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Embryology Chapter 17 - Nervous System
Terms in this set (156)
the nervous system develops from ______
Nervous system formation is induced by
notochord formation and paraxial mesoderm
The process of formation of the neural plate, the neural folds, and their closure to form the neural tube is called __________.
neurulation is completed by the end of the ______________, when closure of the caudal neuropore occurs.
During neurulation, the embryo is sometimes referred to as a __________.
As the notochord develops, the embryonic ____________ over it thickens to form the neural plate. The neural plate formation is induced by the
The ectoderm of the neural plate, called __________, gives rise to the _______________, consisting of the brain and spinal cord.
It also gives rise to other structures.
As the notochord forms and elongates, the neural plate broadens and eventually extends cranially as far as the _________
On about the 18th day, the neural plate invaginates along its central axis to form a ________ that has neural folds on each side.
By the end of the third week, the neural folds have begun to move
together and fuse, converting the neural plate into a ________
The neural tube soon separates from the surface ectoderm. The free edges of the surface ectoderm fuse so that this layer becomes continuous over the back of the embryo. Subsequently, the surface ectoderm differentiates into the __________
epidermis of the skin
Fusion of folds proceeds in cranial and caudal directions until only small areas remain open of both ends. The rostral neuropore closes at about ___________ and posterior neuropore closes at about 2 days later.
The cranial two-thirds of neural plate develops into the ___
Caudal one-third develops into _____
Before the closure, the lumen of the neural tube—neural canal—communicates freely with the _______.
Closure of neuropores coincides with _________?
establishment of a blood vascular circulation for neural tube
The neural canal is converted into ________________ of brain and ______________ of spinal cord.
ventricular system ; central canal system
The sacral and coccygeal segments of the spinal cord (and dorsal and ventral roots) form by _______.
C. A cell mass called the caudal eminence appears caudal to the neural tube. It enlarges
D. It will join the neural tube.
secondary neurulation begins on ___________ and completed by day 42.
A cell mass called the caudal eminence appears caudal to the neural tube. It enlarges and cavitates, and it will
join the neural tube.
______________ results from a thickened, shortened filum terminale that adheres to the sacrum and causes traction on the conus medullaris
-Results in sphincter dysfunction, gait disorders and deformities of
-Deficits may improve after transection
Tethered cord syndrome.
As the neural folds come together and fuse, cells at the tips of the neural folds break away from the neuroectoderm to form _______________. The surface ectoderm of one side becomes continuous with the other side over the neural tube to give rise to _____________
neural crest cells; epidermis
T or F: Neural crest cells do not participate in neural tube formation.
Neural crest cells give rise to:
a. dorsal root ganglia
b. Sympathetic ganglia
c. Enteric ganglia
d. Parasympathetic ganglia of CN VII, IX, and X
e. Schwann cells
g. Satellite cells ofperipheral ganglia
h. Cartilage of pharyngeal arches
i. Ciliary and papillary muscles
j. Chromafin cells of adrenal medulla
k. Pia and arachnoid membranes.
Placodes are formed via the thickening of cephalic surface of ectoderm (head region). They Join neural crest to form sensory ganglia of cranial nerves _____________
V, VII, VIII, IX and X.
During neurulation, neuroepithelial cells get incorporated into surface ectoderm to give rise to _________.
a. Differentiate into neurosensory cells that give rise to the olfactory
nerve (CN I).
b. Induce the formation of olfactory bulbs.
a. give rise to statoacoustic organs of the inner ear.
b. vestibulocochlear nerve (CN VIII)
Consists of cranial, spinal and visceral nerves and cranial, spinal and autonomic ganglia.
1. Neural crest cells
2. Neural tube
Peripheral nervous system
Cell body in spinal cord or brainstem-derived from neural tube.
1. Cell body in spinal cord or brainstem
2. Synapse on ganglia
a. Ganglion cells derived from neural crest.
1. Neural crest in origin
2. Cell body is outside CNS
a. Spinal nerves or autonomic nerves- cell body in DRG
b. Cranial nerves - cell body in sensory ganglia in cranium (Not
Neurons in brain and spinal cord are derived from ______.
Cell body of each afferent neuron is closely invested by a capsule of modified _________.
Its capsule is continuous with neurolemma that surround the axons.
Myelin sheaths in spinal cord begin to form during _____________ and continue forming during the postnatal period.
late fetal period
T or f: In general, fiber tracts become myelinated at about the same time they become functional
Found in CNS-______________ -one cell can myelinate many axons- only
neurons with mylinated axons are invested in ____________ (derived
from neural tube).
Schwann cells are found in PNS, and can only ____________. They develop from neural crest cells.
myelinate one axon
T or F: All PNS neurons are invested in schwann cells but not all have myelin.
