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90 Cards in this Set
- Front
- Back
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The CNS develops from the ______________ |
neural tube |
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The PNS develops from the _______________ |
neural crest |
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The formation of the bilaminar disc occurs during week _______ of embryological development |
week 2 |
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The bilaminar disc has two germ layers: the _________ and ___________ |
-epiblast -hypoblast |
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Just one more set of flashcards! |
you can do it! |
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The _____________ becomes the bilaminar embryonic disc |
inner cell mass |
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During what week does the trilaminar disc develop? (the bilaminar disc further differentiates into the trilaminar disc) |
during week three of embryological development |
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The cells of the _____________ form all three germ layers that give rise to all tissues and organs. What are the three layers? |
Epiblast
-ectoderm -mesoderm -endoderm |
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The body organs and tissues arise from what layers? |
The mesoderm |
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What does the ectoderm give rise to? |
-Sensory organs -skin -the entire nervous system (CNS and PNS) |
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What arises from the endoderm? |
The GI tract and the respiratory system (a bunch of tubes- starts with the oral cavity and ends with the anal cavity) |
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The cells that remain in the epiblast layer become the |
ectoderm |
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The first step in developing the nervous system (or really, developing tissue or cells that will eventually become neural cells) is the formation of a key structure called the ____________ |
Notochord |
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the notocord arises in response to signals from a structure called the _________________ |
primitive streak |
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The notochord first appears during_____1______ and forms in the _______2_______ |
1. gastrulation 2. mesoderm |
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The ___________ defines primordial (longitudinal) axis of an embryo and gives it rigidity
This is also a primary inducer of neural tissue |
notochord
Think of the notochord as a longitudinal organizer |
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How is the notochord formed?
long, winded explanation, sorry in advance!! :) |
Cells that are along the primitive streak begin to produce molecules-they secrete substances that diffuse and effect the cells that are within the surrounding environment. In response to those molecular signals, cells that are deep to this primitive streak (which is part of the ectoderm)- -the diffusible signals go down into the mesoderm causes the formation of cells that are exposed to and cause those substances to kind of clump together and form this dense cellular rod, which is the notocord |
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____________ is the formation of the bilaminar disc and then generation of the trilaminar disc, so it is just the process of disc formation. |
gastrulation |
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After the notochord has formed, it then starts releasing signaling molecules called ______1______, which are critically important and begin the process of ______2_______, or the formation of neural tissue |
1. inducers 2. neurulation |
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The notochord is the the structure that eventually causes the ___________________ to form. |
nervous system |
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The ____________ defines primordial (longitudinal) axis of the embryo and gives it rigidity. It is also the basis for development of the __________________ |
Notochord
Axial skeleton
because it is along the midline of the developing embryo, it also defines the longitudinal axis and produces some rigidity or firmness to that developing embryo |
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Once the notochord forms into the mesoderm and begins releasing signals into the overlying ectoderm, those cells of the ectoderm are now called the ______________ |
neuroectoderm (because those are the cells that will go on to form nervous system tissue). |
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In response to signals from the notochord, what does the neuroectoderm overlying the notochord do? |
It thickens to form the neural plate
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Development proceeds in a _________ to ________ manner |
cranial-to-caudal manner
(the cranial end of the embryo is always a couple of steps ahead) - So for example the upper limbs form a couple of days before the lower limbs |
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The neural plate forms around day _______ |
19 (I believe) (so week three) |
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What is the first sign of brain development and where does it first appear? When does this occur? |
Neural folds are the first sign of brain development, and they first appear at the cranial end of the embryo around the third week |
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Its a dense lecture |
But you can do it :) |
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On the neural plate, the cells adjacent to the midline begin to elevate to form the neural _____1______ on either side of the neural _____2_______. |
1. Fold 2. Groove |
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Where we used to have the primitive streak, we now have the _______________ |
neural groove.
