Autonomics of the pelvis

Question 1

Location of preganglionic parasympathetic neurons

Answer 1

IMLCC at spinal levels S2-S4

Question 2

Preganglionic parasympathetic fibers: origin and distribution

Answer 2

B. These fibers exit the spinal cord with the ventral root and then leave the ventral ramus as pelvic splanchnic nerves.

C. The pelvic splanchnic nerves distribute with the inferior hypogastric and subsidiary plexuses to the pelvic and perineal organs.

Question 3

Where postganglionic parasympathetic fibers are found

Answer 3

found primarily within the walls of the organs.

Question 4

Origination of sympathetic innervation to the pelvis (general)

Answer 4

a. Sympathetic chain continues into pelvis; contributes gray rami to all sacral spinal nerves.
b. Right and left sympathetic trunks merge to form the ganglion impar.

Question 5

Lumbar splanchnics

Answer 5

1. Preganglionic neurons are located in the IMLCC at spinal levels T11-L2.
2. These fibers enter the sympathetic chain, do not synapse, and exit as lumbar splanchnic nerves.
3. The lumbar splanchnic nerves enter the intermesenteric and superior hypogastric plexuses and synapse with postganglionic neurons found here.
4. Postganglionic neurons travel from the superior hypogastric plexus to the inferior hypogastric plexus via the hypogastric nerves.
5. Postganglionic fibers then spread to pelvic viscera via subsidiary plexuses of the inferior hypogastric plexus.
6. This is the major route of sympathetic innervation to the pelvis.

Question 6

Sacral splanchnics

Answer 6

1. Preganglionic neurons are located in the IMLCC at spinal levels T12-L2.
2. These fibers descend within the sympathetic chain to sacral levels and exit, without synapsing, as sacral splanchnic nerves.
3. The sacral splanchnic nerves enter the inferior hypogastric plexus where they synapse with scattered postganglionic neurons within inferior hypogastric ganglia.
4. Postganglionic fibers then spread to pelvic viscera via subsidiary plexuses of the inferior hypogastric plexus
5. This is the minor route of sympathetic innervation to the pelvis.

Question 7

Perineal innervation

Answer 7

A. Parasympathetic innervation of perineal viscera is primarily from the cavernous plexus; a continuation of the uterovaginal or prostatic plexuses; cavernous nerves distribute with branches of the pudendal nerve.

B. Sympathetic innervation mainly courses with the pudendal nerve.

C. Provides autonomic innervation to the erectile tissues, urethral mucosa, and glands.

Question 8

Autonomic Efferent Innervation: Urinary Bladder

Answer 8

a. Inferior hypogastric plexus → vesicle plexus
b. Sympathetic innervation
1. T10-L2 via lumbar and sacral splanchnic nerves.
2. Contraction of trigonal muscle and smooth muscle portion of sphincter urethrae mechanism; vasomotor.
c. Parasympathetic
1. S2-S4 via pelvic splanchnic nerves.
2. Contraction of detrusor mm.

Question 9

Autonomic Efferent Innervation: Urethra

Answer 9

a. Inferior hypogastric plexus → Prostatic or vesicle plexus
b. Sympathetic via lumbar and sacral splanchnic nerves (L1-L3)
c. Parasympathetic via pelvic splanchnic nerves (S2-S4)
d. Innervation of perineal urethra is via pudendal nerve (S2-S4)

Question 10

Autonomic Efferent Innervation: Testes

Answer 10

a. Testicular plexus
1. Sympathetic innervation from T10-T11 via lesser splanchnic nerve and aorticorenal ganglion.
2. Parasympathetic innervation (?) likely from vagus.

Question 11

Autonomic Efferent Innervation: Male internal reproductive organs

Answer 11

a. Inferior hypogastric plexus → subsidiary plexuses (vesicle, deferential, prostatic)
b. Sympathetic – T12-L2 via lumbar and sacral splanchnic nerves.
c. Emission (part of ejaculation) is controlled by the sympathetic nerves; contraction of smooth muscle of ductus deferens, seminal glands, ejaculatory duct, and prostate leads to delivery of semen to urethra.
d. Paraympathetic – S2-S4 via pelvic splanchnic nerves

Question 12

Autonomic Efferent Innervation: Penis and glands of perineum

Answer 12

a. Dorsal n of penis – sensory and sympathetic innervations.
b. Cavernous nerves – parasympathetic nerves from prostatic plexus.
c. Erection is mediated primarily by increased parasympathetic tone (via cavernous nerves) to the erectile tissue arteries (helicine aa.) causes filling and engorgement of erectile bodies. Contraction of the bulbospongiosus and ischiocavernosus mm. is also involved; prevents venous drainage of blood.
d. Ejaculation is controlled sympathetically (emission – see above) and somatically (via pudendal nerves) from forceful contraction of bulbospongiosus m.
e. Remission is a sympathetic response involving contraction of helicine aa.

