Petrosal Nerves

 1. The greater petrosal nerve 

• carries gustatory and parasympathetic fibres. 
• It arises from the geniculate ganglion of the facial nerve, and 
• enters the middle cranial fossa through the hiatus for the greater petrosal nerve on the anterior surface of the petrous temporal bone. 
• It proceeds towards the foramen lacerum,  where it joins the deep petrosal nerve which carries sympathetic fibres to form the nerve of the pterygoid canal
• The nerve of the pterygoid canal passes through the pterygoid canal to reach the pterygopalatine
• ganglion. 
• The parasympathetic fibres relay in this ganglion. 
• Postganglionic parasympathetic fibres arising in the ganglion ultimately supply the lacrimal gland 
• and the mucosal glands of the nose, palate and pharynx.
• The gustatory or taste fibres do not relay in the ganglion and are distributed to the palate.

2. The deep petrosal nerve, 

• sympathetic in nature, 
• is a branch of the sympathetic plexus around the internal carotid artery. 
• It contains postganglionic fibres from the superior cervical sympathetic ganglion. 
• The nerve joins the greater petrosal nerve to form the nerve of the pterygoid canal. 
• The sympathetic fibres in it are distributed through the branches of the pterygopalatine ganglion

3. The lesser petrosal nerve, 

• parasympathetic in nature,
• is a branch of the tympanic plexus, deriving its preganglionic parasympathetic fibres from the tympanic branch of the glossopharyngeal nerve. 
• It emerges through the hiatus for the lesser petrosal nerve, 
• situated just lateral to the hiatus for the greater petrosal nerve, 
• passes out of the skull through the foramen ovale, and ends in the otic ganglion 
• Postganglionic fibres arising in the ganglion supply the parotid gland through the auriculotemporal nerve

4. The external petrosal nerve, 

• sympathetic in nature is an inconstant branch from the sympathetic plexus around the middle meningeal artery to the geniculate ganglion of the facial nerve.