Innervation of the Urinary Bladder and Mechanisms of Micturition

Introduction

The urinary bladder is a highly specialized organ responsible for the storage and controlled expulsion of urine. Its function is meticulously regulated by the nervous system through an intricate interplay of autonomic and somatic pathways.

Neural Control of the Urinary Bladder

Autonomic Regulation

The bladder is primarily innervated by the autonomic nervous system, consisting of sympathetic and parasympathetic components.

• Sympathetic Nervous System: Originates from the thoracolumbar region (T10-L2) and functions primarily in bladder relaxation and internal sphincter contraction via hypogastric nerves.
• Parasympathetic Nervous System: Arises from the sacral spinal cord (S2-S4) and promotes bladder contraction through the pelvic nerves.

Somatic Control

The somatic nervous system provides voluntary control over micturition, primarily through the pudendal nerve (S2-S4), which facilitates contraction of the external urethral sphincter.

Mechanisms of Micturition

Storage Phase

During bladder filling, afferent signals from stretch receptors communicate with the brainstem and higher centers to inhibit detrusor muscle contraction.

Voiding Reflex

When bladder volume exceeds a critical threshold, efferent parasympathetic activation stimulates detrusor muscle contraction while inhibiting sympathetic control, leading to urine expulsion.

Clinical Relevance

Disorders in bladder innervation can result in conditions such as neurogenic bladder, overactive bladder syndrome, and urinary incontinence.