Which type of receptor do antispasmodics primarily block to reduce bladder activity?

Antispasmodics used to reduce bladder activity primarily block M3 receptors. These are a subtype of muscarinic acetylcholine receptors found in various tissues, including the bladder. When M3 receptors are activated by acetylcholine, they promote contraction of the detrusor muscle, which is responsible for bladder contractions during urination. By blocking these receptors, antispasmodics inhibit this overactivity, leading to a reduction in unwanted bladder contractions and providing relief from conditions such as overactive bladder.

Other receptor types mentioned in the options play different roles in the body. Alpha receptors are primarily involved in smooth muscle contraction and vasoconstriction, beta receptors are associated with relaxation of smooth muscle and can influence heart rate, while nicotinic receptors mediate neuromuscular junction transmission and autonomic ganglia responses. None of these receptor types directly regulate the bladder's detrusor muscle activity in the way that M3 receptors do, making the blockade of M3 receptors the most relevant in the context of managing bladder spasticity.