Mictiereflex

Mictiereflex, or the micturition reflex, is the neural mechanism that coordinates the storage of urine in the bladder with its periodic expulsion through the urethra. It involves interactions between the bladder’s detrusor muscle, the urethral sphincters, peripheral nerves, the spinal cord, and higher brain centers, enabling voluntary control over voiding in mature individuals.

Physiology overview

When the bladder fills, stretch receptors in the bladder wall send afferent signals via the pelvic nerves to the sacral spinal cord (S2–S4). During storage, sympathetic pathways (hypogastric nerves, T11–L2) promote detrusor relaxation and internal sphincter contraction, while the somatic pudendal nerve maintains external sphincter tone to prevent leakage. As the bladder fills toward a threshold, afferent signaling can trigger the micturition reflex, leading to coordinated detrusor contraction and relaxation of both internal and external sphincters.

Central control

The reflex is modulated by a network that includes the pontine micturition center (Barrington’s nucleus) in the brainstem, the periaqueductal gray, and higher cortical and subcortical areas. In infants, micturition is predominantly a spinal reflex; in adults, conscious cortical input can inhibit or facilitate the reflex to allow voluntary delay or initiation of urination.

Clinical relevance

Dysfunction of the micturition reflex can result in urinary incontinence (e.g., detrusor overactivity) or urinary retention (e.g., detrusor underactivity). Neurogenic bladder, pelvic surgery, or spinal cord injury can disrupt normal reflex pathways. Diagnosis often involves urodynamic studies and clinical assessment to distinguish storage versus voiding problems and to guide treatment.