Anatomy 6: Anal Triangle and Innervation

Question 1

Define the ischiorectal (ischioanal) fossa

Answer 1

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

Question 2

Define the boundaries of the ischiorectal fossa (3)

Answer 2

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

Question 3

Define the pectineate line

Answer 3

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

Question 4

Location of the external anal sphincter

Answer 4

Around the lower 2/3 of the anal canal

Question 5

Location of the internal anal sphincter

Answer 5

Around the upper 2/3 of the anal canal

Question 6

3 parts of the external anal sphincter

Answer 6

• Deep
• Superficial
• Subcutaneous

Question 7

4 vessels of the anal blood supply

Answer 7

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

Question 8

Define the pudendal canl

Answer 8

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

Question 9

Describe the trajectory of the internal pudendal artery

Answer 9

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

Question 10

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

Answer 10

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

Question 11

Distal branches of the internal pudendal artery

Answer 11

Dorsal artery of the penis/clitoris

Question 12

7 branches of the lumbar plexus (somatic)

Answer 12

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

Question 13

Somatic branches of the sacral plexus (3)

Answer 13

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

Question 14

Trajectory of the lumbosacral trunk

Answer 14

Travels over the pelvic brim to join the sciatic nerve

Question 15

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

Answer 15

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

Question 16

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

Answer 16

Out the greater sciatic foramen inferior to piriformis

Question 17

Parasympathetic innervation for the pelvis

Answer 17

• Pelvic splanchnic nerve

Question 18

Describe the trajectory of the pelvic splanchnic nerves

Answer 18

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

Question 19

Location of inferior hypogastric plexus

Answer 19

Bilaterally on the walls of the rectum

Question 20

2 sympathetic ganglions of the pelvis

Answer 20

Superior hypogastric

Inferior hypogastric

Question 21

Autonomic plexus in the abdomen and pelvis

Answer 21

Sacral planchnic

Question 22

Trajectory of the sacral splanchnic

Answer 22

Extend from the sympathetic ganglion to the inferior hypogastric plexus

Question 23

Trajectory of the postganglionic fibers in the pelvis

Answer 23

• 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)

Question 24

Trajectory of the sacral splanchnic nerves (preganglionic fibers)

Answer 24

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

(Red arrows)

Question 25

Trajectory of pelvic splanchnic nerves (preganglionic fibers)

Answer 25

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)

Question 26

Identify the innervations (3)

Answer 26

• Superior hypogastric plexus
• Right hypogastric nerve
• Sacral trunk