SM_214b: Neural Control Pelvic Function Flashcards
____ innervates striated muscules of the pelvis: external anal and urethral sphincters, bulbospongiosus, ischiocavernosus, and transverse perineal nerve
Pudendal nerve innervates striated muscules of the pelvis: external anal and urethral sphincters, bulbospongiosus, ischiocavernosus, and transverse perineal nerve
(somatic)
Nerves from ____ innervate muscules of the pelvic diaphragm: urogenital diaphragm, levator ani, coccygeus, pubococcygeus, circumvaginal muscles, Kegel muscles, and orgasmic platform
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)
Sympathetic innervation to pelvis is primarily from ____
Sympathetic innervation to pelvis is primarily from hypogastric nerve (T11-L2)
Preganglionic sympathetic neurons use ACh, while postanglionic sympathetic neurons arising from the ___ use NE primarily
Preganglionic neurons use ACh, while postanglionic neurons arising from the pelvic plexus use NE primarily
Colon receives sympathetic fibers via ____
Colon receives sympathetic fibers via lumbar colonic nerve
(from inferior mesenteric ganglion)
Pelvic organs also receive innervation from the caudal ___
Pelvic organs also receive innervation from the caudal sympathetic chain
(primarily to vasculature)
Parasympathetic innervation to the pelvis occurs via the ___
Parasympathetic innervation to the pelvis occurs via the pelvic nerve (S2-4)
Preganglionic and postganglionic (arising from the _____) parasympathetic fevers use ACh
Preganglionic and postganglionic (arising from the pelvic plexus) parasympathetic fevers use ACh
(smooth muscle relaxing neurotransmitter is usually nitric oxide)
External genitalia differentiate from ____ under hormonal control
External genitalia differentiate from common embyrological origins under hormonal control
(androgens: testosterone, dihydroxytestosterone)
Internal genitalia are derived from ____ in males and ____ in females under hormonal control via androgens and Mullerian duct inhibiting factor
Internal genitalia are derived from Wolffian ducts in males and Mullerian ducts in females under hormonal control via androgens and Mullerian duct inhibiting factor
In the absence of testicular hormones, the phenotype is ___
In the absence of testicular hormones, the phenotype is female
Neural circuitry mediating pelvic function is ___ between males and females
Neural circuitry mediating pelvic function is similar between males and females
(sexual dimorphism of pelvic innervation is related to the differentiation of the organs)
Describe coordination of the somatic and autonomic nervous systems
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)
Pelvic control is ____
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
Describe defecation
Defecation
- Intrinsic neural innervation
- Extrinsic innervation
- Internal anal sphincter
- External anal sphincter
Describe mechanical factors in maintenance of bowel continence
Mechanical factors in maintenance of bowel continence
- Rectum is usually empty
- Anal canal is narrow
- Pelvic flexure provides a barrier to feces
Describe neural factors in maintenance of bowel continence
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
Describe spinal and local reflexes involved in the defecation reflex
Spinal and local reflexes involved in the defecation reflex
- Distention of the rectum initiates the defecation reflex
- Pelvic nerve afferents transmit distention signal to the spinal cord
- Inhibition of sympathetic input to the colonic enteric nervous system
- Excitation of colonic motility by pelvic nerve afferents
- Internal anal (smooth muscle) sphincter is inhibited by withdrawal of sympathetic input and increase in pelvic nerve (parasympathetic) activity
- External anal sphincter and other striated pelvic muscles relax by withdrawl of tonic pudendal nerve activity
Describe brainstem mechanisms involved in the defecation reflex
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
Parasympathetic innervation to detrusor and bladder neck is via the ___
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
Sympathetic innervation to the detrusor and bladder neck is via the ____ and ____
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
Somatic innervation to the external urethral sphincter and other striated muscles is via the ____
Somatic innervation to the external urethral sphincter and other striated muscles is via the pudendal nerve
Describe the detrusor muscle
Detrusor muscle
- Smooth muscle
- Acts in two modes: storage and expulsion
- Contracted by ACh (muscarinic)
- Relaxed by NE and nitric oxide
Describe the bladder neck (internal urethral sphincter)
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
External urethral sphincter has a resting tone due to ___
External urethral sphincter has a resting tone due to tonic pudendal nerve activity
Describe spinal reflexes involved in the maintenance of bladder continence
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
Describe brainstem control of bladder continence
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
Describe spinal reflexes involved in the micturition reflex
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
Describe brainstem control of micturition reflex
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
Describe the excitement, plateau, orgasm, and resolution (EPOR) model
Excitement, plateau, orgasm, and resolution (EPOR) model
- Excitement
- Plateau
- Organsm
- Resolution
simplistic
Describe similarities in male and female physiology during sexual function
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
Describe differences in male and female physiology during sexual function
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
Describe neural organization of sexual function
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
___ is a key region for control of sexual behavior
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
Describe physical events in erection
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
Describe neural mechanisms of erection
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
Describe vaginal lubrication in female arousal
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)
Describe clitoral erection
Clitoral erection
- Similar to penile erection
- Vasodilation mediated by NO fibers in cavenrous nerve
- Striated muscle activity probably not important
Describe genital vasocongestion in females
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
Describe physical events involved in emission phase of male climax
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
Describe neural mechanisms involved in emission phase of male climax
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
Describe physical events involved in ejaculation phase of male climax
Physical events involved in ejaculation phase of male climax
- Internal urethral sphincter remains closed, preventing reflux of semen into bladder (retrograde ejaculation)
- When ejaculation threshold is reached, external urethral sphincter opens
- Seminal fluids are ejected into urethral bulb
- Powerful rhythmic contractions of the bulbospongiosus muscles eject the semen
- Simultaneous contractions of the ischiocavernous muscle and external anal and urethral sphincters
Describe neural mechanisms involved in ejaculation phase of male climax
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
Describe physical events involved in female climax
Physical events involved in female climax
- Consists of rhythmic contractions of the perineal muscles
- In general, physiology is similar to that of males
Describe neural mechanisms of female climax
Neural mechanisms of female climax
- Likely identical to males: a response produced by a spinal pattern generator elicited by genital and CNS stimulation
