The document discusses the micturition reflex, which is the reflex by which the urinary bladder empties when full. It describes the physiological anatomy of the bladder, its innervation by sympathetic and parasympathetic nerves, and the normal pathway of the reflex from bladder filling to emptying. It also discusses some abnormalities in micturition that can occur due to deafferentation, denervation, or lesions disrupting control by higher brain centers.

1. MICTURITION REFLEX
BY
K.MANIEVEL RAAMAN
I-YEAR MBBS
MADRAS MEDICAL COLLEGE

2. MICTURITION REFLEX
 Definition
 Physiological anatomy of urinary bladder
 Innervation of urinary bladder
 Filling of urinary bladder
 Pathway of micturition reflex ( in normal
individuals )
 Abnormalities in Micturition
 Deafferentation
 Denervation

3. What is Reflex?
An involuntary and nearly
instantaneous action, in response to a
stimulus.
Mediated via the “REFLEX ARC”,
formed in spinal cord.

4. Definition....
 A reflex by which urinary bladder empties
when it is filled.
Though it is a reflex process, in adults, it
can be controlled voluntarily to some
extent.

5. Physiological Anatomy of
Urinary Bladder…
Urinary bladder is a hollow organ, having parts
namely: BODY – formed by detrusor muscle
NECK - has trigone in its posterior
aspect
Emptying of bladder is mainly guarded by
INTERNAL AND EXTERNAL SPHINCTER
MECHANISM.
INTERNAL SPHINCTER – completely
involuntary. ( smooth muscle)
EXTERNAL SPHINCTER- voluntary. ( skeletal
muscle)

6. Physiological Anatomy of
Urinary Bladder…(Contd.)
DETRUSOR MUSCLE present in
body of bladder is capable of
contraction and expansion, in
response to stimulus.
And hence, it is mainly responsible for
emptying of bladder.

7. Physiological Anatomy of
Urinary Bladder…(Contd.)

8. Innervation of bladder
Urinary bladder and Internal sphincter
are supplied by sympathetic and
parasympathetic nerve fibres.
Sympathetic supply : L1, L2 ( Hypogastric
nerve)
Parasympathetic supply : S2,S3,S4 ( Nervi
erigentes / pelvic nerve)

9. Innervation of bladder(Cont.)
External sphincter is supplied by
somatic nerve fibres. ( Pudendal nerve).
Pelvic nerve ( nervi erigentes) also has
sensory fibres, which carry impulse from the
stretch receptors present on the wall of
urinary bladder and urethra.

10. Innervation of bladder(Cont.)
 CHARACTERISTICS OF SYMPATHETIC SUPPLY :
 Stimulation of hypogastric nerve causes,
RELAXATION OF DETRUSOR MUSCLE and
CONSTRICTION OF INTERNAL SPHINCTER.
It results in filling of bladder
So, this nerve is called NERVE OF FILLING.

11. Innervation of bladder(Cont.)
 CHARACTERISTICS OF PARASYMPATHETIC
SUPPLY :
 Stimulation of pelvic nerve causes
CONTRACTION OF DETRUSOR MUSCLE
and RELAXATION OF INTERNAL
SPHINCTER.
 It results in emptying of bladder.
 So, this nerve is called NERVE OF
MICTURITION.

12. Innervation of bladder(Cont.)
 FUNCTION OF PUDENDAL NERVE :
 Pudendal nerve always keeps the external
sphincter in CONSTRICTED STATE.
 When this nerve is blocked, external
sphincter relaxes.
 Since it’s a somatic nerve fibre, it can be
CONTROLLED VOLUNTARILY.

13. Innervation of bladder(Cont.)

14. Filling of urinary bladder..
 Urine fills the urinary bladder drop by drop
through ureters.
 When volume of urine reaches nearly 150ml, first
sense of filling occurs.
 However, a marked sense of filling occurs only at
about 400ml.
 There is a threshold level in urine volume, which
decides whether to form Micturition reflex or
not.
 This threshold level is adjusted by HIGHER
CENTERS OF MICTURITION.

