Embryo 17: Nervous System
Meningomyelocele: This NTD may occur anywhere along the vertebral column; however, they are most common in the lumbar and sacral region. More than 90% of cases have associated hydrocephalus due to coexistence of an ________________ malformation
Arnold-Chiari NOTE:Most patients require surgical diversion of CSF to avoid high intracranial pressure-related complications CASE RELEVANT
As closure of the ________ neuropore occurs, two lateral outgrowths (optic vesicles) appear, one on each side of the forebrain. These vesicles are the primordia of the retinae and optic nerves
As closure of the rostral neuropore occurs, two lateral outgrowths (optic vesicles) appear, one on each side of the forebrain. These vesicles are the primordia of the retinae and optic nerves
When does neurulation begin?
4th week (22-23 days)
Neurulation begins in the region of what somites?
4th-6th pairs of somites NOTE: At this stage, the cranial two thirds of the neural plate and tube as far caudal as the fourth pair of somites represent the future brain, and the caudal one third of the plate and tube represents the future spinal cord.
The lateral walls of the neural tube thicken, gradually reducing the size of the neural canal until only a minute central canal of the spinal cord exists at ________ weeks
9 to 10 weeks
The pituitary develops from 2 sources what are they?
An upgrowth from the ectodermal roof of the stomodeum, the hypophyseal diverticulum (Rathke pouch) A downgrowth from the neuroectoderm of the diencephalon, the neurohypophyseal diverticulum
In agenesis of corpus callosum, there is a complete or partial absence of the corpus callosum, which is the main neocortical commissure of the ____________________
Cerebral hemispheres NOTE: The condition may be asymptomatic, but seizures and mental deficiency are common. Agenesis of the corpus callosum is associated with more than 50 human congenital syndromes
What type of function is associated with basal plates (ventral)?
Efferent/motor MEMORY TOOL: my Bmw goes Vroom-Vroom. Bmw-basal Vroom-ventral Cars have motors or move
Initially, the wall of the neural tube is composed of a thick, pseudostratified, columnar neuroepithelium. These neuroepithelial cells constitute the ______________________________, which gives rise to all neurons and macroglial cells (macroglia) in the spinal cord
Initially, the wall of the neural tube is composed of a thick, pseudostratified, columnar neuroepithelium. These neuroepithelial cells constitute the ventricular zone (ependymal layer), which gives rise to all neurons and macroglial cells (macroglia) in the spinal cord
What are the three primary brain vesicles from which the brain develops
Forebrain (prosencephalon) Midbrain (mesencephalon) Hindbrain (rhombencephalon)
________________ protein is essential in the microfilament polymerization that promotes changes to the oligodendrocyte cytoskeleton
Profilin 1 (PFN1)
_______________ signaling is essential in the development of the spinal cord from early patterning to neurogenesis.
Retinoic acid
There are multiple closure sites involved in the formation of neural tube. What disease is associated with failure of closure at the following sites? Site 1: Site 2: Site 2, 4, and 1:
Site 1: Spina bifida cystica Site 2: Meroencephaly (aka anencephaly) Site 2,4,1: Craniorachischisis
Some dividing neuroepithelial cells in the ventricular zone differentiate into __________________. These embryonic cells form an _________________ zone (mantle layer) between the ventricular and marginal zone.
Some dividing neuroepithelial cells in the ventricular zone differentiate into primordial neurons (neuroblasts). These embryonic cells form an intermediate zone (mantle layer) between the ventricular and marginal zone.
Membranes covering the spinal cord are called what? what cells do they develop from? What days do they develop?
Meninges Neural crest & mesenchyme B/w 20-35 days NOTE: The cells migrate to surround the neural tube (primordium of the brain and spinal cord) and form the primordial meninges
What is the largest cerebral commissure? What does it connect?
The largest cerebral commissure is the corpus callosum, which connects neocortical areas. NOTE: The corpus callosum initially lies in the lamina terminalis, but fibers are added to it as the cortex enlarges, and it gradually extends beyond the lamina terminalis.
What signaling pathway has been implicated in the proliferation and differentiation of pituitary progenitor cells.
Notch signaling
Neural crest gives rise to cells that form most of what nervous systems?
PNS & ANS
What flexure divides the hindbrain into caudal (myelencephalon) and rostral (metencephalon) parts.
Pontine flexure
What type of Chiari malformation is being described: The inferior part of the cerebellum herniates through the foramen magnum. This is the most common form. It is usually asymptomatic and detected in adolescence.
Type 1
What type of Chiari malformation is being described: cerebellar tissue and the brainstem herniate through the foramen magnum, often accompanied by occipital encephalocele and lumbar myelomeningocele.
Type II ( also known as Arnold-Chiari malformation) CASE RELEVANT
What type of Chiari malformation is being described: the most severe form, there is herniation of the cerebellum and brainstem through the foramen magnum into the vertebral canal, which has serious neurologic consequences.
Type III
What type of Chiari malformation is being described: the cerebellum is absent or underdeveloped; these infants do not survive.
