EMBRYOLOGY OF THE NERVOUS SYSTEM PART II. D. Regional Development of the Brain E. Peripheral Nervous System Development F. Congenital Malformations 1. During the 5th week of development the prosencephalon (forebrain) forms the telencephalon diencephalon rhombencephalon A and B B and C Very good! No, the answer is D. The secondary vesicles formed from the forebrain are the telencephalon (precursor of the cerebral hemispheres) and the diencephalon (which forms the adult epithalamus, hypothalamus, and thalamus). 2. The rhombencephalon (hindbrain) forms which of the following secondary brain vesicles during the 5th week of development diencephalon mesencephalon metencephalon myelencephalon C and D Right. No, the answer is E. The rhombencephalon forms 2 secondary vesicles, the myelencephalon and the metencephalon. 3. The pontine flexure separates the developing _____ from _____ myelencephalon, metencephalon telencephalon, diencephalon mesencephalon, metencephalon spinal cord, myelencephalon none of the above Very good. No, the answer is A. The myelencephalon and metencephalon are separated by the pontine flexure. This flexure is formed by diffe- rential growth in the rhombencephalon. The formation of the pontine flexure results in a thinning of the rhomb- encephalic roof. The midbrain flexure occurs on the ventral surface of the mesencephalon while the cervical flexure separates the hindbrain from the spinal cord. 4. The caudal myelencephalon is termed the "closed portion" of the myelencephalon and resembles the spinal cord. Alar plate derived neuroblasts in this region form the nucleus gracilis nucleus cuneatus nucleus of Darkschewitsch A and B A, B and C Very good. No, the answer is D. The medially located gracile nucleus and laterally positioned cuneate nucleus form from alar plate derived neuroblasts in the "closed", caudal portion of the neural tube. These nuclei receive 1st order neurons carrying discriminative touch and vibratory sensory information from the spinal (dorsal root) ganglia. These 1st order fibers form the fasciculi gracilis and cuneatus. 2nd order neurons from the nuclei cuneatus and gracilis travel upward in the brainstem as the internal arcuate fibers, eventually forming the medial lemniscus. The nucleus of Darkschewitsch is located in the mesencephalic reticular formation. The "open" portion of the myelencephalon surrounds the developing 4th ventricle The alar plates are located lateral to the basal plates because of movement of the medullary walls. Neuroblasts in the alar and basal plates form specific cell columns which may be followed through the "open" portion of the myelencephalon, the metencephalon, and mesencephalon. Abbreviations used in this segment of CAI General somatic efferent = GSE (efferent fibers to the musculature Special (branchial) visceral efferent = SVE (efferents to branchial arch derived muscles) general visceral efferent = GVE (parasympathetics) general visceral afferent = GVA (visceral afferents) special visceral afferent = SVA (taste and olfactory fibers) general somatic afferent = GSA (from the surface of the head through the trigeminal(V) nerve). special somatic afferent = SSA (impulses from the eye and ear) 5. Within the basal plates the organization of cell columns from medial to lateral are GSE, GVE, SVE GVE, GSE, SVE GVA, SVA, SSA, GVA SVA, GVA, GSE none of the above Very good. No, the answer is E. The order of basal plate derived cell columns from medial to lateral are GSE, SVE and GVE. 6. The alar plate derived cell columns are arranged as follows (medial to lateral) SSA, GSA, SVA, GVA SVA, GSA, SSA, GVA GVE, SVE, GSE GVA, SVA, GSA, SSA none of the above Very good. No, the answer is D. The arrangement of cell columns derived from the alar plates is GVA,SVA, GSA, and SSA moving from medial to lateral position. 7. In the rostral myelencephalon GSE fibers are associated with which of the following cranial nerves hypoglossal n. abducens n. oculomotor n. vagus n. A and C Right. No, the answer is A. The XIIth cranial (hypoglossal) nerve innervating the somatic skeletal musculature of the tongue is the GSE representative in the "open" myelencephalon. 8. Special visceral efferent fibers innervate branchial arch derived muscles exit from the nucleus ambiguus are associated with cranial nerves V, VII, IX, X. and XI A and C A, B and C Very good. No, the answer is E. The nucleus ambiguus provides efferent fibers to the muscles derived from the branchial arches. The trigeminal (V), facial (VII),glossopharyngeal (IX), vagus (X), and spinal portion of the spinal accessory (XI) nerve carry SVE fibers. 