Urology & Urogynecology > Education and Reference

There are two electrical pathways that operate as part of the MICTURITION REFLEX.

• The REFLEX LOOP is composed of peripheral nerves in the bladder and their connections to the spinal cord.
• The REGULATORY/SENSORY LOOP is composed of ascending sensory neurons in the spinal cord connected, through the motor cortex in the brain, to motor neurons in the regulatory (motor) tract of the spinal cord.

The most peripheral portion of the reflex loop is a network of PROPRIOCEPTIVE nerve endings. PROPRIOCEPTIVE nerve endings stretch during the STORAGE PHASE and send information to the cortex that is perceived as fullness, discomfort or pain.

In the healthy individual, NEUROSENSORY REGULATION of the micturition cycle follows a specific sequence.

1. The micturition cycle begins with an empty bladder. As the bladder fills, the proprioceptive nerve endings in the detrusor muscle send sensation of filling (stretch) through the reflex loop to the ascending/sensory pathway of the spinal cord.
2. As the sensation of filling increases, the motor cortex sends chemical messages down the motor pathway to inhibit the cholinergic receptors while stimulating the beta receptors in the bladder and the alpha receptors in the internal sphincter. During this time, recruitment messages are also sent to the external urethral sphincter via the descending pathway.
3. When the individual perceives the sensation of filling as a strong, persistent desire to void and makes the voluntary decision to void, the message to relax the external sphincter descends the motor pathway.
4. Following relaxation of the external sphincter, a chemical message is quickly sent down the motor pathway to stimulate the cholinergic receptors and inhibit the beta receptors in the bladder to initiate a detrusor contraction.
5. The onset of the detrusor contraction is followed by a message to inhibit the alpha receptors in the bladder neck and internal urethral sphincter and the urethra open for voiding.
6. When the bladder is empty, the bladder neck closes and the micturition cycle begins again.