Question

Which of the following cranial nerves of man is both sensory and motor ? (a) Olfactory (b) Optic (c) Trigeminal (d) Oculomotor

Short answer

The cranial nerve that is both sensory and motor is the Trigeminal nerve (option c).

Step-by-step solution

Understanding the options

Each option represents one of the cranial nerves in humans. We need to understand the function of each to determine which one is both sensory and motor.

Analyzing option (a) Olfactory nerve

The olfactory nerve is responsible for the sense of smell and is a purely sensory nerve.

Analyzing option (b) Optic nerve

The optic nerve carries visual information from the retina to the brain and is a purely sensory nerve.

Analyzing option (c) Trigeminal nerve

The trigeminal nerve is responsible for sensation in the face and certain motor functions such as biting and chewing. Hence, it is both sensory and motor.

Analyzing option (d) Oculomotor nerve

The oculomotor nerve controls most of the eye's movements along with the constriction of the pupil and maintaining an open eyelid, which are primarily motor functions.

Selecting the correct option

Based on the analysis, option (c) Trigeminal nerve is identified as having both sensory and motor functions.

Key concepts

Sensory and Motor Nerves

Understanding the roles of sensory and motor nerves is fundamental to studying the human nervous system. Sensory nerves, also known as afferent nerves, are pathways that carry messages from the senses towards the central nervous system. They are responsible for conveying information such as touch, taste, sound, vision, and smell from various parts of the body to the brain. Examples include the olfactory nerve for smell and the optic nerve for vision.

Motor nerves, on the other hand, are known as efferent nerves. These nerves travel in the opposite direction, taking instructions from the brain to the muscles to initiate movement. This includes actions like walking, talking, and hand movements. The oculomotor nerve, which controls the movement of the eye muscles, is a prime example of a motor nerve. Most nerves in the body have both sensory and motor fibers, allowing for complex and coordinated functions.

Trigeminal Nerve

The trigeminal nerve, also known as the fifth cranial nerve, is one of the most complex nerves in the human body. It is unique because it possesses both sensory and motor functions. This dual role allows it to transmit sensory information from the face to the brain, such as tactile, thermal, and pain sensations. Additionally, it controls the motor functions related to mastication, which includes biting and chewing.

Furthermore, the trigeminal nerve has three major branches: the ophthalmic, maxillary, and mandibular nerves. Each branch serves a different area of the face. For instance, the ophthalmic branch innervates the scalp and forehead, the maxillary branch serves the cheek region, and the mandibular branch provides sensations to the lower jaw as well as motor functions. Understanding the trigeminal nerve's structure and functions is crucial for diagnosing and treating facial pain disorders such as trigeminal neuralgia.

Nerve Function Analysis

Nerve function analysis involves evaluating how well the sensory and motor components of a nerve are working. Neurologists and healthcare professionals conduct various tests to assess nerve function. For the cranial nerves, this can involve physical examinations that check for reflexes, muscle strength, response to stimuli, and sensory capabilities.

For example, testing the function of the trigeminal nerve would include checking the patient's facial sensation with light touch or pin-prick tests, as well as reflexes like the corneal reflex, which is an involuntary blinking response. Muscle tests to assess jaw movement could evaluate the motor functions. Disorders in nerve function can lead to conditions ranging from loss of sensation and weakness to paralysis. Therefore, it's crucial to assess nerve function through structured analysis and appropriate diagnostic tools.