9. GVE fibers in the rostral myelencephalon are associated with the ______ cranial nerve(s) in the metencephalon. IX II X III A and C Right. No, the answer is E. GVE fibers in the "open" portion of the myelencephalon are associated with the glossopharyngeal (IX) and vagus (X) cranial nerves. 10. The SVA cell column is associated with cranial nerves VII, IX and X contributes fibers to the fasciculus solitarius which terminates in the nucleus solitarius contains taste fibers from different regions of the tongue and palate A and C A, B and C Right! No, the answer is E. Special visceral afferent fibers are associated with the sensation of taste. GSA fibers from the tongue and palate travel in cranial nerves VII, IX and X to reach the nucleus solitarius. 11. The alar plates form the _____ nucleus (nuclei) in the rostral myelencephalon olivary nuclei a portion of the pontine nuclei dentate nucleus A and B A, B and C Right. No, the answer is D. The neuroblasts of the alar plates contribute to the inferior olivary nucleus complex contribute to the olivocerebellar fiber system traversing the in ferior cerebellar peduncle (restiform body). The superior olivary nuclei are associated with cochlear reflexes and reside in the pons of the adult brain. The dentate nucleus is derived from neuroblasts in the metencephalic alar plate. 12. The general visceral efferent column in the myelencephalon and metencephalon is associated with salivatory nuclei nucleus ambiguus fasciculi gracilis and cuneatus A and B A and C Right. No, the answer is A. The inferior and superior salivatory nuclei in the medulla and pons respec tively send parasympathetic (GVE) fibers to the salivary glands. The inferior salivatory nucleus sends GVE fibers to the parotid gland by cranial nerve IX while the superior salivatory nucleus sends GVE fibers to the submandibular and sublingual salivary glands. The nucleus ambiguus is associated with SVE fibers to branchial arch derived muscles. The fasciculi cuneatus and gracilis transmit sensory tactile information to the nuclei of the same name which derived from the alar plates. 13. Which of the following adult structure (s) form (s) from the metencephalon cerebellum superior colliculus pons medulla oblongata A and C Very good. No, the answer is E. The cerebellum and pons form from the metencephalon. 14. Alar plate derivatives in the metencephalon include dentate nucleus portions of the pontine nuclei cochlear and vestibular nuclei sensory nuclei of the trigeminal (V cranial) nerve all of the above Right. No, the answer is E. The cerebellum including cerebellar cortex develops from the rhombic lips (dorsal thickenings of the alar plates) in the metencephalon. In addition, all of the nuclei listed above (a-d) are metencephalic alar plate derivatives. 15. General somatic efferent fibers in the metencephalon are associated with the facial nerve glossopharyngeal nerve abducens nerve optic nerve A and C Very good. No, the answer is C. GSE fibers are associated with the abducens (VI) cranial nerve in the metencephalon. 16. The cerebellum in the adult human may be divided into different lobes based on its phylogenetic development. The newest portion phylogenetically concerned with selective regulation of limb movement is vermis anterior lobe posterior lobe flocculonodular lobe Right. No, the answer is C. The posterior lobe or neocerebellum is the newest phylogenetic lobe concerned with fine tuning of limb movement. The flocculonodular lobe (archicerebellum) is the oldest part with connections to the vestibular apparatus. The paleocerebellum (anterior lobe and vermis) is associated with afferent data from the limbs. 17. In cerebellar histogenesis the internal granular layer is formed by migration of neuroblasts to the superficial part of the cerebellar rudiment the external granular layer is the source for basket, granule, and glial cells in the cerebellar cortex the internal granular layer is the source for basket, granule, and glial cells in the cerebellar cortex differentiation of the cerebellar cortex continues after birth A, B and D Right. No, the answer is E. The internal granular layer forms from neuroblasts derived from neuroepithelial cells lining the ventricular cavity which migrate to the deeper part of the cells lining the ventricular cavity which migrate to the deeper part of the marginal zone. The internal granular layer will form the definitive granular cerebellar cortex. The external granular layer is a fetal structure which is an actively proliferatig zone. The new cells formed in this layer migrate inwards to the internal granular layer where they develop into granular basket and glial cells. Cerebellar differentiation including the formation of basket and glial cells takes place after birth. 