ABSTRACT
This chapter deals with muscarinic receptors present on nerve terminals innervating smooth muscle structures. Two distinct smooth muscle layers can be distinguished within the gastrointestinal tract: an outer longitudinal and an inner circular smooth muscle layer. A great deal of work has been performed in longitudinal muscle preparations of the guinea pig ileum which have associated with them the myenteric plexus. Cholinergic nerves provide the dominant bronchoconstrictor control of airway smooth muscle. Bronchodilator pathways in airway smooth muscle, while somewhat species dependent, include the adrenergic and the inhibitory limb of the non-adrenergic non-cholinergic nervous system. Prejunctional inhibitory muscarinic receptors have been described on sympathetic nerves supplying a number of vascular smooth muscles. The smooth muscle of the bladder, the detrusor muscle, lies between the outer serosal coat and the inner mucous membrane. The detrusor muscle is composed of internal and external longitudinal muscle layers separated by a middle circular muscle layer.
