What is the physiology of bladder function and what abnormalities lead to bladder dysfunction?

Updated: Jan 04, 2019
  • Author: Gregory T Carter, MD, MS; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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Answer

Control of bladder function involves the somatic efferent as well as autonomic sympathetic and parasympathetic systems. Bladder filling as well as emptying is organized by 3 centers along the central nervous system, which act through peripheral nerves on receptors in the neuromuscular junctions of the muscles in the bladder, bladder neck, urethra, diaphragm, abdomen, and pelvic floor.

The sympathetic nervous system regulates the process of urine storage in the bladder. In contrast, the parasympathetic nervous system controls bladder contractions and the passage of urine. The somatic efferent system permits voluntary control over the external periurethral sphincter.

Parasympathetic nerve impulses travel from S2-S4 ventral gray matter via the pelvic nerves to the ganglia near the bladder wall. Postganglionic nerve impulses then travel to the smooth muscle cholinergic receptors to produce bladder contraction. [7]

Sympathetic efferent nerve fibers originate from the lateral gray column of the spinal cord between T11 and L2. The sympathetic system has a long postganglionic chain that runs with the hypogastric nerve to synapse with alpha and beta receptors in the bladder wall and the bladder neck or internal sphincter. Beta receptors are responsible for mediating relaxation of the bladder with filling. Alpha receptors are responsible for tonically contracting the internal sphincter during bladder filling.

The somatic efferent nerve fibers originate from the pudendal nucleus of S2-S4 and supply the external periurethral sphincter. The external sphincter is under voluntary control and normally contracts in response to coughing or the Valsalva maneuver or when a person actively tries to prevent or halt urine flow.

Therefore, when the bladder retains urine, alpha1 receptors on the trigone, bladder neck, and urethra activate contraction, while beta-adrenergic receptors in the bladder body relax the detrusor muscle to permit filling. Somatic efferent fibers from the cerebral cortex permit voluntary contraction of the external sphincter to provide extra support. Alpha-adrenergic receptors in the trigone, bladder neck, and urethra stimulate relaxation, while the muscarinic receptors in the detrusor body stimulate contraction to facilitate bladder emptying.

Central control of micturition is performed by 3 areas: the sacral micturition center, the pontine micturition center, and the cerebral cortex. The sacral micturition center is located at the S2-S4 levels and is responsible for bladder contraction. The pontine micturition center acts as a central relay and may play a role in the coordination of external sphincter relaxation with bladder contraction. The cerebral cortex plays an inhibitory role in relation to the sacral micturition center.

See the image below.

Pons is major relay center between brain and bladd Pons is major relay center between brain and bladder. Mechanical process of urination is coordinated by pons in area known as pontine micturition center (PMC).

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