SM_214b: Neural Control Pelvic Function

Question 1

____ innervates striated muscules of the pelvis: external anal and urethral sphincters, bulbospongiosus, ischiocavernosus, and transverse perineal nerve

Answer 1

Pudendal nerve innervates striated muscules of the pelvis: external anal and urethral sphincters, bulbospongiosus, ischiocavernosus, and transverse perineal nerve

(somatic)

Question 2

Nerves from ____ innervate muscules of the pelvic diaphragm: urogenital diaphragm, levator ani, coccygeus, pubococcygeus, circumvaginal muscles, Kegel muscles, and orgasmic platform

Answer 2

Nerves from pudendal plexus (S2-4) innervate muscules of the pelvic diaphragm: urogenital diaphragm, levator ani, coccygeus, pubococcygeus, circumvaginal muscles, Kegel muscles, and orgasmic platform

(somatic)

Question 3

Sympathetic innervation to pelvis is primarily from ____

Answer 3

Sympathetic innervation to pelvis is primarily from hypogastric nerve (T11-L2)

Question 4

Preganglionic sympathetic neurons use ACh, while postanglionic sympathetic neurons arising from the ___ use NE primarily

Answer 4

Preganglionic neurons use ACh, while postanglionic neurons arising from the pelvic plexus use NE primarily

Question 5

Colon receives sympathetic fibers via ____

Answer 5

Colon receives sympathetic fibers via lumbar colonic nerve

(from inferior mesenteric ganglion)

Question 6

Pelvic organs also receive innervation from the caudal ___

Answer 6

Pelvic organs also receive innervation from the caudal sympathetic chain

(primarily to vasculature)

Question 7

Parasympathetic innervation to the pelvis occurs via the ___

Answer 7

Parasympathetic innervation to the pelvis occurs via the pelvic nerve (S2-4)

Question 8

Preganglionic and postganglionic (arising from the _____) parasympathetic fevers use ACh

Answer 8

Preganglionic and postganglionic (arising from the pelvic plexus) parasympathetic fevers use ACh

(smooth muscle relaxing neurotransmitter is usually nitric oxide)

Question 9

External genitalia differentiate from ____ under hormonal control

Answer 9

External genitalia differentiate from common embyrological origins under hormonal control

(androgens: testosterone, dihydroxytestosterone)

Question 10

Internal genitalia are derived from ____ in males and ____ in females under hormonal control via androgens and Mullerian duct inhibiting factor

Answer 10

Internal genitalia are derived from Wolffian ducts in males and Mullerian ducts in females under hormonal control via androgens and Mullerian duct inhibiting factor

Question 11

In the absence of testicular hormones, the phenotype is ___

Answer 11

In the absence of testicular hormones, the phenotype is female

Question 12

Neural circuitry mediating pelvic function is ___ between males and females

Answer 12

Neural circuitry mediating pelvic function is similar between males and females

(sexual dimorphism of pelvic innervation is related to the differentiation of the organs)

Question 13

Describe coordination of the somatic and autonomic nervous systems

Answer 13

Coordination of the somatic and autonomic nervous systems

• Most pelvic functions require both somatic and autonomic nervous system activity
• Sympathetic, parasympathetic, and somatic activity is highly coordinated
• In general, defecation, micturition, and sexual function are mutually inhibitory to each other
• Coordination is mediated primarily by spinal cord with supraspinal regulation
• Sympathetic and parasympathetic activity may be antagonistic (bladder and colon) or synergistic (exocrine gland secretions)

Question 14

Pelvic control is ____

Answer 14

Pelvic control is hierarchical

• More complex functions are managed by higher levels
• Mediated at several levels: enteric nervous system (for colon), autonomic ganglia, spinal cord, brainstem, hypothalamus, and higher centers

Question 15

Describe defecation

Answer 15

Defecation

• Intrinsic neural innervation
• Extrinsic innervation
• Internal anal sphincter
• External anal sphincter

Question 16

Describe mechanical factors in maintenance of bowel continence

Answer 16

Mechanical factors in maintenance of bowel continence

• Rectum is usually empty
• Anal canal is narrow
• Pelvic flexure provides a barrier to feces

Question 17

Describe neural factors in maintenance of bowel continence

Answer 17

Neural factors in maintenance of bowel continence

• Internal anal sphincter (smooth muscle) and external anal sphincter and puborectalis sling (striated muscles) are usually contracted: maintained contracted by sympathetic and pudendal plexus activity
• Activity of other pelvic diaphragm muscles also contributes to continence
• Conscious responses and unconscious reflexes contract both sphincters when material moves into rectum

Question 18

Describe spinal and local reflexes involved in the defecation reflex

Answer 18

Spinal and local reflexes involved in the defecation reflex

1. Distention of the rectum initiates the defecation reflex
2. Pelvic nerve afferents transmit distention signal to the spinal cord
3. Inhibition of sympathetic input to the colonic enteric nervous system
4. Excitation of colonic motility by pelvic nerve afferents
5. Internal anal (smooth muscle) sphincter is inhibited by withdrawal of sympathetic input and increase in pelvic nerve (parasympathetic) activity
6. External anal sphincter and other striated pelvic muscles relax by withdrawl of tonic pudendal nerve activity

