The extraocular muscles are derived from which of the following structures?
A. Branchial arches B. Optic cup ectoderm C. Somites
D. Somitomeres
E. Splanchnic mesoderm
The correct answer is D. The somitomeres are specialized masses of mesoderm found in the head region that give rise to the muscles of the head. The extraocular muscles are derived from somitomeres 1, 2, 3, and 5.
The branchial arches (choice A) give rise to muscles of mastication (arch 1), muscles of facial expression (arch 2), and muscles of the pharynx and larynx (arches 3-6), as well as additional small muscles.
The optic cup ectoderm (choice B) gives rise to the muscles of the iris (sphincter and dilator pupillae). These are the only muscles not formed from mesoderm.
Somites (choice C) give rise to the inferior muscles of the neck.
Splanchnic mesoderm (choice E) gives rise to smooth muscle of the viscera and the heart muscle.
A CT scan reveals a small tumor at the cerebellopontine angle of the brain. Which of the following nerves is most likely to be affected by this tumor?
A. Facial nerve
B. Glossopharyngeal nerve C. Optic nerve
D. Trigeminal nerve E. Vagus nerve
The correct answer is A. The facial nerve and the vestibulocochlear nerves emerge from the brain stem at the cerebellopontine angle. These are the two nerves that will be initially affected by a tumor in this region. The entire anatomy of the facial nerve is as follows: the facial nerve originates from the taste receptors on the anterior 2/3 of the tongue (sensory) and from nuclei of the pons (motor). It passes through the internal acoustic canal of the temporal bone to reach the stylomastoid foramen.
The glossopharyngeal and vagus nerves (choices B and E) emerge from the brain stem at the postolivary sulcus. This is caudal to the cerebellopontine angle.
The optic nerve (choice C) exits from the optic chiasm on the ventral surface of the diencephalon. This is rostral to the cerebellopontine angle.
The trigeminal nerve (choice D) emerges from the brain stem at the anterolateral surface of the pons. This is rostral and ventral to the cerebellopontine angle.
A patient is unable to close her right eye. Physical examination reveals weakness of the right orbicularis oculi. Which of the following additional symptoms would likely also be present?
A. Blurred vision B. Hyperacusis C. Inability to chew D. Inability to feel the face E. Inability to shrug the shoulder
The correct answer B. The facial nerve innervates the muscles of facial expression. The
visceral motor portion innervates the lacrimal gland and nasal mucous glands via the
sphenopalatine ganglion. The submandibular and sublingual salivary glands are innervated via the submandiublar ganglion. This patient has a lesion of the facial nerve (VII), which leads to an inability to close the ipsilateral eye because of damaged motor fibers to the orbicularis oculi.
This patient would also lose her corneal reflex on that side because of an inability to blink and would have ipsilateral paralysis of the muscles of facial expression distal to the lesion. If the lesion affected the facial nerve more proximally, additional findings would be hyperacusis (increased sensitivity to sound because of stapedius muscle paralysis), lack of taste sensation in the anterior two-thirds of the tongue, and disturbed lacrimation and salivation.
Blurred vision (choice A) could occur with lesions of the oculomotor (CN III), abducens (CN VI), or trochlear (CN IV) nerves, which innervate the extraocular muscles. CN III innervates the medial rectus, inferior rectus, superior rectus, and inferior oblique muscles. CN VI innervates the lateral rectus and CN IV innervates the superior oblique.
An inability to chew (choice C) would probably be the result of a lesion of the trigeminal nerve (CN V). Motor fibers of CN V innervate the muscles of mastication (temporalis, masseter, and medial and lateral pterygoid muscles), and a lesion of these fibers may cause the jaw to deviate to the side of the weak muscles.
An inability to feel the face (choice D) would also be the result of a CN V lesion. This lesion could result in the ipsilateral loss of general sensation of the face and also of the mucous membranes of the oral and nasal cavities.
A lesion of the accessory nerve (CN XI) would cause paralysis of the trapezius muscle, which results in a sagging of the shoulder and a weakness in attempting to shrug the shoulder (choice E).
A patient received a severe blow to the lateral side of the head, resulting in an epidural hematoma. Which of the following blood vessels was most likely torn?
A. Anterior cerebral artery B. Middle cerebral artery C. Middle meningeal artery D. Superficial temporal artery E. Superior cerebral vein
The correct answer is C. The middle meningeal artery is in the interior of the lateral portion of the cranial cavity, embedded in the periosteal (outer) layer of the dura. A tear of this artery results in blood entering the potential space between the outer dural layer and the skull (epidural space), causing an epidural hematoma.
