• Detrusor muscle:
– is a layer of the urinary bladder wall made of smooth
muscle fibers arranged in spiral, longitudinal, and
– The smooth muscle of the bladder, the detrusor is
innervated by sympathetic nervous system fibers from
the lumbar spinal cord and parasympathetic fibers from
the sacral spinal cord.
• External sphincter (sphincter urethrae):
– located at the bladder's distal inferior end in females and inferior
to the prostate (at the level of the membranous urethra) in males
– It is a secondary sphincter to control the flow of urine through the
– Unlike the internal sphincter muscle, the external sphincter is
made of skeletal muscle,
– It is under voluntary control of the somatic nervous system.
– It is innervated by pudendal nerves
• Internal sphincter muscle of urethra:
– It is located at the bladder's inferior end and the urethra's
proximal end at the junction of the urethra with the urinary
– The internal sphincter is a continuation of the detrusor muscle
and is made of smooth muscle,
– it is under involuntary or autonomic control.
– This is the primary muscle for prohibiting the release of urine.
• There are three layers of muscle that are known to control urine
flow through the urethra;
– an inner band of longitudinal smooth muscle
– a middle band of circular smooth muscle
– an external band of striated muscle called the rhabdosphincter.
• The urethra is controlled by the
sympathetic, parasympathetic, and somatic divisions of the
peripheral nervous system.
• The sympathetic innervation (nerve supply) comes from the
sympathetic preganglionic neurons located in the upper lumbar
spinal cord along the hypogastric nerve and terminates in the
longitudinal and circular smooth muscle layers in the urethra.
• The parasympathetic nerve supply comes from the
parasympathetic preganglionic neurons in the sacral spinal cord
and also terminates in the longitudinal and circular smooth muscle
• The somatic nerve supply arises from the urethral sphincter motor
neurons in the ventral horn of the sacral spinal cord; better known
as Onuf’s nucleus. The pudendal nerve that extends from Onuf’s
nucleus, connects directly to the rhabdosphincter muscle to
CENTRE: S2-S4 in intermediolateral column
SUPPLY THROUGH: pelvic splanchnic nerves
END IN : GANGLIA IN BLADDER WALL
NEUROTRANSMITTER : ACh VIA M2, M3
Cholinergic preganglionic neurons within the intermediolateral sacral
cord send axons to ganglionic cells within the pelvic plexus and the
Postganglionic neurons within the bladder wall and pelvic plexus release
acetylcholine, which activates cholinergic receptors M2 and M3 on the
detrusor smooth muscle cells initiates
Bladder detrusor contraction
Internal sphincter relaxation
CENTRE: T11-L2 intermediolateral column
sympathetic chain ganglia-prevertebral gangliahypogastric and pelvic plexus –inferior mesentric
ganglion –post ganglionic fibres
– innervate the bladder via short adrenergic neurons.
– Via β-adrenergic receptors -inhibition and relaxation of
the detrusor muscle.
– Through alpha receptors causes Contraction of internal
– Facilitate bladder storage and continence
• SOMATIC :
CENTRE: ONUF’S NUCLEUS S2-S4
SUPPLY THROUGH: PUDENDAL NERVES
FUNCTION : CONTROLS THE EXTERNAL
LOOP -5 Corticospinal pathways
• from motor cortex to pudendal motor
neurons, which are concerned with the
voluntary control of the sphincters and pelvic
• The sympathetic storage reflex or pelvic-to-hypo-gastric
reflex is initiated when the bladder swells. Stretch
receptors cause postganglionic neurons to release
norepinephrine (NE). NE causes the bladder to relax and
the urethra to contract, thus preventing urine loss.
• The somatic storage reflex or the pelvic-to-pudendal or
guarding reflex is initiated when one laughs, sneezes, or
coughs, which causes increased bladder pressure.
Glutamate is the primary excitatory transmitter for the
reflex. Glutamate activates NMDA and AMPA receptors
which produce action potentials. These action potentials
activate the release of acetylcholine causing the
rhabdosphincter muscle fibers to contract. When the
guarding reflex does not function normally, SUI occurs
SPINAL REFLEX ARC
• AFFERENT ARC:
– Sensation of stretch arising from bladder wall travels
through the parasympathetic nerves to the center for
• DETRUSOR CENTER OR SACRAL PARASYMPATHETIC NUCLEUS
– sacral segments S2,S4 of the spinal cord.
• EFFERENT ARC (PARASYMPATHATIC)
– travels through the pelvic nerves to the pelvic plexus;
short postganglionic fibers travel from the plexus to the
• CORTICAL CENTERS:
– Situated in
• Medial frontal lobe
• Cingulate gyrus
• Corpus collosum
• cortical input is inhibitory on micturition reflexes.