15. CENTERS FOR MICTURITION
 SPINAL CENTRES :
 Located in sacral and lumbar segments.
 Controlled by higher centers of brain.
 HIGHER CENTERS :
Has facilitatory and inhibitory centers.
Facilitatory center : Pontine region, Posterior
hypothalamus.
Inhibitory center : Mid brain.

16. Pathway of Micturition Reflex
1) When the volume of urine in the bladder reaches
nearly 400ml, intra-vesical pressure increases…
2) Bladder wall stretches…
3) Stretch receptors on the bladder wall are
activated…
4) Sensory signal is given to spinal centers through
sensory fibres of parasympathetic(pelvic) nerve…
5) Reflex arc is produced in spinal cord…
6) Motor signal is given to urinary bladder through
motor fibres of parasympathetic nerve ( pelvic
nerve)…

17. Pathway of Micturition Reflex ( Cont.)
7) As a result of parasympathetic activity,
DETRUSOR muscle contracts and INTERNAL
SPHINCTER relaxes…
8) Urine passes down into proximal urethra..
9) Again afferent impulse is given to spinal cord…
10) Afferent impulse reaches the higher centers in
brain… ( pathway of afferent impulse inside
CNS is through spinothalamic tracts)…

18. Pathway of Micturition Reflex ( Cont.)
11) If the signal from brain stem isTO MICTURATE
, impulse created from spinal center BLOCK
PUDENDAL NERVE…
12) At the same time, sympathetic efferents are
inhibited…
13) So, External sphincter relaxes and micturition
occurs…

19. Pathway of Micturition Reflex ( Cont.)
11) If the signal from brain stem is NOTTO
MICTURATE, sympathetic efferents are
stimulated…
12) As a result, DETRUSOR EXPANDS and
INTERNAL SPHINCTER constricts…
13) External sphincter remain constricted…
14) So, Urine continues to accumulate in bladder…

20. Pathway of Micturition Reflex ( Cont.)
 Once a micturition reflex has occurred but has
NOT SUCCEEDED IN EMPTYINGTHE
BLADDER, the reflex remain in inhibited stage
for 1 minute up to an hour before the reflex
occurs again…
 As bladder becomes more and more filled,
micturition reflexes occur more and more often
and more and more powerfully…

21. Pathway of Micturition Reflex ( Cont.)

22. Abnormalities in Micturition
 In all bladder dysfunctions, contractions occur
but they are insufficient to empty the bladder
completely.
 So, the RESIDUAL URINE is left in the bladder.
 Types :
 Deafferentation
 Denervation
 Absence of regulation by higher centers.

23. Abnormalities in Micturition
 DEAFFERENTATION : (i.e.) injury to afferent
(sensory) nerve fibers.
 Individual is unaware of distension of bladder.
 Voluntary micturition is possible.
 If such person fails to micturate at regular intervals,
bladder overflows and causes DRIBBLING OF URINE
/ OVERFLOW INCONTINENCE.
 Since there is no afferent supply, bladder wall
remains flaccid ( ATONIC BLADDER).
 AUTOMATIC BLADDER – bladder empties
automatically and the sphincter relaxes passively by
increased intra-vesical pressure.
 This is seen inTabes dorsalis ( syphilis)-
degeneration of dorsal nerve roots. (TABETIC
BLADDER).

24. Abnormalities in Micturition
 DENERVATION: (i.e.) injury to both afferent
and efferent nerves.
 Voluntary micturition is completely lost.
 Nerve supply completely lost, so it’s called ISOLATED
BLADDER /DECENTRALIZED BLADDER.
 Bladder wall remains flaccid, so it’s called FLACCID
NEUROGENIC BLADDER/ HYPOACTIVE
NEUROGENIC BLADDER.

25. Abnormalities in Micturition
 ABSENCE OF REGULATION BY HIGHER
CENTERS :
 Lesion of superior frontal gyrus ( an area in cerebral
cortex) reduces desire to urinate and difficulty in stopping
micturition once it has started..
 Paraplegia patients initiate micturition by pinching or
stroking their thighs, provoking a mild MASS REFLEX.
 Lesion in midbrain causes continuous excitation of spinal
micturition centers, resulting in frequent and
uncontrollable micturition ( SPASTIC/ HYPERACTIVE
NEUROGENIC BLADDER)