The anterior cerebral artery and middle cerebral artery (choices A and B) lie on the surface of the brain. The anterior cerebral arteries supply the medial surface of the cerebral hemispheres, and the middle cerebral arteries supply the lateral surface of the cerebral hemispheres. A tear of either of these arteries would result in blood entering the subarachnoid space (subarachnoid hemorrhage).
The superficial temporal artery (choice D) is a branch of the external carotid artery and is external to the skull. This artery supplies the skin and other tissue of the temple region.
The superior cerebral veins (choice E) drain the cerebral hemisphere and enter the superior sagittal sinus. A tear of these veins results in blood entering the potential space between the dura and arachnoid (subdural space), causing a subdural hematoma.
The x-ray of a child's arm after a fall appears to show a fracture near, but not at, the distal end of the ulna. Before diagnosing a fracture, you should also consider the possibility that this is
actually which of the following?
A. Articular cartilage B. Epiphyseal plate C. Perichondrium
D. Primary ossification center E. Secondary ossification center
The correct answer is B. The epiphyseal plate of the bone contains cartilage that is radiolucent.
The plate in a bone that is not yet fully ossified can produce a "line" crossing the bone near the end. This may be easily mistaken for a fracture by the inexperienced. Anatomically, the
epiphyseal plate separates the epiphysis from the diaphysis.
Articular cartilage (choice A) is radiolucent, but occurs at the very tip of the long bones.
Perichondrium (choice C) is usually difficult to see on x-ray.
Primary (choice D) and secondary (choice E) ossification centers are radiopaque.
Which of the following embryonic structures gives rise to the adrenal cortex?
A. Ectoderm B. Endoderm C. Mesoderm D. Mesonephros E. Neural crest cells
The correct answer is C. The mesoderm gives rise to the adrenal cortex. In addition, it also gives rise to connective tissue, cartilage, bone, muscle, blood and lymph vessels, kidneys, gonads, serous membranes lining body cavities, and the spleen.
The ectoderm (choice A) gives rise to the central nervous system, peripheral nervous system, epidermis and its appendages, mammary glands, pituitary gland, tooth enamel, and the neural crest.
The endoderm (choice B) gives rise to the parenchyma of the tonsils, thyroid and parathyroid glands, thymus, liver, pancreas, the epithelial lining of the gastrointestinal and respiratory tracts, urinary bladder, urethra, and auditory tube.
The mesonephros (choice D) functions as an interim kidney in the embryo.
The neural crest cells (choice E) give rise to cells of the spinal and cranial nerves, autonomic ganglia, melanocytes, leptomeninges, connective tissue and bone of branchial arch origin, and the adrenal medulla.
The major structural component of the sperm flagellum is the:
A. microtubule B. microfilament
C. actin filament D. mysosin filament E. ciliary body
The correct answer is choice A. This is a basic histological question of a type found commonly on NBDE, which asks about basic cellular organelles and structures. The sperm cell flagellum is notable for a “9+2” arrangement of fibers formed from microtubules. The 9 single fibers form a circular ring in cross section around the 2 doubled fibers in the center. One of the significant facts about the fibers is that they are composed of microtubules, made up of tubulin. The other significant fact is that all eucaryotic flagella and cilia have this same structure (for example, cilia form the tracheal lining). Note that procaryotic (bacterial) flagellea do NOT share this structure.
In cases of dysphagia where the esophagus is compressed, which structure would be most likely to cause the compression?
A. Left atrium B. Left ventricle C. Pulmonary
trunk
D. Right atrium E. Right ventricle
The correct answer is A. The left atrium forms most of the posterior wall of the heart. The esophagus passes immediately posterior to the heart. Enlargement of the left atrium may compress the esophagus and cause dysphagia. Anatomically, the esophagus begins posterior to the cricoid cartilage, at the level of vertebrum C6. From this point, it descends toward the thoracic cavity posterior to the trachea, passes inferiorly along the dorsal wall of the
mediastinum, and enters the abdominopelvic cavity through an opening in the diaphragm, the diaphragmatic hiatus.
The left ventricle (choice B) forms most of the left border of the heart and most of the diaphragmatic surface of the heart. The left ventricle is not related to the esophagus.
The pulmonary trunk (choice C) emerges from the right ventricle on the anterior surface of the
heart. The pulmonary trunk is not related to the esophagus.
The right atrium (choice D) forms the right border of the heart. It is not related to the esophagus.
The right ventricle (choice E) forms most of the anterior wall of the heart and a small portion of the diaphragmatic surface of the heart. It is not related to the esophagus.
Which of the following tissues normally has the highest percentage of mucus-secreting cells?
