Which one is a type of mixed cranial nerve?

BSF Staff Nurse - 2021

Applied Anatomy

Easy

Appeared in: BSF Staff Nurse - 2021

Explanation

The Vagus nerve (CN X) is correctly identified as a mixed cranial nerve.
It is classified as mixed because it possesses multiple functional components: sensory (afferent), motor (efferent), and parasympathetic fibers.
Its sensory fibers transmit information from the pharynx, larynx, and thoracic/abdominal organs.
Its motor fibers control muscles in the palate, pharynx, and larynx, which are essential for swallowing and speech.
Its parasympathetic fibers regulate the function of the heart, lungs, and digestive tract, playing a key role in the autonomic nervous system.

Option B: The Olfactory nerve (CN I) is a purely sensory nerve, responsible only for the sense of smell.
Option C: The Abducent nerve (CN VI) is a purely motor nerve that innervates a single extrinsic eye muscle, the lateral rectus, which abducts the eye.
Option D: The Optic nerve (CN II) is a purely sensory nerve, responsible for transmitting visual information from the retina to the brain.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of cranial nerves based on function (sensory, motor, or mixed) as background academic context rather than a clinical decision trigger.
A key nursing responsibility is monitoring for vagal response. Procedures like suctioning or bearing down can stimulate the vagus nerve, causing bradycardia (slow heart rate). Nurses must be prepared to intervene if the patient becomes symptomatic.
Assessment of vagus nerve function (along with CN IX) includes checking the gag reflex and observing for dysphagia (difficulty swallowing) or dysphonia (hoarseness), which can indicate nerve damage and an increased risk of aspiration.
What if a post-operative thyroidectomy patient develops a hoarse voice? This could signal damage to the recurrent laryngeal nerve, a branch of the vagus nerve. The nurse's priority is to assess the patient's airway for any signs of obstruction and notify the surgeon immediately.

How to Approach the Question

First, identify the key term in the question: 'mixed cranial nerve'. This tells you the question is about classifying cranial nerves based on their function.
Recall the definition of a mixed nerve: one that has both sensory (afferent) and motor (efferent) functions.
Systematically evaluate each option against this definition.
Recall the primary function of the Vagus nerve (swallowing, speech, parasympathetic control), Olfactory nerve (smell), Abducent nerve (eye movement), and Optic nerve (vision).
Using this knowledge, identify that only the Vagus nerve has both sensory and motor roles among the choices.
A helpful mnemonic for nerve types is 'Some Say Marry Money But My Brother Says Big Brains Matter More' (S=Sensory, M=Motor, B=Both/Mixed), which can aid in quick recall during an exam.

Concept Tested & Keywords

Concept Tested: Classification of cranial nerves based on function (sensory, motor, or mixed).
Stem keywords: mixed cranial nerve
Lead-in keywords: Which one
Negative lead-in flag: false

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E6 Anatomy Grays 43e Vol 1 Part 3 p. 34-36

E6 Anatomy Applied Ashalatha 4e p. 431-433