An otherwise healthy 58-year-old man comes to the physician because of a 1-year history of episodic coughing whenever he cleans his left ear. There is no history of hearing loss, tinnitus, or vertigo. Stimulating his left ear canal with a cotton swab triggers a bout of coughing. The physician informs him that these symptoms are caused by hypersensitivity of a cranial nerve. A peripheral lesion of this nerve is most likely to manifest with which of the following findings on physical examination?

Ipsilateral sensorineural hearing loss

Ipsilateral deviation of the tongue

Inability to raise ipsilateral eyebrow

Decreased secretion from ipsilateral sublingual gland

A 55-year-old woman with a 1-year history of left-sided tinnitus is diagnosed with a tumor at the left cerebellopontine angle affecting the glossopharyngeal nerve. Sialometry shows decreased production of saliva from the left parotid gland. The finding on sialometry is best explained by a lesion of the nerve that is also responsible for which of the following?

Afferent limb of the gag reflex

Afferent limb of the cough reflex

Taste sensation of tip of the tongue

A 50-year-old man presents to his primary care provider complaining of double vision and trouble seeing out of his right eye. His vision started worsening about 2 months ago and has slowly gotten worse. It is now severely affecting his quality of life. Past medical history is significant for poorly controlled hypertension and hyperlipidemia. He takes amlodipine, atorvastatin, and a baby aspirin every day. He smokes 2–3 cigarettes a day and drinks a glass of wine with dinner every night. Today, his blood pressure is 145/85 mm Hg, heart rate is 90/min, respiratory rate is 14/min, and temperature is 37.0°C (98.6°F). On physical exam, he appears pleasant and talkative. His heart has a regular rate and rhythm and his lungs are clear to auscultation bilaterally. Examination of the eyes reveals a dilated right pupil that is positioned inferolateral with ptosis. An angiogram of the head and neck is performed and he is referred to a neurologist. The angiogram reveals a 1 cm berry aneurysm at the junction of the posterior communicating artery and the posterior cerebral artery compressing the oculomotor nerve. Which of the following statements best describes the mechanism behind the oculomotor findings seen in this patient?

The unopposed superior oblique muscle rotates the eye downward.

The parasympathetic nerve fibers of this patient’s eye are activated.

The sympathetic nerve fibers of this patient’s eye are inhibited.

The unopposed inferior oblique muscle rotates the eye downward.

The unopposed medial rectus muscle rotates the eye in the lateral direction.

An 87-year-old male presents to his neurologist for a follow-up visit. He is being followed for an inoperable tumor near his skull. He reports that he recently noticed that food has started to lose its taste. He also notes increasing difficulty with swallowing. He has a history of myocardial infarction, diabetes mellitus, hyperlipidemia, hypertension, and presbycusis. He takes aspirin, metoprolol, metformin, glyburide, atorvastatin, lisinopril, and hydrochlorothiazide. On examination, the patient is a frail-appearing male sitting in a wheelchair. He is oriented to person, place, and time. Gag reflex is absent on the right side. A taste evaluation is performed which demonstrates a decreased ability to detect sour and bitter substances on the right posterior tongue. The nerve responsible for this patient’s loss of taste sensation also has which of the following functions?

Parasympathetic innervation to the parotid gland

Somatic sensory innervation to the roof of the pharynx

Parasympathetic innervation to the trachea

Somatic sensory innervation to the lower lip

Parasympathetic innervation to the submandibular gland

A 27-year-old man comes to the physician because of a 1-day history of right-sided facial weakness and sound intolerance. Three days ago, he hit the right side of his head in a motor vehicle collision. He neither lost consciousness nor sought medical attention. Physical examination shows drooping of the mouth on the right side. Sensation over the face is not impaired. Impedance audiometry shows an absence of the acoustic reflex in the right ear. Which of the following muscles is most likely paralyzed in this patient?

Anterior belly of the digastric

Parasympathetic cranial outflow for USMLE Step 3: High-Yield Anatomy Lessons

CN III Oculomotor - Pupillary Power

Origin: Edinger-Westphal nucleus (Accessory Oculomotor Nucleus) in the midbrain.
Pathway: Preganglionic parasympathetic fibers travel on the superficial aspect of CN III.
Synapse: Ciliary ganglion, located in the posterior orbit.
Innervation: Postganglionic fibers (short ciliary nerves) supply:
- Sphincter Pupillae: Constricts pupil (miosis) in response to light.
- Ciliary Muscle: Contracts for accommodation (focusing on near objects).

Oculomotor nerve parasympathetic pathway

⭐ Clinical Pearl: Compressive lesions (e.g., PComm aneurysm) often strike the superficial parasympathetic fibers first, causing a fixed, dilated pupil (“blown pupil”) before somatic motor deficits like eye deviation appear.

CN VII Facial - Gland Central

Function: Drives secretomotor activity for lacrimal, nasal, palatine, submandibular, and sublingual glands.
Mnemonic 📌: "Seven salivates and cries."

⭐ Crocodile Tear Syndrome: Post-Bell's palsy, aberrant nerve regeneration can cause gustatory lacrimation (crying while eating) as salivary fibers miswire to the lacrimal gland.

Facial Nerve (CN VII) Parasympathetic Cranial Outflow

CN IX Glossopharyngeal - Parotid Powerhouse

Nucleus: Inferior salivatory nucleus (medulla).
Ganglion: Otic ganglion.
Target: Parotid gland (serous saliva secretion).
Pathway: Traces a complex route from brainstem to gland.

Glossopharyngeal Nerve (CN IX) Parasympathetic Pathway

⭐ Frey's Syndrome: Post-parotidectomy, damaged parasympathetic fibers may aberrantly reinnervate sweat glands. Result: gustatory sweating (sweating while eating) instead of salivation.

CN X Vagus - The Wanderer's Reach

Origin: Dorsal motor nucleus of the vagus (medulla).
Ganglia: Synapses in microscopic intramural (terminal) ganglia on or within target organ walls.
Thoracic Innervation:
- Heart: ↓ heart rate (SA node) & conduction speed (AV node).
- Lungs: Promotes bronchoconstriction and ↑ mucus secretion.
Abdominal Innervation:
- Supplies GI tract from esophagus to the splenic flexure.
- ↑ peristalsis, ↑ gastric acid, ↑ digestive enzyme secretion.

Parasympathetic Innervation: Cranial Outflow & Organ Targets

⭐ Vagal nerve stimulation (VNS) is an established therapy for refractory epilepsy and treatment-resistant depression.

High‑Yield Points - ⚡ Biggest Takeaways

The vagus nerve (CN X) provides the dominant parasympathetic supply to thoracic and abdominal organs up to the splenic flexure.

CN III (Oculomotor) mediates pupillary constriction (miosis) and lens accommodation via the ciliary ganglion.

CN VII (Facial) stimulates secretion from the lacrimal, submandibular, and sublingual glands.

CN IX (Glossopharyngeal) innervates the parotid gland for salivation via the otic ganglion.

Preganglionic fibers are long, synapsing in ganglia located near or within the target organs.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play