A. Esophageal mucosa B. Oral mucosa
C. Parotid gland D. Sublingual gland E. Submandibular gland
The correct answer is D. The sublingual salivary glands are located beneath the mucous membrane of the floor of the mouth. Numerous sublingual ducts open along either side of the lingual frenulum. Salivary glands can contain predominantly serous cells, predominantly mucous cells, or both in their acini. As you proceed from the midline laterally, acini in the sublingual gland are almost pure mucous cells, whereas acini in the submandibular gland (choice E) contain a mixture of serous and mucous cells. Acini in the parotid gland (choice C) are mostly pure serous cells.
The esophageal mucosa (choice A) and the oral mucosa (choice B) are squamous epithelia that do not form acini.
The primary arterial supply to the nasal mucosa is a direct branch of which of the following arteries?
A. Facial artery B. Maxillary artery
C. Superficial temporal artery
D. Superior labial artery E. Transverse facial artery
The correct answer is B. The major source of blood supply to the nasal mucosa is the
sphenopalatine artery, which is the terminal branch of the maxillary artery. The sphenopalatine artery enters the nasal cavity from the pterygopalatine fossa by passing through the
sphenopalatine foramen in the lateral wall of the nasal cavity.
The facial artery (choice A) is a direct branch of the external carotid artery. It provides most of the blood supply to the superficial face.
The superficial temporal artery (choice C) is a terminal branch of the external carotid artery. The other terminal branch is the maxillary artery. The superficial temporal artery provides blood supply to the temporal region and the lateral portion of the scalp.
The superior labial artery (choice D) is a branch of the facial artery. The superior labial artery provides blood supply to the upper lip. It has a septal branch that provides some of the blood supply to the anterior portion of the septal mucosa of the nasal cavity. However, this is not the major blood supply to the nasal cavity.
The transverse facial artery (choice E) is a branch of the superficial temporal artery. It provides blood supply to the parotid gland, the parotid duct, and the skin of the lateral face.
Which of the following cranial nerves carries the pain sensation from the tip of tongue?
A. V2 B. V3 C. VII D. IX E. X
The correct answer is B. This question is essentially asking "which of the following nerves innervates the tip of the tongue?" The innervation of the tongue is complex. The mandibular division of the trigeminal nerve (V3) carries general somatic sensation from the anterior
two-thirds of the tongue. The mandibular branch is also a sensory nerve for the lower gingiva, teeth, and lips, as well as the palate.
The maxillary division (V2, choice A) carries somatic sensation from the palate, upper gingiva, and upper lip, as well as the lower eyelid, cheek, nose, and a portion of the pharynx.
The facial nerve (VII, choice C) carries taste from the anterior two-thirds of the tongue, as well as innervating the lacrimal gland and the submandibular and sublingual salivary glands.
The glossopharyngeal nerve (IX, choice D) carries sensation and taste from the posterior one-third of the tongue.
The vagus nerve (X, choice E) carries sensation from the lower pharynx.
A mass is noted at the back of a young man's tongue. A biopsy's pathology report comes back with a diagnosis of normal thyroid tissue. This finding is related to the embryonic origin of the thyroid near which of the following structures?
A. First pharyngeal pouch B. Foramen cecum
C. Nasolacrimal duct D. Second pharyngeal arch E. Third pharyngeal
pouch
The correct answer is B. The thyroid gland originates as a mass of endodermal tissue near the foramen cecum, which is near the tuberculum impar (which becomes the central part of the tongue). During development, the thyroid descends in front of the pharynx, maintaining a connection to the tongue via the thyroglossal duct. Usually, the thyroglossal duct disappears.
Uncommonly, residual ectopic thyroid tissue can be left anywhere along the path, including at the back of the tongue. (In rare cases, all of the thyroid tissue remains at this site, forming a mass that should not be excised, for obvious reasons!) Anatomically, the thyroid gland curves across the anterior surface of the trachea just below the thyroid cartilage that forms the majority of the anterior surface of the larynx. The two lobes of the thyroid gland are united by a slender
connection, the isthmus.
The first pharyngeal pouch (choice A) develops into the middle ear and eustachian tube.
The nasolacrimal ducts (choice C) connect the eyes to the oropharynx.
The second pharyngeal arch (choice D) develops into many muscles of the face and the styloid process of the temporal bone.
The third pharyngeal pouch (choice E) develops into the thymus and inferior parathyroid glands.
If the nerve that accompanies the superior laryngeal artery is damaged, which of the following functional losses will ensue?
A. Loss of sensation in the laryngeal mucosa above the vocal folds B. Loss of sensation in the laryngeal mucosa below the vocal folds C. Loss of sensation in the pharyngeal mucosa
D. Paralysis of the cricothyroid muscle
E. Paralysis of the lateral cricoarytenoid muscle
The correct answer is A. The superior laryngeal artery is a branch of the superior thyroid artery. It enters the larynx by passing through the cricothyroid membrane. In this region, it is accompanied by the internal branch of the superior laryngeal nerve. This nerve provides sensory innervation to the laryngeal mucosa above the vocal folds.
