Urinary bladder的nerve innervation

Bladder nerves

Somatic

• Pudental nerves (S2,S3,S4)
  • motor & sensory fibres
• External urethral sphincter

Sympathetic

• Hypogastric nerves (L1,L2,L3)
  • motor & sensory fibres
• Bladder wall relaxation
• Internal sphincter contraction

Parasympathetic

• Pelvic nerves (S2,S3,S4)
  • motor & sensory fibres
• Bladder wall contraction
• Internal sphincter relaxation

Actions of bladder nerves

• Sympathetic postganglionic neurons release noradrenaline (NA)
  • activates b3 adrenergic receptors
    • relax bladder smooth muscle
  • activates a1 adrenergic receptors
    • contract urethral smooth muscle (internal sphincter?)
• Parasympathetic postganglionic axons in pelvic nerve release acetylcholine (ACh)
  • stimulate M3 muscarinic receptors in the bladder smooth muscle
    • bladder contraction
• Somatic axons in the pudendal nerve release ACh
  • activates nicotinic cholinergic receptors (neuromuscular junction)
    • contract external sphincter striated muscle

Bladder nerve supply

• Sensory fibers in pelvic nerves sense the degree of stretch in the bladder wall
  • Stretch signals from posterior urethra are more powerful in initiating the micturition reflex
  • Motor nerves transmitted in the pelvic nerves terminate on ganglion cells located in the wall of the bladder
    • postganglionic nerves innervate the detrusor muscle
• Pudendal nerves carry skeletal motor fibers to external sphincter
  • Control the voluntary skeletal muscle sphincter
• Sympathetic innervation from the sympathetic chain through the hypogastric nerves
  • Sympathetic innervation mainly to blood vessels
  • Important in the sensation of fullness/pain
    • lower abdomen
  • In males – mediate the contraction of the bladder muscle (internal sphincter)
    • that prevents semen from entering the bladder during ejaculation
    • retrograde ejaculation