214. Neuronal Control of Pelvic Function

Question 1

Where are the following nerves (in the pelvis)?

• Sympathetics
• Parasympathetics
• Somatomotor

Answer 1

Symp: hypogastric nerves via thoracolumbar splanchnics (T11-L2)

Parasymp: exit SPN of S2-S4 to pelvic nerve via pelvic plexus

Somatomotor: exit Onuf’s nucleus to pudendal n. to striated perineal m.

Question 2

Micturition

• what happens at each phase
• explain the two reflexes (where, what)

Answer 2

1. Storage Phase: high symp stim (NE) causes detrusor m. relaxation (B3) and bladder neck m. constriction (A); somatomotor nerves constrict ext urethral sphincter (conscious control)
   - hypogastric and pudendal activated at same time
2. Evacuation Phase: high parasymp stim (ACh) to M3 mAChRs on bladder = detrusor m contraction, bladder neck/urethra relaxation
   - activated by increased firing (higher pressure) from pelvic nerve afferents

Continence Reflex: Pressure sensor - Pelvic Nerve Afferent - Symps (bladder neck tone, relax detrusor) and Pudendal (high EUS tone)
- Modulated by PONTINE STORAGE CENTER

Voiding Relfex: Pressure sensor - pelvic n. afferent - inhibited symp (modulated by pons), activate PAG and PONS MICTURITION CENTER = less EUS tone (pudendal n.) and increased parasymp

• both reflexes stim by high pressure (high neuronal control from PONS)

Question 3

Defecation

• unique fibers
• stages
• reflexes

Answer 3

Has ENS - symp/parasymp fibers stim ENS to control activity (indirect innervation)
- pelvic n. afferents: stretch receptors in rectum induce storage/evacuation reflex

1. Continence Phase: high symp = less colon/rectum peristalsis, high int anal sphincter tone
2. Evacuation Phase: high parasymp = more colon/rectum peristalsis, low int anal sphincter tone

Pudendal nerve (conscious control) = increase tone of ext anal sphincter

Reflex: PONS switches from storage to evacuation phases
- need supraspinal control for Valsalva maneuver (contracting chest/abd increases abd pressure and facilitates evacuation)

Question 4

Female Sexual Response

• what are the 4 parts of the sexual response cycle and what happens during each
• what is an orgasm, neurogenically?

Answer 4

1. Excitement: large VD of organs (clitoral enlargement, labia swell, vagina lubrication (plasma exudate) via starlings from VD)
2. Plateau: UG diaphragm tonically contracted
3. Orgasm: regular rhythmic contractions of smooth and striated muscle
4. Resolution

Question 5

Male Sexual Response

• what are the 4 parts of the sexual response cycle and what happens during each
• what are the 2 male erectile tissues and what do they contain?
• how does an erection occur?
• what is an orgasm, neurogenically?

Answer 5

1. Excitation - huge VD = full erection, partial testes elevation
2. Plateau: Cowper’s glad secretions, prostate enlarges, color deepens, scrotum thickens, testes fully elevate and enlarge
3. Orgasm: regular rhythmic contractions of smooth and striated muscle (ejaculation: semen propulsions through urethra)
4. Resolution

Corpus cavernosum: paired, when flaccid = smooth muscle is contracted; consists of sinusoids (epithelium and smooth muscle); surrounded by indistendible tunica; drainage via emissary veins (thru tunica)
Corpus spongiosum: around urethra

Erection: increase blood flow (VD) = smooth muscle sinusoids relax (NO = cGMP = PKG = K hyperpolarization channel = less Ca influx) and fill with blood; corpus cavernosum pushes against tunica = blocks emissary vein outflow = engorgement (high pressure >300mmHg);

Orgasm: somatomotor and symp rhythmic stim and contractions

Question 6

What are the generator cells for orgasm? Where are they and what are their inputs/outputs?

Answer 6

Lumbar Spinothalamic Cells

• input: brain and genital afferents - activated when summatively above threshold
• output: to brain and genitals for orgasm sensation