• Subcortical centers:
– thalamic nuclei
– limbic system,
– Red nucleus
– Substantia nigra
– Subthalamic nucleus.
• Cerebellum :
– anterior vermis of the cerebellum
– fastigial nucleus are concerned with micturition.
• Lesions resulting from tumors, aneurysms, or
cerebrovascular disease remove the cortical
inhibition, which results in increased excitatory
input to the brainstem, facilitation of the
micturition reflex, and the clinical appearance of
urinary frequency and urgency.
• Descending fibers in the corticospinal tracts
emanate from the cortical region to innervate
sacral parasympathetic neurons and the motor
nucleus controlling voluntary sphincter function
PONTINE MICTURITION CENTERS
– pontomesencephalic reticular formation micturition
center (located in the locus ceruleus, pontomesencephalic
gray matter, and nucleus tegmentolateralis dorsalis).
– collection of cell bodies located in the rostral pons in the
brainstem involved in the supraspinal regulation of
– The PMC makes connections with other brain centers to
control micturition, including the medial frontal
cortex, insular cortex, hypothalamus and periaqueductal
– The PAG in particular acts a relay station for ascending
bladder information from the spinal cord and incoming
signals from higher brain areas.
Course from higher centres
• From the pontomesencephalic micturition center,
efferents to the spinal cord descend by way of
the reticulospinal tracts (located medially and
anteriorly in the anterior funiculus) to the
detrusor motor neurons in the intermediolateral
cell columns of the sacral gray matter (S2–S4).
• Efferents from the cortical and subcortical
micturition centers descend by way of the
pyramidal tracts to the pudendal nuclei (Onuf’s
nucleus) in the sacral spinal cord (S2–S4).
• The pudendal nerves, whose motor neurons are
located in the ventral horns of sacral segments
S2–S4, innervate the striated muscle around the
• Onuf’s nucleus
– It is a distinct group of neurons located in the ventral part
(laminae IX) of the anterior horn of the sacral region of the spinal
cord . It extends from S1 to S3 mainly in S2
– It is involved in the maintenance of micturition and defecatory
continence, as well as muscular contraction during orgasm.
– It contains motor neurons, and is the origin of the pudendal
– The neurons of Onuf’s nucleus are responsible for controlling external
sphincter muscles of the anus and urethra.
– The dorsomedial subnucleus innervates the the ventrolateral subgroup
connects to the urethral striated sphincter (vonluntary sphincter) and
rectal striated sphincter
– Onuf’s nucleus controlled the ischiocavernosus and bulbocavernosus
muscles which function in penile erection and ejaculation in males.
– Neurotransmitters in Onuf's nucleus
– The motoneurons in Onuf’s nucleus contain a dense array of serotonin
and norepinephrine receptors and transmitters and are activated by
glutamate. When the 5-HT and NE receptors are stimulated, the
guarding reflex occurs to prevent voiding of the bladder caused by
unexpected abdominal pressure sneezing, coughing etc.
• REGULATION OF MICTURITION:
– Micturition is a spino-bulbo-spinal reflex. In response to stretch,
afferent impulses are carried to the sacral spinal cord.
– Sacral cord projections to the PAG are relayed to the pontine
micturition center (Barrington's nucleus)
– The pontine micturition center is under the control of centers in
– During bladder filling, neurons within the PMC are turned off.
– at a critical level of bladder distention, the afferent activity arising
from mechanoreceptors in the bladder wall switches the PMC on
and enhances its activity.
– neurons in the PMC send descending excitatory projections to
spinal parasympathetic preganglionic neurons innervating the
bladder and inhibitory interneurons regulating Onuf's nucleus.
– This activation results in relaxation of the urethra and contraction
of the bladder due to stimulation of parasympathetic and
inhibition of sympathetic outflow to the bladder, and the removal
of somatic activation of the external urethral sphincter. This
pattern of activity can also be elicited through the conscious
desire to void
• There is a curious preservation of the Onuf nucleus
neurons in amyotrophic lateral sclerosis.
• The internal uretheral sphincter at the neck of the
bladder receives its innervation from the
intermediolateral column at the T12-L1 level, via
the sympathetic prevertebral plexus and the
• In the infant, bladder function is purely reflex, but
with cortical maturation and the completion of
myelination inhibitory control over this reflex
develops, as well as voluntary regulation of the
• Normal micturition requires intact autonomic and
spinal pathways, and cerebral inhibition and control
of the external sphincter must be normal
• Forebrain lesions may cause loss of voluntary bladder control, but do not
affect the spino-bulbo-spinal reflex mechanisms.
