Urinary Bladder Innervation and Types of Bladder

Innervation of the Urinary Bladder

1. Parasympathetic Innervation (Motor - Voiding)

• Origin: Sacral parasympathetic nucleus, spinal cord segments S2, S3, S4
• Pathway: Pre-ganglionic fibers exit via the pelvic splanchnic nerves (nervi erigentes) → synapse at ganglia near or within the detrusor wall → short post-ganglionic fibers innervate the detrusor muscle
• Neurotransmitter: Acetylcholine (ACh) stimulating M3 muscarinic receptors on the detrusor (M2 is more abundant but M3 drives contraction)
• Function: Detrusor contraction (bladder emptying/voiding)
• Note: Parasympathetic postganglionic neurons in humans are located both in the detrusor wall and in the pelvic plexus - patients with cauda equina injuries may retain some innervation via intramural ganglia

2. Sympathetic Innervation (Storage)

• Origin: Thoracolumbar spinal cord, segments T10 to L2
• Pathway: Pre-ganglionic fibers → sympathetic chain ganglia (SCG) → inferior splanchnic nerves (ISN) → inferior mesenteric ganglia (IMG) → hypogastric nerves (HGN) → pelvic plexus/ganglia → bladder and urethra
• Neurotransmitters and receptors:
  • Beta-3 (β3) adrenergic receptors on the detrusor body: noradrenaline causes detrusor relaxation (storage)
  • Alpha-1 (α1) adrenergic receptors on the bladder neck and urethra: noradrenaline causes smooth muscle contraction (continence)
  • Dense α1-receptors are present at the bladder neck in males - important for antegrade ejaculation and continence
• Function: Facilitates urine storage by relaxing the bladder body and contracting the outlet

3. Somatic Innervation (Voluntary Sphincter Control)

• Origin: Onuf's nucleus, ventral horn of sacral spinal cord (S2, S3, S4)
• Pathway: Via the pudendal nerve
• Target: External urethral sphincter (EUS), pelvic floor muscles (levator ani)
• Neurotransmitter: ACh acting on nicotinic receptors at the neuromuscular junction (striated muscle)
• Function: Voluntary contraction of the external sphincter (maintaining continence) and voluntary relaxation during micturition

4. Afferent (Sensory) Pathways

• From the bladder wall: Stretch receptors signal bladder filling via A-delta (myelinated, tension) and C fibers (unmyelinated, pain/temperature)
• Route: Travel with the hypogastric plexus → dorsal root ganglia → spinal cord
• Stretch signals from the posterior urethra are particularly strong in triggering the micturition reflex
• Afferent signals ascend to the Pontine Micturition Center (PMC) in the brainstem, which coordinates bladder-sphincter synergy
• Higher control: Cerebral cortex and hypothalamus provide voluntary inhibition of micturition until socially convenient

5. Non-Adrenergic, Non-Cholinergic (NANC) Fibers

• Use purines (ATP) and nitric oxide as neurotransmitters
• Nitric oxide synthase-containing neurons found in the bladder neck and trigone - promote relaxation during voiding
• Contribution to normal contraction is small, but may become pharmacological targets in pathological states

Summary Table

Types of Bladder (Lapides Classification - Neurogenic Bladder)

1. Sensory Neurogenic Bladder

• Lesion: Selective interruption of sensory (afferent) fibers between bladder and spinal cord/brain
• Common causes: Diabetes mellitus, tabes dorsalis, pernicious anemia
• Clinical features: Impaired sensation of bladder distension; voiding must be initiated by timed schedule
• Cystometry: Large-capacity bladder, flat high-compliance low-pressure filling curve; large residual urine if voiding is neglected

2. Motor Paralytic Bladder (Motor Neurogenic Bladder)

• Lesion: Destruction of parasympathetic motor innervation (efferent fibers)
• Common causes: Extensive pelvic surgery or trauma, herpes zoster
• Clinical features: Ranges from painful urinary retention to inability to maintain normal voiding; no voluntary detrusor contraction
• Cystometry: Normal filling curve initially, but no detrusor contraction at capacity; chronic overdistension leads to large-capacity flat low-pressure bladder

3. Uninhibited Neurogenic Bladder

• Lesion: Damage to the corticoregulatory tract (upper motor neuron lesion above sacral micturition center) - loss of cortical inhibition
• Common causes: CVA (stroke), brain or spinal cord tumor, Parkinson's disease, demyelinating disease (MS)
• Clinical features: Urgency, frequency, urge incontinence; patient can usually initiate voiding voluntarily but cannot hold
• Cystometry: Normal sensation with involuntary detrusor contractions at low filling volumes; low residual urine

4. Reflex Neurogenic Bladder

• Lesion: Complete interruption of sensory and motor pathways between sacral spinal cord and brainstem (suprasacral spinal cord lesion) - equivalent to complete upper motor neuron (UMN) lesion
• Common causes: Traumatic spinal cord injury, transverse myelitis, extensive demyelinating disease
• Clinical features: No bladder sensation; no voluntary voiding; incontinence without sensation; detrusor-sphincter dyssynergia (DSD) is the rule
• Cystometry: Involuntary contractions at low volumes; no voluntary control

5. Autonomous Neurogenic Bladder

• Lesion: Complete motor AND sensory separation from the sacral spinal cord (destruction of sacral cord, sacral roots, or pelvic nerves) - equivalent to complete lower motor neuron (LMN) lesion
• Common causes: Sacral cord destruction (tumors, trauma), cauda equina injuries, radical pelvic surgery
• Clinical features: Cannot initiate micturition, no reflex activity, no bladder sensation; bladder empties only by abdominal straining or manual compression (Crede maneuver)
• Cystometry: Flat filling curve; no detrusor contractions; large residual urine

Clinical Correlations by Spinal Level

• Campbell-Walsh Wein Urology - Innervation of the Bladder, Lapides Classification (Ch. 110-111)
• Bailey and Love's Short Practice of Surgery, 28th ed. - Innervation of the Bladder (Ch. 83)
• Berek & Novak's Gynecology - Innervation of the Bladder and Urethra (Ch. 29)
• Guyton and Hall Textbook of Medical Physiology - Physiological Anatomy and Innervation of the Bladder (Ch. 26)
• Mulholland and Greenfield's Surgery, 7th ed. - Neurogenic Bladder (Ch. 10)