What is Micturition?
Micturition is the physiological process of urination, involving the coordinated storage and voluntary release of urine from the bladder through complex neural control mechanisms. 1
Physiological Definition
Micturition represents the complete cycle of bladder function, encompassing two distinct phases 2:
- Storage phase: Urine accumulates in the bladder with maintenance of continence
- Voiding/emptying phase: Voluntary release of urine through coordinated bladder contraction and sphincter relaxation
Neural Control Mechanisms
The micturition reflex involves a sophisticated multi-level neural circuit 1:
- Spinal reflex arc: In infants, bladder distention triggers automatic detrusor contraction and sphincter relaxation via spinal cord pathways 2
- Brainstem coordination: The pontine micturition center (PMC) orchestrates the voiding reflex when the periaqueductal gray (PAG) signals adequate bladder filling 3
- Voluntary cortical control: Prefrontal cortex and limbic system projections to the PAG enable conscious postponement of micturition until socially appropriate 3
Developmental Aspects
The acquisition of voluntary micturition control follows a predictable sequence 2:
- First 2 years: Voiding occurs reflexively without voluntary control
- Age 2 years: Sensation of bladder fullness develops
- Age 3 years: Voluntary sphincter control emerges
- Age 3-5 years: Ability to inhibit the micturition reflex is achieved, establishing full continence 1
The typical developmental sequence progresses from bowel control during sleep, followed by bladder and bowel control during wakefulness, and finally bladder control at night 2
Clinical Relevance
Understanding the micturition reflex is essential for recognizing pathological conditions 2:
- Abnormalities in voiding phase: Significant uroflow abnormalities indicate dysfunction in the voiding phase of the micturition cycle 2
- Red flag symptoms: New difficulties in micturition with preserved control (urgency, poor stream, hesitancy) may indicate serious neurological conditions like cauda equina syndrome 4
- Neurological injury: Diseases or injuries affecting the nervous system can cause re-emergence of involuntary reflex micturition, leading to incontinence 1
Common Clinical Pitfalls
When evaluating micturition disorders, avoid these errors:
- Dismissing bladder symptoms in sciatica: Any bladder dysfunction with sciatica requires urgent evaluation, as even subtle changes may indicate cauda equina syndrome 4
- Confusing obstruction with detrusor dysfunction: Poor urinary flow may result from either urethral obstruction or bladder underactivity—uroflowmetry alone cannot distinguish between these 2