Question 13

Autonomic Efferent Innervation: Ovarian Plexus

Answer 13

a. Innervates ovary, uterine tube
b. Sympathetic
1. Sympathetic innervation from T10-T11 via lesser splanchnic nerve and aorticorenal ganglion.
2. Vasomotor
c. Parasympathetic
1. Vagus (?)
2. Vasomotor

Question 14

Autonomic Efferent Innervation: Uterus, cervix, superior portion of vagina

Answer 14

2. Inferior hypogastric plexus → Uterovaginal plexus
   a. Uterus, cervix, superior portion of vagina
   b. Sympathetic
3. T12-L2 via lumbar and sacral splanchnic nerves.
4. Vasomotor
   c. Parasympathetic
5. S2-S4 via pelvic splanchnic nerves
6. Vasomotor; contraction of smooth muscle

Question 15

Autonomic Efferent Innervation: inferior 1/4 of vagina

Answer 15

pudendal nerve (somatic)

Question 16

Autonomic Efferent Innervation: Rectum and anal canal superior to pectinate line

Answer 16

a. Inferior hypogastric plexus → rectal plexus
b. Sympathetic
1. L1-L2 via lumbar and sacral splanchnic nerves.
2. Vasomotor, inhibit gland secretion.
c. Parasympathetic
1. S2-S4 via pelvic splanchnic nerves
2. Contraction of smooth muscle (peristalsis); stimulate glandular secretion.

Question 17

Autonomic Efferent Innervation: Anal canal

Answer 17

a. Superior to pectinate line → Inferior hypogastric plexus
b. Inferior to pectinate line → Inferior rectal nerves

Question 18

Autonomic control of defecation

Answer 18

a. The sigmoid colon initially adjusts to increasing volumes of fecal matter without initiation of peristaltic contractions. However, once a critical mass is obtained, a sensation of fullness and an urge to defecate are felt due to stimulation of parasympathetic afferents.
b. Fecal material is held in the rectum by the puborectalis and external anal sphincter (voluntary control) until appropriate measures can be taken.
c. The internal anal sphincter (autonomic control) is tonically contracted. Must relax for defecation to proceed.
d. Peristaltic contractions (parasympathetic fibers) move feces through rectum.

Question 19

Visceral Afferent innervation (general)

Answer 19

A. Reflexive sensations (distention) travel with parasympathetic nerves to S2-S4.

B. Acute pain fibers travel with both parasympathetic and sympathetic nerve fibers depending on whether the organ is above or below the pelvic pain line.

1. The pelvic pain line refers to the inferior limit of pelvic peritoneum.
2. Distinguishes organs (or portions of organs) covered with pelvic peritoneum versus organs (or portions of organs) not covered with pelvic peritoneum.
3. Superior to pain line (i.e, organs which are peritonealized) – visceral pain fibers travel with sympathetic nerves to T11 – L2 spinal cord segments.
4. Inferior to pain line (i.e. organs which are subperitoneal) – visceral pain fibers travel with parasympathetic nerves to S2 – S4 spinal cord segments.

Question 20

Afferent innervation: Urinary Organs

Answer 20

1. Ureter – all pain afferents travel with sympathetic fibers.
2. Urinary bladder
   a. Superior portion (peritonealized) – acute pain afferents with sympathetic nerves to T10-L2.
   b. Inferior portion (subperitoneal) – pain afferents travel parasympathetic fibers to S2-S4.
3. Urethra – all pain afferents travel with parasympathetic fibers.

Question 21

Afferent innervation: GI organs

Answer 21

1. The pelvic pain line for GI viscera occurs at the recotsigmoidal junction.
2. Rectum – all pain afferents travel with parasympathetic fibers to S2-S4.
3. Anal canal
   a. Above pectinate line – pain afferents travel with parasympathetic fibers to S2-S4.
   b. Below pectinate line – somatic innervation (pudendal nerve).

Question 22

afferent innervation: male internal reproductive organs

Answer 22

all pain afferents travel with parasympathetic fibers to S2-S4; except testes, epididymis, and distal ductus deferens (travel with sympathetic fibers to T0-T11). Penis is somatically innervated by the pudendal nerve.

Question 23

Afferent innervation: female internal reproductive organs

Answer 23

1. Ovary and Uterine Tubes – all acute pain afferents travel with sympathetic fibers to T10-T11.
2. Uterus
   a. Fundus and Body– all acute pain afferents travel with sympathetic fibers to T12-L2.
   b. Cervix – all pain afferents travel with parasympathetic fibers to S2-S4.
3. Vagina
   a. Superior ¾ of vagina – all pain afferents travel with parasympathetic fibers to S2-S4.
   b. Inferior ¼ of vagina – somatic innervation (pudendal nerve)

Question 24

Pain management for childbirth

Answer 24

a. LUMBAR EPIDURAL – anesthetic delivered around LV3/LV4 epidural space. Level of anesthesia is usually 3-4 levels higher than insertion. Complete anesthesia of pelvis, perineum, and lower limbs. Mother does not experience pain from uterine contractions or passage of infant through birth canal. Anesthetic agent can be continuously delivered via an indwelling cather.
b. CAUDAL EPIDURAL – anesthetic delivered into epidural space of sacral canal; producing anesthesia of S2-S4 spinal cord levels. Loss of pain from cervix, vagina, and perineum. Recall: pain from cervix and superior vagina travel with parasympathetic fibers to S2-S4 spinal cord levels. Uterine contractions are still felt. Recall: pain from fundus and body of uterus travel with sympathetic fibers to T12-L2 spinal cord levels.
c. PUDENDAL NERVE BLOCK – provides anesthesia of majority of perineum and inferior ¼ of vagina. Pain from uterine contractions, passage through birth canal is still felt. Pudendal nerve is localized by palpating the ischial spine and sacrospinous ligament. Will minimize pain from potential tearing or episiotomy.