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37 Cards in this Set

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From where does the nervous system develop?
Ectoderm of germ disc
What are the precursors to the brain and spinal cord?
Notochord and adjacent mesoderm induce the overlying ectoderm to form a neural plate that ultimately becomes the neural tube which will differentiate into brain and spinal cord
Describe the formation of the neural tube
1) Neural plate- thickened ectoderm
2) Neural folds
3) Neural tube
Fusion begins in midportion of neural groove and extends in both cranial and caudal directions
Cranial (anterior) neuropore closes about day 25, and the caudal (posterior) neuropore closes about 2 days later
The completely closed neural tube detaches from the ectoderm and sinks into the underlying mesoderm
Describe the molecular regulation of the neural tube
1) Noggin, chordin, and follistatin inactivates BMP-4 causing the ectoderm to become neuralized (neural plate- forebrain and midbrain)
2) WNT-3a and FGF are needed to allow induction of the caudal neural plate to form hindbrain and spinal cord
3) Initially, the PAX3, PAX7, MSX1, and MSX2 genes are expressed throughout the neural plate
4) Shh expression from notochord induces neural plate to ventralize and the floor plate to form by repression of PAX and MSX (basal plate)
5) BMPs upregulate PAXs expression in the dorsal neural tube that will form the roof plate and alar plate
What are the two main portions of the neural tube?
1) Cranial portion- expands to form the brain
2) Caudal portion- elongates to form spinal cord
What are the 3 formations of the cranial portion of the neural tube?
1) Three vesicles form: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)
2) Ventricle formation: lateral, interventricular foramena (monro), third, cerebral aquaduct (sylvius), and fourth
3) Brain flexures- cervical, cephalic (midbrain), and pontine
Describe 9 aspects of the caudal portion of the neural tube
1) Neural tube is formed from neuroepithelial cells that rapidly divide thereby thickening the wall of the tube
2) Some neuroepithelial cells become neuroblasts which form the mantle layer around the neuroepithelial layer. The mantle layer becomes the gray matter of the spinal cord
3) Neuroepithelial cells will also give rise to astrocytes and oligodendroglia. Microglial cells are derived from mesoderm which migrate into the neural tube
4) A layer of neuroepithelial cells will line the cavity of the neural tube. These become the ependymal cells of the ventricles and spinal cord
5) As neuroblasts differentiate into neurons they extend processes to the periphery of the neural tube. As the processes become myelinated, this layer is termed the marginal layer (white matter)
6) Mantle layer
7) Neural crest
8) Spinal nerve
9) Positional changes of spinal cord
List the 5 components of the mantle layer
1) Basal plate- ventral horn- motor
2) Alar plate- dorsal horn- sensory
3) Sulcus limitans
4) Roof plate and floor plate
5) Intermediolateral cell column- sympathetic T1-L3- ANS
List 9 components of the neural crest
1) Spinal ganglia (dorsal root)
2) Sympathetic ganglia
3) Schwann cells (neurilemma)
4) Leptomeninges (pia and arachnoid)
5) Melanocytes
6) Odontoblasts (dentin of teeth)
7) Head mesoderm- pharyngeal arches
8) Suprarenal medulla
9) Heart (septum)
List and describe 4 components of spinal nerve
1) Ventral root- axons from neurons in basal plate
2) Dorsal root- axons from neurons of spinal (sensory) ganglia
3) Dorsal and ventral roots combine peripherally to form the spinal nerve (mixed sensory and motor)
4) Spinal nerve will further subdivide into dorsal and ventral primary rami supplying epimeric and hypomeric musculature
Describe the positional changes of the spinal cord
1) Initially, spinal cord extends entire length of embryo
2) Dura and vertebrae grow faster than spinal cord
3) At birth, end of cord (conus medullaris) is at L3 level
4) Cord ends between L1 and L2 in adult
List 4 possible neural tube defects
1) Spina bifida- results from vertebral rachischisis
2) Cranium bifida- ossification defect of skull
3) Exencephaly- cranial neuropore remains open which results in the condition termed anencephaly
4) Hydrocephalus- caused by aquaductal stenosis
List 3 types of spinal bifida
1) Occulta
2) Cystica- meningocele and meningomyocele
3) Myeloschisis (spina bifida aperta)- Arnold-Chiari malformation- herniation of cerebellum due to tethering of cord in spina bifida cystica
List 3 types of cranium bifida
1) Meningocele
2) Meningoencephalocele
3) Meningohydroencephalocele
Describe the formation of the pituitary gland (hypophysis)
1) Rathke's Pouch- adenohypophysis, pars tuberalis, and pars intermedia
2) Infundibulum- stalk and pars nervosa
List 4 characteristics of spinal nerves
1) All cranial nerves except olfactory (I), optic (II), and spinal accessory (XI) arise from brainstem
2) All that arise from brainstem do so from the rhombencephalon except oculomotor (III) and trochlear (IV) which arise from mesencephalon
3) Rhombomeres- induction is by signaling of underlying somitomeres formed from paraxial mesoderm, give rise to motor nuclei of cranial nerves V, VI, VII, IX, X, and XII
4) Ectodermal placodes- give rise to sensory ganglia along with neural crest cells
List the 3 types of ectodermal placodes
1) Nasal- sensory epithelium in nose
2) Otic- ear
3) Epibranchial (4)- contribute ganglia to the cranial nerves V, VII, IX, and X which supply the pharyngeal arches
What are the 2 divisions of the autonomic nervous system?
1) Sympathetic
2) Parasympathetic
List 3 characteristics of the parasympathetic nervous system
1) Fibers carried by cranial nerves III, VII, IX, and X
2) Ganglia are derived from neural crest
3) Also in sacral spinal nerves S2, S3, and S4
List 2 characteristics of the sympathetic (T1-L2 or L3) nervous system
1) Thoracic neural crest migrates the entire length of the developing spinal cord and these neuroblasts form the chain ganglia
2) Other neural crest derived neuroblasts migrate further to form the preaortic (collateral) ganglia and sympathetic organ plexus ganglia (cardiac, pulmonary, and gastrointestinal)
Preganglionic cell fibers (intermediolateral cell column)
White ramus communicans
Postganglionic fibers
Gray ramus communicans
What does the blocking of BMP4 expression cause?
Formation of the neural plate in the middle of the ectoderm
What do PAX3 and PAX7 become?
Bipolar sensory neurons
What does Shh signaling initiate?
Invagination of the neural plate into the embryo
When does the cranial neuropore close? The caudal neuropore?
Around day 25
Two days later
What is the fate of neuroepithelial cells?
Remain on central canal and will form part of CSF
Ganglia are derived from what?
Neural crest
What direction does epimeric musculature grow?
Dorsally
What direction does hypomeric musculature grow?
Ventrally
What part of the vertebrae is missing in spina bifida occulta?
Pedicle and part of lamina
What is lacking to complete development in spina bifida aperta?
Shh
What is Arnold-Chiari malformation?
The brain stem and cerebellum are pulled through the formen magnum due to a stretching of the spinal cord. Spinal cord is tethered in place due to spina bifida aperta
Define exencephaly
Cranial neural tube failed to close
Define craniorachischisis
Skull failed to completely form
Molecular signaling from where influence development of the rhombencephalon (hindbrain)?
Occipital somites
Where do motor nuclei develop?
Rhombomeres of neural tube
Describe ectodermal placodes
Form from surface ectoderm
Move into embryo then populated by neural crest cells which form neurons of the sensory ganglia of cranial nerves
What do neural crest cells of the caudal neural tube form?
Neurons of the DRG and sympathetic ganglia