Type IV
When the neuroepithelial cells cease producing neuroblasts and glioblasts, they differentiate into ___________ cells, which form the _____________ lining the central canal of the spinal cord
When the neuroepithelial cells cease producing neuroblasts and glioblasts, they differentiate into ependymal cells, which form the ependyma (ependymal epithelium) lining the central canal of the spinal cord
When do myelin sheaths form around nerve fibers within the spinal cord?
begin during the late fetal period & continue to form during the 1st postnatal year
Midbrain: The neural canal narrows and becomes the ________________________, a channel that connects the third and fourth ventricles.
cerebral aqueduct
Rarely, impaired CSF circulation results from congenital _________________ stenosis
aqueductal NOTE: In a few cases, stenosis results from transmission of an X-linked recessive trait, but most cases appear to result from a fetal viral infection (e.g., cytomegalovirus) or Toxoplasma gondii NOTE: Blood in the subarachnoid space may cause obliteration of the cisterns or arachnoid villi (thin, limiting membrane).
The main site of absorption of CSF into the venous system is through the ______________, which are protrusions of arachnoid mater into the dural venous sinuses
arachnoid villi NOTE: dural venous sinuses (large venous channels between the layers of the dura mater). NOTE: The arachnoid villi consist of a thin cellular layer derived from the epithelium of the arachnoid and the endothelium of the sinus.
The telencephalon consists of a median part and two lateral diverticula, the cerebral vesicles. These vesicles are the primordia of the _________________
cerebral hemispheres NOTE: At first, the cerebral hemispheres are in wide communication with the cavity of the third ventricle through the interventricular foramina
Prenatal risk factors, such as maternal infection or thyroid disorder, Rh factor incompatibility, and some hereditary and genetic conditions, cause most cases of ______________, but the central motor deficit may result from events during birth.
cerebral palsy
What flexure demarcates the hindbrain from the spinal cord
cervical flexure NOTE: Later, this junction is arbitrarily defined as the level of the superior rootlet of the first cervical nerve, which is located roughly at the foramen magnum.
The _______________- forms the ventricular system of the brain and the central canal of the spinal cord.
neural canal
What differentiates into CNS?
neural tube
Syndecan 4 (SDC4) and van gogh-like 2 (VANGL2) proteins appear to be involved with what aspect of nervous system development?
neural tube closure.
The myelin sheaths around the axons of peripheral nerve fibers are formed by the plasma membranes of the what cells?
neurilemma (sheath of Schwann cells)
The ___________________ cells of the wall of the neural tube thicken to form the brain and spinal cord
neuroprogenitor
What induces overlying ectoderm to differentiate into the neural plate?
notochord and paraxial mesenchyme
What cells form the myelin sheaths around nerve fibers in the spinal cord
oligodendrocytes (oligodendroglial cells NOTE:these are types of glial cells that originate from the neuroepithelium NOTE: .The plasma membranes of these cells wrap around the axon, forming several layers
Some neuroblasts from the alar plates migrate ventrally and form the neurons in the ______ nuclei
olivary nuclei
The neural tube, _________ to the fourth pair of somites, develops into the brain.
cranial
Some cases of meningomyelocele are associated with _________________ (defective development of the calvaria), which results in depressed, nonossified areas on the inner surfaces of the flat bones of the calvaria.
craniolacunia
Fibers growing from the cerebrum (principal part of brain, including the diencephalon and cerebral hemispheres) form the ________________ (cerebral peduncles) anteriorly
crus cerebri NOTE: The peduncles become progressively more prominent as more descending fiber groups (corticopontine, corticobulbar, and corticospinal) pass through the developing midbrain on their way to the brainstem (the medulla is the caudal subdivision of the brainstem that is continuous with the spinal cord) and spinal cord
A _________________- is lined with epidermis and skin appendages extending from the skin to a deeper-lying structure, usually the spinal cord.
dermal sinus NOTE: The sinus (channel) is associated with closure of the neural tube and formation of the meninges in the lumbosacral region of the spinal cord
Studies indicate that secreted inductive molecules (e.g., FGF8, BMP4, and WNT5A) from the ___________________ are involved in the formation of the anterior and intermediate lobes of the pituitary gland.
diencephalon
What parts of the meninges end at the S2 vertebra in adults?
dura & arachnoid
What does the pia mater become as it continues distal to the caudal end of the spinal cord?
filum terminale NOTE: which indicates the original level of the caudal end of the embryonic spinal cord NOTE: The filum extends from the medullary cone and attaches to the periosteum of the first coccygeal vertebra
The caudal end of the spinal cord in fetuses gradually comes to lie at relatively higher levels. In a 24-week-old fetus, it lies at the level of what vertebra?
first sacral vertebra
As the cerebral hemispheres expand, they cover successively the diencephalon, midbrain, and hindbrain. The hemispheres eventually meet each other in the midline, and their medial surfaces become flattened. The mesenchyme trapped in the longitudinal fissure between them gives rise to the _______________, a median fold of dura mater.
