ANS Pelvis

Question 1

When does voluntary control of micturition and defecation usually arise?

Answer 1

Between 2 and 2.5 years postnatally

Question 2

What is the course of PANS to the pelvis?

Answer 2

Preganglionic cell body: S2-S4 in intermediate gray matter
Preganglionic axons: pelvic splanchnics, passing through pelvic plexus (inferior hypogastric) to subsidiary plexuses around branches of internal iliac to walls of viscera
Postganglionic cell body: terminal ganglion in wall of viscera
Postganglionic axons: innervate smooth muscle, glands in bladder, rectum, prostate, seminal vesicles, ejaculatory ducts, urethra, uterus, and erectile tissue

Question 3

How do pelvic splanchnics get into the abdomen?

Answer 3

Enter the mesenteries (i.e. mesosigmoid) and follow arterial branches (inferior mesenteric and rectal arteries) to enteric plexus for descending and sigmoid colons.

Question 4

Where is the inferior hypogastric plexus located, and what types of fibers are found in it?

Answer 4

Located anterior to the sacrum, lateral to the rectum within the endopelvic fascia. Contains:
Postganglionic SANS
Preganglionic PANS
Visceral afferent

Question 5

What is the superior hypogastric plexus, and what types of fibers are found in it?

Answer 5

Plexus at the level of the common iliac artery, formed by lumbar splanchnics only.
Contains:
Postganglionic SANS
Visceral afferent

NO PANS

Question 6

How do SANS fibers from lumbar splanchnics enter the inferior hypogastric plexus?

Answer 6

From communication with the superior hypogastric plexus, which is done via the hypogastric nerve.

Question 7

What is the SANS course to the pelvis and perineum?

Answer 7

Preganglionic cell body: L1-L2 (two most caudal spinal levels of ILC, in conus medullaris)
Preganglionic axons: Follow white communicating rami to SANS lumbar and sacral ganglia in sympathetic chain ganglion
Postganglionic cell body: Lumbar and sacral ganglia
Postganglionic axons: Join lumbar and sacral splanchnic nerves to hypogastric plexuses + subsidiaries.

Question 8

What are some of the subsidiary plexus?

Answer 8

Branches of internal iliac, including: Vesical (to bladder), hemorrhoidal (to rectum), prostatic, deferential, uterine, vaginal, urethral

Question 9

Where is the integrating reflex center for the micturition reflex? What symptoms does this explain?

Answer 9

Conus medullaris at S2-4 spinal levels. Explains why destruction of conus in spinal injury causes urinary and fecal incontinence

Question 10

What are the first two steps for the micturition reflex?

Answer 10

1. Bladder passively filling causes distension, stimulating sensory VA stimulation
2. Sensory VA impulses course with pelvic splnachnics to S2-S4, triggering activity in 2nd order spinal neurons which convey the urge to urinate to the brain

Question 11

What are the third and fourth steps for the micturition reflex?

Answer 11

3. Incoming VA impulses also activate PANS preganglionic fibers to detrusor which contracts bladder, as well as somatic fibers to external urethral sphincter to prevent urination. Detrusor action is countered by SANS fibers to effect contraction of internal urethral sphincter.
4. Entry of urine into prostate urethra causes more intense VA stimulation

Question 12

What are the final steps of the micturition reflex?

Answer 12

5. A voluntary signal descends from upper brain to conus medullaris causing inhibition of somatic pudendal motor neuron to external urethral sphinchter.
6. Relaxation of bladder’s external sphinchter, allowing bladder’s detrusor to contract uniformly while internal sphincter relaxes

Question 13

How is the internal urethral sphincter controlled and why is this important?

Answer 13

SANS for contraction via lumbar splanchnics
PANS for relaxation: pelvic splanchnics via inferior hypogastric plexus to relax

Excessive PANS stimulation during micturition reflex causes relaxation, and also excessive SANS stimulation during ejaculation causes contraction to prevent reflux of semen into bladder, or urine into urethra.

Question 14

What type of neuron is the visceral afferent for stretch sensation to the bladder?

