214 - Neural control of Pelvic function Flashcards
A woman suffers a pudendal nerve injury from a bicycle accident. What is the most likely dysfunction from this injury?
a. Impaired detrusor contractions
b. Anal sphincter weakness
c. Reduced colonic peristalsis
d. Absent bladder fullness sensation
b. Anal sphincter weakness
* Pudendal nerve controls the external anal sphincter, partly responsible for fecal continence*
What stimulus induces the defecation reflex?
Describe the effect
Distension of the rectum
Results in all of the following, basically simultaneously
- Sustained peristalsis in teh left colon
- Relaxation of the internal anal sphincter
- Smooth muscle relaxes; due to less hypogastric (sympathetic), more parasympathetic (pelvic) tone
- Relaxation of the external anal sphincter
- Striated muscle, pudendal nerve
- Increased intra-abdominal pressure via Valsalva
Describe what each of the following nerves are doing in the bladder storage state:
- Hypogastric nerve:
- Pelvic nerve:
- Pudendal nerve:
-
Hypogastric nerve: (sympathetic)
- Tonic contraction of the bladder neck, urethra
- Inhibition of parasympathetic innervation to the detrusor
-
Pelvic nerve: (parasympathetic)
- Inhibited by hypogastric tone
-
Pudendal nerve: (somatic)
- Contracts the urethral sphincter
Which nerve is most active during the continence phase of defecation?
Lumbar colonic nerve (sympathetic) [equivalent to hypogastric for bladeer]
Inhibits enteric nerve peristalsis
Which nerves sense distension in the rectum?
Pelvic nerve afferents
- Signal to enteric NS to initiate peristalsis (on command of pelvic nerve efferents)
Describe what each of the following nerves are doing in the bladder evacuation state:
- Hypogastric nerve:
- Pelvic nerve:
- Pudendal nerve:
-
Hypogastric nerve: (sympathetic)
- Inhibited by pontine micturition center, pelvic efferents
- Alpha-1 receptor activation
-
Pelvic nerve: (parasympathetic)
- Pelvic afferents signal stretch to the brain
- Excitation from pontine micturition center -> increased parasympathetic tone -> detrusor contraction via pelvic efferents (M3 receptor activation)
-
Pudendal nerve: (somatic)
- Decreased stimulation to urethral sphincter -> relaxation
How do inflammatory processes in the bladder change the normal bladder physiology?
Inflammatory processes sensitize afferent bladder fibers
This results in increased urgency, even when pressure is low
Feels like you have to go, even though maybe you don’t
Which of the following elements of the defecation process requires input from higher centers of the brain in a healthy person under normal conditions?
a. Peristaltic contractions of the sigmoid colon
b. Rectal distention
c. Rectal peristalsis
d. Relaxation of external anal sphincter
e. Relaxation of internal anal sphincter
d. Relaxation of external anal sphincter
* External anal sphincter is under somatic control*
Which part of the nervous system is most active during sexual arousal and plateau?
Parasympathetic
Main role is vasodilation -> increased blood flow
Via smooth muscle relaxation
What is the “hallmark” of orgasm?
Simultaneous, rhythmic contractions of all muscles innervated by the pudendal nerve
Uterus, rectal sphincter, orgasmic platform
During the voiding phase, what happens when the bladder starts to fill up?
- Which nerves carry this signal to the brain?*
- How does the brain modulate what happens next?*
- Pelvic afferents signal stretch to the brain
- When it’s time to go, the pontine micturition center modulates voiding
- Basically, parasymathetics are active, sympathetics and somatics are inhibited
- Inhibition of hypogastric (sympathetic) nerve inhibits the inhibition of voiding (usually hypogastric nerve stops us from peeing our pants)
- This allows the pelvic (sympathetic) nerve to contract the detrusor
- Relaxation of the pudendal (somatic) nerve allows pee to flow out
Note: Both the continence and voiding reflexes are activating by stretch; unknown mechanisms in the brain help us choose whether to hold it or to go
Which nervous system is responsible for resolution following an orgasm?
Sympathetics
Mediate vasoconstriction (to reverse the vasodilation during the excitement/plateau phase)
What is the neural control center for bladder function?
Pontine micturition center
- Integrates pelvic sensory information, integrates with input from higher centers
During the continence phase, what happens when the bladder starts to fill up?
- Which nerves carry this signal to the brain?*
- How does the brain modulate what happens next?*
- Pelvic afferents signal stretch to the brain
- -> Reflex contraction of the external urethral sphincter (via somatic pudendal nerve)
- -> Reflex activation of sympathetic (hypogastric) preganglionic nerves, resulting in inhibition of the detrusor muscle
- -> Reflex inhibition of parasympathetic (pelvic) nerves, resulting in inhibition of detrusor contraction
A 65-year-old man with a longstanding history of BPH has the acute onset of a sensation of urinary urgency followed by urinary incontinence.
Which of the following is the most likely mechanism for his urinary leakage?
- Pelvic nerve afferent fibers inhibiting pelvic nerve efferent fibers
- Hypogastric nerve inhibition of detrusor muscle
- Pudendal nerve efferent fiber stimulation of the external sphincter
- Brainstem inhibition of the parasympathetic preganglionic neurons
- Acetylcholine (muscarinic) fibers stimulation of bladder smooth muscle
Acetylcholine (muscarinic) fibers stimulation of bladder smooth muscle
Stimulation of bladder smooth muscle -> detrusor contraction -> peeing
