What is the main motor nerve supply to the urinary bladder?

The Main Motor Nerve Supply to the Urinary Bladder

The main motor nerve supply to the urinary bladder is the pelvic nerve (option a).

Neuroanatomy of Bladder Innervation

• The pelvic nerve provides the primary parasympathetic innervation to the bladder detrusor muscle, which is responsible for bladder contraction during micturition 1
• The pelvic nerve originates from the inferior hypogastric plexus and forms a web-like complex within the endopelvic fascial sleeve, with multiple branches innervating the bladder detrusor 2
• Cholinergic neurons in the pelvic ganglion are the source of motor axons that innervate the lower urinary tract, with connections from spinal preganglionic neurons to pelvic ganglion neurons established early in development 1

Other Nerves Involved in Bladder Function

• The hypogastric nerve (option b) provides sympathetic innervation to the bladder, primarily causing relaxation of the detrusor muscle and contraction of the bladder neck during urine storage 3
• The pudendal nerve (option c) primarily innervates the external urethral sphincter rather than the bladder itself, controlling voluntary continence 4, 5
• The pudendal nerve traverses the pelvis in the pudendal canal and gives branches to the urinary sphincter, not the bladder detrusor 2
• The presacral nerve (option d) is not a primary motor nerve for bladder function 2

Functional Significance of Bladder Innervation

• Coordinated lower urinary tract function relies on both autonomic and somatic nerve activity 2
• The pelvic nerve supplies parasympathetic innervation that causes detrusor contraction during micturition 3
• Injury to detrusor branches of the pelvic nerve can cause detrusor denervation and urinary retention 2
• Diabetic cystopathy, which occurs in up to 80% of type 1 diabetic patients, is characterized by impaired detrusor contractions due to autonomic neuropathy affecting these parasympathetic pathways 6

Clinical Implications

• Urodynamic studies in patients with bladder dysfunction show detrusor overactivity as the most common finding (48%), followed by impaired detrusor contractility (30%) 6
• Damage to the pelvic nerve during radical pelvic surgery can result in urinary retention due to detrusor denervation 2
• In diabetic patients, changes in bladder function can be observed as early as within 1 year from diagnosis, with decreased acceleration of detrusor muscle contraction being an early sign of autonomic neuropathy 6
• Yearly post-void residual (PVR) measurement and urine dipstick testing should be performed in all patients with insulin-dependent diabetes to monitor for bladder dysfunction 6