Anatomy 6: Anal Triangle and Innervation Flashcards
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
- Leaves the pelvis through the greater sciatic foramen close to the ischial spine
- 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
- Arise from the ventral rami of S2-S4
- Travel from each side of the pelvis to the corresponding inferior hypogastric plexus
- Travel to the distal 1/3 of the transverse colon, sigmoid colon, rectum, bladder and genitalie
- 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)
- Synapse in the inferior hypogastric plexus
- Provide sympathetic innervation to pelvic organs
(Red arrows)
Trajectory of pelvic splanchnic nerves (preganglionic fibers)
- Enter the inferior hypogastric plexus and pass through
- Synapse in the walls of the organs
- Provide parasmpathetic innervation to the pelvic organs
(Purple arrow)
Identify the innervations (3)
- Superior hypogastric plexus
- Right hypogastric nerve
- Sacral trunk
