Nervous System Development Flashcards
Tissue of neural plate
Simple columnar
Tissue of early neural tube wall
- pseudostratified
- 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?
- Shh
- restricts expression of Pax-7 (related to formation of alar plate)
What is the master gene of eye formation?
- Pax-6
- 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?
- chemoattraction
- contact attraction
- chemorepulsion
- contact repulsion
What are some microenvironment cues of axon guidance?
- caudal half of somite
- fibronectin and laminin
- integrins
- cadherins
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