Question 19

Describe brainstem mechanisms involved in the defecation reflex

Answer 19

Brainstem mechanisms involved in the defecation reflex

• Defecation is accompanied with closure of the glottis and thoracic and abdominal contractions (Valsalva maneuver)
• These responses are probably mediated by areas in the dorsolateral pontine tegmentum and ventrolateral medullary reticular formation
• Supraspinal input is the means by which voluntary control is maintained

Question 20

Parasympathetic innervation to detrusor and bladder neck is via the ___

Answer 20

Parasympathetic innervation to detrusor and bladder neck is via the pelvic nerve

• Postganglionic neurons are in the pelvic plexus and in ganglia on the bladder wall
• Parasympathetic postganglionic neurons use ACh

Question 21

Sympathetic innervation to the detrusor and bladder neck is via the ____ and ____

Answer 21

Sympathetic innervation to the detrusor and bladder neck is via the hypogastric nerve and sympathetic chain

• Postganglionic neurons are located in the pelvic plexus and sympathetic chain
• Sympathetic postganglionic neurons use NE

Question 22

Somatic innervation to the external urethral sphincter and other striated muscles is via the ____

Answer 22

Somatic innervation to the external urethral sphincter and other striated muscles is via the pudendal nerve

Question 23

Describe the detrusor muscle

Answer 23

Detrusor muscle

• Smooth muscle
• Acts in two modes: storage and expulsion
• Contracted by ACh (muscarinic)
• Relaxed by NE and nitric oxide

Question 24

Describe the bladder neck (internal urethral sphincter)

Answer 24

Bladder neck (internal urethral sphincter)

• Smooth muscle
• Acts to prevent leakage of urine
• Relaxed primarily by NO and to a lesser extent ACh: muscarinic relaxation is due to contraction of longitudinal urethral smooth muscle
• Contracted by NE

Question 25

External urethral sphincter has a resting tone due to \_\_\_

Answer 25

External urethral sphincter has a resting tone due to tonic pudendal nerve activity

Question 26

Describe spinal reflexes involved in the maintenance of bladder continence

Answer 26

Spinal reflexes involved in the maintenance of bladder continence * Bladder filling promotes increased external and internal sphincter contraction: afferents are in the pelvic nerve, efferents are in the pudendal nerve (external sphincter) and hypogastric (internal sphincter) * Bladder filling also leads to an inhibition of the detrusor muscle by the hypogastric nerve (afferents in pelvic nerve) and by inhibition of pelvic nerve activity, accomodation of bladder * Leakage of urine into urethra leads to contraction of external urethral sphincter, both afferents and efferents are in the pudendal nerve

Question 27

Describe brainstem control of bladder continence

Answer 27

Brainstem control of bladder continence * Bladder filling leads to inhibition of pelvic efferent activity: afferents are in the pelvic nerve * Information ascends in the dorsal and lateral funiculus, polysynaptically to pontine micturition center * Descends in ventral reticulospinal pathway * Inhibits parasympathetic preganglionic nerve

Question 28

Describe spinal reflexes involved in the micturition reflex

Answer 28

Spinal reflexes involved in the micturition reflex * Bladder distention leads to relaxation of external and internal sphincters * Afferents are in the pelvic nerve * Relaxation of external sphincter is mediated by withdrawal of pudendal activity * Internal sphincter relaxed by withdrawal of sympathetic activity and increased parasympathetic activity * Contraction of the bladder evoked by distention can be demonstrated in chronically spinal cord transections

Question 29

Describe brainstem control of micturition reflex

Answer 29

Brainstem control of micturition reflex * Essential for normal micturition * Distention of the bladder leads to a coordinated reflex: contraction of the detrusor, relaxation of the internal and external sphincters * Afferents are in the pelvic nerve: ascend polysynpatically to pontine micturition center -\> causes inhibition of pudendal and sympathetic activity

Question 30

Describe the excitement, plateau, orgasm, and resolution (EPOR) model

Answer 30

Excitement, plateau, orgasm, and resolution (EPOR) model 1. Excitement 2. Plateau 3. Organsm 4. Resolution simplistic

Question 31

Describe similarities in male and female physiology during sexual function

Answer 31

Similarities in male and female physiology during sexual function * BP, HR, respiration, and sweating during arousal are the same * Perineal muscle contractions during climax are very similar * Variety of pelvic reflexes (bulbocavernous reflex) are the same * Subjective reports of sexual arousal and climax are usually very similar * Genitalia have homologous innervation

Question 32

Describe differences in male and female physiology during sexual function

Answer 32

Differences in male and female physiology during sexual function * Several organs have sex-specific activities: secretory glands, male ductus deferens, vaginal and uterine activity * Males have a significantly longer refractory period following climax