Neuroblast in sensory ganglia ( DRG) form what two process (pseudounipolar neuron)?
-one will form dorsal root to enter dorsal horn of spinal cord
-one will terminate on sensory receptors
Failure of neural crest to migrate and form enteric ganglia to lower bowel will cause
Hirschprung disease (congenital megacolon)
The spinal cord is formed from the neural tube caudal to ___________
The central canal is formed by week_________
9 or 10
After the formation of the neural tube, three layers appear in rapid
succession. These layers are the ventricular, _____________ and intermediate zones.
This zone forms first. Initially it is the only layer. Neuroepithelium in the walls form here.
-Neuroblasts arise here, and will become monocellular layer of ependymal cells that line the central canal and brain ventricles.
The ventricular zone (ependymal zone)
Neuroblasts give rise to:
all neurons and macroglial cells (astroglia and oligodendroglia and ependymal cells) in the spinal cord.
The outer parts of the neuroepithelial cells differentiate into the __________ which will give rise to the white matter of the spinal cord as axons grow into it from neurons in the spinal cord, spinal ganglia and brain. These neurons are located in intermediate zone and the processes extend into this zone.
The ___________ is formed between the ventricular and marginal zone.
As cells undergo their last division, they begin to
migrate away from the ventricular zone on transient glial cell
guides called ____________. As they migrate, they form a moving
front of cell bodies between the marginal and ventricular zones.
__________ forms at the interface of the ventricular and intermediate zones. The cells do not migrate. The progenitor cells
give rise to macroglial cells of CNS and specific neurons of the
brainstem and forebrain.
Although controversial, both neurons and glia seem to originate from a single precursor cell population. Two main lineages arise:
neuroblastic and glioblastic
-Initially have a transient dendrite that extends into lumen
-Lost when neuroblast migrate to intermediate zone.
Differentiation of neuroblastic cells include two cytoplasmic processes:
-one elongates to become axon
-one shows a number of cytoplasmic arborizations (primitive dendrites) - cell is now called multipolar neuroblast will become neurons.
hose in alar plate (dorsal horn) -ascend or descend -form association neurons.
Axons from the neuroblastic lineage in the basal plate will break through neural tube and give rise to:
Axons from the neuroblastic lineage in alar plate (dorsal horn) ascend or descend to form
Includes precursors of radial glial cells,
astroglial cells, and oligodendrocytes. This lineage is thought
to split into three main branches.
a. Type 1 astrocyte precursors
b. Oligodendrocyte/type 2 astroctye precursor (called the O2A
c. Radial glial progenitor.
While most cell types persist into adulthood, the radial glia in most
regions of the brain appear to be converted to
astocytes, ependymal cells or tanycytes (specialized ependymal cells).
Where are the two places where radial glial cells seem to retain their features?
In the cerebellum (Bergmann cells) and retina (muller cells)
Differentiation of glial cells is influenced by a variety of growth factors such as platelet-derived growth factor, __________________ and fibroblast growth factor which are secreted by neighboring glia and neurons.
ciliary neurotrophic factor
Microglia are derived from the________. They invade the
nervous system late in the fetal period after penetration from blood
The dorsal and ventral walls of the neural tube remain thin and are called ______________. But the lateral walls thicken.
roof and floor plates
What structure separates the thickened lateral walls into a basal plate and alar plate?
The cells of the basal plate and alar plate are arranged into:
Receive sensory axons from sensory ganglia such as the dorsal root ganglia.
Gives rise to motor fibers
T or F: Proliferation and differentiation of the neuroepithelial cells in the developing spinal cord produce thick walls and thin roof and floor plates.
In the developing spinal cord, sulcus limitans separates the lateral walls into
dorsal and ventral regions
The alar and basal plates consist of the _____________ and adjacent ______________.
ventricular zone; intermediate zone.
In the developing spinal cord, the posterior part of the ventricular zone and intermediate zone represents the:
Cells in the alar plate form the ___________________ and will have ____________ functions. The second order sensory neurons form here. These receive axons from spinal ganglion (DRG).
dorsal horns; afferent
The anterior part of the ventricular zone and intermediate zone represents the:
Cells from the basal plate form the _______________ and will have _____________ functions. Axons grow out of the spinal cord to form the ventral roots. The basal plate somewhat precedes the alar plate. Motor neuroblast of anterior and posterior horns form here.
ventral and lateral horns; efferent
The sulcus limitans will disappear from the spinal cord but will remain in the ____________.
The dorsal root ganglia are formed from ______. Their axons enter the spinal cord and form the ______.
the neural crest cells; dorsal roots
T or F: Each spinal nerve and its associated ganglion are associated with a somite.
SVE (special visceral efferent) fibers are found in
skeletal muscle developed from pharyngeal arches; nucleus ambiguous
-Gives rise to SVE of cranial nerves IX, X and XI.