cerebral falx (falx cerebri)
Spina bifida cystica: Sphincter paralysis (bladder or anal sphincters) is common with _______________. A saddle block anesthesia typically occurs when the sphincters are involved; loss of sensation occurs in the body region that would contact a saddle.
lumbosacral meningomyelocele CASE RELEVANT
Defects involving the embryonic neural arches are referred to as_____________-
spina bifida NOTE: The term spina bifida denotes nonfusion of the halves of the embryonic neural arches, which is common to all types of spina bifida
Severe types of spina bifida, which involve protrusion of the spinal cord and/or meninges through defects in the vertebral arches, are referred to collectively as ________________because of the meningeal cyst
spina bifida cystica
Microcephaly can be detected in utero by ultrasound scans carried out over the period of gestation. A small head may result from premature _____________ (osseous union) of all the cranial sutures; however, the neurocranium is thin with exaggerated convolutional markings.
synostosis
What is the tela choroidea?
the sheet of pia covering the lower part of the fourth ventricle
Signaling molecules for nervous system development involve members of what three groups?
transforming growth factor β family, Sonic hedgehog (SHH), and bone morphogenic proteins (BMPs).
Closure of neuropores coincides with establishment of what for the neural tube?
vascular circulation
Axons of ventral horn cells grow out of the spinal cord and form the _________________________
ventral roots of the spinal nerves. NOTE: As the basal plates enlarge, they bulge ventrally on each side of the median plane. As this occurs, the ventral median septum forms, and a deep longitudinal groove (ventral median fissure) develops on the ventral surface of the spinal cord
The choroid plexuses secrete_______________, which becomes CSF as additions are made to it from the surfaces of the brain, spinal cord, and the pia-arachnoid layer of the meninges
ventricular fluid
The walls of the developing cerebral hemispheres initially show three typical zones of the neural tube: What are they?
ventricular, intermediate, and marginal NOTE: later a fourth one, the subventricular zone, appears.
What regulates myelination?
β1-integrins
Cells in the posterior wall of the hypophyseal pouch do not proliferate; they give rise to the thin, poorly defined __________________
pars intermedia
The ________________________________ includes the neurons outside the CNS as well as the cranial nerves and spinal nerves (and their associated ganglia), which connect the brain and spinal cord with peripheral structures
peripheral nervous system (PNS)
The ___________develops as a median diverticulum of the caudal part of the roof of the diencephalon
pineal gland (pineal body) NOTE: Proliferation of cells in its walls soon converts it into a solid, cone-shaped gland.
What are the primary cells of the posterior lobe of the pituitary gland
pituicytes
The rest of the lamina terminalis lies between the corpus callosum and the fornix. It becomes stretched to form the ___________________, a thin plate of brain tissue containing nerve cells and fibers
septum pellucidum
The ventral area of the medulla contains a pair of fiber bundles ___________________________ that consist of corticospinal fibers descending from the developing cerebral cortex
(pyramids)
At what week can fetal vertebral column be detected by ultrasound?
10-12 weeks NOTE: and if there is a defect in the vertebral arch, a meningeal cyst may be detected in the affected area CASE RELEVANT
In adults, the spinal cord usually terminates at the inferior border of the _________ vertebra
1st lumbar NOTE: This is an average level because the caudal end of the spinal cord in adults may be as superior as the 12th thoracic vertebra or as inferior as the third lumbar vertebra.
At what week do peripheral nerve fibers have a whitish appearance resulting from the deposition of myelin?
20 weeks
The cavities of the telencephalon and diencephalon contribute to the formation of the ____________ ventricle, although the cavity of the diencephalon contributes more
3rd
When does the brain begin to develop?
3rd week
When does the 1st indication of developing nervous system appear? What is it?
3rd week Neural plate & neural groove develop on posterior aspect of trilaminar embryo
By the ____ week, the hypophyseal diverticulum projects from the roof of the stomodeum and lies adjacent to the floor (ventral wall) of the diencephalon. By the ______ week, the diverticulum has elongated and constricted at its attachment to the oral epithelium. By this stage, it has come into contact with then fundibulum (derived from the neurohypophyseal diverticulum), a ventral downgrowth of the diencephalon. During the _______ week, the connection of the diverticulum with the oral cavity degenerates.
3rd; 5th; 6th
CSF begins to form during which week?
5th
Fusion of the neural folds and formation of the neural tube begins at which somite? In which direction does it continue?
5th somite; proceeds in cranial and caudal directions until only small areas of the tube remain open at both ends
During the ___ week the forebrain partially divides into two secondary brain vesicles _____________ & ____________. The midbrain does not divide. The hindbrain partly divides into two vesicles, the ______________ &_________________
5th week; Telencephalon & diencephalon; metencephalon and myelencephalon.
