Week 5: Defecation and Micturition Flashcards
What gross anatomical part of the sympathetic nervous system is involved in defecation and micturition?
SNS has thoracolumbar outflow (t1 to L2)
Specifically lumbar splanchnic (L1,2,3) which becomes the hypogastric nerve travelling through the inferior hypogastric plexus to become pelvic nerves
What is the gross anatomy of the parasympathetic nervous system involved in defecation and microturition?
PNS has cranioscaral outflow
In this scenario - sacral spinal nerves are involved - form pelvic splanchnic nerves which travel through the inferior hypogastric plexus to form pelvic nerves.
What is the ganglionic transmission like in the sympathetic nervous system?
Preganglionic release ACh
Post ganglionic release noraderenaline, adrenalin or Ach (eccrine sweat glands or in junctional receptors)
The effect depends on the receptor
What is the ganglion transmission like in parasympathetic nervous system?
Preganglionic release ACh
Post ganglioninc ACh
The cell receptor tends to be muscurinic
Where are the two intramural plexus of the enteric nervous system located?
Myenteric - between longitudinal and circular smooth muscle in muscuris external
Submucosal - deep to the circular smooth muscle (this is smaller than the myenteric)
How do the myenteric and submucosal plexus initiate communication with the CNS?
Via sensory afferents.
Where are the preganglionic fibres, ganglions and postganglionic fibres of the parasympathetic nervous system found in the gut?
Preganglionic:
Vagus (CNX) in midgut and forgeut
Pelvic splanchin S2-4 in hindgut.
Ganglions - found in both the myenteric and submucosal plexus
Postganglionic fibres - found in ENS
Where are the preganglionic fibres, ganglions and postganglionic fibres of the sympathetic nervous system found in the gut?
Preganglionic fibres - originate from lateral horn of spinal cord from T1 to L2
Ganglion - prevertebral splanchnic ganglion
Postganglionic - ENS plexus
What sensory innervation is present in the gut?
Visceral afferents can communicate with the CNS
Pain - via parasympathetic (lower GIT) or sympathetic (upper GIT)
Distenstion - parasympathetic
Enter the spinal cord via the dorsal nerve roots into the grey horn of the spinal cord.
What are the different functions that the enteric nervous system can effect?
Smooth muscle
Gland secretion
Endocrine function
Blood vessels.
What are the different movements in peristalsis?
Haustral contractions - slower
Mass movement - faster
What is different about the anatomy of the internal and external anal sphincter?
internal - smooth muscle, autonomic control - ENS
External - skeletal muscle, somatic control - pudendal nerve
What are the effects of sympathetic control over defecation?
Rectal smooth muscle is relaxed - no defecation
Internal sphincter is under tonic contraction
What are the reflex pathways in the defecation reflex?
Urge to defecate appears when stretch receptors are activated
Unconscious control=
intrinsic pathway - activates myenteric plexus and imitates local peristalsis
Extrinsic pathway - activates parasympathetic input to further stumlate peristalsis and cause internal anal sphincter relaxation
Voluntary control=
When social acceptable - relaxation of external anal sphincter and the pubrorectalise via the pudendal nerve allows defecation. Postponed if this does not occur
What is the intrinsic reflex in defecatino?
Stimulus - distention in rectum activates stretch receptors in rectal wall
Causes local activation of myenteric plexus - causes smooth muscle to contract in the sigmoid colon and rectum
Response - weak peristalis causing feaces to table distally towards the rectum
What is the extrinsic reflex in defecation?
distention in the sigmoid colon and rectum activates stretch receptors in the wall.
Activates sensory afferents - relay and terminate in the spinal cord and activate parasympathetic nerves (S2-S4)
Causes strong peristalsis causing feaces to travel distally to rectum and relaxation of the internal anal sphincter.
What is the role of voluntary input in defecation?
Inhibition of the external anal sphincter via the pudendal nerve (s2-s4) causes relaxation of the striated muscle of the sphincter
Pubrectalis relxes
Valsalva manoeuvre - close glottis, deep inhalation, contraction of abdominal muscles.
What is the role of pubrectalis in faecal continence?
Part of pelvic floor
Forms a sling around the anal rectal junction - must relax to allow defecation
What are some common causes of faecal incontinence?
Youth - not yet toilet trained, need to be trained to develop voluntary control which then normally persists for the rest of the adult life
Temporarly loss may occur in diahorrea for large stool volume
Other causes: childbirth, nerve injury or surgery, causa equina syndrome
How does a spinal cord injury present affect the defecation reflex?
Loss of sensory afferents to cerebral cortex so..
Loss of voluntary motor function
Short arc intrinsic reflex normally remains intact
Long arc parasympathetic reflex may or may not be intact. Is lost if injury is below or at L1 level as sensory afferents no longer able to reach L1.
What is reflex bowel damage?
Damage to the spinal cord above T12/L1 (UMN)
results in a los of bowel sensation
loss of descending control from the brain
Defecation reflex still intact
Sphincters still have tone
What is a flaccid bowel damage?
Damage belwo T12/L1 (LMN)
Loss of bowel sensation
Loss of descending control from the brain
Loss of defecation reflex
Loss of reflex tone of sphincters.
What are the different sections of the male urethra?
The prostatic urethra - in the prostate gland
The membranous urethera - travels through pelvic floor
The penil urethra - after gone through the pelvic floor to terminal
What somatic nerve gives control over the defecation and micturition reflex?
Pudendal nerve (s2,3,4)
