A 55-year-old man is brought to the emergency department by ambulance from a long term nursing facility complaining of severe shortness of breath. He suffers from amyotrophic lateral sclerosis and lives at the nursing home full time. He has had the disease for 2 years and it has been getting harder to breath over the last month. He is placed on a rebreather mask and responds to questions while gasping for air. He denies cough or any other upper respiratory symptoms and denies a history of cardiovascular or respiratory disease. The blood pressure is 132/70 mm Hg, the heart rate is 98/min, the respiratory rate is 40/min, and the temperature is 37.6°C (99.7°F). During the physical exam, he begs to be placed in a sitting position. After he is repositioned his breathing improves a great deal. On physical examination, his respiratory movements are shallow and labored with paradoxical inward movement of his abdomen during inspiration. Auscultation of the chest reveals a lack of breath sounds in the lower lung bilaterally. At present, which of the following muscles is most important for inspiration in the patient?

Muscles of anterior abdominal wall

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

An 85-year-old man who recently immigrated to the US from Spain presents to your office complaining of hoarseness and dysphagia for the past 2 months. He says his symptoms have been getting progressively worse, and he expresses concerns about the difficulty swallowing as he cannot eat well and has even lost 9 kg (20 lb) since his last visit 3 months ago. He denies any shortness of breath, coughing of blood, and chest pain. His bowel and bladder habit are normal. Past medical history is unremarkable. He has a 60-pack-year history of smoking tobacco and drinks alcohol occasionally. Which of the following is the most likely cause of his symptoms?

Malignant proliferation of squamous cells

Transformation leading to metaplasia in the lower esophagus

Malignant proliferation of glandular tissue in the esophagus

Reduced lower esophageal pressure

A professional musician visits his physician after a morning concert. He complains of painless swelling in his right cheek when he plays his tuba. Physical examination of the patient reveals slight facial asymmetry due to minor swelling on the right side of the face. The skin over the swelling is smooth without any secondary changes. Palpation reveals a soft and non-tender swelling. The oral opening is normal without any trismus. Further examination reveals swelling of the right buccal mucosa extending from the first to the third molar. Bedside ultrasound shows small areas of high echogenicity consistent with pneumoparotid. Which nerve is associated with motor function to prevent air from entering the affected duct in this patient?

CN VII – Marginal mandibular branch

A patient undergoes an MRI of the brain that reveals a tumor compressing the facial nerve at the internal acoustic meatus. Which of the following symptoms would most likely be present?

Facial muscle weakness and hyperacusis

Loss of taste in the posterior third of the tongue

Loss of taste in the anterior two-thirds of the tongue

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

Larynx and vocal apparatus for USMLE Step 1: High-Yield Anatomy Lessons

Laryngeal Skeleton - Framework of Voice

Larynx and associated neurovasculature

Framework composed of nine cartilages connected by membranes and ligaments, providing structure and enabling phonation.

Unpaired Cartilages (3)
- Thyroid: Largest, forms laryngeal prominence (Adam's apple).
- Cricoid: Complete ring, signet-shaped. Landmark for cricothyrotomy.
- Epiglottis: Elastic cartilage; covers laryngeal inlet during swallowing.
Paired Cartilages (3x2)
- Arytenoid: Pyramidal; anchors vocal ligaments.
- Corniculate: Sit atop arytenoids.
- Cuneiform: Within aryepiglottic folds.

⭐ The cricoid cartilage is the only complete cartilaginous ring in the airway. Its posterior lamina is broad, and the anterior arch is narrow, creating a signet ring shape. This integrity is vital for maintaining airway patency.

Laryngeal Muscles - The Larynx's Puppeteers

Intrinsic Muscles: Fine-tune vocal cord movement. All are innervated by the Recurrent Laryngeal Nerve (RLN) except the cricothyroid.
- Tensors:
  - Cricothyroid: Tenses cords (↑ pitch). Innervated by the Superior Laryngeal Nerve (external branch).
  - Thyroarytenoid (Vocalis): Relaxes cords (↓ pitch).
- Adductors (close cords):
  - Lateral Cricoarytenoid
  - Transverse Arytenoid
- Abductor (opens cords):
  - Posterior Cricoarytenoid

Superior view of intrinsic laryngeal muscles

⭐ The Posterior Cricoarytenoid (PCA) is the sole abductor of the vocal cords. Bilateral paralysis can cause acute airway obstruction, as it prevents breathing.

Innervation & Vasculature - Laryngeal Lifelines

Innervation (Vagus Nerve, CN X):
- Superior Laryngeal N. (SLN):
  - Internal branch: Sensory mucosa above vocal cords.
  - External branch: Motor to cricothyroid (tenses cords, ↑ pitch).
- Recurrent Laryngeal N. (RLN):
  - Motor to all other intrinsic muscles (phonation, respiration).
  - Sensory mucosa below vocal cords.
  - 📌 Mnemonic: Cricothyroid is the Chief Tensor, supplied by the eXternal branch of X (SLN).
Vasculature: Arteries travel with corresponding nerves.
- Superior Laryngeal Artery (from Sup. Thyroid a.)
- Inferior Laryngeal Artery (from Inf. Thyroid a.)

Laryngeal Nerves and Blood Supply

⭐ The left RLN has a longer course, looping under the aortic arch, making it more susceptible to injury from thoracic conditions (e.g., aortic aneurysm, lung cancer), causing hoarseness.

Clinical Correlates - When Things Go Wrong

Vocal Cord Paralysis:
- Cause: Injury to the Recurrent Laryngeal Nerve (RLN) is the most common cause.
- Etiology: Thyroid surgery, aortic arch pathology (left RLN), Pancoast tumor.
- Symptoms: Hoarseness, dysphonia, and risk of aspiration.
Laryngitis:
- Inflammation of the larynx, typically from viral infections or vocal overuse.
Laryngeal Carcinoma:
- Strongly associated with smoking and alcohol (synergistic effect).
- Presents with persistent hoarseness, dysphagia, and weight loss.
- Most common type is squamous cell carcinoma.

⭐ Ortner's Syndrome: Cardiovocal syndrome where a large left atrium or aortic arch aneurysm compresses the left recurrent laryngeal nerve, causing hoarseness.

Recurrent laryngeal nerve course and vulnerability points

High‑Yield Points - ⚡ Biggest Takeaways

The recurrent laryngeal nerve (RLN) innervates all intrinsic laryngeal muscles except the cricothyroid. Unilateral damage causes hoarseness.

The cricothyroid muscle, innervated by the external branch of the superior laryngeal nerve, tenses the vocal cords to control pitch.

The posterior cricoarytenoid (PCA) is the sole abductor of the vocal cords; bilateral paralysis can cause airway obstruction.

Internal branch of the superior laryngeal nerve provides sensation to the supraglottis; injury leads to aspiration risk.

Cricothyrotomy is performed through the cricothyroid membrane.

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