The urinary bladder stores urine and empties through micturition. It has a muscular wall and is innervated by both the autonomic and somatic nervous systems. During filling, afferent nerves signal bladder fullness to the spinal cord. Above 300-400ml, the micturition reflex is triggered, causing detrusor muscle contraction and internal sphincter relaxation for voiding. Higher brain centers can facilitate or inhibit this reflex. Abnormalities like denervation can cause an overactive or underactive bladder unable to empty fully.

1. Physiology of urinary bladder
and Micturition

2. Functional anatomy of urinary
bladder
• Hollow organ
• lined by transitional epithelium
• stretched enormously
• Mucosa is thrown into folds called rugae
• except triangular area at the base - Trigone
• Smooth muscle – Detrusor
• Interlacing of fibres

4. • Internal sphincter – sphinteric mechanism
• Function – maintain tonic closure of urethral
opening
• prevent reflux of semen into urethra during
ejaculation
• External sphinter – voluntary skeletal m.
• can be reflexely/ voluntarily relaxed at the time
of micturition
• Upper end – Ureteric opening – ureters enter
obliquely

6. Physiological capacity
• Birth – 20-50 ml
• 1 year – 200 ml
• Adults – 600 ml
• Anatomical capacity – 1L – capacity just before the
bladder ruptures
• Never happens under physiological conditions
• First urge to void urine – 150ml
• Marked sense of fullness / discomfort – 400ml –
Initiation of micturition reflex

7. Bladder innervation
Urinary bladder is innervated by autonomic and
somatic nerves:
A. Efferent nerve supply: ( Motor)
1. Parasympathetic
2. Sympathetic
3. Somatic
B. Afferent nerve supply ( Sensory)

8. Efferent supply

9. Afferent nerve supply
1. From the external sphincter and posterior
urethra, afferent fibers pass along the
Pudendal Nerves (dorsal nerve roots of
S2,3,4)
2. From the body, trigone and internal
sphincter, afferent fibers take a double route
along:
 sympathetic nerve (dorsal nerve roots of L1,2 and
lower thoracic segment)
 sacral parasympathetic nerves (sacral dorsal
nerve roots)

11. Functions
1. Indicates the degree of distension of the
urinary bladder. (afferent nerves along sacral
parasympathetic)
2. To convey pain sensibility. (afferent nerves
along sympathetic)

12. Mechanics of micturition
• 2phases – Emptying and filling – interplay of
pressures in the bladder and internal sphincter
• Spinal reflex – facilitated and inhibited by higher
brain centres
• Plasticity – when it is stretched tension is not
maintained for long

13. Cystometrogram
• Plot of intravesical pressure against volume of
fluid in the bladder – Cystometrogram
1.Initial slight rise of pressure – Ia
2.Long nearly flat segment – Ib
3.Sudden sharp rise of pressure when the
micturition reflex is triggered – II

14. Cystometrogram

15. • Flatness of segment Ib - Law of LaPlace
• P = 2T / R
• Tension increases as the bladder is filled but
so does the radius
• The pressure is slight until the organ is
relatively well filled

16. Voluntary micturition-Afferent
pathway
Bladder fills with urine –stretch receptors++
↓
Sensory signals to the dorsal nerve root S2,3,4
segments of the spinal cord (pelvic nerves)
↓
Back to the bladder by the parasympathetic fibres
in the same nerve
↓
Micturition reflex

18. • Sympathetic efferents are reflexely
inhibited
• Reflex is integrated in the sacral segment of
spinal cord
• Volume of urine that initiates reflex
contraction – 300-400 ml

19. Higher control of micturition reflex
Threshold for voiding reflex is adjusted by :
Facilitatory areas
 Pontine
 Post. Hypothalamus
Inhibitory areas
 midbrain
• Voluntary contraction of abdominal muscles
aids in expulsion of urine

20. Mechanism of micturition
• During micturition – perineal muscle and
external urethral sphincters are relaxed
↓
Detrusor muscles contract
↓
Urine passes out through the urethra

21. • Voluntary contraction – relaxation of muscles of
pelvic floor
↓
Downward tug on detrusor muscles
• Perineal muscles and external urethra can be
contracted voluntarily – preventing urine from
passing down or interruption of flow

23. Abnormalities
1. Deafferentation
• Interruption of afferent nerves from the bladder
• Tabes dorsalis(syphillis)
• All reflex contractions of the bladder are lost
Bladder
1.Distended,
2.Thin walled and
3.Hypotonic
• Some contractions occur due to intrinsic
response of smooth muscles to stretch

24. 2. Denervation
• Afferent and efferent nerves are destroyed
• Tumor of cauda equina / filum terminale
• Bladder flaccid and distended for a while
• DECENTRALISED BLADDER
• Later Muscles become active with many
contraction waves that cause dribbling
• Bladder becomes shrunken and bladder wall is
hypertrophied

26. 3. Spinal cord transection
• During spinal shock – bladder is flaccid and
unresponsive
• Sphinter tone returns first
• Overfilled and urine dribbles out through the
sphincter (Overflow incontinence )

27. • After spinal shock has passed,
• voiding reflex returns
• no voluntary control and
• no facilitation/ inhibition from higher centres
• Paraplegic – Initiate voiding – mild mass reflex

28. • Sometimes voiding reflex becomes
hyperactive – capacity is reduced – walls
become hypertrophied (Spastic neurogenic
bladder )
• infection of the urinary bladder

30. • In all these defects the bladder contracts but
these contractions are not sufficient to empty
the viscus completely
• Residual urine is left in the bladder