Micturition + defaecation

Question 1

Describe sympathetic innervation to the bladder

Answer 1

Involuntary control that inhibits micturition

Lumbar splachcnic -> hypogastric nerve -> inferior hypogastric plexus -> pelvic nerves

Question 2

Describe the actions of the SNS in micturition

Answer 2

• Relax the detrusor ( storage of urine)

- Contract the internal urethral sphincter

Question 3

Describe parasympathetic innervation to the bladder

Answer 3

Sacral outflow
Involuntary control that activates micturition

Pelvic splachnic nerves -> inferior hypogastric plexus -> pelvic nerves

Contract detrusor to expell urine
Relax internal urethral sphincter

Question 4

Describe somatic innervation to the bladder

Answer 4

Via the pudendal nerve S2-S4
Voluntary control
Contracts the external urethral sphincter and levator ani

Question 5

Describe the guarding reflex

Answer 5

Low level vesical afferent firing triggers sympathetic outflow via the hypogastric nerve

• Relaxes detrusor + contracts internal urethral sphincter
• Firing also increases somatic pudendal outflow to the external urethral sphincter and levator an
  i
• Pontine storage centre can further increase pudendal outflow

Question 6

Describe the micturition relfex

Answer 6

High level vesical afferent firing activates the bulbospinal reflex

Activates parasympathetic innervation to cause contraction of the detrusor and relaxation of the internal urethral sphincter

Pontine centre Inhibits sympathetic and somatic outflow

Question 7

What are the plexi of the enteric nervous system?

Answer 7

Myenteric plexus - found between the longitudinal and circular muscle layers of muscularis
Submucosal plexus - found between circular layer and submucosa

Question 8

Describe parasympathetic division of the ENS

Answer 8

Stimulatory effect on digestion
Pre ganglionic = CN 10 + Pelvic splachnic nerves ( S2-S4)

Ganglia are within the intramural plexuses

Post ganglionic fibres = myeneteric and submucosal plexus

Question 9

Describe sympathetic division of the ENS

Answer 9

Inhibitory effect on digestion
Pre ganglionic = T1-L2

Ganglia are pre vertebral ganglia ( coeliac, mesenteric, )

Post ganglionic fibres project onto the myenteric and submucosal plexuses

Question 10

Describe visceral afferents of the ENS

Answer 10

Pain travels with SNS or PSNS fibres
Distension travels with parasympathetic fibres

Sensory information is returned to the dorsal horn of the spina cord via nerve roots

Question 11

What sphincter is made of smooth muscle and which is made of striated muscle?

Answer 11

Internal anal sphincter

External anal sphincter

Question 12

Describe the defaecation reflex

Answer 12

Distension activates stretch receptors in the walls of the sigmoid colon and rectum

This activates intrinsic ( short arc) and extrinsic ( long arc) pathways

Intrinsic pathway is activated -> activates myenteric plexus to causes smooth muscle contraction + weak peristalsis

Extrinsic pathway : Distension stimulates afferent sensory fibres to travel to dorsal horn and activate the parasympathetic fibres

Relaxation of the internal anal sphincter + STRONG peristalsis

When socially acceptable somatic outflow allows for relaxation of external anal sphincter and puborectalis

Question 13

Describe Reflex bowel damage: Above T12/L1 ( Upper motor nerve)

Answer 13

• Loss of bowel sensation
• Reduced anal tone
• Intrinsic + extrinsic pathways intact as parasympathetic fibres can still reach the spinal cord:
• Loss of descending control

Question 14

Describe Flaccid Bowel damage ( Below T12//L1) Lower motor neurone

Answer 14

Flaccid Bowel damage ( Below T12//L1) Lower motor neurone

Loss of bowel sensation
Loss of descending control
Loss of defaecation reflex
Loss of sphincter tone