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1

when does the nervous system arise

3rd week of life

- when 3 principal layers are being generated by process of gastrulation

2

what are the 3 principal layers of the nervous sytem

ectoderm

medoderm

endoderm

3

what happens during gastrulation?

- outer cells (epiblast) of embryo detach, migrate through primitive streak (groove) --> mesoderm and ectoderm are generated

- remaining outside cells (epiblast) form ectoderm, from which NS develops. Later becomes epidermis

4

what happens at the beginning of the 3rd week of development to the ectoderm layer

in response to signals from midline tissues (notochord and prechordal mesoderm)

the ectoderm layer begins to thick and form neural plate

5

what do the cells of the neural plate do? (2 things)

- invaginate and form canal (basis of NS)

- make up neuroectoderm and their induction represents the initial event of neurulation

6

what is neurulation

formation of the nervous system

7

in which way does the NS mature?

top to bottom

8

the CNS begins initially from....

uniform sheet of cells= neuroepitheliu m

9

when is the neural plate formed and how

3rd week of development

- longitudinal band of ectoderm thickens to form the plate

10

how is the neural groove formed

neural plate folds inwards forming neural groove, flanked by neural folds

11

how is neural tube formed

as neural groove deepens, the folds move medially and begin to fuse forming the neural tube

12

what is the function of notochord?

instruct NS to become ventral

13

what do somites give rise to

give rise to skeleton, skin, and specialized cells called melanocytes

-- they are called dermomyotome

14

rostral vs caudal

rostral= top/upper

caudal= bottom/lower

15

cephalic and caudal ends of neural tube comminicate with...

until the fusion is complete, they communicate with amniotic cavity by way of cranial (anterior) and caudal (posterior) neuropores

16

what happens at day 25

closure of cranial neuropore

18-20 somites

17

what happens at day 27

closure of caudal neuropore

25 somites

18

close of neural tube sensitive to... (2)

- environmental agents
- aberrant gene activity

failure of proper closure leads to neural tube defects

19

neural tube separating from the ectoderm

as the tube closes (fusion occuring rostrally and caudally), it separates from overlying ectoderm

20

notochord involved in ... and becomes

it is the transient axial mesodermal structure

- involved in ventral patterning of NS

- becomes incorporate in developing intervertebral disks of the skeleton

21

mesoderm-derived somites will form...

most of the vertebral column and segmental units of muscle (myotomes) and dermis (dermatome)

22

what happens at day 24 and 26

24: tube is closed at rostral end

26: closed at caudal end, local enlargements (primary vesicles) are apparent

23

3 primary vesicles

prosencephalon
mesencephalon
rhombencephalon

24

in early development, 2 types of tissues

epithelium (have basement membrane)

mesenchyme

25

what does the sulcus limitans do during closing of neural tube

separates dorsal and ventral tubes

26

neural tube defects frequency (live births)

occurs in 1 per 1000 live births

27

3 types of neural tube defects

cranioarchischisis
anencephaly
spina bifida

28

cranioarchischisis

- open spinal cord and spine
- CNS is abnormally open on dorsal surface

- complete failure neural tube fusion

29

anencephaly

- failure rostral end of neural tube to close

- fetus born no/reduced head

30

spina bifida

- failure of caudal end of neural tube to close
- caudal walls are continuous with skin of the back, the cord and meninges are displaced into a saclike cavity on back
- vertebrate fail to form over lesion

- can be corrected by surgery