The corpus striatum appears during the _________ week as a prominent swelling in the floor of each cerebral hemisphere
6th NOTE:" The floor of each hemisphere expands more slowly than its thin cortical walls because it contains the rather large corpus striatum, and the cerebral hemispheres become C shaped
Subnormal intellectual development may result from exposure of the embryo or fetus during the ______week period to viruses such as Rubella virus and high levels of radiation
8-16
After formation of midbrain & cervical flexure, unequal growth of the brain between these flexures produces the _________________ in the opposite direction. This flexure results in thinning of the roof of the hindbrain
After formation of midbrain & cervical flexure, unequal growth of the brain between these flexures produces the pontine flexure in the opposite direction. This flexure results in thinning of the roof of the hindbrain
After optic vesicles appear, a second pair of diverticula, the telencephalic vesicles, soon arise more dorsally and rostrally. They are the primordia of the ______________, and their cavities become the_______________
After optic vesicles appear, a second pair of diverticula, the telencephalic vesicles, soon arise more dorsally and rostrally. They are the primordia of the cerebral hemispheres, and their cavities become the lateral ventricles
Is meroencephaly associated with high or low polyhydramnios?
An excess of amniotic fluid (polyhydramnios) is often associated with meroencephaly, possibly because the fetus lacks the neural control for swallowing amniotic fluid. The fluid does not pass into the intestines for absorption and subsequent transfer to the placenta for disposal.
As the alar plates enlarge, the_____________________ forms. Cell bodies in the basal plates form the ventral and lateral gray columns.
As the alar plates enlarge, the dorsal median septum forms. Cell bodies in the basal plates form the ventral and lateral gray columns. NOTE: In transverse sections of the spinal cord, these columns are the ventral gray horns and lateral gray horns, respectively
Cell bodies in the _____ plates form the dorsal gray columns, which extend the length of the spinal cord.
Cell bodies in the alar plates form the dorsal gray columns, which extend the length of the spinal cord. NOTE: In transverse sections of the cord, these columns are the dorsal gray horns
Cells of the anterior wall of the hypophyseal diverticulum proliferate and give rise to the pars _________ of the pituitary gland. Later, an extension, the pars ________, grows around the infundibular stem. The extensive proliferation of the anterior wall of the hypophyseal diverticulum reduces its lumen to a narrow cleft ( residual cleft).
Cells of the anterior wall of the hypophyseal diverticulum proliferate and give rise to the pars anterior of the pituitary gland. Later, an extension, the pars tuberalis, grows around the infundibular stem. The extensive proliferation of the anterior wall of the hypophyseal diverticulum reduces its lumen to a narrow cleft ( residual cleft).
______________- malformation: is a structural defect of the cerebellum. It is characterized by a tongue-like projection of the medulla and inferior displacement of the cerebral tonsil through the foramen magnum into the vertebral canal
Chiari NOTE: The posterior cranial fossa is usually abnormally small, causing pressure on the cerebellum and brainstem.
The axons of cells in the spinal ganglia are at first bipolar, but the two processes soon unite in a T-shaped fashion. Which process (peripheral/central) becomes the dendrite? Which process becomes the dorsal roots of spinal nerves?
Dendrite- peripheral process Central processes- constitute dorsal roots of spinal nerves NOTE:Both processes of spinal ganglion cells have the structural characteristics of axons, but the peripheral process is a dendrite in that there is conduction toward the cell body. The peripheral processes of spinal ganglion cells pass in the spinal nerves to sensory endings in somatic or visceral structures. The central processes enter the spinal cord and constitute the dorsal roots of spinal nerves.
What does the external layer of primordial meninges become? internal layer?
Dura mater- external pia & arachnoid mater- internal NOTE: leptomeninges= pia & arachnoid mater NOTE: The origin of the pia mater and arachnoid from a single layer is indicated in the adult by arachnoid trabeculae, which are numerous, delicate strands of connective tissue that pass between the pia and arachnoid
During the fifth week, the embryonic brain grows rapidly and bends ventrally with the head fold. The bending produces the ____________in the midbrain region and the _______________ at the junction of the hindbrain and spinal cord
During the fifth week, the embryonic brain grows rapidly and bends ventrally with the head fold. The bending produces the midbrain flexure in the midbrain region and the cervical flexure at the junction of the hindbrain and spinal cord
______________- is a herniation of intracranial contents resulting from a defect in the cranium (cranium bifidum).
Encephalocele NOTE: The hernia may contain meninges (meningocele), meninges and part of the brain (meningoencephalocele), or meninges, part of the brain, and part of the ventricular system (meningohydroencephalocele)
Neuroblasts in the alar plates of the medulla form neurons that are arranged in four columns on each side. What are these from medial to lateral
GVA SVA GSA SSA NOTE: General visceral afferent, which receives impulses from the viscera Special visceral afferent, which receives taste fibers General somatic afferent, which receives impulses from the surface of the head Special somatic afferent, which receives impulses from the ear
Neuroblasts in the basal plates of the medulla, like those in the spinal cord, develop into motor neurons. The neuroblasts form nuclei (groups of nerve cells) and organize into three cell columns on each side. From medial to lateral what are they columns?
