Mechanism of Micturation

The passing of urine from the bladder is referred to as micturition or urination. Muscle contractions that are both voluntary and involuntary combine to cause urination. Pressure inside the bladder rises as 200–400 ml of pee accumulate, activating stretch receptors in the bladder wall. Nerve impulses are sent into the spinal cord through stretch receptors. Stretch receptor sensory nerve impulses travel to the spinal cord's micturition center, where they activate the micturition reflex. In this reflex, the internal sphincter relaxes and the bladder contracts as a result of motor impulses traveling from the spinal cord to the bladder's muscle cells via parasympathetic nerves. The brainstem and the cerebrum receive sensory impulses from the stretch receptors, and this causes awareness of the need to urinate. Even when the micturition reflex is present, the brain centers typically prevent micturition until the situation is right. The external urinary sphincter is then relaxed by the action of parasympathetic fibers, which are thus able to start micturition. Before exiting the body, urine leaves the bladder and travels through the urethra.

This sphincter contracts except during micturition to stop urine from dribbling continuously. It relaxes voluntarily while urinating.

Steps of Micturition:

• Sensory signals travel from the bladder to the spinal cord and then to the brain as the bladder fills with pee (200ml).
• Urge to urinate can be suppressed by the brain.
• The bladder contracts and the internal and external sphincters open in response to motor nerve impulses.
• Afferent impulses deliver signals to the brain once 400 cc of urine have gathered. The cerebrum of the brain is where the choice to urinate is made.
• Voiding reflexes start to work.