1 - Neuroembryology

Question 1

what environmental factors can cuases neurodevelopment defects?

Answer 1

alcohol
tobacco
nutrional deficiencies

Question 3

Outline the basic developmental stages in the first 12 weeks of pregnancy, during the weeks:
1. week 0
2. week 2
3. week 3
4. week 3-8

Answer 3

1. implantation
2. blastulation
3. gastrulation
4. organogenesis

Question 4

Outline the process of implantation in 6 steps:

Answer 4

1. Blastocyte enlarges as it obtains nutrients from glycogen rich fluid secreted from endometrium.
2. On contact with endometrium - trophoblast cells in blastocyte divide rapidly increasing thickness of throphoblast layer.
3. Cytotrophoblasts (closest to interior) differentiate into syncytiotrophoblasts – break down stratum functionalis by secreting hyaluronidase
4. Produce hCG – binds to CL + sustains it.
5. Decidual change
6. Blastocyst is burrowed into stratum functionalis + endometrium closes

Question 5

outline the 4 major outcomes in blastulation:

Answer 5

• Trophoblast differentiates into two layers – cytotrophoblasts and syncytiotrophoblasts
• Embryoblast forms two layers – hypoblast + epiblast
• Extraembryonic mesoderm – somatic layer + splanchnic layer
• Two cavities form – amniotic cavity + yolk sac

Question 6

in what weeks does embryogenesis occur?

Answer 6

0-8

Question 7

in what week does gastrulation occur?

Answer 7

week 3

Question 8

what occurs in week 3 of fetal development?

Answer 8

gastrulation

Question 9

outline the 3 basic steps of gastrulation:

Answer 9

1. Primitive streak formed on base of amniotic cavity
2. Epiblast cells migrate towards the streak and slip beneath it – invagination
3. Leads to formation of 3 germ layers

Question 10

what are the 3 germ layers formed during gastrulation called?

Answer 10

• ectoderm
• mesoderm
• endoderm

Question 11

what does the ectoderm give rise to?

Answer 11

nervous system

Question 12

during what weeks does organogenesis occur?

Answer 12

weeks 3-8

Question 13

at what point in fetal development does the nervous system begin to form?

Answer 13

between 19-21 days AF

Question 14

when does most nervous sytem development occur?

Answer 14

during embryogenesis

Question 15

what are the 3 stages of nervous system development?

Answer 15

1. induction of neural plate
2. patterning of CNS
3. neuronal differentiation/neurogenesis

Question 16

the mesoderm develops into what?

Answer 16

somites –> skeletal and muscle tissue

Question 17

the endoderm develops into what?

Answer 17

epithelium of organs

Question 18

what process leads to the formation of the neural plate?

Answer 18

gastrulation

Question 19

what forms directly beneath the primitive streak from mesoderm cells?

Answer 19

notochord

Question 20

what is the notochord composed of?

Answer 20

mesoderm cells

Question 21

what is the role of the notochord?

Answer 21

secretes growth factors which stimulates the differentiation of ectoderm into neuroectoderm

Question 22

in what week of development does the notochord appear?

Answer 22

third week

Question 23

describe the folding of the neural plate

3 steps

Answer 23

1. median hinge point forms - notochord signalling
2. lateral hinge points form - signalling from nearby mesoderm
3. meet in midline to form neural tube

Question 24

what structure forms as the neural folds fuse?

Answer 24

neural crest - then delaminates and migrates

Question 25

what does the neural crest give rise to?

Answer 25

a diverse cell lineage incl. melanocytes, craniofacial cartilage and bone

Question 26

when is neurulation achieved by?

Answer 26

end of the fourth week of development

Question 27

in 4 steps, outline the induction of the neural plate to form the dorsoventral axis

Answer 27

1. induction 2. elevation 3. convergence 4. closure

Question 28

in what region does neurulation first occur?

Answer 28

cervical region

Question 29

what happens after neurulation occurs in the cervical region?

Answer 29

* neural tube zips up toward head and tail * leaves anterior and posterior neuropores

Question 30

when does the anterior neuropore close?

Answer 30

day 25

Question 31

when does the posterior neuropore close?

Answer 31

day 28

Question 32

what occurs if the anterior neuropore fails to close?

Answer 32

anencephaly - loss of telencephalon | usually results in death

Question 33

what happens if the posterior neuropore fails to close?

Answer 33

spina bifida

Question 34

what is the main goal of patterning of the nervous system?

Answer 34

helps cells acquire specific identities

Question 35

what are morphogens?

Answer 35

secreted proteins that act in a dose dependent manner

Question 36

what are the two main morphogens that act across the dorsoventral axis of the neural tube/

Answer 36

BMP - bone morphogenetic protein SHH - sonic hedgehog

Question 37

# w what morphogen is secreted in the dorsal "roof plate" of the nervous system?

Answer 37

BMP

Question 38

what morphogen is secreted in the ventral "floor plate" of the nervous system/

Answer 38

SHH

Question 39

what determines the identities of neurons along the DV axis?

Answer 39

combination of SHH and BMP gradients

Question 40

a cell with motor neuron status has what relative levels of SHH and BMP?

Answer 40

high SHH low BMP

Question 41

list these transcription factors according to location in the dorsoventral axis: * Olig2 * pax7 * pax6 * Nkx6.1 | (from most dorsal to most ventral)

Answer 41

1. Pax7 2. Pax6 3. olig2 4. Nkx6.1

Question 42

what is the antero-posterior axis also known as?

Answer 42

rostral-cordal axis

Question 43

how is the nervous system patterned along the AP axis?

Answer 43

* posterior region secretes fibroblast growth factor * somites (found centrally) secrete reinoic acid * forms opposing gradients * cells closer to RA secretion acuire spinal cord identity

Question 44

what determines patterning in the anterior part of the CNS (the brain, not the spinal cord)?

Answer 44

combination of the morphogen signals from DV axis and diffusible molecules from AP axis

Question 45

holoproscencephaly

Answer 45

failure of the proscencephalon (embryonic forebrain) to divide into two hemispheres

Question 46

what causes holoprosencephaly?

Answer 46

mutation in SHH

Question 48

morphogens are responsible for patterning the AP axis. what else is required for this?

Answer 48

homeotic genes

Question 49

what is neurogenesis?

Answer 49

process through which nurones are formed in the developing embryo

Question 51

neural progenitor cells are polarised. at which surface do they proliferate - apical or basal?

Answer 51

apical (nucleus moves back and forward from apical to basal surfaces)

Question 52

in early development, how do progenitor cells divide?

Answer 52

symmetrically- equal inheritance of polarity complex proteins

Question 53

during later stages of development, how do progenitor cells divide?

Answer 53

* asymmetically * one daughter cell becomes a neuron * other dauther cell becomes a progenitor cell and divides again