GVE (general visceral efferent) fibers are found in
parasympathetic & sympathetics; smooth muscle of iris, glands, and blood vessels
-give rise to neurons of the vagus nerve (dorsal motor nuclei) and glossopharyngeal nerve (inferior salivatory nucleus).
-Parasympathetic to thorax and abdomen.
GSE (general somatic efferent) fibers are found in
skeletal muscle; non- pharyngeal; give rise to the hypoglossal nerve which innervates the tongue
T or F: SSE (special somatic efferent) fibers do not exist
SVA (special visceral afferent) fibers are responsible for
-taste and smell
-vagus nerve, glossopharyngeal nerve
GVA (general visceral afferent) fibers:
-responsible for sensation relating to digestive tract, starting with post 1/3 of tongue, all other visceral organs and tissue, e.g., heart, lungs, lining of the body cavity; reflex involving stretch receptors, chemoreceptors, baroreceptors.
GSA (general somatic afferent) fibers are responsible for
tactile sensation from regions of ear and posterior cranial fossa.
-spinal trigeminal nucleus
-CN IX and X
SSA (special somatic afferent) fibers are found where
vision, auditory and vestibular system, balance
Axons from the basal plate in the lateral horn give rise to
Axons from the basal plate will give rise to GSE in the
GVEs will innervate that spinal cord at what positions?
T1-L2 - sympathetic
Sacral levels S2-S4 - parasympathetic
Alar plate receives sensory input; ________ innervates skin and receptors in joint capsules, tendons and muscles
In early fetal period, two layers of _______________ appear around the brain and spinal cord.
In regards to the coverings of the spinal cord: The thick outer layer of mesenchyme is derived from mesoderm and becomes the
In regards to the coverings of the spinal cord: the thin inner layers are derived from ___________ and become the leptomeninges (pia and arachnoid mater).
Fluid-filled spaces appear between the pia and arachnoid that will form the:
What is the origin of pia and arachnoid mater?
arachnoid trabeculae, a fine CT
Embryonic CSF begins to form when?
In the embryo, the spinal cord extends the entire length of the vertebral canal and the spinal nerves pass through the _______________ near their levels of origin.
This relationship does not persist because the spine and the dura mater grow more rapidly than the spinal cord.
At month 6 of gestation, the end of the spinal cord lies at the level of____.
T or F: the spine and the dura mater grow more rapidly than the spinal cord, so the caudal end of the spinal cord comes to lie at relatively higher levels.
In the newborn infant, the end of the spinal cord lies at ___
In the adult, it lies at vertebral levels _____. Lumbar and sacral spinal
nerve roots run obliquely from the spinal cord to their corresponding
intervertebral foramina inferiorly.
The dural sac and subarachnoid space extend to____.
Below L2-3, a threadlike extension of pia mater forms the ____________, which is attached to periosteum of the first coccygeal vertebra
and which marks the regression tract of the spinal cord.
Spina bifida occulta is a defect in the vertebral arch (neural arch) resulting from:
failure of the halves of the vertebral arch to grow normally and fuse in the median plane.
Nerve roots below the terminal end of spinal cord collectively constitute the __________.
congential malformations are usually due to the
defective closure of the caudal neuropore at the end of week 4.
Malformations involving the spinal cord and vertebral arches are called __________ (nonfusion of the vertebral arches)
In about 10% of the population, spina bifida occulta occurs where?
at L 5 or S 1 vertebra
People with Spina bifida occulta may present with
small dimple with a tuft of hair.
-Tuft of hair may be result from overexposure of the developing skin to other inductive influences from the neural tube or its covering
spina bifida aperta
-most common form of spina bifida;
-results in an open lesions not covered by skin and a mass that protrudes from the spine
spina bifida cystica
a protrusion of the spinal cord and/or meninges through the defective neural arch.
-is present in 1/1000 births
-may result in loss of sensation in corresponding dermatome, complete or partial skeletal muscle paralysis, sphincter paralysis (with lumbar meningomyeloceles) and saddle anesthesia.
The neural tube cranial to the ________ of somites becomes the brain.
Spina bifida with meningocele
Protrusion of a sac through the spine, containing CSF and meninges; however does not include the spinal cord.
Spina bifida with meningomyelocele or myelomeningocele
-spinal cord and nerve roots included with meninges and CSF in the sac, covered by skin or thin membrane.
-There are marked neurological deficits inferior to the sac, due to incorporation of the neural tissue into the wall of the sac
Spina bifida with meningomyelocele or myelomeningocele usually occurs in the _______________ and may be associated with craniolacunia or defective calvarium).
-usually associated with ____________ malformation
lumbar region; Arnold-Chiari
Cystica and/or meroanencephaly (absence of part of the brain) is suspected in utero when there is a high-level of _________________ in the amniotic fluid or in the maternal blood serum.
