Salivary gland innervation

Nature is economical in her means. She uses many of the same chemicals to accomplish her nervous purposes within the brain that she has already used to the same ends throughout the body. The good news is that once you have worked out the biochemistry and pharmacology of a neuromodulator in the body, you can apply a lot of what you know to its action in the brain. The bad news is that every time you target, for example, the acetylcholine system of the brain, you also hit the body. That means that the heart, the bowel, the salivary glands, and all the rest of the organs innervated by the autonomic nervous system are influenced. What is worse, the target sites within the brain may not only be as spatially dispersed as in the periphery, but may also be as functionally differentiated ... 

Most blood vessels, the sweat glands, and the spleen are innervated only by one division of the autonomic nervous system. In the salivary glands, the two divisions of the autonomic nervous system supplement one another. In the bladder, bronchi, gastrointestinal tract, heart, pupil, and sex organs, the two divisions of the autonomic nervous system have opposing effects (see Figure 14.5). 

The salivary glands are innervated by parasympathetic nerves. Increased activity of acetylcholine in this location would greatly increase the secretion of saliva in the mouth and would account for Jim s drooling. 

Muscarinic receptors play an essential role in regulating the functions of organs innervated by the autonomic nervous system to maintain homeostasis of the organi.sm. The action of ACh on muscarinic receptors con re.sull in. stimulation or inhibition of the organ system affected. ACh stimulates secretions from salivary and sweat glands, secretions and contraction of the gut. and constriction of the airways of the respiratory tract. It inhibits contraction of the heart and relaxes smooth muscle of blood vc.ssels. 

The influence of ACh and parasympathetic innervation on various organs and tissues is discussed in detail in Chapter 6. ACh and its analogs stimulate secretion by all glands that receive parasympathetic innervation, including the lacrimal, tracheobronchial, salivary, and digestive glands. The effects on the respiratory system, in addition to increased tracheobronchial secretion, include hronchoconstriction and stimulation of the chemoreceptors of the carotid and aortic bodies. When instilled into the eye, muscarinic agonists produce miosis (see Chapter 63). 

---