18. Which of the following is (are) true of the mesencephalon? the superior and inferior colliculi and the mesencephalic nucleus are basal plate derivatives. the GVE column is associated with cranial nerves III (oculomotor) and IV (trochlear) GSE column is associated with the Edinger-Westphal nucleus A and B none of the above Right. No, the answer is E. In the mesencephalon, the inferior and superior colliculi (which are associated with auditory and visual reflexes respectively) are derived from alar plates. The GVE column includes parasympathetic fibers in the Edinger-Westphal nucleus associated with the III (oculomotor) cranial nerve. These fibers pass to the ciliary ganglion and are involved in the pupillary light reflex. The oculomotor (III) and trochlear (IV) cranial nerves send GSE fibers to the extraocular eye muscles. The IV cranial nerve specifically innervates the superior oblique muscle. 19. The diencephalon is the precursor of the thalamus epithalamus hypothalamus cerebral hemispheres A, B and C Very good. No, the answer is E. The thalamus, epithalamus, and hypothalamus develop from the diencephalon. 20. The pineal gland is formed from Rathke's pouch an outgrowth of the diencephalon Rathke's pouch and a downgrowth from the diencephalon mesencephalic basal plate A and B Very good. No, the answer is B. The pineal gland (epiphysis) forms from a midline diverticulum of the diencephalic roof. 21. The pituitary gland develops from an oral ectodermal outpocketing (Rathke's pouch) a neural ectodermal downgrowth from the diencephalon mesencephalic alar plate A and B A, B and C Very good. No, the answer is D. The pituitary gland consists of 2 ectodermally derived parts adenohypophysis and neurohypophysis. The adenohypophysis originates from oral ectoderm (Rathke's pouch) while the neurohypophysis forms as a downgrowth of the diencephalon. 22. As the cerebral hemispheres develop from the telencephalon the thicker basal portions of each hemisphere form the corpus striatum the thinner portion superior to the striatum forms the pallium the caudate and lentiform nuclei are formed from the corpus striatum by the projection and expansion of internal capsule fibers to the cortex A and B only A, B and C Very good. No, the answer is E. As each cerebral hemisphere develops it forms a thicker, basal or striated portion which will form the corpus striatum and a thin-walled supra-striatal portion, the pallium which is the primordium of the cerebral cortex. The corpus striatum is divided into a dorsomedial portion which forms the caudate nucleus and a ventrolateral portion which develops into the lentiform nucleus. This division occurs by the projection and expansion of afferent and efferent axons passing to and from the cortex through the internal capsule. 23. The lamina terminalis is an important connection between the cerebral hemispheres and forms the anterior commissure hippocampal commissure corpus callosum optic chiasma A, B and C only Right. No, the answer is E. As the cerebral cortex develops the commissures connect corresponding areas between right and left hemispheres. The anterior commissure connects olfactory areas while the hippocampal commissure connects the hippocampal areas of the 2 cerebral hemispheres. The largest commissure is the corpus callosum connecting neocortical areas while the optic chiasma represents crossing optic tracts. A,B and C develop in the lamina terminalis, however, extension beyond the lamina terminalis occurs, especially in regard to the corpus callosum. 24. Which of the following is true of cerebral cortex histogenesis migration of newly formed neuroblasts occurs from the internal granular layer successive waves of neuroblast differentiation and migration form the cortical layers the newest ontogenically-formed cells occupy the most superficial regions of the cortex B and C A and C Right! No, the answer is D. Migration of cells from the internal granular layer is involved in cerebellar cortex development. Successive waves of development and migration form the cerebral cortex. The most recently (ontogenically) formed cells migrate through previously formed layers to reach the most superficial position. 