Amniocentesis or ultrasound should be performed at about _____________ when the vertebral column becomes visible.
Spina bifida with myeloschisis
(with myelocele): open spinal cord due to failure of neural folds to fuse. The spinal cord in this area is a flattened mass. Most are stillborn.
Fusion of the neural folds in the cranial region and closure of rostral neuropore form 3 primary brain vesicles
During the 5th week, the prosencephalon divides into 2 secondary brain vesicles.
telencephalon and diencephalons
The rhombencephalon divides into 2 secondary vesicles
Myelencephalon and Metencephalon
T or F: The mesencephalon does not divide
How many brain vesicles are there?
During the 4th week, the embryonic brain grows rapidly and bends ventrally with the head fold. This bending of the cephalic end of embryo into a C shape is a prominent force in shaping the early nervous system. This produces the what?
midbrain flexure at the level of the mesencephalon
Within each brain vesicle, the __________ expands to form primitive ventricles.
the midbrain flexure is convex dorsally (concave ventrally) and appears at the____________
-is at the junction of the hindbrain and spinal cord
-is convex dorsally and appears at the junction of hindbrain and spinal cord making a right-angled bend between them.
Unequal growth of the brain between midbrain and cervical flexures produces the ______________ (concave ventrally) in the opposite direction. This results in thinning of the roof of the hindbrain a. The part of hindbrain caudal to pontine fl
The part of hindbrain caudal to pontine flexure is the:
The part of hindbrain rostral to pontine flexure is the _______________ (gives rise the cerebellum and pons)
In the development of the brain, the sulcus limitans extends cranially to the junction of the midbrain and forebrain and the alar and basal plates are recognizable only in ___________ and _____________.
midbrain and hindbrain.
The ventricular system of the brain represents an expansion of?
central canal of neural tube
The cavities of the telencephalic vesicles become the ______
Openings between lateral vesicles and the 3rd ventricle are called what:
The cavities of the diencephalic cavity becomes the_______
The cavity of the mesencephalon becomes the __________ (connects the 3rd and 4th ventricles)
narrow cerebral aqueduct
The cavity of myelencephalic cavity becomes the ________
The fourth ventricle will communicate with the subarachnoid space via
a. Medial aperture (foramen of Magendie)
b. Two lateral apertures (foramen of Luschka)
The ventricles are lined by ependymal cells (epithelium) and are filled
with clear CSF formed in choroid plexuses of ___________.
3rd, 4th and lateral ventricles.
The thin ependymal roof of the 4th ventricle is covered externally by pia mater derived from?
mesenchyme associated with hindbrain
What is the order of CSF flow?
lateral ventricle > 3rd ventricle> 4th ventricle
Much of CSF escapes through 3 small holes in roof of the ____________- and enters subarachnoid space between two layers of meninges.
Because of the active proliferation of the pia mater, the tela chorodea invaginates into the 4th ventricle where it differentiates into the ________ (also happens in other ventricles). _____________ secretes ventricular fluid, which becomes cerebrospinal fluid.
The vascular pia mater, together with the ependymal roof, forms the __________
T or F: Arnold-Chiari malformation can lead to hydrocephalus
Arnold-Chiari malformation occurs when
Parts of the cerebellum gets herniated into foramen magnum, thereby mechanically preventing the escape of cerebrospinal fluid from the skull (obstructs foramen of luska and foramen of Magendie)
-May have spastic dysphonia, difficulty swallowing, diminished gag reflex, apnea, vocal cord paralysis
Characterized by two layers of mesenchyme that appear around the brain and spinal cord.
The thick outer layer of meninges, is of ____________,
forms the tough dura mater as well as membrane bones of calvarium.
A thin inner layer of the meninges is of ____________ subdivides into a thin pia mater which is closely apposed to the neural tissue and a middle
neural crest origin
the cranial nerve motor nuclei develop from the:
brainstem basal plates
The nuclei of the 3rd to 12th cranial nerves are located in the ________________. Some of these nerves are sensory, some are motor, most are both; therefore, some of the arise from more than one nucleus.
The myelencephalon becomes the medulla oblongata
the cranial nerve sensory nuclei develop from the:
brainstem alar plates
The cervical flexure separates the ___________ from the ____________.
hindbrain; spinal cord
Much of medulla serves as a:
conduit for tracts that link the brain with input and output nodes in spinal cord but it also contains centers for regulation of vital functions such as heart beat and respiration.
walls of the metacephalon form the
pons and cerebellum
the cavity of metencephalon forms the
the superior part of the 4th ventricle
T or F: As in the myelencephalon, neuroblasts, in each basal plate develop in the motor nuclei and organize into three columns on each side of the metencephalon
PONS is derived from
derived from basal plate of metencephalon
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