2. Important notes
• Has a Max Capacity of 500ml
• Pyramidal in shape
• It’s muscle coat is called the Detrusor Muscle
• Pressure in the bladder when Detrusor Contracts is 40 – 60 mm
Hg
• It’s thickened circular component of the muscle coat found
on its’ neck is called the Sphincter Vesicae (Involuntary)
• Synonyms: annulus urethralis, internal urethral sphincter, musculus
sphincter vesicae, preprostate urethral sphincter,proximal, sphincter
muscle of urinary bladder.
• External Sphincter of the Bladder (Voluntary)

3. Nerve Supply is formed from the Hypogastric Plexuses
Sympathetic (Sensation of Fullness of the bladder and Pain) : Originates
from the 1st and 2nd Lumbar Ganglia to form the Hypogastric Plexuses
Parasympathetic (Motor; Internal Sphincter; Detrusor Muscle; Involuntary)
: Originates from the 2nd, 3rd, and 4th Sacral Nerves to form the Pelvic
Splanchnic Nerves
• Most afferent sensory fibers from the bladder reach the CNS via the
Pelvic Splanchnic Nerves
• Some afferent fibers travel with the sympathetic nerves via the
Hypogastric Plexuses
The Detrusor Muscle fuse with one another so that low-resistance
electrical pathways exist from one muscle cell to the other making an
action potential spread throughout it, causing the entire bladder to
contract at once
Somatic Nerve Fibers (Motor; External Sphincter; Voluntary): Skeletal
motor fibers that innervate and control the voluntary skeletal muscle of
the sphincter are transmitted through the Pudendal Nerve

4. Sympathetic (Sensation of Fullness of the bladder and Pain) : Originates from the 1 st and 2nd Lumbar Ganglia to form the
Hypogastric Plexuses
Parasympathetic (Motor; Internal Sphincter; Detrusor Muscle; Involuntary) : Originates from the 2 nd, 3rd, and 4th Sacral Nerves to
form the Pelvic Splanchnic Nerves

5. Sympathetic (Sensation of Fullness of the bladder and Pain) : Originates from the 1 st and 2nd Lumbar Ganglia to form the
Hypogastric Plexuses
Parasympathetic (Motor; Internal Sphincter; Detrusor Muscle; Involuntary) : Originates from the 2 nd, 3rd, and 4th Sacral Nerves to
form the Pelvic Splanchnic Nerves

6.  Plexus : A network of intersecting nerves, blood
vessels or lymph vessels
 Ganglia / Ganglion: Collection of nerve cells forming
a knot like shape and usually lying outside the brain
and spinal cord (Outside CNS)
 Afferent : Carrying inward or towards the Center
(Brain), as a nerve carrying a sensory impulse to the
brain
 Efferent : Carrying outward or away from the center
(Brain), as a nerve carrying impulses from the brain to
a muscle, gland or other effector organ
 Action Potential : Electrical charge developed in a
muscle or nerve cell that leads to its discharge or
contraction
 Distended / Distention: State of being stretched out
or enlarged

7.  Before  Today’s Theory
› Sympathetic Nerves inhibit › Sympathetic Nerves have little or
contraction of the detrusor no action on the smooth muscle
muscle of the bladder wall of the bladder wall and are
and stimulate closure of the distributed mainly to the blood
sphincter vesicae vessels and plays a minor role in
the contraction of the sphincter
› Parasympathetic Nerves
vesicae
stimulate contraction of the
detrusor muscle of the › In males the Sympathetic
bladder wall and inhibit the Innervation of the sphincter
action of the sphincter causes active contraction of the
vesicae bladder neck during
ejaculation, thus preventing the
semen to enter the bladder

8. Clinical Notes
• Urinary Calculus : Stone formed in any part of the
urinary system also known as Kidney stone and/or Renal
Calculus
• Urinary Hesitancy : Difficulty in beginning the flow of
urine and decrease in the force of the urine stream. In
men it is associated with prostate gland enlargement; in
women with narrowing of the opening of the urethra or
obstruction between the bladder and urethral it may
also be caused in either sex by emotional stress and
other factors

9. Picture Rendering Actual Dissection

11.  The reflex is initiated when the volume of the
urine reaches 300 ml
 Stretch receptors in the bladder wall are
stimulated an transmit impulses to the CNS, this
gives the individual the conscious desire to
micturate (urinate)
 Sensory signals from the bladder are conducted
to the sacral segments of the cord through the
pelvic nerves and then reflexively back again to
the bladder through the parasympathetic nerve
fibers by way of these same nerves.
 These impulses from the parasympathetic nerve
fibers causes the Detrusor Muscle to Contract
and at the same time make the Urethral
Sphincter Relax

12.  Efferent impulses also pass to the urethral
sphincter via the pudendal nerve (S2, S3, and
S4), and this undergoes relaxation.
 Once urine enters the urethra, addition
afferent impulses pass to the spinal cord from
the urethra and reinforce the reflex action
› Note: Micturition can be assisted by contraction of
the abdominal muscles to raise the intra-
abdominal and pelvic pressure and exert external
pressure on the bladder
› Muscles that compress abdominal Contents :
 External Oblique, Internal
Oblique, Transversus, Rectus Abdominis

13.  Children  Adults
› A simple reflex that › The same simple
acts and takes reflex is inhibited by
place whenever the the Cerebral Cortex
bladder becomes until the time and
distended. place for micturition
are favorable
› Voluntary
Movement is
Controlled by
Brodmann’s Area
4,6,8

14. Clinical Notes
•Overflow Incontinence : When sensory fiber nerves from
the bladder to the spinal cord are destroyed preventing
transmission of stretch signals from the bladder a person
loses bladder control. Instead of emptying periodically, the
bladder fills to capacity and overflows a few drops at a time
through the urethra.
•Automatic Bladder caused by spinal cord damage above
the Sacral Region : Since the damage is above the sacral
region normal micturition reflex can occur. However they
are no longer controlled by the brain. Hence periodic but
unannounced bladder emptying occurs.

16.  The micturition reflex is the basic cause of
micturition, but the higher centers of the brain
(cortex) normally exert final control of
micturition as follows:
1. the micturition reflex partially inhibited, except
when micturition is desired
2. Prevent micturition, even if the micturition reflex
occurs, by continual tonic contraction of the
external bladder sphincter until a convenient
time presents itself
3. When it is time to urinate, the cortical centers
can facilitate the sacral micturition centers to
help initiate a micturition reflex and at the same
time inhibit the external urinary sphincter so that
urination can occur.

17.  Usually initiated in the following way:
1. A person voluntarily contracts his or her
abdominal muscles, which increases the pressure
in the bladder and allows extra urine to enter the
bladder neck and posterior urethra under
pressure, thus stretching their walls
2. This stimulates the stretch receptors, which
excites the micturition reflex
3. Simultaneously inhibits the external urethral
sphincter allowing urine to flow

18. Important Notes
• The function of the kidney is to excrete most of the
waste products of metabolism. They play a major role in
controlling the water and electrolyte balance within the
body
• The urine is propelled along the ureter by peristaltic
contractions of the muscle coat, assisted by the filtration
pressure of the glomeruli

19.  Urine formation begins when a large amount
of fluid that is virtually free of protein is filtered
from the glomerular capillaries into Bowman’s
Capsule.
 As the filtered fluid leaves Bowman’s capsule
and passes through the tubules, it is modified
by reabsorption of water and specific solutes
back into the blood.
 The rate at which the substance is excreted in
the urine depends on the relative rate of
filtration, reabsorption, and secretion.
 Urinary excretion rate = Filtration rate –
Reabsorption rate + Secretion rate