A and B secrete acetylcholine . Stimulation of A leads to bladder contraction via a postganglionic neuron and B stimulates skeletal muscle directly. Receptors on bladder are muscarinic . Receptors on sphincter are nicotinic. The IPSP develops on the cell body of the motor neuron to the sphincter.
Urination requires relaxation of the sphincter muscle.
Since this is skeletal muscle, the motor neuron innervating it releases only ACh, which stimulates muscle contraction. To relax the muscle, it's necessary to inhibit the neuron which is stimulating it. This overstimualtes the thyroid gland, leading to oversecretion of thyroid hormone. A. Acetylcholine is released from motor neurons, stimulates receptor on skeletal muscle, leading to muscle contraction. Normally, acetylcholinesterase breaks down ACh, to prevent continued stimulation of the muscle membrane, and the muscle relaxes.