SDL: Neuroembryology

Question 1

what does the midline axial mesoderm form from?

Answer 1

the notochord

Question 2

what does the notochord induce?

Answer 2

the overlying ectoderm, to form the neural plate

Question 3

what is the difference between primary and secondary neurulation?

Answer 3

primary: developing notochord induces the overlying embryonic ectoderm to thicken and form the neural plate– secondary: coalescence of caudal mass mesenchymal cells into a rod followed by cavitation to form a tube and fusion with primary neural tube

Question 4

in which process (primary or secondary neurulation) does the notochord play a role?

Answer 4

primary neurulation: notochord induces the overlying embryonic ectoderm to thicken and form the neural plate

Question 5

what embryonic germ cell layer forms from the neural tube in primary and secondary neurulation?

Answer 5

primary: ectoderm fusion; secondary: mesenchymal condensation, epithelial translocation

Question 6

what structures related to the PNS do neural crest cells give rise to?

Answer 6

spinal nerve ganglia, cranial nerve ganglia, ANS ganglia, schwann cells

Question 7

what is the specific timing difference between closure of the anterior and posterior neuropores? which occurs last?

Answer 7

anterior neuropore closes on day 25; posterior neuropore closes on day 27

Question 8

the 2 types of spina bifida

Answer 8

closed skin (occulta), open skin condition (neural plate is directly exposed to amniotic fluid)

Question 9

spina bifida occulta typically occurs where? this is an example of what type of neurulation defect?

Answer 9

lumbar/upper sacral junction; secondary neurulation defect

Question 10

if spina bifida occulta occurs in the upper regions of the vertebral column, it would arise from incomplete fusion of post. neuropore during..

Answer 10

primary neurulation (this is rare)

Question 11

what is the difference between spina bifida occulta versus a meningocele versus a myelomeningocele? which would cause more severe neurological symptoms?

Answer 11

occulta: defect in vertebral arches, doesn’t involve neural tissue (no symptoms); meningocele: fluid-filled sac of meninges pokes through defect (Neuro symptoms); myelomeningocele: neural tissue in the fluid sac (neuro symptoms)

Question 12

5 neural tube defects that are examples of primary neurulation defects

Answer 12

craniorachischisis totalis, anencephaly, myeloscisis, encephalocele and myelomeningocele

Question 13

what would you call a defect where primary neurulation failed to occur anywhere in the fetus?

Answer 13

craniorachischisis totalis?

Question 14

what would you call a defect where the ant neuropore failed to close in the region overlying the top of the head? what happens to the neural plate that is located in this region?

Answer 14

anencephaly; exposed neural tissue dies

Question 15

what would you call a defect where there is an outpocketing of neural tissue in an instance where there is a partial failure of closure of the anterior neuropore in the region of the back of the head?

Answer 15

encephalocele

Question 16

what would you call a defect in which there is complete failure to close the post neuropore?

Answer 16

myeloschisis

Question 17

what risk factors are there for neural tube defects? how can a pregnant mother reduce the risk of having a baby with a neural tube defect?

Answer 17

folic acid deficiency (sexually active women should take folic acid 2 mos before conception and throughout pregnancy), diabetic mothers, alcoholics, nutritional deficiencies

Question 18

which protein would increase in maternal serum and amniotic fluid in cases of neural tube defect?

Answer 18

alpha-fetal protein

Question 19

when should women of childbearing age begin taking daily supplements of folic acid? why?

Answer 19

2 mos before conception and throughout pregnancy to prevent neural tube defects

Question 20

what are the molecular mechanisms of neurulation? (will only be tested on sonic, bone morogenic protein, homeobox genes)

Answer 20

notochord secretes hedgehog protein that induces overlying ectoderm to differentiate into neuroectoderm; opposing sonic hedgehog bone morphogenic protein gradients promote the dorsoventral differentiation; spatial and temporal differences in the homeobox genes are important for anterior-posterior axis development and secondary neurulation

Question 21

which cells give rise to neuroblasts in the developing spinal cord?

Answer 21

neural crest cells in the cerebral cortex

Question 22

which cells give rise to the astrocytes and oligodendroglia?

Answer 22

neuroepithelial cells

Question 23

what causes holoprosencephaly?

Answer 23

failure to form the two cerebral hemispheres- fails to cleave, remains fused as a single midline entityra

Question 24

what is the function of the radial glia in the developing cerebral cortex?

Answer 24

neurons migrate along them; also progenitor cells

Question 25

what is the difference between schizencephaly, lissencephaly, pachygyri or polygyri?

Answer 25

schizencephaly (cleft brain, paralysis, seizures); lissencephaly (smooth brain, few gyri); pachygyri (broad gyri, too few gyri); polygyri (small gyri)

Question 26

what is the underlying cause of schizencephaly, lissencephaly, pachygyri or polygyri?

Answer 26

disorders of migration

Question 27

which condition has an abnormal cleft in the brain?

Answer 27

schizencephaly

Question 28

which condition has a generalized absence of cerebral cortical gyri?

Answer 28

lissencephaly