Which of these cranial nerves contains preganglionic parasympathetic fibers?

• A. Abducens nerve (CN VI)
• B. Oculomotor nerve (CN III)
• C. Optic nerve (CN II)
• D. Trochlear nerve (CN IV)

Answer: (B)

Verified step by step guidance

1. Understand the role of the parasympathetic nervous system, which is part of the autonomic nervous system responsible for 'rest and digest' functions.
2. Recognize that preganglionic parasympathetic fibers are those that originate in the central nervous system and synapse in a peripheral ganglion.
3. Identify the cranial nerves that are associated with parasympathetic functions. These are typically the oculomotor nerve (CN III), facial nerve (CN VII), glossopharyngeal nerve (CN IX), and vagus nerve (CN X).
4. Evaluate each option: The abducens nerve (CN VI) is primarily involved in eye movement and does not carry parasympathetic fibers. The optic nerve (CN II) is involved in vision and also does not carry parasympathetic fibers. The trochlear nerve (CN IV) is involved in eye movement and does not carry parasympathetic fibers.
5. Conclude that the oculomotor nerve (CN III) is the correct answer as it contains preganglionic parasympathetic fibers that innervate the ciliary ganglion, which controls the pupil constriction and lens shape for focusing.