So the neural plate becomes the neural fold and the primitive streak becomes the neural groove (around the end of third week) |
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The neural folds continue to elevate and eventually will join together to form the _____________. |
neural tube (enclosed tube) |
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Once these cells of the now neural tube have come together, we also have cells of the overlying ectoderm that migrate medially, and they will close over the top, so we do have a layer of surface ectoderm that remains over the top of the now enclosed neural tube. This will eventually be the __________ |
skin (future epidermis) |
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The open ends of the developing neural tube from rostral (anterior) and caudal (posterior) _____________. what do these do? |
Neuropores- they communicate with the amniotic cavity |
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Towards the end of week three, is there closure of the neural tube yet? |
No, it is still the neural fold and the neural groove around day 20 |
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The ___________ line up adjacent to the developing neural tube (in the mesoderm), and will eventually become the dermatomes, myotomes, etc. |
somites |
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Where does the fusion of the neural tube begin (the first closure of the neural tube? When does this occur? |
fusion begins in the cervical region (5th somite) around day 22 (beginning of fourth week) |
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We have almost complete closure of the neural tube by _________ days, but the ends of the neural tube, called ___________ and ____________ are still open |
23 days (Fourth week)
-anterior neuropore -posterior neuropore (still open to amniotic cavity) |
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The neural tube gives rise to everything that is part of the ___________. What structures? |
CNS
-brain -spinal cord |
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Where does the PNS arise from? |
It arises from the neural crest
-dorsal root ganglion -sympathetic ganglion -developing suprarenal gland -preaortic ganglion enteric ganglia |
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Remember development occurs in a cranial to caudal fashion, so the first structure in the CNS to start developing is the ________ |
brain (its always a couple of steps ahead of the spinal cord) |
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As soon as the neural tube closes, immediately after that you have a massive increase in cellular proliferation or division, so you're now making many more cells, and that causes the most cranial portions of the closed neural tube to form dilations (bulges). These dilations start to form about day ________, and the initial dilations are referred to as ____________ |
25
primary brain vesicles |
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What are the 3 primary brain vesicles? |
F,M,H:
-Prosencephalon (F; forebrain) -Mesencephalon (M;midbrain) -Rhombencephalon (H; hindbrain) |
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Around what day does the anterior (cranial) neuropore close?
What about the posterior (caudal) neuropore closure? |
Day 25 is when the anterior (cranial) neuropore closes and you start to see dilations, or primary brain vesicles
Day 27 is around when the posterior (caudal) neuropore closes (this is not a straight tube) |
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At the three primary vesicle stage, we have two primary flexures, or bends. What are they called and where do they occur? |
1. cephalic flexure- occurs about the level of the midbrain
2. cervical flexure -between the hindbrain and what will become the spinal cord |
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Which of the flexures persists in the adult? |
The cephalic flexure persists in adults
(the cervical flexure does not persist in the adult) |
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The longitudinal axis of the brainstem and spinal cord is at about a _______ degree angle to the longitudinal axis through the cerebrum |
90 degree angle |
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Over the next few days, the first 3 primary vesicles subdivide to become ___ ___________ vesicles
When does this occur? |
5 secondary brain vesicles
This occurs after, or at about the same time that the caudal neural pore closes (around day 27) |
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The prosencephalon, one of the 3 primary brain vesicles, will further divide into the ________________ and ______________ |
telencephalon and diencephalon |
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the mesencephalon, one of the 3 primary brain vesicles, will divide into: |
nothing, it does not further subdivide and remains the mesencephalon |
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The rhombencephalon, one of the 3 primary brain vesicles, will further subdivide into what? |
the metencephalon and the myelencephalon |
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The telencephalon will become the ________________?
The diencephalon will become? |
Telencephalon will become cerebral hemispheres
The diencephalon will become the thalamus and hypothalamus
(so all originally from the prosencephalon) |
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The mesencephalon will develop into the __________ |
midbrain |
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The metencephalon will become _______ and _______
and the myelencephalon will be come: |
metencephalon will become the pons and the cerebellum
myelencephalon will become the medulla
(and all are originally from the rhombencephalon) |
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During this time, another flexure, the ______1___ flexure appears (between the more cranial metencephalon and the more caudal myelencephalon), but does not persist. Instead, it contributes to the formation of the ______2__________ |
1. pontine flexure
2. fourth ventricle |
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The lumen of the neural tube becomes the __________ ___________of the adult CNS |
ventricular system (which is a closed system except for the 3 apertures at the fourth ventricle) |
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Keep going! |
So close to the end :) |
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The wall of the neural tube is composed of what type of cells? |
neuroepithelial cells
It is initially a single layer of cells, but it is called pseudo-stratified epithelium because it looks like multiple layers |
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Once the final round of mitosis occurs in the neuroepithelial cells in the wall of the neural tube (about 32 rounds), those cells are now referred to as ______1______ and are now destined to become ____2_______. |
1. neuroblasts
2. neural cells |
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neuroblasts are ____________ |
post mitotic,which means the vast majority of neurons are post mitotic |
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The neuroepithelium will form three cell layers. What are they? |
-mantle layer -marginal layer -ventricular zone (the inner cell layer)
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In the spinal cord, which layer is the future gray matter cells? What is this layer initially formed by? |
the mantle layer- formed by neuroblasts |
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The neuroblasts from the mantle layer will then extend processes out that will become axons or dendrites, and this forms the ____________ layer. This layer is the future ____________ of the spinal cord. |
marginal layer
future white matter |
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What is the ventricular sone layer made of and what will it eventually do? |
It is the layer of cells closest to the lumen that remain epithelial.
This layer will line the ventricles.