General somatic efferent (GSE) Special visceral efferent (SVE) General visceral efferent (GVE) NOTE: GSE: represented in txtbook as hypoglossal nerve SVE: "" as neurons innervating muscles derived from pharyngeal arches GVE: "" as neurons of vagus & glossopharyngeal NOTE: As the walls of the medulla move laterally, the alar plates become lateral to the basal plates. As the positions of the plates change, the motor nuclei usually develop medial to the sensory nuclei
________________________ results from incomplete separation of the cerebral hemispheres and most are associated with facial abnormalities
Holoprosencephaly (HPE) NOTE: Maternal diabetes and teratogens (e.g., alcohol) can destroy embryonic cells in the median plane of the embryonic disc during the third week, producing a wide range of birth defects resulting from defective formation of the forebrain NOTE: HPE is often indicated when the eyes are abnormally close together (hypotelorism). Molecular studies have identified several holoprosencephaly-related genes, including SHH.
______________________: The cerebral hemispheres are absent or represented by membranous sacs with remnants of the cerebral cortex dispersed over the membranes. The brainstem (midbrain, pons, and medulla) is relatively intact. These infants appear normal at birth, but the head grows excessively after birth because of CSF accumulation.
Hydranencephaly NOTE: A ventriculoperitoneal shunt is usually made to prevent further enlargement of the neurocranium. Mental development fails to occur, and there is little or no cognitive development
_________________ results from impaired circulation and absorption of CSF and, in rare cases, from increased production of CSF by a choroid plexus adenoma
Hydrocephalus NOTE: Blockage of CSF circulation results in dilation of the ventricles proximal to the obstruction, internal accumulation of CSF, and pressure on the cerebral hemispheres
Hydrocephalus usually refers to obstructive or noncommunicating hydrocephalus, in which all or part of the ventricular system is enlarged. All ventricles are enlarged if the apertures of the ______ ventricle or the ______________are blocked, whereas the lateral and third ventricles are dilated when only the _____________ is obstructed. Obstruction of an_______________________ can produce dilation of one ventricle
Hydrocephalus usually refers to obstructive or noncommunicating hydrocephalus, in which all or part of the ventricular system is enlarged. All ventricles are enlarged if the apertures of the fourth ventricle or the subarachnoid spaces are blocked, whereas the lateral and third ventricles are dilated when only the cerebral aqueduct is obstructed Obstruction of an interventricular foramen can produce dilation of one ventricle
The______________ gene appears to control development of the posterior lobe.
LIM homeobox gene LHX2
Side note: What levels of AFP would we expect to see if down syndrome?
Low
___________________ cells are the larger members of the neuroglial family of cells, which includes astrocytes and oligodendrocytes
Macroglial
Maternal alcohol abuse is a common identifiable cause of mental deficiency. The _____________ week of development is also the period of greatest sensitivity for fetal brain damage resulting from large doses of radiation. By the end of the 16th week, most neuronal proliferation and cell migration to the cerebral cortex are completed.
Maternal alcohol abuse is a common identifiable cause of mental deficiency. The 8th to 16th week of development is also the period of greatest sensitivity for fetal brain damage resulting from large doses of radiation. By the end of the 16th week, most neuronal proliferation and cell migration to the cerebral cortex are completed.
________________ is a severe defect of the calvaria and brain that results from failure of the rostral neuropore to close during the fourth week. The forebrain, midbrain, and most of the hindbrain and calvaria are absent
Meroencephaly NOTE: always associated with acrania (complete or partial absence of neurocranium). It may be associated with rachischisis (failure of fusion of neural arches) when defective neural tube closure is extensive
_______________ is a neurodevelopmental disorder. The calvaria and brain are small, but the face is normal sized
Microcephaly NOTE: These infants are grossly mentally deficient because the brain is underdeveloped. Microcephaly is the result of a reduction in brain growth. Inadequate pressure from the growing brain leads to the small size of the neurocranium (bones of cranium) NOTE: Exposure to large amounts of ionizing radiation, infectious agents (e.g., cytomegalovirus, rubella virus, Toxoplasma gondii), and certain drugs (e.g., maternal alcohol abuse) during the fetal period are contributing factors in some cases
_______________________, a family of related polypeptide isoforms, are essential in myelination
Myelin basic proteins NOTE: Fiber tracts become functional at approximately the time they become myelinated
The lumen of the neural tube becomes what? Which communicates freely with what?
Neural canal; amniotic cavity
________________ cells are derived from neural crest cells that migrate peripherally and wrap themselves around the axons of somatic motor neurons and preganglionic autonomic motor neurons as they pass out of the CNS
Neurilemma NOTE: These cells also wrap themselves around the central and peripheral processes of somatic and visceral sensory neurons and around the axons of postsynaptic autonomic motor neurons.
