8. Development of the Nervous System

Question 1

what is the first stage of embroygenesis

Answer 1

cleavage

Question 2

describe the first two cleavages

Answer 2

perpendicular equal and holoblastic

Question 3

why is cleavage 3 different from cleavage 1 and 2

Answer 3

it is no unequal and holoblastic

Question 4

cleavage continues until how many cells are made

Answer 4

32

Question 5

during cleavage what is the early embryo contained in

Answer 5

the zona pellucida

Question 6

once it reaches 32 cells what is the embryo now termed

Answer 6

a morula

Question 7

what occurs during the compaction stage

Answer 7

cells get closer together and the cells on the outside differentiate into trophoblast cells.

the inner cells are called embryoblasts

Question 8

what occurs on day 5

Answer 8

embryoblast cells clump together at one end, the remainder of the space inside the layer of trophoblast cells becomes the blastocoel

Question 9

what is a blastocoel

Answer 9

a fluid filled cavity

Question 10

what happens to the zona pellucida on day 5

what does this facilitate

Answer 10

it decomposes and is replaced by the underlying layer of trophoblastic cells

this facilitates implantation into the endometrium

Question 11

what then occurs to the inner cell mass

Answer 11

it flattens out, the two cells become epiblasts and the layer below become hypoblasts

Question 12

what is the term given for the inner cell mass once it has flattened out

Answer 12

the bilaminar disk

Question 13

once the bilaminar disk is formed, what happens next

Answer 13

the primitive streak forms at the midline of epiblast cells, from this they ingress into the blastocoel

Question 14

what dictates epiblast fate

Answer 14

the order of which they enter the blastocoel

the first cells become endoderm
the middle cells become mesoderm
the last cells become ectoderm

Question 15

name 2 things the endoderm goes on to form

Answer 15

liver
lungs

Question 16

name 2 things the mesoderm goes on to form

Answer 16

muscle
blood

Question 17

name 2 things the ectoderm goes on to form

Answer 17

all parts of the nervous system
ear
lens of eye…

Question 18

what directs the migration of epiblast cells into the blastocoel

Answer 18

the organiser

Question 19

what determines the dorso-ventral axis

Answer 19

the point of sperm entry = ventral side
from this microtubules contract and the cytoplasm rotates facilitating the formation of a signalling centre on the dorsal side

Question 20

what is the name of signalling centre generated in response to sperm entry

Answer 20

the nieuwkoop centre

Question 21

describe the process of mesoderm specification along the axis

Answer 21

1. BMP4 is expressed in the marginal zone and induces ventral mesoderm
2. VegT and Vg1 induce nodal-related in the vegetal hemisphere
3. beta catenin boosts nodal related in the nieuwkoop centre which induces dorsal mesoderm and the organiser
4. the organiser produces chordin which acts as a dorsalising signal
5. colloid cleaves chordin in the vegetal hemisphere allowing BMP4 to act.

Question 22

what does the dorsal most aspect of mesoderm develop into

Answer 22

the notochord

Question 23

what does the ventral most aspect of mesoderm develop into

Answer 23

blood

Question 24

name the organiser in chicks

Answer 24

hensens node

Question 25

name the organiser in amphibians

Answer 25

spemann's organiser

Question 26

name the organiser in mammals

Answer 26

primitive knot (or node)

Question 27

describe Spemann and Mangold's experiment

Answer 27

they confirmed the role of the organiser by transplanting tissue from a pigmented embryo into a non-pigmented embryo this could induce the formation of two new embryos by implanting the specific tissue that included the organiser

Question 28

what happens if you cut a blastula in two

Answer 28

the ventral side will not develop into muscle - only ventral mesoderm fates such as blood develop the organiser must be present in the dorsal marginal zone to produce muscle

Question 29

what happens if you induce beta-catenin mRNA into the ventral side of the vegetal region

Answer 29

a second nieuwkoop centre will develop and duplicated axis will develop

Question 30

what signalling molecule is essential for specifying the nieuwkoop centre

Answer 30

Wnt

Question 31

what does the notochord form from after gastrulation

Answer 31

mesoderm cells

Question 32

what do signals from the notochord do?

Answer 32

drive inward folding of ectoderm at the neural plate

Question 33

what happens after the neural plate is formed

Answer 33

the ends fuse and disconnect to form an autonomous neural tube

Question 34

once the neural tube is formed, which bit does the brain and spinal cord develop from

Answer 34

the brain forms from the anterior end the rest of the tube forms the spinal cord

Question 35

what tissue is the neural tube derived from

Answer 35

ectoderm

Question 36

what molecule inhibits neurulation

Answer 36

BMP4

Question 37

what happens to ectodermal cultures with BMP4

Answer 37

they differentiate into epidermis rather than neural cells

Question 38

name 3 molecules that inhibit BMP4

Answer 38

chordin noggin follistatin

Question 39

what is the evidence that BMP4 is an inhibitor of neurulation

Answer 39

KO mice for chordin and noggin = BMPs are not inhibited so epidermal fate is not inhibited and neural fate is not induced produces mice without a forebrain, nose or facial structure

Question 40

do it again! describe the process of neurulation! hahah

Answer 40

1. neuroectodermal cells dive down and differentiate into the neural plate 2. on either side of the neural plate is a band of cells called the neural crest 3. neural plate invaginate and the neural crest tissue sitting at the top forms the neural groove 4. the neural groove pinches off forming an autonomous neural tube

Question 41

what do neural crest cells eventually produce

Answer 41

peripheral nervous system neurons

Question 42

what happens to the notochord after neurulation

Answer 42

it is only retained in some primitive chordates (e.g. hagfish) in most higher order vertebrates it is replaced by the vertebral column

Question 43

what does fusion of the neural plate require

Answer 43

cell adhesion molecules: N-cadherin and N-CAM

Question 44

what process stops the binding of neural tissue to epidermis, and why

Answer 44

homophillic adhesion they can now recognise each other as being the same

Question 45

neural crest cells show some plasticity, depending on their positional cues what do they produce?

Answer 45

either sympathetic or parasympathetic neurons depending on their anterior-posterior position.