Cranial Nerves MCQs

The optic nerve is derived from nervous tissue, therefore ectoderm, but not neural crest. Optic sulci of the neural folds forming the forebrain send out the optic vesicles, which then develop into the optic cups connected to forebrain by the optic stalk. The optic stalk becomes the optic nerve. Reference - Textbook of Langman's, 12th Edition, Head and Neck Embryology Page number - 268

Formation of primordial germ cells Structures derived from neural crest are neurons of spinal posterior (dorsal) nerve root ganglia, neurons of sensory ganglia of the 5 to 10th cranial nerves, neurons and satellite cells of sympathetic ganglia etc. In the region where testes is to develop, the germinal epithelium gets thickened and is known as genital ridge. The cells of germinal epithelium proliferate and forms sex cords which gets converted into medullary cords and finally gets canalized to form seminiferous tubules Chorion is formed by the parital/ somatopleuric extraembryonic mesoderm (on the inside) and the overlying Trophoblast The cells of the ovaries and the testes, from which germ cells are formed, are believed to be segregated early in the life of the embryo.

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. Reference - Textbook of Langman's, 12th Edition, Head and Neck Embryology Page number - 268

Explanation: The glossopharyngeal nerve CN IX carries sensory fibres (taste, general sensation from posterior 1/3 tongue, pharynx, tonsil, middle ear), parasympathetic fibres to the parotid gland, and brachial motor fibres to stylopharyngeus. Hence, it contains GVA, GVE, GSA, SVA and SVE components. It does not carry general somatic efferent (GSE) fibres because it does not supply any skeletal muscle of somite origin.

The organ of Corti is a cellular layer sitting on top of the BM in which sensory hair cells are found. As previously mentioned, these sensory hair cells are activated by the potential difference between the perilymph and the endolymph. These hair cells are topped with hair-like structures called stereocilia. There is one single row of inner hair cells (IHC) and three rows of outer hair cells (OHC), separated by the tunnel of Corti.Sound waves cause vibrations, which bend the hair cell stereocilia via an electromechanical force, leading to electrical impulses. These electrical impulses travel to the brain via the vestibulocochlear nerve (CN VIII). Reference: Textbook of Gray's Anatomy, Volume 2, 3rd Edition, Page number - 958

The cranial nerves carrying parasympathetic fibers are listed below: Cranial nerve. Associated Ganglia Oculomotor (Ill) Ciliary ganglion Facial (VII). Pterygopalatine and submandibular ganglion Glossopharyngeal(IX) Otic ganglion Vagus (X) Visceral ganglions Reference: Textbook of Gray's Anatomy for students, 3rd Edition, Head and neck, Page number- 232

The abducens nerve arises from the abducens nucleus in the pons of the brainstem. It exits the brainstem at the junction of the pons and the medulla. It then enters the subarachnoid space and pierces the dura mater to travel in an area known as Dorello's canal. Reference: Textbook of Gray's Anatomy for students, 3rd Edition, Head and neck, Page number- 678

The acoustic stapedius reflex (ASR) is the sound-evoked contraction of the stapedius muscle. The ASR is mediated by a neural network, receiving its afferent input from the VIIIth cranial (auditory) nerve and sending its efferent output to the VIlth cranial (facial) nerve. Several centers in the brain stem comprise the central portion of the reflex pathway. The stapedius muscle in each ear responds to ipsilateral, contralateral, and binaural stimulation. Reference: Textbook of Gray's Anatomy, Volume 2, 3rd Edition, Page number - 878