While the bladder is filling, what does sympathetic traffic in the hypogastric nerves do?

1. Continence during filling needs two things at once: a shut sphincter and a quiet detrusor. 2. Cholinergic neurons keep the external sphincter contracted, holding urine in. 3. Sympathetic activity carried by the hypogastric nerves suppresses detrusor contraction so the bladder stays relaxed as it fills. 4. Only with further stretch do sacral pelvic afferents recruit parasympathetic neurons. 5. Those parasympathetic efferents release acetylcholine at the neuromuscular junctions to contract the detrusor and empty the bladder. 6. Contracting the detrusor during filling would defeat storage, so that cannot be the sympathetic role. 7. Relaxing the external sphincter is a somatic event at voiding, not a sympathetic one during filling. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.2 Gross Anatomy of Urine Transport_