The laryngeal mucosa below the vocal folds (choice B) receives its sensory innervation from the recurrent laryngeal nerve.
The pharyngeal mucosa (choice C) receives its sensory innervation from the glossopharyngeal nerve.
The cricothyroid muscle (choice D) receives its motor innervation from the external branch of the superior laryngeal nerve.
The lateral cricoarytenoid muscle (choice E) receives its motor innervation from the recurrent laryngeal nerve.
An atrial septal defect results from failure of the
A. ostium primum to form within the septum primum B. ostium secundum to form within the septum primum C. septum primum to fuse with the endocardial cushions D. septum primum to fuse with the septum secundum E. septum secundum to fuse with the endocardial cushions
The correct answer is C. The septum primum (first interatrial septum) develops by growing from the cranial end of the embryonic atrium toward the endocardial cushions. The gap that exists between the two atria during this period is the ostium primum. As the septum primum continues its growth, the ostium primum gets smaller until it is closed when the septum primum completes its growth and completely fuses with the endocardial cushions. Failure of the septum primum to fuse completely with the endocardial cushions leaves a persistent ostium primum, known as a primum-type atrial septal defect.
The ostium primum does not form within the septum primum (choice A). The ostium primum is the communication between the two atria that exists during the formation of the septum primum.
That is, the ostium primum is the space within the developing atrium not yet occupied by the septum primum.
The ostium secundum normally forms within the septum primum (choice B) before the ostium primum closes by fusion of the septum primum with the endocardial cushions. Failure of the ostium secundum to form would result in embryonic death because there would be no pathway for blood to pass from the right atrium to the left atrium when the ostium primum closes, thus depriving the embryo of oxygenated blood.
Most of the septum primum normally disappears. The part that remains forms the valve of the foramen ovale. This part of the septum primum normally does not fuse with the septum
secundum (choice D) during prenatal life. After birth, the valve of the foramen ovale is pushed against the septum secundum as a result of the increased pressure in the left atrium. This
achieves functional closure of the foramen ovale. Fusion does not normally occur at this time; it usually occurs later in life in most people. In some people, however, complete fusion never occurs (probe patency).
The septum secundum normally does not fuse with the endocardial cushions (choice E).
A CT scan of the head demonstrates a mass in the olfactory groove area. The axons likely compressed by this mass project to which of the following structures?
A. Insula
B. Nucleus ambiguus C. Postcentral gyrus D. Precentral gyrus E. Pyriform cortex
The correct answer is E. The olfactory nerves can be damaged by head injury, severe infection, and tumors (such as meningiomas) that may compress the olfactory bulbs. Unilateral damage is often not noticed by the patient, but bilateral damage (which surprisingly can also be missed if it develops slowly) may lead to occasional bizarre errors in odor identification. The olfactory nerves are technically the neurons on the mucosal side of the cribriform plate that send processes through the plate to synapse in the olfactory bulb, which in turn sends axons to the pyriform cortex (the primary olfactory cortex).
The insula (choice A) is thought to contain the primary gustatory (taste) cortex.
The nucleus ambiguus (choice B) provides the special visceral efferent fibers carried by the glossopharyngeal and vagus nerves.
The postcentral gyrus (choice C) contains the primary sensory cortex.
The precentral gyrus (choice D) contains the primary motor cortex.
A biopsy specimen demonstrates a ciliated columnar epithelium. From which of the following locations in the female genital tract was the biopsy obtained?
A. Cervix B. Endometrium C. Fallopian tube D. Ovary
E. Vagina
The correct answer is C.The fallopian tube is the only structure in the female genital tract with a ciliated columnar epithelium; the beating of the cilia helps move the egg into the uterus. This fact is also sometimes clinically helpful because dilated and deformed fallopian tubes can be microscopically distinguished from cystic ovarian tumors by the presence of the cilia. Each uterine tube is a hollow, muscular tube measuring approximately 13 cm in length. Each uterine tube is divided into three regions: the infundibulum, the ampulla, and the isthmus.
The correct answer is C.The fallopian tube is the only structure in the female genital tract with a ciliated columnar epithelium; the beating of the cilia helps move the egg into the uterus. This fact is also sometimes clinically helpful because dilated and deformed fallopian tubes can be microscopically distinguished from cystic ovarian tumors by the presence of the cilia. Each uterine tube is a hollow, muscular tube measuring approximately 13 cm in length. Each uterine tube is divided into three regions: the infundibulum, the ampulla, and the isthmus.