Embryology

Question 1

the presence of _____ beneath the _____, through a process called induction, causes a thickening of the _____ to form a _____

Answer 1

notochord
embryonic ectoderm
ectoderm
neural plate

Question 2

neural plate consists of…

Answer 2

neural ectoderm

Question 3

what does the neural plate do around day 18

Answer 3

invaginates along the midsagittal plane to form a neural groove

Question 4

what happens in the neural plate by the end of the third week

Answer 4

neural folds adjacent to neural groove fuse above neural ectoderm to form a neural tube

Question 5

developing neural tube is open where?

-what are these openings called?

Answer 5

open at the anterior and posterior ends

anterior and posterior neuropores, respectively

Question 6

neural tube eventually separates from…

Answer 6

overlying ectoderm

Question 7

what are the neural crest cells

Answer 7

group of neuroectodermal cells that are “left behind” on the dorsolateral sides as the neural tube is formed

Question 8

when does the neural tube begin to close

-where does it begin

Answer 8

around day 22

at the level of future somite 4-6

Question 9

how does the closure of the neural tube progress

Answer 9

rostrally and caudally

Question 10

which neuropore of the neural tube (rostral or caudal) closes last?
-when does it close

Answer 10

caudal closes last

around day 27

Question 11

failure of the neuropores to close results in…

Answer 11

spina bifida

-deformities of the nervous system and investing skeleton

Question 12

where is the most common area for spina bifida to occur

• cause
• resulting neural tube defects may also involve…

Answer 12

lumbar region
due to failure of the posterior neuropore to close
may also involve
-overlying tissues
-meninges
-vertebral column
-dorsal muscles
-skin

Question 13

neural tube develops into…

Answer 13

central nervous system

Question 14

CNS

-consists of…

Answer 14

brain and spinal cord

Question 15

neural crest cells

-responsible for development of…

Answer 15

peripheral nervous system, including the autonomic nervous system
Schwann cells

Question 16

Schwann cells

-purpose

Answer 16

myelinate the peripheral nervous system and the melanocytes noted in stratum basale of the epithelial lining of the skin

Question 17

development of CNS is marked by rapid proliferation of the ____ end

Answer 17

rostral

Question 18

“head fold” created due to…

Answer 18

overgrowth of the oropharyngeal membrane by the neural plate

Question 19

lumen of neural tube becomes…

Answer 19

ventricular system of CNS

Question 20

due to rapid growth of cranial end of CNS, what occurs

-these are termed

Answer 20

begins to bend

termed flexures

Question 21

what are the flexures?

-where do they occurs

Answer 21

cervical flexure
-between spinal cord and brainstem
cephalic flexure
-between brainstem and cerebral hemispheres

Question 22

brain region expands laterally into three _____

Answer 22

vesicles

Question 23

what are the three vesicles?

Answer 23

rhombencephalon
-hindbrain
mesencephalon
-midbrain
prosencephalon
-forebrain

Question 24

secondary vesicle formation occurs in the…

-what is created in each

Answer 24

rhombencephalon
-myelencephalon
-metencephalon
prosencephalon
-diencephalon
-telencephalon

Question 25

myelencephalon turns into...

Answer 25

medulla

Question 26

metencephalon turns into

Answer 26

pons and cerebellum

Question 27

diencephalon turns into

Answer 27

thalamus hypothalamus pineal gland

Question 28

telencephalon turns into

Answer 28

cerebral hemispheres | basal ganglia

Question 29

CNS develops from _____ division and _____ followed by _____

Answer 29

develops from mitotic cell division and proliferation followed by migration of cells lining the neural tube

Question 30

``` developing cells (that form the CNS) eventually form... -what do these cells do? ```

Answer 30

neuroblasts (precursor neurons) spongioblasts (precursor glial cells) cells migrate away from the luminal surface to form the structures of the cord and brain

Question 31

neural tube divided into...

Answer 31

alar, basal, roof and floor plate

Question 32

what neural elements do the alar, basal, roof and floor plates turn into?

Answer 32

``` roof and floor -do not differentiate into neuronal elements alar (located dorsally) -sensory component of the cord and brain basal (located ventrally) -motor component of the card and brain ```

Question 33

neural crest cells form...

Answer 33

``` sensory peripheral nerves, including -dorsal root ganglia -autonomic ganglia -myelinating cells of the PNS melanocytes ```

Question 34

embryonic mesoderm located lateral to the notochord is divided into...

Answer 34

3 divisions - paraxial - intermediate - lateral plate

Question 35

near the cervical flexure, the paraxial mesoderm begins to develop... - this begins when? - continues until...

Answer 35

furrows begins at about 20 days continues until about 30 days

Question 36

how many somite pairs develop | -how are they classified

Answer 36

``` 42-45 cranial -4-5 cervical -8 thoracic -12 lumbar -5 sacral -5 coccygeal -8-10 ```

Question 37

every somite differentiates into... | -these are precursors to...

Answer 37

``` sclerotome dermomyotome -dermatome -myotome precursors for the formation of the various dermal layers of the skin, muscles and bones and are associated with specific segmental levels of the developing nervous system ```

Question 38

initially, what is the relationship of the specific developing segmental nerve with a somite

Answer 38

direct

Question 39

what occurs to result in the somewhat altered image we have of a dermatome map

Answer 39

changes in the orientation of the limb bud | overlap mixing in the development of the specific muscle and dermal parts of the skin

Question 40

where does limb bud development begin

Answer 40

preaxial and postaxial border

Question 41

in which direction do the limb buds develop

Answer 41

ventrally, with hand and footplates facing each other

Question 42

arm development takes place _____ rapidly than that of the leg

Answer 42

more

Question 43

originally, the flexor aspect of the limbs is _____ and the extemsor aspect is_____, with the preaxial border being _____ and the postaxial border being _____

Answer 43

ventral dorsal cranial (rostral) caudal

Question 44

a rotation begins in the arm that results in a _____ | -consequence

Answer 44

lateral 90 degree displacement along the longitudinal axis consequence -puts future elbow pointing posteriorly, with the extensor muscles (of the proximal bone) lateral and posterior

Question 45

a rotation begins in the leg that results in a _____ | -consequence

Answer 45

medial 90 degree displacement places bend of knee facing forward, with the extensor compartment of the proximal bone now on the anterior part of the limb

Question 46

critical time of limb bud formation

Answer 46

24-42 days after fertilization

Question 47

day 24 (beginning of critical time of limb bud formation) coincides with _____

Answer 47

differentiation of the somites and the consequent organization of the limb differentiation

Question 48

drugs that disrupt limb bud differentiation may result in_____

Answer 48

deformities including lack of formation of limbs | -thalidomide: drug used in the 50's to control morning sickness