25. The sensory portions of both somatic and visceral peripheral nerves are derived from neuroepithelium neural crest ventricular zone of neural tube A and B none of the above Right. No, the answer is B. All sensory cells in the peripheral nervous system are derived from neural crest and are located outside the CNS. 26. Motor nerve fibers in the spinal nerves arise from the alar plates form the ventral nerve roots are myelinated by oligodendrocytes A and B none of the above Right. No, the answer is B. Motor nerve fibers arise from the basal plates of the spinal cord and form the ventral nerve roots. Fibers are myelinated by Schwann cells in the periphery. Oligodendrocytes are involved in myelination only in the CNS. 27. Which of the following is (are) true of the sympathetic nervous system ? sympathetic fibers originate only in the cervicothoracic region of the spinal cord postganglionic sympathetic fibers are derived from neural crest sympathetic chain ganglia are derived from neural crest all of the above B and C only Right. No, the answer is D. Sympathetic nervous system forms the thoracolumbar outflow of the spinal cord. Preganglionic fibers exit the intermediolateral cell column in the thoracolumbar region and synapse with neural crest-derived sympathetic ganglia. After synapses occur,postganglionic sympathetic neural crest-derived fibers pass into the spinal nerves. 28. The parasympathetic nervous system constitutes the craniosacral outflow of the CNS includes fibers in cranial nerves III (oculomotor), VII (facial) ,IX (glossopharyngeal), and X (vagus) parasympathetic ganglia may arise with preganglionic fibers of appropriate cranial nerves containing GVE fibers or from neural crest A and C A, B and C Very good. No, the answer is E. The origin of parasympathetic ganglia is still debated and may either migrate out of the CNS along with preganglionic fibers of the oculomotor (III), facial (VII), glossopharyngeal (IX) and vagus (X) cranial nerves. The GVE fibers constitute the craniosacral outflow of the CNS. 29. The III (oculomotor), IV (trochlear) and VI (abducens) cranial nerves carry SVE fibers to the branchial arch-derived muscles are located in the somatic efferent column distribute axons to extraocular eye muscles A and B B and C Right. No, the answer is E. Cranial nerves III, IV, and VI carry general somatic efferent fibers to the extraocular eye muscles. These muscles are derived from the head myotomes (preotic and occipital) not from the branchial arches. Branchial arch derived muscles are innervated by SVE fibers. 30. The hypoglossal (XII) cranial nerve carries SVE fibers carries GVE fibers carries GSE fibers innervates the muscles of the tongue derived from occipital myotomes C and D Right. No, the answer is E. The hypoglossal nerve carries GSE fibers to the muscles of the tongue. 31. Cranial nerves associated with the branchial arches include V VI IX X A, C and D Right No, the answer is E. SVE fibers are associated with the mandibular division of V, and with nerves IX and X. These fibers innervate branchial arch-derived muscle. 32. The bony spinal column is usually closed by the _____ week of intrauterine life 6th 8th 10th 12th Right. No, the answer is D. Closure usually occurs about the 12th week (first trimester). 33. Incomplete closure of the bony vertebral arch usually occurs in the _______ region of the spine. cervical thoracic lumbosacral Right. No, the answer is C. The simple failure of closure of one or more vertebral arch in the lumbosacral region is a common finding on routine X-rays. 34. The bony defect in the lumbar or sacral spine is called Spina Bifida Occulta due to failure of closure of the _____ altered vertebra. pedicles articulating processes laminae vertebral bodies Right. No, the answer is C. The laminae fail to close to complete the vertebral arch. Sometimes this defect can be palpated. Hypertrichosis, fat deposits and skin vascular changes can occur over the defect. 35. Herniation of the meninges through the bony vertebral defect (usually lumbosacral) may appear as a soft,cystic midline tumor in the lower back. This is called spina bifida occulta cranium bifidum meningocoele syringomyelia Right. No, the answer is C. The herniation of tissue through the vertebral defect is called spina bifida cystica. When the meninges herniate into the cyst the condition is referred to as spina bifida cystica-meningocoele or just meningocoele. 36. In a meningomyelocele the nerve roots and spinal cord usually adhere to the wall of the meningeal sac enter and leave the sac, intact never grow into the meningeal sac none of the above Very good. No, the answer is A. The cord and nerve roots usually adhere, but occasionally are incorporated into the inner wall of the bulging meningeal sac. This results in severe neurological deficit, particularly loss of bowel and bladder control as well as paraplegia. Meningomyelocoele may be associated with herniation of the medulla and cerebellum into the foramen magnum (Arnold Chiari Syndrome). 