Micturition Reflex Physiology SlideshowMicturition Reflex Physiology Slideshow

Learning Objectives

•By the end of lecture, the student should be able to
–Explain the structural anatomy of urinary bladder
–Comment on the nerve supply of urinary bladder and control Of sphincters
–Outline the Micturition Reflex arc
–Comment on the abnormalities of bladder


The process by which the urinary bladder empties when it becomes filled with urine
•Max capacity—-500 ml
•Involves 2 process
1.Filling of bladder uptothreshold level (increase in tension)
2.Initiation of nervous reflex–micturition reflex

Urinary Bladder

•Smooth muscle chamber
–Empty bladder —pelvis
–Bladder fills—-superior wall rises in the hypogastricregion
–Base (post surface)
•Superior surface
•2 inferolateral surfaces


–Urine collects in it
•Neck (2-3cm)
–Funnel shaped extension of body
–Connects to urethra
–Composed of detrusor muscles and elastic muscles
–Internal sphincter
–Passes inferiorly and anteriorly in to urogenital triangle

•Posterior urethra
–Lower part of bladder neck
•External sphincter
–Below urogenital diaphragm
–Voluntary control
–Skeletal muscle

•DETRUSOR MUSCLE—Smooth muscles of bladder
•Contraction increase the pressure by 40-60 mmHg
•Posterior wall
–Trigone—a triangular area
–Lowermost portion extends into urethra
–Ureter enters at upper part of trigone
–Rugae—-mucosal foldings

Nervous supply of bladder

1.Higher (Midbrain, Pons, Post. Hypothalamus, Cerebral cortex)
a.Pelvic Nerves
•Parasympathetic (S2-3)
–Sensory (stretch)
–Motor (detrusor, Internal sphincter)
•Somatic (Pudendal) (S2-3)
–Sensory (stretch)
–Motor (external sphincter)
•Sympathetic (L2 mainly)
–Sensory (fullness, pain


•Relaxation of detrusor
•Constriction of internal sphincter
•Filling of urinary bladder
•Stimulate mainly the blood vessels
•Some sensory nerve fibers—important in the pain sensation

•Contraction of detrusor
•Relaxation of internal sphincter
•Emptying of urinary bladder
•Tonic contraction of external sphincter
•Voluntary control of micturition

Urine Transport

Vesicoureteral Reflux

•Vesicoureteral reflux
–Course of ureter inside bladder wall is less
–Incomplete occlusion
–Backflow of urine into ureter
–Dilatation of ureter, calyces & renal pelvis
–Damage to kidney

Ureterorenal Reflex

–Protective mechanism
–Ureter blocked
–Richly supplied by pain nerve fibers
–Reflex constriction
–Generates sympathetic reflex
–Constricts afferent arterioles
–Decreases urine output
–Prevents excessive fluid flow in blocked ureter


Urinary bladder –reservoir
–Spinal reflex
–Spinal reflex
–Higher control
–Pelvic muscles & external urethral sphincter

•Cystometry—recording of pressure when the bladder is filled
•Self regenerative once begins
•Periodic acute increase in pressure
•Last few sec—min
•Pressure:100 cm of H2O
•Complete cycle
–Rapid increase in pressure
–Period of sustained pressure
–Return to basal tone


•The chart generated that plots volume of liquid emptied from bladder against intravesical pressure.
•A filling cystometrogram(CMG) assesses the bladder capacity, compliance, and the presence of phasic contractions (detrusor instability)

Micturition Reflex

•Stimulus: Filling/Distension of bladder & urethra
•Receptors: Stretch Receptors
•Afferent: Pelvic nerve (visceral –parasympathetic)
•Centre : Spinal segment (S2 –S4)
•Efferent: Pelvic nerve ( Motor–parasympathetic)
Pudendalnerve ( somatic skeletal nerve)
•Effectors: Detrusor Muscles, Ext. & Int. sphincters
•Effect : Contraction of Detrusor Muscles
Relaxation of internal sphincter
Relaxation of external sphincter
•Response: Voiding of urine

Facilitation/Inhibition of Micturition by Brain

–Inhibitory signals
–Facilitatoryand inhibitory centers
•Post. Hypothalamus
–Facilitatory signals
–Mainly inhibitory centers + excitatory signals
–Voluntary control during reflex

Urination Act

•Contraction of abdominal muscles
•Increase pressure in bladder neck and posterior urethra
•Stretching their walls
•Stimulates stretch receptors
•Excites micturition reflex and inhibits external urethra
•Bladder emptied

Atonic Bladder

•Destruction of sensory (pelvic) nerve fibers
•Loss of tone in detrusor muscle (flaccid)
•Bladder completely filled
•Overflow incontinence
•Injury to the sacral segments of spinal cord
–Spinal shock
–Degeneration of dorsal (sensory) nerve roots

Automatic Bladder

•Hyperactive micturition reflex
•Voluntary control of micturition is lost
•Absence of facilitation of micturition by:
–Higher centers
•Periodic emptying
–Damage of the spinal cord above the sacral region
–Sacral cord segments are still intact

Neurogenic Bladder

•Frequent and uncontrollable micturition
–Lesion in brain stem
–Interrupts most of the inhibitory signals
–Facilitatoryimpulses passing continually down
–Continuous excitation of spinal micturition centers

Nocturnal Micturition

•Involuntary voiding of urine during sleep
•Bed wetting
–Common in children under 3 years
–Absence of voluntary control of micturition
–Incomplete myelination of motor nerve fibers of the bladder (under 3 years)
–Lumbosacral vertebral defects
–Psychological factors

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