In a case of fracture of middle cranial fossa, lesion of which of the following structure result in absence of tears?
## **Core Concept**
The question tests knowledge of the innervation of the lacrimal gland and the nerves involved in tear production. The middle cranial fossa contains critical structures, including the nerves that control facial expressions and lacrimal gland function. The **greater petrosal nerve**, a branch of the **facial nerve (cranial nerve VII)**, carries parasympathetic fibers that stimulate tear production.
## **Why the Correct Answer is Right**
The correct answer, **greater petrosal nerve**, is involved in the parasympathetic innervation of the lacrimal gland. The greater petrosal nerve arises from the **geniculate ganglion** of the facial nerve and joins the **deep petrosal nerve** to form the **nerve of the pterygoid canal (Vidian nerve)**. It eventually synapses in the **pterygopalatine ganglion**, and postganglionic fibers stimulate the lacrimal gland to produce tears. Damage to this nerve can result in decreased tear production or absence of tears.
## **Why Each Wrong Option is Incorrect**
* **Option A:** The **mandibular division of the trigeminal nerve** primarily carries sensory and motor fibers to the face but is not directly involved in tear production.
* **Option B:** The **lesser petrosal nerve** carries preganglionic parasympathetic fibers from the glossopharyngeal nerve (cranial nerve IX) to the parotid gland, not the lacrimal gland.
* **Option D:** The **auriculotemporal nerve** carries sensory fibers and parasympathetic fibers to the parotid gland but is not directly involved in tear production.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **facial nerve (cranial nerve VII)** has a complex course and is responsible for both motor control of facial expressions and parasympathetic innervation of glands, including the lacrimal gland. Damage to the facial nerve or its branches in the middle cranial fossa can lead to **Frey's syndrome**, **Bell's palsy**, or decreased tear production.
## **Correct Answer:** . greater petrosal nerve