• Disruption of the bulbospinal pathway from the pontine micturition center
to the sacral cord, and lesions affecting the afferent and efferent
connections between the bladder and the conus medullaris may cause
severe disturbances in bladder function.
• The term neurogenic bladder refers to bladder dysfunction caused by
disease of the nervous system.
• Symptoms of bladder dysfunction are often among the earliest
manifestations of nervous system disease.
• Frequency, urgency, precipitate micturition, massive or dribbling
incontinence, difficulty in initiating urination, urinary retention, and loss of
bladder sensation may occur.
• One practical classification of neurogenic bladder dysfunction is based on
urodynamic criteria and includes the following types:
Uninhibited neurogenic bladder
• there is a loss of the cortical inhibition of reflex
• while bladder tone remains normal.
• Bladder distention causes contraction in
response to the stretch reflex.
• There is frequency, urgency, and incontinence
that are not associated with dysuria.
• Hesitancy may precede urgency.
• Bladder sensation is usually normal.
• There is no residual urine.
Reflex neurogenic bladder/SPASTIC/hyperreflexic
• lesions above the level of the sacral bladder center and
below the level of the pontomesencephalic micturition
• occurs with severe myelopathy or extensive brain lesions
causing interruption of both the descending autonomic tracts
to the bladder and the ascending sensory pathways above the
sacral segments of the cord.
• UMN CUT OFF LMN INTACT
• associated with quadriplegia or paraplegia and in advanced
cases of multiple sclerosis
• Detrusor spinter synergia lost results in obstructed
voiding, an interrupted urinary stream, incomplete
emptying, and high intravesical pressures because the
sphincter fails to relax correctly .
• Upper urinary tract dilatation and kidney damage may
• Loss of the normal inhibition from higher centers results in
detrusor contraction during bladder filling.
• contractions occur spontaneously or may be provoked
by coughing or changing posture.(stress incontinence)
• detrusor becomes overactive, so there is urinary
frequency, urgency, urge incontinence (the patient is
unable to inhibit the detrusor reflex),
• inability to initiate micturition voluntarily.
• Small volumes of urine stimulate uninhibited detrusor
muscle contraction; the bladder capacity is reduced
but residual urine may be increased (increased
postmicturit ion residual volume).
• bulbocavernosus and superficial anal reflexes are
• With lesions above the splanchnic out flow, bladder
fullness may induce a “mass reflex” with paroxysmal
hypertension, headaches, diaphoresis, and bradycardia.
Autonomous/FLACID neurogenic bladder
• is one without external innervation.
• seen with complete lesions below the T12 segment that
involve the conus medullaris and cauda equina. , S2-S4 motor or
sensory roots, or the peripheral nerves, and with congenital
anomalies such as spina bifida.
• It occurs with sacral myelomeningocele and tumors of the
conus medullaris–cauda equina region
• There is destruction of the parasympathetic supply.
• Sensation is absent
• There is no reflex or voluntary control of the bladder;
• contractions occur as the result of stimulation of the intrinsic neural
plexuses within the bladder wall.
• The amount of residual urine is large, but the bladder capacity is
not greatly increased
• urinary retention because the tone of the detrusor
muscle is abolished
• the bladder distends as urine accumulates. Inability
to initiate micturition,
• overflow incontinence, and increased residual urine
• There is associated saddle anesthesia with absence
of the bulbocavernosus and superficial anal
• Anal sphincter control is often similarly affected.
• The bladder capacity may greatly increase, and
• its walls may become fibrotic.
• A large residual urine volume may therefore occur
because of incomplete detrusor contractions.
Motor paralytic bladder
• develops when the motor nerve supply to the bladder is
• The bladder distends and decompensates,
• but sensation is normal.
• The residual urine and bladder capacity vary.
• Occurs in lumbar spinal stenosis, lumbosacral
meningomyelocele, or following radical hysterectomy or
abdominop erineal resect ion.
• In most of these cases, pat ients suffer from painful urinary
retention or imp aired bladder emptying.
• Residual urine is markedly increased.
• The bulbocavernosus and sup erficial anal reflexes are usually
absent , but sacral and bladder sensation are present .
Sensory paralytic bladder
• occur in tabes dorsalis, syringomyelia, or diabetes mellitus
• is found with lesions that involve the posterior roots or posterior
root ganglia of the sacral nerves, or the posterior columns of the
• Sensation is absent, and there is no desire to void. He can void
voluntarily (motor intact)
• There may be distention, dribbling, and difficulty both in initiating
micturition and in emptying the bladder.
• There is a large amount of residual urine
• Urinary retention, overflow incontinence, or urinary tract
infection may be early symptoms.
• The bulbocavernosus and superficial anal reflexes may be absent ,
decreased, or present .