Cranial nerves not carrying parasympathetic fibres?

SCTIMST Staff Nurse - 2016

Applied Physiology

Easy

Appeared in: SCTIMST Staff Nurse - 2016

Explanation

The Fourth cranial nerve, also known as the Trochlear nerve (CN IV), is a somatic efferent (motor) nerve.
Its only function is to provide motor innervation to the superior oblique muscle of the eyeball.
It does not have a visceral efferent component, meaning it lacks any parasympathetic fibers.

Option B: The Ninth cranial nerve (Glossopharyngeal) contains parasympathetic fibers. These fibers originate from the inferior salivatory nucleus and travel to the otic ganglion, from where they innervate the parotid gland to stimulate saliva production.
Option C: The Third cranial nerve (Oculomotor) has a significant parasympathetic component. These fibers originate from the Edinger-Westphal nucleus and are responsible for constricting the pupil (miosis) and accommodating the lens for near vision.
Option D: The Seventh cranial nerve (Facial) carries parasympathetic fibers that control secretions. These fibers innervate the lacrimal gland (for tears) and the submandibular and sublingual glands (for saliva).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Parasympathetic components of cranial nerves as background academic context rather than a clinical decision trigger.
Understanding which cranial nerves have parasympathetic functions is crucial for neurological assessment. For example, a fixed, dilated pupil can indicate compression of the Oculomotor nerve (CN III), a potential neurosurgical emergency.
Damage to the parasympathetic fibers of the Facial nerve (CN VII) can lead to a dry eye (xerophthalmia) and dry mouth (xerostomia), requiring nursing interventions like lubricating eye drops and oral care.
What if? If a patient presents with double vision (diplopia), especially when looking down and in, the nurse should suspect a lesion of the Trochlear nerve (CN IV). This is a purely motor deficit and would not be accompanied by pupillary changes, which would point to CN III instead.

How to Approach the Question

First, identify the core of the question: it asks to find the cranial nerve that LACKS parasympathetic fibers.
Recall the specific set of cranial nerves that DO have parasympathetic functions. A useful mnemonic is '1973', which stands for cranial nerves X (10), IX (9), VII (7), and III (3).
Systematically evaluate each option against this recalled set.
Option A (Fourth) is not in the set {III, VII, IX, X}.
Options B (Ninth), C (Third), and D (Seventh) are all in the set.
Therefore, the Fourth cranial nerve is the one that does not carry parasympathetic fibers.

Concept Tested & Keywords

Concept Tested: Parasympathetic components of cranial nerves
Stem keywords: Cranial nerves, parasympathetic fibres
Lead-in keywords: not carrying
Negative lead-in flag: Question asks which nerve does NOT have a specific feature.

Q8JIJFnXRz7TYUX-QG7tCK

E6 Physiology Essentials Sembulingam 10e Part 3 p. 32-34

E6 Anatomy Applied Ashalatha 4e p. 426-428

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