the presence of _____ beneath the _____, through a process called induction, causes a thickening of the _____ to form a _____
notochord
embryonic ectoderm
ectoderm
neural plate
neural plate consists of…
neural ectoderm
what does the neural plate do around day 18
invaginates along the midsagittal plane to form a neural groove
what happens in the neural plate by the end of the third week
neural folds adjacent to neural groove fuse above neural ectoderm to form a neural tube
developing neural tube is open where?
-what are these openings called?
open at the anterior and posterior ends
anterior and posterior neuropores, respectively
neural tube eventually separates from…
overlying ectoderm
what are the neural crest cells
group of neuroectodermal cells that are “left behind” on the dorsolateral sides as the neural tube is formed
when does the neural tube begin to close
-where does it begin
around day 22
at the level of future somite 4-6
how does the closure of the neural tube progress
rostrally and caudally
which neuropore of the neural tube (rostral or caudal) closes last?
-when does it close
caudal closes last
around day 27
failure of the neuropores to close results in…
spina bifida
-deformities of the nervous system and investing skeleton
where is the most common area for spina bifida to occur
- cause
- resulting neural tube defects may also involve…
lumbar region due to failure of the posterior neuropore to close may also involve -overlying tissues -meninges -vertebral column -dorsal muscles -skin
neural tube develops into…
central nervous system
CNS
-consists of…
brain and spinal cord
neural crest cells
-responsible for development of…
peripheral nervous system, including the autonomic nervous system
Schwann cells
Schwann cells
-purpose
myelinate the peripheral nervous system and the melanocytes noted in stratum basale of the epithelial lining of the skin
development of CNS is marked by rapid proliferation of the ____ end
rostral
“head fold” created due to…
overgrowth of the oropharyngeal membrane by the neural plate
lumen of neural tube becomes…
ventricular system of CNS
due to rapid growth of cranial end of CNS, what occurs
-these are termed
begins to bend
termed flexures
what are the flexures?
-where do they occurs
cervical flexure
-between spinal cord and brainstem
cephalic flexure
-between brainstem and cerebral hemispheres
brain region expands laterally into three _____
vesicles
what are the three vesicles?
rhombencephalon -hindbrain mesencephalon -midbrain prosencephalon -forebrain
secondary vesicle formation occurs in the…
-what is created in each
rhombencephalon -myelencephalon -metencephalon prosencephalon -diencephalon -telencephalon
myelencephalon turns into…
medulla
metencephalon turns into
pons and cerebellum
diencephalon turns into
thalamus
hypothalamus
pineal gland
telencephalon turns into
cerebral hemispheres
basal ganglia
CNS develops from _____ division and _____ followed by _____
develops from mitotic cell division and proliferation followed by migration of cells lining the neural tube
developing cells (that form the CNS) eventually form... -what do these cells do?
neuroblasts (precursor neurons)
spongioblasts (precursor glial cells)
cells migrate away from the luminal surface to form the structures of the cord and brain
neural tube divided into…
alar, basal, roof and floor plate
what neural elements do the alar, basal, roof and floor plates turn into?
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
neural crest cells form…
sensory peripheral nerves, including -dorsal root ganglia -autonomic ganglia -myelinating cells of the PNS melanocytes
embryonic mesoderm located lateral to the notochord is divided into…
3 divisions
- paraxial
- intermediate
- lateral plate
near the cervical flexure, the paraxial mesoderm begins to develop…
- this begins when?
- continues until…
furrows
begins at about 20 days
continues until about 30 days
how many somite pairs develop
-how are they classified
42-45 cranial -4-5 cervical -8 thoracic -12 lumbar -5 sacral -5 coccygeal -8-10
every somite differentiates into…
-these are precursors to…
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
initially, what is the relationship of the specific developing segmental nerve with a somite
direct
what occurs to result in the somewhat altered image we have of a dermatome map
changes in the orientation of the limb bud
overlap mixing in the development of the specific muscle and dermal parts of the skin
where does limb bud development begin
preaxial and postaxial border
in which direction do the limb buds develop
ventrally, with hand and footplates facing each other
arm development takes place _____ rapidly than that of the leg
more
originally, the flexor aspect of the limbs is _____ and the extemsor aspect is_____, with the preaxial border being _____ and the postaxial border being _____
ventral
dorsal
cranial (rostral)
caudal
a rotation begins in the arm that results in a _____
-consequence
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
a rotation begins in the leg that results in a _____
-consequence
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
critical time of limb bud formation
24-42 days after fertilization
day 24 (beginning of critical time of limb bud formation) coincides with _____
differentiation of the somites and the consequent organization of the limb differentiation
drugs that disrupt limb bud differentiation may result in_____
deformities including lack of formation of limbs
-thalidomide: drug used in the 50’s to control morning sickness
