Development of the Nervous System

Question 1

Describe the sequence of events from the establishment of the notochord through the formation of the early central nervous system.

Answer 1

1. mesoderm gives rise to notochord which induces ectoderm to differentiate into the neuroectoderm
2. neuroectoderm thickens into neural plate
3. neural plate develops a neural groove
4. neural grooves neural folds rise and eventually meet each other forming the neural tube
5. neural tube closes 1st in the occipital region and proceeds craniad and caudad & openings at each end are the rostral/caudal neuropores
6. neural crest will become the PNS

Question 2

what is the precursor for CNS

Answer 2

neural tube

Question 3

Describe the mitosis, differentiation, and migration of neuroepithelial cells of the neural tube into layers

Answer 3

1. germinal layer - neuroectoderm of early neural tube undergoes mitosis
2. mantle layer - daughter cels move outward creating this layer of neuroblasts which differentiate into neuronal cell bodies & glia
3. marginal layer - neuroblasts continue outward to form this third layer of developing bundles of cell processes “tracts”

Question 4

how the layers relate to the layers of the adult spinal cord

Answer 4

1. most centrally, ependymal cells are the remnant of the germinal layer
2. spinal cord gray matter composed of neurons and glia remnant of the mantle layer
3. spinal cord white matter made of axons of neurons remnant of marginal layer

Question 5

origin of the pituitary gland

Answer 5

Anterior pituitary “adenohypophysis” originates from the ectoderm of roof of the mouth

Posterior pituitary “neurohypophysis” originates from the neuroectoderm layer “infundibulum”

Question 6

Identify the elements of the nervous system that derive from neural crest

Answer 6

the PNS

Question 7

What is meant by the assertion that motor neurons and the muscles are reciprocally dependent on one another for development?

Answer 7

muscles need to be innervated and produce early embryonic contractions to fully develop

motor neurons depend on targets for development and those that do not find targets undergo apoptosis

Question 8

Describe the evagination and differentiation of the optic vesicle to form the retina

Answer 8

optic vesicle bunds from the forebrain (diencephalon)
optic vesicle forms optic cup which becomes retina
optic stalk (optic cup connection to the diencephalon) becomes optic nerve

Question 9

How is the lens formed? From what tissue does it derive?

Answer 9

lens forms from the lens placode (thickening of the ectoderm and optic vesicle)
lens derived from ectoderm

Question 10

what is the choroid fissure

Answer 10

the optic cup has a cleft on its ventral side where the eye receives embryonic arterial supply from hyaloid a.

eventually fuses with development and artery disappears

Question 11

what is a dysraphism

Answer 11

midline abnormality
most severe ones associated with nervous tissue (bone < meninges < nervous tissue)

Question 12

Answer 12

spina bifida

dysraphism of bone
split or absent vertebral arch

Question 13

Answer 13

meningoceles

dysraphism of meninges (connective tissue)

Question 14

myelodysplasias

Answer 14

dysraphism of nervous tissue
abnormal formation of spinal cord due to failure of closure of caudal neuropore

associated with spina bifida

Question 15

Answer 15

myeloschisis

dysraphism of nervous tissue
split of neural tube

Question 16

anencephaly

Answer 16

dysraphism of nervous tissue
failure of brain development due to failure of closure of rostral neuropore

Question 17

what is the cauda equina

Answer 17

bundle of dorsal and ventral roots in the sacrum after the adult spinal cords ends at L6/7

Question 18

Answer 18

coloboma
failure of the choroid fissure to close completely

Question 19

Answer 19

cyclopia

failure of prosencephalon to produce 2 separate telencephalic vesicles