Neuroblasts are embryonic nerve cells that migrate from the alar plates of the midbrain into the tectum and aggregate to form four large groups of neurons, the paired __________ &_____________, which are concerned with visual and auditory reflexes, respectively
Neuroblasts are embryonic nerve cells that migrate from the alar plates of the midbrain into the tectum and aggregate to form four large groups of neurons, the paired superior and inferior colliculi, which are concerned with visual and auditory reflexes, respectively
Neuroblasts become _____________ as they develop cytoplasmic processes
Neuroblasts become neurons as they develop cytoplasmic processes
Neuroblasts from the ________ plates may give rise to groups of neurons in the tegmentum of the midbrain (red nuclei, nuclei of third and fourth cranial nerves, and reticular nuclei).
Neuroblasts from the basal plates may give rise to groups of neurons in the tegmentum of the midbrain (red nuclei, nuclei of third and fourth cranial nerves, and reticular nuclei).
What neuropore closes first?
Rostral/cranial
_________ signaling controls the proliferation, survival, and patterning of neuroepithelial progenitor cells by regulating GLI transcription factors
SHH
Some neuroblasts in the intermediate zone of the alar plates migrate to the marginal zone and differentiate into the neurons of the ____________ Other neuroblasts from these plates give rise to the central nuclei, the largest of which is the __________ Cells from the alar plates also give rise to the pontine nuclei, cochlear and vestibular nuclei, and the sensory nuclei of the trigeminal nerve.
Some neuroblasts in the intermediate zone of the alar plates migrate to the marginal zone and differentiate into the neurons of the cerebellar cortex. Other neuroblasts from these plates give rise to the central nuclei, the largest of which is the dentate nucleus. Cells from the alar plates also give rise to the pontine nuclei, cochlear and vestibular nuclei, and the sensory nuclei of the trigeminal nerve.
Soon after establishment of a ventricular zone a _______________ zone composed of the outer parts of the neuroepithelial cells becomes recognizable. This zone gradually becomes the white matter of the spinal cord as axons grow into it from nerve cell bodies in the spinal cord, spinal ganglia, and brain
Soon after establishment of a ventricular zone a marginal zone composed of the outer parts of the neuroepithelial cells becomes recognizable. This zone gradually becomes the white matter of the spinal cord as axons grow into it from nerve cell bodies in the spinal cord, spinal ganglia, and brain
________________ is an NTD resulting from failure of the halves of one or more neural arches to fuse in the median plane
Spina bifida occulta
The adenohypophysis (glandular tissue), or anterior lobe, arises from ____________ The neurohypophysis (nervous tissue), or posterior lobe, arises from _______________
The adenohypophysis (glandular tissue), or anterior lobe, arises from oral ectoderm The neurohypophysis (nervous tissue), or posterior lobe, arises from neuroectoderm
Cerebellum: What is the oldest part evolutionary (phylogenetically)? What does it have connections with?
The archicerebellum (flocculonodular lobe), the oldest part phylogenetically, has connections with the vestibular apparatus, especially the vestibule of the ear
What causes dermal sinus?
The birth defect is caused by failure of the surface ectoderm (future skin) to detach from the neuroectoderm and meninges that envelop it. As a result, the meninges are continuous with a narrow channel that extends to a dimple in the skin of the sacral region of the back NOTE:The dimple indicates the region of closure of the caudal neuropore at the end of the fourth week and therefore represents the last place of separation between the surface ectoderm and the neural tube.
Cerebral Hemispheres: The caudal end of each hemisphere turns __________ and then___________, forming the temporal lobe
The caudal end of each hemisphere turns ventrally and then rostrally, forming the temporal lobe NOTE: in so doing, it carries the lateral ventricle (forming its temporal horn) and choroid fissure with it NOTE: The thin medial wall of the hemisphere is invaginated along the choroid fissure by vascular pia mater to form the choroid plexus of the temporal horn
What part of the myelencephalon corresponding to the medulla is closed and what part is open?
The caudal part of the myelencephalon (closed part of the medulla) resembles the spinal cord developmentally and structurally The rostral part of the myelencephalon (open part of the medulla) is wide and rather flat, especially opposite the pontine flexure
The cavity of the hindbrain becomes the ____________ and the _________in the medulla
The cavity of the hindbrain becomes the fourth ventricle and the central canal in the medulla
What are the 1st commissures to form?
The first commissures to form are the anterior commissure and hippocampal commissure NOTE: They are small fiber bundles that connect phylogenetically older parts of the brain
The rostral (anterior) part of the forebrain, including the primordia of the cerebral hemispheres, is the ____________; the caudal (posterior) part of the forebrain is the _________________
The rostral (anterior) part of the forebrain, including the primordia of the cerebral hemispheres, is the telencephalon; the caudal (posterior) part of the forebrain is the diencephalon.
The thin roof of the fourth ventricle evaginates in three locations. These outpouchings rupture to form openings, the median and lateral apertures (foramen of ________ and foramina of __________, respectively), which permit the CSF to enter the _________ space from the fourth ventricle
The thin roof of the fourth ventricle evaginates in three locations. These outpouchings rupture to form openings, the median and lateral apertures (foramen of Magendie and foramina of Luschka, respectively), which permit the CSF to enter the subarachnoid space from the fourth ventricle
The unipolar neurons in the spinal ganglia (dorsal root ganglia) are derived from what cells?
