Lacrimal gland innervation

Q7 Intestinal cramps are produced by the intense stimulation of muscarinic receptors (mainly type M3) on intestinal smooth muscle, because of prolonged activity of released acetylcholine from postganglionic parasympathetic nerves. Intestinal motility and secretion are greatly stimulated while the sphincters are relaxed, leading to rapid transit of the gut contents and diarrhoea. Lacrimal glands are similarly stimulated by activation of tissues innervated by the parasympathetic nervous system, causing eyes to water profusely (lacrimation). 

Figure 9-1 Cholinergic innervation to the eye (iris sphincter muscle and ciliary body) and lacrimal gland. (C = populations of muscarinic receptor sites, N = nerve.)...

A number of CWAs exert their effects by modulating neuronal control over ocular function (Table 38.2). Autonomic neurons provide input to the intrinsic ocular muscles (the sphincter pupillae, the dilator pupillae, and the ciliary muscle) and e lacrimal glands. Neuronal afferents in the eye include sensory neurons from the conjunctiva and cornea, reflexive contributions to the iris, ciliary muscle, and eyelids, and the densely innervated retina. Finally, the extraocular muscles and eyelids are controlled by cholinergic motor neuron inputs. 

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). 

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