1. Physiological anatomy of urinary bladder
2. Innervation of urinary bladder
3. Filling of urinary bladder
4. micturition reflex ( in normal individuals )
5. Abnormalities in Micturition
3. • Urine formed in the kidney is transferred to
urinary bladder by ureters.
• Urinary bladder accumulates urine without
much rise in pressure in it & empties its content
at appropriate time following suitable rise in
• Urine from kidneys flows down to the bladder
through ureters due to the action of gravity,
which is aided by peristaltic movements of
4. Peristaltic waves in ureters originate by a
pacemaker tissue located close to the calyces
at a frequency of about one per minute .
Urinary bladder is a sac like structure present in
the pelvic cavity.
It is a distensible organ made up of smooth
muscle, called detrusor muscle.
The epithelium of the bladder is formed by a
superficial layer of flat cells and a deep layer of
Bladder is innervated by both sympathetic and
Parasympathetic fibers originate from the sacral
2, 3 and 4 segments of the spinal cord and
reach the bladder via pelvic nerves.
The sympathetic fibers originate from lumbar 1,
2 and 3 segments of the spinal cord and reach
the bladder via hypogastric nerve.
7. The somatic fibers originate horn S2, S3 and S4
and innervate bladder and external sphincter via
Filling of bladder, desire to pass urine and
painful distension, all these sensations of
bladder are mediated by afferents in the pelvic
9. Urethral Sphincters:
There are two sphincters:
The internal sphincter, which is located at the
neck of the bladder, is made up of a bundle of
smooth muscle, and innervated by sympathetic
(hypogastric) and parasympathetic (pelvic)
The internal sphincter is under autonomic
10. The external sphincter is made up of a flap of
skeletal muscle, which is present around the
urethra in its proximal part (below the origin
The external sphincter is innervated by somatic
(pudendal) nerve and therefore is under
1.Storage of urine up to a critical volume.
2.Emptying urine into urethra when the critical volume
The external sphincter is kept closed most of the time.
The sensation of bladder filling is experienced at the
bladder volume of about 150 ml and the sensation to
pass urine is experienced at the volume of 150-250 ml.
At volume of about 400 ml, the sensation to pass urine
becomes uncomfortable and at about 700 ml, it
becomes very painful leading to loss of control on
It is the technique used to demonstrate the relationship
between the intravesical pressure and the volume of urine in
It is the graphical recording of pressure changes in urinary
bladder in relation to rise in the volume of urine.
• 3 PHASES.
• Phase Ia – upto 50 ml –
pressure changes to 0-
• Phase Ib – from 50 ml -
400 ml, pressure does
not change much,
remains 10 cm of H2O,
due to adaptation By
Wednesday, May 18, 2016
15. NORMAL CYSTOMETROGRAM
Phase II – starts beyond
400 ml, pressure changes
raises pressure more
by 20-40 cm of H2O
16. Micturition reflex
Micturition is the process of passing urine.
This is primarily a reflex phenomenon, which is mostly
integrated in the spinal cord.
This spinal reflex is influenced by activities of the
Unless the bladder is filled, urine accumulates in
urinary bladder without much increase in the
intravesical pressure, as bladder wall is made up of
smooth muscles that exhibit the property of plasticity.
17. Filling of urinary bladder → stretch receptors →
sensory impulse via pelvic nerve to S2 – S4 →
Parasympathetic impulse via pelvic nerve →
Contraction of detrusor muscle & relaxation of internal
sphincter → urine in urethra stimulates stretch
receptors → sensory impulse via pelvic nerve to S2
– S4 → inhibition of somatic fibers in pudendal nerve
→ relaxation of external sphincter → results in
18. Mechanism of Micturition
The urge to pass urine is initiated with filling of the
bladder, which is sensed by stretch receptors.
The stretch receptors that are present in the wall of the
bladder send impulses in afferent nerves that initiate
Micturition is a parasympathetic activity.
Parasympathetic stimulation causes contraction of
detrusor and relaxation of internal sphincter, so that
the urine passes forcefully into the urethra.
19. During micturition, the pelvic, perineal and
levator ani muscles relax.
This causes downward pull of detrusor muscle
and aids to initiation of its contraction.
At this stage, perineal muscles and external
sphincter can be made to contract voluntarily to
prevent micturition to occur.
20. The voluntary control of micturition is influenced by
cortical activities and by learning to contract the
external urethral sphincter.
Once in the urethra, the urine is emptied in females by
the effect of gravity and pressure from the pelvic floor,
whereas in males, urine is emptied by contractions of
The voluntary contraction of abdominal muscles helps
in expulsion of urine.
21. Reflex control of micturition
The fibers in the pelvic nerve form the afferent
limb for the micturition reflex.
The center for this spinal reflex is the sacral 2,
3, and 4 segments of the spinal cord.
The parasympathetic fibers to bladder constitute
efferent limb, which also travel in the pelvic
The reflex is initiated at about 300-400 ml of
23. Normally, the sympathetic fibers do not play a
role in micturition.
However, the sympathetic activation causes
contraction of bladder muscle that prevents
semen from entering the bladder during
ejaculation. (retrograde ejaculation) .
The micturition reflex is controlled by centers in
24. The facilitatory area is present in pons and the
inhibitory area is present in midbrain.
Therefore, section of neuraxis above pons
promotes activity of micturition reflex in which
less filling of bladder triggers its reflex
evacuation, and section above midbrain does
not affect it.
25. Posterior hypothalamus also contains a facilitatory
area for micturition.
Cortex has voluntary inhibitory control on micturition.
In children, below three years of age, cortical inhibition
is not well developed; hence they often pass urine
without their knowledge.
Control on urination starts to develop at about two
years of age and completes by three years.
26. Abnormalities of micturition
The lesions at different segments of neuraxis result in
bladder dysfunctions. There are three major neural
defects that produce bladder dysfunctions:
1. Interruption of afferent fibers (deafferentation)
2. Interruption of both afferent and efferent fibers
3.Interruption of influences from the fascilitatory and
inhibitory areas in the brain (spinal cord transection).
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 (
AUTOMATIC BLADDER – bladder empties automatically and the
sphincter relaxes passively by increased intra-vesical pressure.
This is seen in Tabes dorsalis ( syphilis)- degeneration of dorsal
nerve roots. ( TABETIC BLADDER).
When both the afferent and efferent fibers are cut,
bladder becomes flaccid and distended at the
However, gradually the muscle of the bladder becomes
active and the contraction of the bladder muscle
removes urine in the form of dribbles.
Later, the bladder shrinks and bladder wall becomes
29. Spinal Cord Transection
When the spinal cord is transected, typically three
phases are observed: phase of shock, phase of
recovery (increased reflex activity), and phase of
During the phase of spinal shock, the bladder
becomes flaccid and unresponsive.
The overflow incontinence (urine dribbles through the
sphincter when the bladder is overfilled) occurs.
30. In the phase of recovery, micturition reflex is the first
reflex activity to return.
Voluntary control or control by the higher centers is
abolished after transection.
The bladder capacity is decreased and the muscle of
bladder is hypertrophied.
This type of bladder is known as spastic neurogenic
In the phase of failure, the infection of bladder makes
the reflex activity worse.
31. Write short note on
1. Micturition reflex
3. Draw well labelled diagram of innervation of urinary
Ganang ’s review of medical physiology
Comprehensive textbook of medical physiology G.K.PAL
Guyton & hall Text book of medical physiology
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