The unipolar neurons in the spinal ganglia (dorsal root ganglia) are derived from neural crest cells
Unlike those of the spinal cord, neuroblasts from the alar plates in the myelencephalon migrate into the ____________ zone and form isolated areas of gray matter: the _______ nuclei medially and the ____________ nuclei laterally
Unlike those of the spinal cord, neuroblasts from the alar plates in the myelencephalon migrate into the marginal zone and form isolated areas of gray matter: the gracile nuclei medially and the cuneate nuclei laterally NOTE: These nuclei are associated with correspondingly named nerve tracts that enter the medulla from the spinal cord.
Spina bifida occulta: Occurs at what vertebra? What may be the only evidence?
Vertebra: L5 or S1 Evidence: small dimple with a tuft of hair NOTE:An overlying lipoma dermal sinus or other birthmark may also occur. Spina bifida occulta usually produces no symptoms. A few affected infants have functionally significant defects of the underlying spinal cord and dorsal roots
Differential expression of _________________signaling is involved in the patterning of the hypothalamus.
Wnt/β-catenin
What type of function is associated with alar plates (dorsal)?
afferent/sensory MEMORY TOOL: Alar=Afferent; A=A
The cerebellum develops from thickenings of dorsal parts of the _________ plates
alar
In familial ____________________________, the forebrain is small, and the lateral ventricles often merge to form one large ventricle.
alobar holoprosencephaly
The __________________________ has parts in the CNS and PNS and consists of the neurons that innervate smooth muscle, cardiac muscle, glandular epithelium, and combinations of these tissues
autonomic nervous system (ANS
The nerve roots inferior to the end of the cord (medullary cone) form a bundle of spinal nerve roots called the ____________, which arises from the lumbosacral enlargement (swelling) and medullary cone of the spinal cord
cauda equina
The neural tube _______ to the 4th pair of somties develops into the spinal cord.
caudal NOTE: The primordial spinal cord develops from the caudal part of the neural plate and caudal eminence
The neural canal of the neural tube forms the small______________ of the myelencephalon.
central canal
The_______________________consists of the brain and spinal cord and is protected by the cranium and vertebral column.
central nervous system (CNS)
Because of the active proliferation of the pia, the tela choroidea invaginates the fourth ventricle, where it differentiates into the _________________, infoldings of choroidal arteries of the pia
choroid plexus NOTE: Similar plexuses develop in the roof of the third ventricle and the medial walls of the lateral ventricles NOTE: The epithelial lining of the choroid plexus is derived from neuroepithelium, whereas the stroma develops from mesenchymal cells
What does the anterior commissure connect
connects the olfactory bulb (rostral extremity of the olfactory tract) and related areas of one hemisphere with those of the opposite side.
When does the rostral neuropore close? When does the caudal neuropore close?
day 25- rostral day 27- caudal
The pituitary gland (hypophysis) is ___________ in origin
ectodermal
The _________________ develops from the roof and dorsal portion of the lateral wall of the diencephalons
epithalamus NOTE: Initially, the epithalamic swellings are large, but later they become relatively small.
What is neurulation?
formation of neural plate & neural tube
Most defects of spinal cord result from failure of fusion of one or more neural arches of the developing vertebrae during the _________week
fourth
Most major birth defects, such as meroencephaly and meningoencephalocele, result from defective closure of the rostral neuropore (an NTD) during the ____________-week
fourth
What are the supporting cells of the CNS called? What do they differentiate from?
glioblasts; differentiate from neuroepithelial cells, mainly after neuroblast formation has ceased NOTE:The glioblasts migrate from the ventricular zone into the intermediate and marginal zones. Some glioblasts become astroblasts and later astrocytes, whereas others become oligodendroblasts and eventually oligodendrocytes
What levels of AFP would we expect to see in maternal serum for spina bifida cystica or abdominal wall defect?
high CASE RELEVANT
What does the hippocampal commissure connect?
hippocampal formations
Cell depletion of sufficient degree in the cerebral cortex results in severe mental deficiency. Disorders of protein, carbohydrate, or fat metabolism may also cause mental deficiency. Maternal and fetal infections (e.g., syphilis, rubella virus, toxoplasmosis, cytomegalovirus) and congenital _____________________ are commonly associated with mental deficiency
hypothyroidism NOTE: Deficient mental development throughout the postnatal growth period can result from birth injuries, toxins (e.g., lead), cerebral infections (e.g., meningitis), cerebral trauma from head injuries, and poisoning.
As the cerebral cortex develops, groups of nerve fibers (commissures) connect corresponding areas of the cerebral hemispheres with one another. Where does the most important commisure cross?
in the lamina terminalis NOTE: which is the rostral (anterior) end of the forebrain NOTE: This lamina extends from the roof plate of the diencephalon to the optic chiasm (decussation or crossing of the optic nerve fibers).
