Micturition Reflex.ppt

Urinary Reflex

1. Urinary Reflex
V.Mythily
JCE

2. Micturition
•Micturitionorurinationistheprocessof
emptyingurinefromthestorageorgan,
namely,theurinarybladder.
•Thefunctionalanatomyandnervesupplyof
urinarybladderareessentialfortheprocess
ofmicturition.
•Thedetrusoristhesmoothorinvoluntary
muscleoftheurinarybladderwall.
•Theurethralmusclesconsistoftheexternal
andinternalsphincter.

3. Micturition
•Theinternalsphincteranddetrusormuscleareboth
underautonomiccontrol.
•Theexternalsphincter,however,isavoluntary
muscleunderthecontrolofvoluntarynerves.
•Thebladdernormallyaccommodatesupto300-400
mlinadults.
•Whenthebladderisdistended(expanded)itsends
signalstothebrain,whichisperceivedasthe'full
bladder'sensation.

4. Micturition / Urination
•TheprocessofMicturitionis
regulatedbynervoussignals,
bothfromthesomaticandthe
autonomicnervoussystem.
•Theautonomicnervoussystem
comprisesboththesympathetic
andtheparasympathetic
nervoussystem.
•Thebladderhastwostatesof
function;thestorageand
emptyingphases.

5. Micturition / Urination Reflex
•Themicturitionreflexisareflexpathwaybywhich
urinationormicturitionoccurs.
•Thisreflexisinducedbythestimulationofstretch
receptorspresentonthewallofthebladderand
urethra.
•Theintravesicalpressureincreaseswhenthebladder
collectsabout300to400mLofurine.
•Thisstretchesthewalloftheurinarybladderandthus
resultsinstimulationofstretchreceptorsandthe
creationofsensoryimpulsesleadingtourination.
•Inhealthyadults,thisprocessofmicturitionisunder
voluntarycontrol.

6. Urinary Reflex

7. Urinary Reflex Process
•When the bladder is full, it sends the sensory signal to the brain
for the process of emptying. The bladder emptying phase is
called micturition, and
•it involves the co-ordinated reflexes of the outer and inner
urethral sphincter under somatic and sympathetic regulation,
respectively.
•At first, theafferent impulsesor the sensory impulses from the
receptors reach the sacral segments of spinal cordthrough the
sensory fibres of the pelvic nerve (parasympathetic nerve).
•The motor impulses created in the spinal cord run through the
motor fibres of the pelvic nerve towards the bladder and the
internal sphincter.
•These motor impulses (efferent impulses) create contraction of
the detrusor muscle and also the relaxation of the internal
sphincter. Thus, the urine enters the urethra from the bladder.

8. Urinary Reflex Process
•Once urine reaches the urethra, thestretch receptorspresent
in the urethra are stimulated, and they send afferent impulses
to the spinal cord through pelvic nerve fibres.
•Now the impulses created from the spinal centres obstruct
thepudendal nerve. This leads to the relaxation of the
external sphincter, and micturition occurs.
•Facilitatory centresfor micturition are present in the pons,
and some are even in the cerebral cortex. It facilitates
micturition through spinal centres.
•Inhibitory centresfor micturition are present in the cerebral
cortex and midbrain. It inhibits the micturition by repressing
spinal micturition centres.

9. Micturition Reflex Process

10. Urination Reflex
•Themicturitionreflexprocessisself-regenerative.
•Thisisbecausetheinitialcontractionoftheurinarybladder
activatesthestretchreceptorstocreateanincreasein
sensoryimpulsesfromtheurethraaswellasthebladder.
•Theseimpulses,inturn,createafurtherincreaseinreflex
contractionoftheurinarybladder.
•Thiscycleofeventsrepeatsuntiltheforceofcontractionof
theurinarybladderreachesthemaximum,leadingtothe
voidingofurineorthemicturitionprocess.
•Duringmicturition,theurineflowisfacilitatedbythe
increaseinabdominalpressure.Thisisduetothevoluntary
contractionofthemusclesintheabdomen.

11. Urination Reflex-control
Higher Centers for Micturition
•Spinal centersfor micturitionare present in sacral and
lumbar segments. But, these spinal centersare
regulated by higher centers.
•The higher centers, which control micturitionare of
two types, inhibitory centersand facilitatorycenters.
Inhibitory centers for micturition
•Centersin midbrain and cerebral cortex inhibit the
micturitionby suppressing spinal micturitioncenters.
Facilitatorycenters for micturition
•Centers in ponsfacilitate micturitionvia spinal centers.
Some centersin cerebral cortex also facilitate
micturition.

12. Micturition Reflex
•Themicturitionreflexprocess can be
summarised as follows –
•Filling of the urinary bladder
•Stimulation of stretch receptors
•Afferent impulses pass through the pelvic
nerve and reach the spinal cord
•Efferent impulses through the pelvic
nerve
•Contraction of the detrusormuscle and
relaxation of the internal sphincter
•The flow of urine into the urethra and
stimulation of stretch receptors
•Afferent impulses through the pelvic
nerve
•Inhibition of pudendalnerve
•Relaxation of the external sphincter
•Voiding of the urine or micturition