Neural Control of Pelvic Function 1

Question 1

What is the somatic innervation of pelvic function?

Answer 1

• Pudendal nerve innervates striated muscles in pelvis:
  
  • external anal and urethral sphincters
  • bulbospongiosus
  • ischiocavernosus
  • transverse pineal
• Pudendal plexus (S2-S4) innervates muscles of the pelvic diaphragm:
  
  • urogenital diaphragm
  • levator ani
  • coccygeus
  • pubococcygeus
  • circumvaginal muscles
  • Kegel muscles
  • orgasmic platform

Question 2

What is the sympathetic innervation of pelvic function?

Answer 2

• Hypogastric nerve (T11-L2)
  
  • preganglionic neruons use ACh
  • postganglionic neruons arise from pelvic plexus, use NE
• Lumbar colonic nerve (from inferior mesenteric ganglion)
  
  • innervates colon
• Caudal sympathetic chain
  
  • pelvic organs
  • especially vasculature

Question 3

What is the parasympathetic innervation of pelvic function?

Answer 3

• Pelvic nerve (S2-S4)
  
  • both pre- and postganglionic (arising from the pelvic plexus) use ACh
  • peptide co-transmitters also important
  • inhibitory neurotransmitter usually nitric oxide

Question 4

Where do afferent nerves of the pelvis travel?

Answer 4

• Pelvic and pudendal nerves - few in hypogastric nerve
• Visceral afferents in the pelvic nerve transmit distension information from:
  
  • bladder
  • colon
  • pain from viscera
  • other visceral sensations

Question 5

What are some important developmental considerations regarding sexual dimorphism in innervation of the pelvis?

Answer 5

• External genitalia differentiate from common embryological origins with homologous innervation
• Internal genitalia from Wolffian ducts and Mullerian ducts under hormonal control
• Default phenotype is female, and some organs (bladder and colon) don’t show any significant dimorphism.

Question 6

What are some functional consequences of sexual dimorphism when considering pelvic innervation?

Answer 6

• Sexual dimorphism of the pelvic innervation related to differentation of organs
• However, neural circuitry mediating pelvic function is very similar

Question 7

Describ the coordination of somatic and autonomic nervous systems

Answer 7

• Most pelvic functions require both somatic and ANS activity
• Defecation, micturition, and sexual function are mutually inhibitory to each other
• Coordination is mediated primarily by the spinal cord
• Sympathetic and parasympathetic activity is also highly coordinated, primarily by the spinal cord
• Sympathetic and parasympathetic may be antagonistic or synergistic

Question 8

Describe the hierarchical control of the nervous system supplying the pelvis.

Answer 8

• Mediated at several levels
  
  • enteric nervous system (for colon)
  • autonomic ganglia
  • spinal cord
  • brainstem
  • hypothalamus
  • higher centers
• More complex functions are managed by higher levels

Question 9

What are the parasympathetic, sympathetic, and somatic innervations involved in micturition?

Answer 9

• Parasympathetic
  
  • goes to detrusor and bladder neck via pelvic nerve
  • postganglionic neurons in pelvic plexus and ganglia on bladder
  • postganglionic neurons use ACh
• Sympathetic
  
  • to detruser and bladder neck via hypogastric nerve and sympathetic chain
  • postganglionic neurons in pelvic plexus and sympathetic chain
  • postganglionic neurons use NE
• Somatic
  
  • to external urethral sphincter and other striated muscles via pudendal nerve

Question 10

What is the role of the detrusor muscle in micturition?

Answer 10

• Smooth muscle
• Acts in two modes - storage and expulsion
• Contracted by ACh (muscarinic)
• Relaxed by NE (beta) and nitric oxide

Question 11

What is the role of the bladder neck in micturition?

Answer 11

• Smooth muscle
• Acts to prevent leakage of urine
• Relaxed by nitric oxide and ACh (muscarinic)
  
  • due to contraction of longitudinal urethral smooth muscle
• Contracted by NE

Question 12

What is the role of the external urethral sphincter in micturition?

Answer 12

has a resting tone due to pudendal nerve activity