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What does apolar mean? |
no process from the cell |
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differentiation of neurons into their mature form occurs after they arrive in the __________ layer |
mantle |
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99% of neurons are what type of neurons? |
multipolar neurons |
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bipolar cells are _________ neurons |
special sensory |
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The _______________ is a groove at about the midway point that separates future sensory and motor areas |
The sulcus limitans |
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The ___________ is posterior to the sulcus limitans and will become a sensory structure, while the _________ is anterior and will become a motor structure. |
alar plate- sensory structure
basal plate- motor in orientation
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Why does the posterior aspect (alar plate) become sensory and the anterior aspect (basal plate) become motor? |
because they are exposed to different signaling molecules (opposing gradients of signaling molecules between ectoderm and notochord determine neuronal differentiation) |
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As far as signaling molecules, the posterior aspect of the neural tube is closer to the ______1__________ and the anterior (ventral) aspect is closer to the ______2______ |
1. overlying surface ectoderm
2. notochord |
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The ectoderm and the notochord are each releasing different signaling molecules. The ectoderm releases __________________, and the notochord releases ___________________. This causes the cells in the alar plate and the cells in the basal plate to take on different functions, even though they are both part of the neural tube |
1. ectoderm releases bone morphogenetic proteins (BMPs) (signals sensory)
2. notochord releases sonic hedgehog (SHH) (signals motor) |
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Cells in the alar plate that are exposed to BMPs are going to become ____1______ neurons and cells in the basal plate that are exposed to SHH are going to become ______2________ neurons |
1. sensory
2. motor |
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With the formation of growth cones, what do they allow the axon to do? |
Allows the leading edge of the axon to "smell" its way through the environment (work its way through) following guidance cues |
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what is synaptogenesis? |
formation of synapses. -induce post synaptic evens in target cells |
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Failure to form synapse results in ________ neuron |
apoptosis (programmed cell death)
We form about two times the neurons we need during development, so about half of our developing neurons end up dying by programmed cell death (apoptosis) |
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When does myelination in the CNS begin?
When does it peak? When does it end? |
-Begins at 4-6 months of developments (not complete when we are born)
-peaks at 12-18 months of age
-continues into adulthood |
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_______1____ and ______________ tracts mature early, but _______2______ tracts mature relatively late |
1. motor and sensory tracts- early
2. association tracts- relatively late |
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A ____________ sign is normal in infants and can return in pathological states |
Babinski (positive is toes are splayed and negative is when toes are curled when stroked along bottom of foot) |
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The _________ is everything that is not brain and spinal cord and it arises from the neural crest |
PNS |
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Where do the neural crest cells come from? |
The neural crest cells arise from the dorsal part of the developing neural tube, and then they detach from the neural tube and migrate (after closure of the neural tube) to multiple locations along specific pathways |
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What are derivatives of the neural crest? |
-Sensory neurons in posterior root ganglion -cranial nerve ganglia -prevertebral ganglia -paravertebral ganglia (sympathetic chain) -postganglionic neurons of SNS and PSNS -Schwann cells (glial cells of the PNS) |
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What is the neural tube defect that occurs if the anterior neuropore fails to close? |
anencephaly (no brain development -this is typically fatal in utero, but some infants survive up to a week) |
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What occurs when the posterior neuropore fails to close? |
spina bifida |
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What are the types of spina bifida? What differentiates them? |
-Spina bifida occulta: defect is hidden (may have a lipoma or a tuft of hair or something on skin- the neural structures themselves are fine)
-Spinabifida cystica: the spinal cord is open to the body surface - you form a cyst in the area of the defect- differs in severity
-(Cranio)rachischisis |
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What occurs in (Cranio)rachischisis |
The neural folds do not elevate, resulting in failure of the neural tube to fuse |
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How can neural tube defects be detected? |
They can be detected by an increase in alpha-fetoprotein in maternal serum or amniotic fluid
50-70% can be prevented by folic acid supplementation prior to and during pregnancy |
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What are the different types of spina bifida cystica? |
spina bifida cystica is a presence of a cyst, but it is variable in involvement of neural tissue
-meningocele: no neural tissue in cyst (just meningies and CSF) -meningomyelocele: neural tissue presence in cyst (most common and most destructive- neural tissue within cyst) Myeloschisis |
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An __________________ malformation is a deformity of the hindbrain |
Arnold-chiari malformation (herniation of the caudal brainstem components- type 2) |
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What is the difference between type 1 and type 2 Arnold-chiari malformation |
Type 1 is not associated with other neural tube defects and it may be asymptomatic at birth. (idiopathic) |
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What is the most common congenital viral infection in the US (1:150) and the leading cause of brain abnormalities? |
Congenital cytomegalovirus (cCMV) infection |
