Pharyngeal Arches, Skeletal & Muscular Systems MCQs

The long left recurrent laryngeal nerve is due to the persistence of the left 6th arch artery. During the development, the laryngeal nerves initially arise below the 6th arch artery and cross here to innervate the intrinsic muscles of the larynx. As the larynx moves cranially relative to the aortic arch arteries, the recurrent laryngeal nerves on the right and left sides are caught under the 6th arch arteries. Reference - Textbook of Langman's, 12th Edition, Central Nervous System Embryology Page number - 287

The pharyngeal arches have their own mesodermal core, giving rise to cartilaginous & muscular components, cranial nerve components, vascular components and derivatives of neural crest cells, which supplement much of the connective tissue of the face. Reference - Textbook of Langman's, 12th Edition, Head and Neck Embryology Page number - 268

The tympanic cavity is endodermal in origin, derived from the 1st pharyngeal pouch. The internal ear, including the cochlea, bony labyrinth and semicircular canals, are derived from the ectodermal otic placode. External auditory meatus, from 1st pharyngeal cleft, is also ectodermal. Reference - Textbook of Langman's, 12th Edition, Ear Embryology Page number - 321

Answer- A. Malignant hyperthermia Malignant hyperthermia is a pharmacogenetic condition caused due to mutation of the "Ryanodine receptor gene". Ryanodine receptor gene controls the level of "cytosolic calcium" and therefore skeletal muscle contraction.

The question describes a lateral cervical cyst that is draining by way of a branchial fistula. This forms due to a failure of the 2nd arch to grow caudally over the third and fourth arches, and causes the persistence of the opening of the 2nd branchial groove and the cervical sinus. Reference - Textbook of Langman's, 12th Edition, Head and Neck Embryology Page number - 268

The 3rd pharyngeal pouch gives rise to the inferior parathyroid glands and the thymus gland. The parafollicular cells are from the ultimobranchial body of the 5th pharyngeal pouch. Thyroid arises from the epithelium of the pharynx, via the thyroid diverticulum Reference - Textbook of Langman's, 12th Edition, Head and Neck Embryology Page number - 268

The auditory ossicles form from the mesenchyme of the 1st and 2nd pharyngeal arches. Malleus & incus come from the 1st arch, while stapes arises from the 2nd arch. Reference - Textbook of Langman's, 12th Edition, Head and Neck Embryology Page number - 268

Macro- and microstomia results from too little or too much fusion between maxillary and mandibular swellings. Oblique facial cleft represents failure of maxillary & lateral nasal process fusion. External ear develops from first pharyngeal cleft region dorsally. Cleft lip is usually between maxillary & medial nasal prominences. Reference - Textbook of Langman's, 12th Edition, Head and Neck Embryology Page number - 278