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Embryology Exam II > Nervous System Development > Flashcards

Flashcards in Nervous System Development Deck (32):

Tissue of neural plate

Simple columnar


Tissue of early neural tube wall

-single layer of columnar cells with nuclei at varying heights
-limiting membranes (basal lamina)


Tissue of late neural tube wall

Stratified epithelium


Describe the importance of orientation of plane of metaphase plate.

-if metaphase plate is perpendicular to inner margin of neural tube, two resulting daughter cells will remain proliferative
-if metaphase plate is parallel to inner margin:
+daughter closest to lumen will remain proliferative
+daughter cell further from lumen wall will express Notch, become postmitotic, move to external limiting membrane, become a neuroblast


What does neuroepithelium refer to?

-initial epithelial layer of the neural tube


What is a bipotential progenitor cell?

-refers to the fact that the cell has been restricted to one of two pathways: neuronal lineage progenitor or glial lineage progenitor


Ventral signaling

-notochord induces formation of the floor plate of the neural tube via Shh

-Shh produced induces the formation of motor neurons


Dorsal signaling

-ectoderm flanking the neural plate uses BMP to induce snail-2 in the future neural crest and later to maintain Pax-3 and Pax-7 to creat dorsalizing effect

-expression of Pax-3 and Pax-7 is suppressed by Shh to suppress dorsalizing in the basal plate


Describe primary neural induction.

-the primitive node and notochordal process act as the primary inductors of the nervous system

-cranial end divides into tripartite brain and caudal becomes subdivided into segments (neuromeres) of which rhombomeres are most prominent

-specific homeobox genes are expressed in a regular order in the rhombomeres

-the isthmian organizer is located at the junction between the midbrain and the hindbrain and acts by the production of Wnt-1 anteriorly and FGF-8 posteriorly


What does cranial nerve V innervate?

-innervates structures derived from the first pharyngeal arch
+progeny of a single neuroblast remain within rhombomere 2
+axons from rhombomere 3 join those of rhombomere 2


What does cranial nerve VII innervate?

-innervates structures derived from the second pharyngeal arch
+progeny of a single neuroblast remain within rhombomere 4
+axons from rhombomere 5 join those of rhombomere 4


What does cranial nerve IX innervate?

-innervates structures derived from the 3rd pharnygeal arch
+progeny of single neuroblast remain within rhombomere 6
+axons from rhombomere 7 join those of 6


What causes the segmented nature of spinal nerves?

-pattern of somitic mesoderm along neural tube
+motor neurons can penetrate anterior mesoderm of somites but not posterior mesoderm


Where is the isthmic organizer found?

-between mesencephalon and metencephalon


What does the isthmic center do?

-principle signaling molecule is FGF-8

-FGF-8/Wnt-1 induce expression of:
+En-1, En-2, Pax-2, Pax-5

-organizes and polarizes dorsal midbrain and cerebellum


What causes the dorsoventral patterning of the midbrain?


-restricts expression of Pax-7 (related to formation of alar plate)


What is the master gene of eye formation?


-expressed in alar plate of diencephalon


What signaling molecules result in the formation of the diencephalic-mesencephalic border?

-Pax-6 inhibiting En-1


What represents forebrain formation?

-P1-P3 define the diencephalon

-P2-P3 define the dorsal and ventral thalamus


What is the secondary rhombencephalon field?

-large area of the forebrain cranial to P3 and represents the prechordal region of the neural tube
+basal plate develops into hypothalamus
+alar plate develops into cerebral cortex, basal nuclei, and optic vesicles


Describe motor axon outgrowth.

-axons grow out from the motor neuroblasts located in the basal plate of the spinal cord

-boundary caps created by neural crest cells maintain separation between central nervous system components and peripheral nervous system components


Describe the formation of sensory neurons.

-cell bodies of sensory neurons are derived from neural crest cells

-cell bodies of sensory neurons form sensory spinal ganglia

-axons grow from these cell bodies both toward the spinal cord and the periphery

-boundary caps maintain separation


What is the growth cone of the axon outgrowth?

-characterized by expanded region of cytoplasm with filopodia

-growth cones advance via extension/resorption cycles that involves microfilaments


What environmental factors influence axon outgrowth?

-contact attraction
-contact repulsion


What are some microenvironment cues of axon guidance?

-caudal half of somite
-fibronectin and laminin


How are normal neuron components/processes involved?

-Axonal transport, microtubules, neurofilaments


What happens when a motor axon meets a muscle fiber?

-cessation of outgrowth of axon

-preparation by neuron for release of neurotransmitter molecules:
+synaptic vesicles fill with ACh
+induction of synaptic vesicle release sites

-muscle fiber preparations for signal transduction
+junction specific ACh receptors become concentrated in postsynaptic folds
+nonfunctional ACh receptors are eliminated
+ACh-esterase accumulates in basal lamina


How do autonomic. Neurons differentiate?

-BMPs determine whether migrating neural crest cells differentiate into I autonomic neurons or other neural crest derivatives

-shift if determined autonomic neurons into sympathetic or parasympathetic neurons
+due to multitude of transcription factors
+involves selecting the specific type of neurotransmitter to be used (sym -> adrenergic, para -> Cholinergic)


How do parasympathetic preganglionic motor neurons arise?

-from intermediate/lateral horns of gray matter (midbrain, hindbrain, and S2-S4) -> associated with cranial nerves III, VII, IX, and X

-neurons are typically long and synapse with postganglionic neurons within plexues in or near the walls of the target organ

-gut wall may have considerable influence in the migratory and mitotic activity of these neurons


How do sympathetic preganglionic neurons arise?

-intermediate/lateral gray matter (levels of origin are T1 through L2)

-myelinated axons move through the ventral roots of the spinal cord and then through the white communication rami

-axons enter sympathetic chain ganglia or collateral ganglia -> neural crest cells

-preganglionic axons synapse with cell bodies of postsynaptic sympathetic motor neurons within the ganglia


Describe the sympathetic motor neurons.

-not myelinated

-may extend directly from collateral ganglia to target organs

-may reenter ventral root of spinal nerve through gray ramus comminicans


Tissue of early neural epithelium

Simple cuboidal