The ________________ gives rise to the median eminence, infundibular stem, and pars nervosa
infundibulum
As each cerebral hemisphere grows, the cortex covering the external surface of the corpus striatum grows relatively slowly and is soon overgrown . This buried cortex, hidden from view in the depths of the lateral sulcus of the cerebral hemisphere, is the ______________
insula
The hypothalamus arises by proliferation of neuroblasts in the _______________ zone of the diencephalic walls, ventral to the hypothalamic sulci
intermediate
The thalami meet and fuse in the midline in approximately 70% of brains, forming a bridge of gray matter across the third ventricle, which is the _________________
interthalamic adhesion NOTE: the bridge is absent in about 20% of brains.
A premature infant may develop ______________________ hemorrhage leading to hydrocephalus through the obstruction of the lateral aperture (foramen of Luschka) and median aperture (foramen of Magendie
intraventricular hemorrhage
A pair of nuclei forms pea-sized swellings (________________) on the ventral surface of the hypothalamus
mammillary bodies
What does the myelencephalon become?
medulla oblongata
NTDs affect the tissues overlying the spinal cord: including (4?)
meninges, neural arches, muscles, and skin
Spina bifida cystica: When the cyst contains meninges and CSF, the defect is spinal bifida with ________________
meningocele NOTE: The spinal cord and spinal roots are in the normal position, but there may be spinal cord defects. Protrusion of the meninges and CSF of the spinal cord occurs through a defect in the vertebral column.
Spina bifida cystica: If the spinal cord or nerve roots are contained within the meningeal cyst, the defect is spina bifida with __________________
meningomyelocele CASE RELEVANT
Spina bifida cystica: Severe cases involving several vertebrae are associated with absence of the calvaria (skullcap), absence of most of the brain, and facial abnormalities; these severe defects are called ____________________
meroencephaly NOTE: The defects entail drastic effects in some brain areas and lesser or no effects in others. For these neonates, death is inevitable. NOTE: used to be called anencephaly- The term anencephaly for these severe defects is inappropriate because it indicates that no part of the brain exists
Microglia (microglial cells), which are scattered throughout the gray and white matter of the spinal cord, are small cells that are derived from what cells?
mesenchymal cells NOTE: Microglia invade the CNS rather late in the fetal period after it has been penetrated by blood vessels. Microglia originate in the bone marrow and are part of the mononuclear phagocytic cell population
The sulcus limitans extends cranially to the junction of the midbrain and forebrain. Therefore the alar & basal plates are recognizable only in what brain vesicles?
midbrain & hind brain
What becomes myelinated first motor roots or sensory roots?
motor
What is the most severe type of spina bifida?
myeloschisis NOTE: In this defect, the spinal cord in the affected area is open because the neural folds failed to fuse. As a result, the spinal cord is represented by a flattened mass of nervous tissue. Myeloschisis usually results in permanent paralysis or weakness of the lower limbs
Cerebellum: The _____________ (posterior lobe), the newest part phylogenetically, is concerned with selective control of limb movements
neocerebellum
Chiari may lead to a type of __________ hydrocephalus that obstructs the absorption and flow of CSF; thus the entire ventricular system is distended
non-communicating
Hydrocephalus resulting from obliteration of the subarachnoid cisterns or malfunction of the arachnoid villi is called __________________ hydrocephalus
nonobstructive or communicating hydrocephalus
Cerebellum: The ________________ (vermis and anterior lobe), of more recent development, is associated with sensory data from the limbs.
paleocerebellum
What does the metencephalon become?
pons and cerebellum
Initially, the cerebellar swellings project into the fourth ventricle. As the swellings enlarge and fuse in the median plane, they overgrow the rostral half of the fourth ventricle and overlap the ___________ & _________________--
pons and medulla
The spinal cord in neonates terminates at the level of the ______________ vertebra
second or third lumbar
What groove separates the alar plate (dorsal) from the basal plate (ventral)
sulcus limitans NOTE: Proliferation and differentiation of neuroepithelial cells in the developing spinal cord produce thick walls and thin roof plates and floor plates . Differential thickening of the lateral walls of the spinal cord soon produces a shallow longitudinal groove on each side, the sulcus limitans
The walls of the metencephalon form the pons and cerebellum, and the cavity of the metencephalon forms the _____________ part of the fourth ventricle
superior NOTE: As in the rostral part of the myelencephalon, the pontine flexure causes divergence of the lateral walls of the pons, which spreads the gray matter in the floor of the fourth ventricle
The lamina ______________ is the natural pathway from one hemisphere to the other.
terminalis
Three swellings develop in the lateral walls of the third ventricle, which later become the what (3?)
thalamus, hypothalamus, and epithalamus NOTE: The thalamus is separated from the epithalamus by the epithalamic sulcus and from the hypothalamus by the hypothalamic sulcus NOTE: The latter sulcus is not a continuation of the sulcus limitans into the forebrain, and it does not, like the sulcus limitans, divide sensory and motor areas
Fluid-filled spaces appear within the leptomeninges that soon coalesce to form what space?
the subarachnoid space