37. The most severe type of spina bifida is occulta meningocoele meningomyelocoele myeloschisis Right. No, the answer is D. In spina bifida cystica myeloschisis the neural plate is open because the neural folds failed to meet and fuse. 38. The formation of defects in the skull similar to those found in the spina bifida (at the vertebral level) are known as occipitalocoele crania bifida cranialocoele none of the above Very good. No, the answer is B. Defects in the formation of the cranium are known as crania bifida. The defect often occurs in the occipital bone and includes the same sub-types as spina bifida. When the defect is small the meninges may herniate forming a meningocoele. A larger defect including a portion of brain tissue is known as a meningoencephalocele. If a portion of the ventricular system of the brain is included then the term meningohydroencephalocele is used. Crania bifida occurs once in every 2,000 births. 39. Anencephaly occurs as an uncommon malformation may be eliminated as a diagnosis when elevated alpha fetoprotein levels occur in the amniotic fluid may be related to genetic factors but follows a multifactorial pattern of inheritance A and B B and C Right. No, the answer is C. Anencephaly is a common malformation (1/1000 births). It is related to genetic factors, but follows a multifactorial pattern of inheritance. Alpha fetoprotein levels are elevated in the amniotic fluid when anencephaly and/or severe neural tube defects occur. 40. Congenital hydrocephalus is enlargement of the head associated with accumulation of blood cerebrospinal fluid (CSF) tumor tissue none of the above Right. No, the answer is B. Hydrocephalus is the accumulation of CSF, usually within the ventricles of the brain. 41. The most important method for detecting hydrocephalus is percussion of the head illumination of the head with a bright light measurement of head circumference at regular intervals inserting a needle in the ventricle for CSF pressure measurement. Right. No, the answer is C. Hydrocephalus is usually diagnosed by measuring head circumference. The tape should be placed over the most prominent part of the occiput and just above the supraorbital ridges. The average head circumference at birth is 35 cm. It should increase 5 cm the first 4 months and another 5 cm the second 4 months. 42. Hydrocephalus may be due to malformed aqueduct of Sylvius obstruction of foramen of Luschka and Magendie both neither Right. No, the answer is C. Blockade of the aqueduct and blockade of the outflow of CSF from 4th ventricle (foramen of Luschka and Magendie) often cause hydrocephalus. These obstructions are usually malformations but meningitis may cause adhesions in these outflow tracts. 43. Syringomyelia is probably due to improper closure of the neural tube. This defect in the spinal cord is usually in the _____ area lumbosacral thoracic lower cervical upper cervical Very good. No, the answer is C. The lower cervical segments are usually affected. Pathologically, there is central gliosis in the spinal cord and often cystic cavitation with thick yellow fluid in the cyst. 44. The classic symptoms with cervical cord involvement include all, except painless burns of fingers and forearm atrophy of small hand muscles atrophy of shoulder girdle muscles hyperactive deep tendon reflexes of upper extremities Right. No, the answer is D. The cervical cord involvement leads to diminished deep tendon reflexes in the upper limbs (lower motor neuron involvement) and hyperactive reflexes in 45. The diagnostic characteristic which allows screening of anencephaly or spina bifida cystica is elevated TSH in amniotic fluid lower alpha-fetoprotein levels in amniotic fluid high alpha-fetoprotein levels in amniotic fluid none of the above Right. No, the answer is C. High levels of alpha-fetoprotein in the amniotic fluid is indicative of neural tube related congenital defects such as anencephaly or spina bifida cystica. The diagnosis may be confirmed by ultrasound to identify the presence of a neural tube defect. 46. Hirschsprung's Disease occurs only in the small intestine results from failure of neural crest cells to migrate into a colonic segment results in an aganglionic segment of colon B and C only A, B and C Very good. No, the answer is D. Congenital aganglionic megacolon (Hirschsprung's Disease) accounts for 20% of the cases of intestinal obstruction in infants. Lack of neural crest migration results in an aganglionic colonic segment characterized by decreased muscular tone, contractile activity and peristalsis. Fecal retention and abdominal distention begin at or soon after birth.