Final answer:
Urination is controlled by the sacral micturition center, assisted by both the autonomic and somatic nervous systems, with the external urethral sphincter playing a key role in the voluntary release of urine.
Step-by-step explanation:
New research has shown that urination is actually controlled by the sacral micturition center which is a group of neurons in the sacral region of the spinal cord. The process of urination is managed by both the autonomic and somatic nervous systems. The autonomic system helps in the relaxation of the detrusor muscle as the bladder fills. However, when it's time to urinate, the somatic nervous system controls the external urethral sphincter muscle which must relax to allow urine to leave the body.
The pituitary gland also plays a role in urination by releasing hormones that aid the kidneys in filtering water from the blood, affecting urine production. On the other hand, the somatic nerves ensure the voluntary control over the sphincter at the distal end of the urethra. Voluntary micturition would need a functional spinal cord and pudendal nerve originating from the sacral micturition center to properly contract and maintain bladder continence during filling, and effectively empty the bladder when necessary.