Nervous System Development

Question 1

Tissue of neural plate

Answer 1

Simple columnar

Question 2

Tissue of early neural tube wall

Answer 2

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

Question 3

Tissue of late neural tube wall

Answer 3

Stratified epithelium

Question 4

Describe the importance of orientation of plane of metaphase plate.

Answer 4

-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

Question 5

What does neuroepithelium refer to?

Answer 5

-initial epithelial layer of the neural tube

Question 6

What is a bipotential progenitor cell?

Answer 6

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

Question 7

Ventral signaling

Answer 7

• notochord induces formation of the floor plate of the neural tube via Shh
• Shh produced induces the formation of motor neurons

Question 8

Dorsal signaling

Answer 8

• 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

Question 9

Describe primary neural induction.

Answer 9

• 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

Question 10

What does cranial nerve V innervate?

Answer 10

-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

Question 11

What does cranial nerve VII innervate?

Answer 11

-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

Question 12

What does cranial nerve IX innervate?

Answer 12

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

Question 13

What causes the segmented nature of spinal nerves?

Answer 13

-pattern of somitic mesoderm along neural tube

+motor neurons can penetrate anterior mesoderm of somites but not posterior mesoderm

Question 14

Where is the isthmic organizer found?

Answer 14

-between mesencephalon and metencephalon

Question 15

What does the isthmic center do?

Answer 15

-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

Question 16

What causes the dorsoventral patterning of the midbrain?

Answer 16

• Shh

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

Question 17

What is the master gene of eye formation?

Answer 17

• Pax-6

- expressed in alar plate of diencephalon

Question 18

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

Answer 18

-Pax-6 inhibiting En-1

Question 19

What represents forebrain formation?

Answer 19

• P1-P3 define the diencephalon

- P2-P3 define the dorsal and ventral thalamus

Question 20

What is the secondary rhombencephalon field?

Answer 20

-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

Question 21

Describe motor axon outgrowth.

Answer 21

• 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

Question 22

Describe the formation of sensory neurons.

Answer 22

• 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

Question 23

What is the growth cone of the axon outgrowth?

Answer 23

• characterized by expanded region of cytoplasm with filopodia
• growth cones advance via extension/resorption cycles that involves microfilaments

Question 24

What environmental factors influence axon outgrowth?

Answer 24

• chemoattraction
• contact attraction
• chemorepulsion
• contact repulsion

Question 25

What are some microenvironment cues of axon guidance?

Answer 25

• caudal half of somite
• fibronectin and laminin
• integrins
• cadherins

Question 26

How are normal neuron components/processes involved?

Answer 26

-Axonal transport, microtubules, neurofilaments

Question 27

What happens when a motor axon meets a muscle fiber?

Answer 27

-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

Question 28

How do autonomic. Neurons differentiate?

Answer 28

-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)

Question 29

How do parasympathetic preganglionic motor neurons arise?

Answer 29

• 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

Question 30

How do sympathetic preganglionic neurons arise?

Answer 30

• 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

Question 31

Describe the sympathetic motor neurons.

Answer 31

• not myelinated
• may extend directly from collateral ganglia to target organs
• may reenter ventral root of spinal nerve through gray ramus comminicans

Question 32

Tissue of early neural epithelium

Answer 32

Simple cuboidal