3. What is micturition?
• Micturition is a release of urine from bladder to
the outside of the body.
4. Anatomy Of Urinary Bladder
The urinary bladder is a smooth muscle chamber
composed of two main parts:
(1) the body, which is the major part of the
bladder in which urine collects, and
(2) the neck, which is a funnel-shaped extension
of the body, passing inferiorly and anteriorly into
the urogenital triangle and connecting with the
urethra.
The smooth muscle of the bladder is called the
detrusor muscle - contraction of the detrusor
muscle is a major step in emptying the bladder
5.
6. Nerve supply of urinary bladder
Sympathetic nerve supply
and Internal urethral sphincter apparently play no role no
micturition. They prevent reflux of semen into the bladder
during ejaculation.
Parasympathetic nerve supply
Sensory fibers in the pelvic nerve cary impulses from stretch
receptors present on the wall of the urinary bladder to the
spinal centre of micturition. Stimulation of parasympathetic
efferent fibers causes contraction of detrusor muscle leading
of emptying bladder.
7. Somatic nerve supply
This maintains the tonic contractions of the skeletal
muscle fibers of the external sphincter, so that this
sphincter is contracted always. During micturition
this nerve is inhibited, causing relaxation of external
sphincter and voiding of urine
9. Innervation Continued…..
• Afferents (sensory nerves)
• Pelvic nerve: impulses due to bladder fullness;
micturition reflex;
• Hypogastric nerve: pain impulses
• Pudendal nerve: sensory impulses from urethra
• Somatic Efferent (Pudendal nerve)
• Impulses originate in S1 and S2; innervate external
sphincter
• Mediate voluntary control of micturition
10. Micturition Reflex
- It is autonomic spinal cord re
fl
ex ,it can also be inhibited or
facilitated by centers in cerebral cortex or brain stem
-As bladder
fi
lls sensory stretch receptors send signals via pelvic
nerves to sacral segments of spinal cord
-
Parasympathetic stimulation of the bladder smooth muscle via
the same pelvic nerves occurs
-
It is "self-regenerative", subsides, then regenerates again until the
external sphincter is relaxed and urination can occur.
11. Micturition Reflex (cont..)
When the micturition is facilitated, perineal muscles and
external urethral sphincter are relaxed, the detrusor muscle
contracts and urine passes out through the urethra. During
micturition, the
fl
ow of urine is facilitated by increase in the
abdominal pressure due to voluntary contractions of
abdominal muscles.
12. Atonic Bladder
• Sensory nerve fibres damage.
• No micturition reflex
• Bladder fills to capacity and overflows
• Overflow incontinence
13. Automatic Bladder
• During spinal shock after complete transection of spinal-
cord above sacral centres of micturition, the urinary bladder
looses its tone and becomes flaccid and unresponsive. So,
the bladder is completely filled,and later urine overflow by
dribbling. After the spinal shock has passed, the voiding
reflex returns although there's no voluntary and high center
control. Whenever the balder is filled with some amount of
urine ,there is automatic evacuation of the bladder.
14. References
Guyton & Hall Textbook of Medical Physiology: Third
South Asia Edition
Comprehensive Textbook Of Medical Physiology GK Pal