Question 33

Describe neural organization of sexual function

Answer 33

Neural organization of sexual function * All levels of neuraxis participate in expression of sexual behaviorSexual function is organized at the spinal level: these spinal responses are under descending control

Question 34

\_\_\_ is a key region for control of sexual behavior

Answer 34

Medial preopetic region of hypothalamus is a key region for control of sexual behavior * Lesions diminish or abolish sexual behavior * Stimulation elicits sexual behavior * Many sexual responses and sexual responses remain after lesions * Receives input from limbic, olfactory, and cortical regions * Contains receptors for androgens, estrogen, progesterone: allows integration of hormonal status and behavior

Question 35

Describe physical events in erection

Answer 35

Physical events in erection * Penile erection is mediated by vasodilation in the erectile tissue producing tumescence * Contraction of striated penile muscles leads to rigid erection * Arterial blood flow increases several fold during erection -\> reduces venous outflow -\> causes tumescence * Penile volume increases 80-200 mL: pressures during full erection are much greater than SBP

Question 36

Describe neural mechanisms of erection

Answer 36

Neural mechanisms of erection * Penile vasodilation is mediated by the cavernous nerve, which originates in the pelvic plexus and travels alongside the prostate and urethra * Cavernous nerve contains parasympathetic postganglionic neurons: vasodilation caused by parasympathetic activity is primary mediator of erection * Vasodilation is mediated by NO * Contraction of penile muscles is mediated by pudendal nerve: responsible for suprasystolic pressures during full rigid erection * Erection may be mediated by both direct genital stimulation (reflexogenic) or by CNS control (psychogenic): genital sensory info is carried by pudendal nerve * Detumescence is an active process mediated by vasoconstriction: probably due to NE released from sympathetic postganglionic fibers (from caudal sympathetic chain) and primarily travelling in the pudendal nerve branch to the penis

Question 37

Describe vaginal lubrication in female arousal

Answer 37

Vaginal lubrication in female arousal * First sign of sexual arousal in females (5-15 sec after stimulation begins) * Vaginal secretion is mostly an exudate from the vaginal mucosa and some active transport: high in K+, low in Na+ * Exudate is probably generated by Starling mechanism because of vasodilation * Neurotransmitters responsible for vasodilation of the vagina are unknown (not NO)

Question 38

Describe clitoral erection

Answer 38

Clitoral erection * Similar to penile erection * Vasodilation mediated by NO fibers in cavenrous nerve * Striated muscle activity probably not important

Question 39

Describe genital vasocongestion in females

Answer 39

Genital vasocongestion in female * Genital tissue becomes greatly engorged with blood during sexual arousal * Due to great increases in blood flow (vasodilation) * Autonomic mechanisms and neurotransmitters unclear * Returns to basal state following orgasm: probably due to active sympathetic vasoconstriction

Question 40

Describe physical events involved in emission phase of male climax

Answer 40

Physical events involved in emission phase of male climax * There is a strong contraction of the internal and external urethral sphincter * Fluids from the prostate, seminal vesicle, and ductus deferens enter into the prostatic urethra * Pressure within the urethra increases due to the fluid and contraction of both smooth and striated muscle contraction

Question 41

Describe neural mechanisms involved in emission phase of male climax

Answer 41

Neural mechanisms involved in emission phase of male climax * Both sympathetic and parasympathetic mechanisms are involved in emission * Glandular secretion is increased by stimulation of fluid production by ACh and Ne and by contraction of myoepithelial cells by NE * Ductus deferens motility is increased by both NE and ACh

Question 42

Describe physical events involved in ejaculation phase of male climax

Answer 42

Physical events involved in ejaculation phase of male climax 1. Internal urethral sphincter remains closed, preventing reflux of semen into bladder (retrograde ejaculation) 2. When ejaculation threshold is reached, external urethral sphincter opens 3. Seminal fluids are ejected into urethral bulb 4. Powerful rhythmic contractions of the bulbospongiosus muscles eject the semen 5. Simultaneous contractions of the ischiocavernous muscle and external anal and urethral sphincters

Question 43

Describe neural mechanisms involved in ejaculation phase of male climax

Answer 43

Neural mechanisms involved in ejaculation phase of male climax * Ejaculation reflex is a stereotyped response mediated by a spinal central pattern generator * Response is elicited by a combination of genital sensory stimulation and supraspinal control * Sensory fibers travel in the pudendal nerve * Pudendal nerve also mediates the contractions of the muscle * Ejaculation is generated in lumbar spinal cord * Spinal pattern generator is under tonic descending inhibition * Mechanisms mediating male refractory period are unknown

Question 44

Describe physical events involved in female climax

Answer 44

Physical events involved in female climax * Consists of rhythmic contractions of the perineal muscles * In general, physiology is similar to that of males

Question 45

Describe neural mechanisms of female climax

Answer 45

Neural mechanisms of female climax * Likely identical to males: a response produced by a spinal pattern generator elicited by genital and CNS stimulation