Neural Control of Pelvic Function 2

Question 1

What are the mechanical factors that contribute to maintenance of continence?

Answer 1

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

Question 2

What are the neural factors that lead to maintenance of continence?

Answer 2

• Internal external sphincter, external anal sphincter, and puborectalis string are usually contracted
  
  • maintained by sympathetic and pudendal plexus activity, respectively
• Activity of other pelvic diaphragm muscles also contribute to continence
• Conscious and unconscious reflexes contract both sphincters when material moves into the rectum

Question 3

What are the spinal reflexes involved in maintenance of continence?

Answer 3

• Bladder filling promotes increased external and internal sphincter contractions
  
  • afferents in pelvic nerve
  • efferents in pudendal (external sphincter) and hypogastric (internal sphincter)
• Bladder filling also leads to inhibition of detrusor muscle by hypogastric nerve
  
  • afferents in pelvic nerve
• Leakage of urine into the urethra leads to contraction of external sphincter
  
  • both afferents and efferents in pudendal nerve

Question 4

What is the role of brainstem control in micturition?

Answer 4

• Bladder filling leads to inhibition of pelvic efferent activity
• Information ascends in the dorsal and lateral funiculus
• Polysynaptically to pintine micturition center - descends in ventral reticulospinal pathway
  
  • inhibits parasympathetic preganglionic neurons