Answer 14

A bipolar sensory neuron with cell body in the dorsal root ganglion. It has cell processes which synapse with 2nd order neuron, as well as PANS cell bodies to contract the detrusor muscle and somatic motor cell bodies to make the external urethral spincter to contract

Question 15

What causes overactive bladder and who is most susceptible?

Answer 15

Involuntary contraction of detrusor muscle prior to it being fully, causing urge to go and urinary incontinence. Happens most in females.

Question 16

How is overactive bladder treated?

Answer 16

Via Vesicare (solifenacin succinate, an anticholinergic agent) to block the acetylcholine receptor in detrusor, since PANS is overworking and causing overcontractility.

Question 17

What causes urinary problems in benign prostatic hyperplasia (BPH) and how is it treated?

Answer 17

Resistance to urine flow is via hyperactivity of prostate smooth muscle and internal sphincter which results in severely contstricted urethra.

Relieved by Flomax (tamsulosin, an alpha 1 adrenergic blocker) which stops the SANS and acts to improve urine flow.

Question 18

How does the defacation reflex work?

Answer 18

1. Peristaltic wave forces feces into rectum.
2. Distension of rectal wall and sensory stimulation triggers VA impulses in pudendal nerve and pelvic splanchnics. These reach the S2-S4 spinal levels and activate 2nd order neurons in brain which convey message of “urge” to defacate.
3. VA impulses activate PANS and somatic motor in conus.
4. PANS stimulation relaxes IAS and causes peristalsis of lower rectum. Somatic motor causes increased contraction of external anal sphincter preventing defecation.
5. Voluntary signal from brain inhibits pudendal motor signal, causing relaxation of external sphincter.
6. Peristaltic wave in rectum takes over and pushes feces out of canal until there is enough defecation that the PANS of the rectum is no longer stimulated.

Question 19

What else aids in the expelling of feces from the anal canal?

Answer 19

Contraction of abdominal muscles, diaphragm, closure of glottis, and relaxation of pelvic diaphragm.

Question 20

How is erection triggered via PANS?

Answer 20

1. Erotic cutaneous or psychic stimulation triggers VA impulses that course in pelvic splanchnics.
2. VA impulses from brain or skin reach the conus medullaris (S2-S4) and activate PANS neurons which ultimately control innervation of smooth muscle in erectile tissue of both male and female genitalia.

Question 21

How do PANS postganglionics trigger erection?

Answer 21

They cause the release of nitric oxide from endothelium of helicine arteries, thus relaxing the smooth muscle and causing vasdilation. Distension of the tunica albuginea decreases the venous return to deep dorsal vein via circumferential veins.

Question 22

How do Viagra, Cialis, and Levitra work?

Answer 22

Act to enhance NO production, relaxation of vascular smooth muscle, and vasodilation

Question 23

How is ejaculation controlled?

Answer 23

SANS, integrated at L1 spinal level. It is triggered by a massive SANS impulse wave which originates from upper brain to L1 spinal level.

Travels in hypogastric plexuses and subsidiary plexus. Works to synchronously contract smooth muscle in seminal vesicle, prostate gland, and vas deferens, with expulsion of semen andsperm into prostatic urethra.

Question 24

What is the ANS innervation of the lower limb?

Answer 24

There is no PANS.
Only SANS from T10-L2 ILC, synapsing in lumbar and sacral ganglia of SCG. Postganglionic fibers then join lumbosacral plexus and its nerves to the lower limb. Fibers follow nerves to ultimate targets.

Question 25

What do SANS fibers in the lower limb do?

Answer 25

They innervate sweat glands in lower limb for heat dissipation, cutaneous vascular structures for vasoconstriction (heat conservation), and erector pili muscle (elevate hairs, heat conservation)

Question 26

What is lumbar sympathectomy and when might it be indicated?

Answer 26

Removal of upper three lumbar ganglia may be needed when you have intermittent claudication during exercise. Intermittent claudication is pain in the leg due to arterial occlusive disease. SANS functions in vasoconstriction, so removing this stimulus will keep arteries patent and prevent pain.