Structure and Origin - The greater petrosal nerve is a nerve of the head. - It contains pre-ganglionic parasympathetic fibers. - It branches from the facial nerve (CN VII). - It is derived from the parasympathetic part of the nervus intermedius component of CN VII. - Its cell bodies are located in the superior salivary nucleus. - Preganglionic parasympathetic fibers arise in the superior salivary nucleus. - They join with general somatic sensory and special sensory fibers to form the nervus intermedius. - The nervus intermedius exits the cranial cavity at the internal auditory meatus. - It joins with the motor root of the facial nerve at the geniculate ganglion. - Preganglionic parasympathetic fibers exit the geniculate ganglion as the greater petrosal nerve.

Gustatory Sensory Component - The greater petrosal nerve conveys gustatory (taste) sensory information from the palate. - This information is relayed to the pterygopalatine ganglion by the lesser palatine nerves. - The gustatory sensory fibers synapse in the geniculate ganglion. - The greater petrosal nerve carries these fibers to the ganglion. - The ganglion is involved in taste sensation.

Course - The greater petrosal nerve enters the petrous part of the temporal bone. - It travels anteromedially through the bone at a 45° angle. - It emerges into the middle cranial fossa through the hiatus for greater petrosal nerve. - The nerve is situated between the two layers of the dura mater in the middle cranial fossa. - It passes obliquely anterior-ward along a groove upon the floor of the fossa.

Clinical Significance - During surgery of the middle cranial fossa, manipulation of the dura mater may affect the greater petrosal nerve. - This can cause hemorrhaging or edema at the geniculate ganglion. - Compression of the facial nerve may result in transient facial paralysis. - The greater petrosal nerve is involved in autonomic innervation of the lacrimal gland. - The terminal parts of the pathway can vary between individuals.

Notable Points - The greater petrosal nerve is derived from the nervus intermedius component of CN VII. - Its cell bodies are located in the superior salivary nucleus. - The nervus intermedius exits the cranial cavity at the internal auditory meatus. - Preganglionic parasympathetic fibers exit the geniculate ganglion as the greater petrosal nerve.