A 10-month-old boy is brought to the clinic with a history of recurrent episodes of stridor and wheezing. His mother reports that his wheezing is exacerbated by crying, feeding, and flexion of the neck, and is relieved by extension of the neck. Occasionally he vomits after feeding. What is the most likely diagnosis?

Gastroesophageal reflux disease

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

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 61-year-old man sustains an intracranial injury to a nerve that also passes through the parotid gland. Which of the following is a possible consequence of this injury?

Paralysis of lateral rectus muscle

Loss of taste from posterior 1/3 of tongue

Loss of general sensation in anterior 2/3 of tongue

A 10-year-old boy comes for a post-operative clinic visit with his ENT surgeon three months after airway reconstruction surgery and placement of a tracheostomy tube. Since the surgery, he says that he has been able to breathe better and is now getting used to tracheostomy care and tracheostomy tube changes. In addition to this surgery, he has had over twenty surgeries to implant hearing aids, reconstruct his cheekbones, and support his jaw to enable him to swallow. He was born with these abnormalities and had difficult breathing, hearing, and eating throughout his childhood. Fortunately, he is now beginning to feel better and is able to attend public school where he is one of the best students in the class. Abnormal development of which of the following structures is most likely responsible for this patient's malformations?

Third and fourth branchial pouches

Second pharyngeal arch derivatives for USMLE Step 1: High-Yield Anatomy Lessons

The Hyoid Arch - Reichert's Cartilage

Second Pharyngeal Arch Derivatives

Cartilage: Reichert's cartilage
Nerve: Facial Nerve (CN VII)
Derivatives:
- Bones: Stapes (excluding the base), Styloid process, Lesser horn (cornu) & superior part of the body of the hyoid bone.
- Ligament: Stylohyoid ligament.
- Muscles: Muscles of facial expression, Stapedius, Stylohyoid, posterior belly of digastric, auricular muscles.

⭐ Clinical Pearl: The Stapedius muscle, innervated by CN VII, dampens ossicle vibration from loud noises. Facial nerve palsy can cause hyperacusis (sound sensitivity) due to stapedius paralysis.

📌 Mnemonic: "Seven S's" - Stapes, Styloid process, Stylohyoid ligament, Smaller horn of hyoid, Stapedius, Smile muscles (facial expression), innervated by cranial nerve Seven.

Skeletal Derivatives - Stapes, Styloid & Hyoid

Pharyngeal Arch Cartilage Derivatives

Originates from Reichert's cartilage, the cartilaginous bar of the second pharyngeal arch.
Gives rise to several "S" structures:
- Stapes (superstructure)
- Styloid process of the temporal bone
- Stylohyoid ligament
- Lesser horn (cornu) and superior part of the body of the hyoid bone

⭐ Reichert's cartilage forms the scaffold for these bones and ligaments. Its persistence or abnormal ossification can lead to clinical conditions like Eagle syndrome (pain from an elongated styloid process).

📌 Mnemonic: "S" structures from the Second arch.

Muscular Innervation - The Face-Making Nerve

Nerve: All muscles derived from the second pharyngeal arch are supplied by the Facial Nerve (CN VII).
Primary Function: Controls the muscles of facial expression, crucial for communication and displaying emotion.
- Occipitofrontalis
- Orbicularis oculi & oris
- Buccinator
- Platysma
Other Key Muscles:
- Stapedius: Dampens ossicles against loud noises.
- Stylohyoid: Elevates and retracts the hyoid bone.
- Posterior belly of the digastric: Aids in swallowing and depressing the mandible.

📌 Mnemonic: "Please Stop Smiling So Funnily" - Posterior belly of digastric, Stapedius, Stylohyoid, Muscles of Facial expression.

Facial nerve palsy affecting facial expression

⭐ High-Yield Fact: A lesion of the facial nerve proximal to the branch to the stapedius causes hyperacusis (sensitivity to sound). This is because the stapedius muscle can no longer contract to dampen the vibrations of the stapes, making it a critical localizing sign.

High‑Yield Points - ⚡ Biggest Takeaways

Nerve of the Arch: The Facial Nerve (CN VII) is the principal nerve, innervating all muscular derivatives.

Key Muscles: Includes all muscles of facial expression, the stapedius, stylohyoid, and the posterior belly of the digastric.

Skeletal Derivatives: Reichert's cartilage gives rise to the Stapes, Styloid process, Stylohyoid ligament, and the lesser horn (cornu) of the hyoid bone.

Mnemonic: Think "S" for the Second arch derivatives.

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