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20 Cards in this Set
- Front
- Back
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what is gastrulation? |
the process during wk three of development whereby the bilaminar disc (epiblast and hypoblast) is taken to a three layers structure (ectoderm, mesoderm, endoderm) |
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to what will the ectoderm layer give rise? |
- CNS - peripheral nervous system - sensory epithelium of the ears, eyes, nose - the epidermis, hair and nails - the subcutaneous, mammary and pituitary glands - the enamel of teeth |
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how and when does the CNS first appear? |
at the end of week three
as thickening of the ectoderm in the mid-dorsal region in front of the primitive streak |
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tell me about the formation and role of the notochord |
- from the primitive node a tube extends under the ectoderm layer in the opposite direction to the primitive streak
- this tube forms the axial process, then the notochordal process before becoming the notochord (from endodermal cells)
- the notochord is a transient patterning structure, involved in molecular signalling and controlling the direction of folding - very important in neurulation
- its appearance (and that of the mesoderm) induce the overlying ectoderm to thicken up and form the neural plate (the cells of which make up the neuroectoderm)
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what is neurulation?
tell me what happens |
neurulation is the process by which the neural plate forms from the neural tube
neuroectoderm cells, which make up the neural plate, become more columnar
the neural plate lengthens and the lateral edges elevate forming the neural folds, the depressed mid region forms the neural groove
the fold approach each other in the midline and fuse, forming the neural tube
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how is complete neurulation represented? |
by a closed tubular structure with a narrower portion at the caudal end and a broader portion at the cephalic end
complete layer of ectoderm
neural crest cells separate the neural tube from the surface ectoderm, but quickly disperse and migrate |
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tell me about the formation of hinges in neurulation |
the median hinge point is at the midline of the neural plate, the cells decrease in height and become wedge shaped
convergence of the neural folds occur as the dorsolateral hinge points become wedge shaped and the epidermal cells push towards the centre
the neural crest cells some into contact and link the epidermal cells to the neural tube before dispersing and migrating |
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tell me about signalling in neuraltion |
initially due to up regulation of FGF and inhibitions of BMP-4 - causing induction of the neural plate (if ectoderm is protected from BMP exposure then it forms nervous tissue by default)
neural plate switches from expressing E-cadherin to N-cadherin - allowing the two ends to recognise each other and fuse together - and not to the overlying ectoderm
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what happens to neural crest cells after the neural tube has formed? |
they migrate by various routes and at different times to form
- ganglia - Schwann cells - adrenal medulla - melanocytes - connective tissue in the head |
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what problems can one get with disruption of neural crest migration? |
Treacher Collins syndrome - underdevelopment the zygomatic bones and ears
Di George syndrome - cleft palate, cardiac abnormalities
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tell me about the timing and direction of neural crest closure |
closure of the neural tube begins in the cervical region and proceeds in both cephalic and caudal directions
closure occurs in week 4, anterior by day 25 and posterior by day 27 |
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differentiation of the spinal cord |
the walls of the recently closed neural tube consist of neuroepithelial cells, which give rise to primitive nerve cells called neuroblasts
the neuroblasts form the mantle layer, which will later from the grey matter
nerve fibres emerging from the mantle layer make up the marginal layer, this nerves will become myelinated making the white matter of the spinal cord
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development of the spinal cord |
neuroblasts get added to the mantle layer on both sides of the neural tube giving a ventral and dorsal thickening
basal plate will contain ventral motor horn cells
alar plate will contain dorsal motor horn cells
sulcus limitans marks the boundary between the alar and the basal plate
roof plate and floor plate do not contain neuroblasts
intermediate horn cells contain sympathetic neurons (T1-L2) |
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growth of the spinal nerves |
week 4 motor axons grow out of the neurons in the basal plate (ventral horn)
sensory axons grow out of neurons in dorsal root ganglia and extend to both the alar plate (dorsal horn) and the periphery
spinal nerves contain both sensory and motor root fibres |
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development of the brain week 3 |
week 3 3 primary brain vesicles
prosencephalon - forebrain mesencephalon - midbrain rhombencephalon - hindbrain
uneven growth in these result in folds or flexures
midbrain - cephalic flexure - convex dorsally pontine flexure - convex ventrally cervical flexure at hindbrain/spinal cord junction, temporary (weeks 5-7) - convex dorsally |
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development of the brain week 5 |
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what does failure of closure of the neural tube lead to? |
failure in anterior neuropore - anencephaly
failure to posterior neuropore - spina bifida |
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how is spina bifida diagnosed?
can can incidence be reduced? |
usually prenatally by USS or raised alpha feet protein in amniotic fluid/maternal serum
folic acid prior to conception and in the early stages of pregnancy |
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what's the relationship between spina bifida and hydrocephalus? |
in spina bifida cystica there is a build up of CSF (made in choroid plexus where the ependyma comes in contact with the pia mater - mainly the roof of the fourth ventricle) due to obstruction of the foramen magnum but the cerebellum |
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describe anencephaly |
absence of a major portion of the brain, skull and scalp due to failed closure of the anterior neuropore normally it is the telencephalon structures that fail to form (cerebral hemisphere) babies with anencephaly seldom survive for more than a few hours |
