Question

Which cranial nerve is responsible for the motor innervation of pharyngeal muscles and parotid salivary glands?

Answer 1

In general, the pharyngeal muscles are innervated by the pharyngeal branch of the Vagus nerve (CN X). However, the stylopharyngeus muscle is innervated by the glossopharyngeal nerve (CN IX). This specific muscle is involved in swallowing and the CN IX provides the motor innervation for this muscle movement. The parotid salivary glands are also innervated by the glossopharyngeal nerve. It is not possible to separately test the functions of the vagus and glossopharyngeal nerve. This is because the vagus nerve is predominantly controlling the motor function of the larynx and pharynx.

Answer 2

Parasympathetic innervation to the salivary glands is carried via cranial nerves. The parotid gland receives its parasympathetic input from the glossopharyngeal nerve (CN IX) via the otic ganglion, while the submandibular and sublingual glands receive their parasympathetic input from the facial nerve (CN VII) via the submandibular ganglion. These nerves release acetylcholine and substance P, which activate the IP3 and DAG pathways respectively. Direct sympathetic innervation of the salivary glands takes place via preganglionic nerves in the thoracic segments T1-T3 which synapse in the superior cervical ganglion with postganglionic neurons that release norepinephrine, which is then received by β-adrenergic receptors on the acinar and ductal cells of the salivary glands, leading to an increase in cyclic adenosine monophosphate (cAMP) levels and the corresponding increase of saliva secretion. Note that in this regard both parasympathetic and sympathetic stimuli result in an increase in salivary gland secretions.