15/08/2011

innervation of urinary bladder


Nerve supply of urinary bladder   ----------
  §  Autonomic
o   Parasympathetic --- S2-S4 ---motor to detrusor , inhibitory to internal urethral sphincter
o   Sympathetic -----T10- L2  —---motor to sphincter, inhibitory to detrusor
  §  Somatic—pudendal nerve(S2,S3,S4)

Origin of fibres in spinal cord to urinary bladder
  §  Parasympathetic----------- intermediolateral grey horn
  §  Sympathetic---------------- intermediolateral grey horn
  §  Somatic / Pudendal -------- nucleus of ONUF /sacral pudendal nucleus  in ventral  horn

Parasympathetic nerve supply
Stretch receptors present on the wall of the urinary bladder à Sensory fibers in the pelvic nerve à intermediolateral column of spinal cord àemptying of urinary bladder

Sympathetic nerve supply &  Internal urethral sphincter-----  no significant  role in micturition;  They prevent reflux of semen into the bladder during ejaculation

Somatic nerve supply
This maintains the tonic contractions of the skeletal muscle fibers of the external sphincter, so that this sphincter is contracted always. During micturition this nerve is inhibited, causing relaxation of the external sphincter and voiding of urine.

The pain fibres from bladder ascend in anterolateral column of spinal cord
If parasympathetic fibres are destroyed, normal micturition is NOT possible
The sympathetic fibres are chiefly vasomotor
Sympathetic activity is NOT involved in micturition
Increased sympathetic discharge to bladder occurs during ejaculation & helps to prevent  the reflux of sperms from the prostatic urethra  into the bladder

Voluntary control of micturition is attained by age of ----------   2 – 3 yrs

Nocturnal micturition (Bed wetting)
o   Considered normal  upto age < 3 yrs
o   It occurs due to incomplete myelination of motor nerve fibers of the bladder resulting loss of voluntary control of micturition . 

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