Number of pure motor nerves in the following: Trigeminal,Olfactory, trochlear, hypoglossal, glossopharyngeal,accessory, Optic, occulomotor

**Core Concept**
The question is testing the student's knowledge of the anatomy of the cranial nerves, specifically the classification of these nerves into pure motor and mixed nerves. The trigeminal, trochlear, and hypoglossal nerves are considered pure motor nerves as they primarily carry motor fibers, whereas the other nerves listed have a mix of sensory, motor, and parasympathetic fibers.

**Why the Correct Answer is Right**
The trochlear nerve (cranial nerve IV) is the thinnest and longest of the cranial nerves, and it is a pure motor nerve that innervates the superior oblique muscle of the eye. The hypoglossal nerve (cranial nerve XII) is also a pure motor nerve that innervates the muscles of the tongue, controlling its movements. The trochlear and hypoglossal nerves are the only two pure motor nerves among the options listed.

**Why Each Wrong Option is Incorrect**
**Option A:** The trigeminal nerve (cranial nerve V) is a mixed nerve with both sensory and motor fibers, including the motor fibers that innervate the muscles of mastication.
**Option B:** The olfactory nerve (cranial nerve I) is a sensory nerve that carries information from the olfactory receptors in the nasal cavity to the brain, and it is not a motor nerve.
**Option C:** The glossopharyngeal nerve (cranial nerve IX) is a mixed nerve with sensory fibers that transmit taste and touch from the pharynx and motor fibers that innervate the stylopharyngeus muscle.
**Option D:** The accessory nerve (cranial nerve XI) is a mixed nerve with sensory and motor fibers, including the motor fibers that innervate the sternocleidomastoid and trapezius muscles.
**Option E:** The optic nerve (cranial nerve II) is a sensory nerve that carries visual information from the retina to the brain, and it is not a motor nerve.
**Option F:** The oculomotor nerve (cranial nerve III) is a mixed nerve with sensory and motor fibers, including the motor fibers that innervate most of the eye muscles.

**Clinical Pearl / High-Yield Fact**
The trochlear nerve is unique in that it is the only cranial nerve that decussates before exiting the brainstem, which can lead to a condition called superior oblique palsy if it is injured.

**Correct Answer:** B.