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___ span the length of the cortex and allow for a high degree of correspondence b/t where neurons are produced and where they migrate to in the cortex
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radial glia cells
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the embryonic stage ends at __ wks with the formation of the ___
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week 8; neural tube
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cell adhesion molecules like N-Cam and N-cadherin, along with neurotrophic factors like BDNF are important in which stage of nervous system development?
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synaptogenesis /targetting
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the ___ induces ectoderm to become neural tissue
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notocord
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give rise to melanocytes, schwann cells, chromaffin cells, and others
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trunkal neural crest cells
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in humans, the ___ induces the ectoderm to become the nervous system by blocking ___
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notocord; BMP
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what is the placodal ectoderm?
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the area just outside the neural crest. not neurectoderm. gives rise to sensory epithelia of the nose, inner ear, lens, ant. pituitary, and some neurons of sensory ganglia of cranial nerves
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describe the process of gastrulation.
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3rd weekin the embryonic disc, epiblast cells migrate medially and dive down into the center of the embryonic disc, creating the primitive groove. the first epiblast cells that dive in become the endoderm. the next epiblast cells that dive in become the mesoderm. the epiblast cells that dont dive in become the ectoderm
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gradients of molecules establish dorsal-ventral patterning of the neural tube. the dorsal epidermis establishes a gradient of __ and the notocord establishes a gradient of ___
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dorsal epidermis - BMP (BMP 4,7,and dorsalin)notocord - Sonic hedge hog (Shh)
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the PNS is derived mainly from ___
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neural crest cells
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when neurons lose in the competition for neurotrophic factors, what happens?
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they undergo synaptic elimination or apoptosis
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the apical pole cells of the spinal cord face ___
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the central canal
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where does neurogenesis occur postnatally?
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hippocampussubventricular region of the cortex
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why does the ventricular epithelium appear pseudostratified?
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it is the proliferative zone, and the cells are at different stages of proliferation. the nucleus changes relative position as the cells prepare to divide and divide.
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what is flexure of the neural tube?
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the cephalic flexure occurs at the mesencephalon allowing the forebrain to tuck under the hindbrain. the cervical flexure occurs b/t the hindbrain and spinal cord and allows for bulging and segmentation.
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which cells in the brain are not derived from neurectoderm?
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microglia
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what is primary neurulation
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when the sides of the neural plate fold up to form the neural tube
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describe the process of corticogenesis
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the whole brain develops from a single layer of neuroepithelium"progenitor cells" capable of becoming cortical neurons or glia proliferate in the ventral epithelium. they then migrate to the intermediate zone and then along radial glia to the cortical plate. layer VI (the innermost layer) forms first. Layer I forms last. the cortex forms from the inside outwards. the cells destined to become glia keep dividing once they reach the cortical plate
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the part of the neural plate found at its lateral margins
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neural crest
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the notocord is formed from ___
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midline axial mesoderm
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where does neural groove begin to fuse?
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the 4th somite. extends rostrally and caudally. rostral neuropores fuse first
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what is the neural plate?
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prior to neurulation, the notocord induces the overlying ectoderm to thicken and differentiate into neurectoderm, which makes up the neural plate.
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the part of the neural plate that is midline and directly over the notocord
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floor plate
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fusion of the neural folds require the cell adhesion molecules ___ and ____
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N-cadherin and N-Cam
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what establishes the alar and basilar plates of the spinal cord
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a dorsal gradient of BMP established by the dorsal epidermis a ventral gradient of Sonic hedge hog established by the notocord
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noggin, chordin, and follistatin block the ____ signalling pathway
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BMP
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which stage of nervous system development does not end until six months postnatally
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differentiation
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holoprosencephaly results from a mutation of ____
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Shh (sonic is such a bastard!)
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a herniation of brain tissue through a hole in the skull
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encephalocoele
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2 parts of the embryonic disc and what they form
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1.epiblast - forms the embryo proper2.hypoblast - forms part of the yolk sac
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transcription factors differentially expressed along the anterior-posterior axis that regulate other transcription factors involved in development
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hox (homeobox domain) genes
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the zygotic ends at week __ with the formation of the ___
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week 2; embryonic disc
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the majority of myelination occurs prenatally/postnatally?
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postnatally
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failure of the lobes of the brain to separate
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holoprosencephaly
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neurulation occurs prenatally/postnatally?
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totally prenatally
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condition in which the cerebellar tonsils slip into the foramen magnum
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Arnold Chiari formation
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the furrow between the alar and basal plates?
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sulcus limitans
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neurofibromatosis is a tumor associated w/ __
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NCC's
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Reelin is an extracellular matrix molecule involved in ____
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migration
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what is wedging?
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the change in cell shape in parts of the neural tube where the basal domain becomes much larger than the apical domain resulting in a hinge point.
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what germ layer forms the excretory system and gonads?
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mesoderm
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2 parts of the blastocyst and what they form
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1.trophectoderm - the placenta2.inner cell mass - everything else, including the embryo proper
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caused by failure of the anterior neural pore to fuse
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anencephaly
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how does segmentation of the rostral neural tube occur?
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there are constrictions dividing the rostral neural tube into 3 vesicles: the prosencephalon, mesencephalon, and rhombencephalon. some sections have weaker cell-cell interactions and are more easily expanded by fluid pressure (blown up like a balloon?)
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what germ layer forms the glands, including the pancreas and liver?
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endoderm
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caused by inappropriate closing of the posterior neural tube during the first month of pregnancy (wk 4?)
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spina bifida
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which neurons of the PNS do not arise from the neural crest cells?
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1. motor neurons - their cell bodies lie in the ventral horn and their axons grow into the somites2. preganglionic autonomic neurons - their cell bodies lie in the lateral horn (symp) or in the brain? (para)3. placodal ectoderm gives rise to certain cranial nerve sensory neurons.ex. sensory epithelia of the nose, inner ear, lens, some neurons of the sensory ganglia
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basal and apical pole cells are linked by _____
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junctional complexes
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malignant melanoma is a tumor associated w/ __
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NCC's (melanocyte)
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the majority of neurons are formed prenatally/postnatally?
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prenatally
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what parts of the ventricular system do the vesicle cavities form?
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prosencephalon - 1,2,3 ventriclesmesencephalon - cerebral aqueductrhombencephalon - 4th ventricle
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Wnt, BMP, retinoic acid, and FGF are examples of ____
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anteriorizing and posteriorizing factors
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the default pathway of the ectoderm is development into ___
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neural tissue
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proneural genes and gliogenic genes
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genes whose expression determine whether a progenitor cell will develop into neuron or glia
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___ acts on the ectoderm to cause formation of epidermis
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BMP
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what causes closure of the neural tube? what time does this occur?
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4th weekthe neural folds are brought close together and form cell-cell junctions at the dorsal midline.
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what is the neural groove?
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the midline fold of the neural plate as the neural folds rise up to become the sides of the neural tube
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ApoER2 and VLDLR are two signalling receptors involved in ____
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neuronal migration (to the cortex)
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give rise to the branchial arches and periocular tissues
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cranial neural crest cells
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where and why is there a transient blockage in the neural vesicles?
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between the hindbrain and spinal cord during the bulging of segmentation.
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5 stages of neural development?
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1. neurulation2. proliferation3. migration4. differentiation5. synaptogenesis / targetting
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origin of the sensory epithelia of the nose and inner ear?
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placodal ectoderm
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