Final answer:
Micturition, or urination, is the process of emptying the bladder. It involves the coordination of involuntary and voluntary actions of the internal and external urethral sphincters. The micturition reflex is a spinal reflex that causes the bladder to contract and the sphincters to relax, allowing urine to flow out of the body.
Step-by-step explanation:
Micturition, also known as urination or voiding, is the process of emptying the bladder. It involves both involuntary and voluntary actions of the internal and external urethral sphincters. When the bladder becomes full, stretch receptors in the bladder wall send nerve impulses to the spinal cord, triggering the micturition reflex.
The micturition reflex is a spinal reflex that causes the detrusor muscle of the bladder to contract and the internal urethral sphincter to relax. At the same time, the external urethral sphincter, which is under voluntary control, relaxes. This coordinated relaxation of the sphincters and contraction of the bladder allows urine to flow out of the body.
During early childhood, children learn to override the micturition reflex through external sphincter control, delaying voiding. However, in some cases, such as spinal cord injuries, the reflex may be preserved but voluntary control may not be possible, leading to the need for periodic catheterization to empty the bladder.