

Extend from the sympathetic ganglion to the inferior hypogastric plexus


Trajectory of the postganglionic fibers in the pelvis

  • Leave the sympathetic chain and join a sacral nerve (S1)
  • Leave the pelvis with it to go to the legs to innervate blood vessels, sweat glands, hair follicle, etc

(Green arrow)


Trajectory of the sacral splanchnic nerves (preganglionic fibers)

  1. Synapse in the inferior hypogastric plexus
  2. Provide sympathetic innervation to pelvic organs

(Red arrows)


Trajectory of pelvic splanchnic nerves (preganglionic fibers)

  1. Enter the inferior hypogastric plexus and pass through
  2. Synapse in the walls of the organs
  3. Provide parasmpathetic innervation to the pelvic organs

(Purple arrow)


Identify the innervations (3)

  • Superior hypogastric plexus
  • Right hypogastric nerve
  • Sacral trunk