Seventh cranial nerve

The cell bodies of parasympathetic preganglionic neurons are located in the brainstem and the sacral spinal cord. Parasympathetic outflow is channeled from the brainstem (1) through the third cranial nerve (oculomotor n.) via the ciliary ganglion to the eye (2) through the seventh cranial nerve (facial n.) via the pterygopalatine and submaxillary... 

The seventh cranial nerve is responsible for eyelid closure during the blink reflex. Partial or complete disturbance of cranial nerve VII can interrupt these impulses, resulting in incomplete lid closure. Loss of muscular tone can also lead to ectropion, disruption of the lacrimal pump, and ultimately impaired tear drainage. 

In some cases the central nervous system may have been affected (109,130,131), and cranial nerve palsies have been reported (132). In a survey of ear deformities attributed to thalidomide (133) there were also 19 cases of seventh cranial nerve lesions and 18 cases of sixth nerve lesions (134). 

In fish, both taste and olfactory stimuli are waterborne. However, taste involves the seventh, ninth or tenth cranial nerves, in contrast to the first cranial nerve for smell. Elasmobranchs have their taste buds in the mouth and pharynx, but in bony fish they occur around the gills, on barbels and pectoral fins, and also scattered over the rest of the body surface. They crowd particularly in the roof of the mouth, forming the palatal organ. The taste receptor cells are arranged as a bundle to form a taste bud. Like other vertebrates, fish have receptors for sweet, sour, salty, and bitter. For instance, goldfish reject quinine-treated food pellets (Jobling, 1995). Many fish species are particularly sensitive to acidic taste characteristics. The responses of fish to amino acids will be discussed in Chapter 12. 

Neurosarcoidosis most frequently involves the cranial nerves (143,146). A peripheral seventh nerve palsy (Bell s Palsy) is the most common neurologic manifestation of sarcoidosis (29,146). It may be unilateral, bilateral, and frequently predates the diagnosis of sarcoidosis (146). Any other cranial nerve may be affected, and in many series the nerves supplying the extraocular muscles or optic nerves are not rarely involved (148-150). 

The parasynqtathetic system is also known as the craniosacral portion of the autonomic nervous system because of the sites of origin of the pre-ganglionic fibers. The cranial portion has ganglia associated with the third, seventh, ninth, and tenth cranial nerves. Spinal cord segments S2, S3, and S4 comprise the sacral portion. 

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