Embryology Flashcards
Concerning the development of the brain
- entire nervous system is of____ origin and its first rudiment is seen in the neural___ which extends along the___ aspect of the embryo
- By ____week, neural folds have begun to move together & fuse, converting the neural___ into neural____, the primordium of the CNS.
ectodermal
groove
dorsal
end of 3rd
plate
tube
Gastrulation
- the process by which the bilaminar embryonic disc is converted into a___ embryonic disc.
- Begins with formation of the ____at the caudal end of the embryo.
- Cranial end proliferates to form____
- Some mesenchymal cells migrate cranially from primitive node & pit, forming a median cellular cord-____/_____
trilaminar
primitive streak
primitive node.
notochordal/head process.
Primitive streak results from proliferation & migration of cells of the____ to the____ plane of the embryonic disc.
epiblast
median
Primitive____ develops in the primitive streak.
-Primitive___ – small depression in primitive node.
groove
pit
Primitive groove & pit result from invagination of_____ cells.
epiblastic
GASTRULATION
By the ____ day floor of the notochordal process fuses with____
-With further development the notochordal cells proliferate & form a solid cord- the______/_____ (_____wk).
-Primitive streak undergoes degenerative changes & disappears by the _____week
-As the notochord develops, the embryonic ___derm over it thickens to form an elongated,___-shaped plate-____
18th
underlying endoderm.
definitive notochord/chordamesoderm
end of 3rd
end of the 4th
ecto; slipper; neural plate.
Fate of the notochordal lumen
Gradually the lumen of notochordal process disappears completely.
The ectoderm of the neural plate forms the CNS.
T/F
T
NEURULATION
- Neural plate appears (cranial or caudal?) to the primitive node & (ventral or dorsal?) to the notochord & mesoderm adjacent to it.
- As the notochord elongates, the neural plate (narrows or broadens) & eventually extends cranially as far as the ____ membrane
Cranial
Dorsal
Broadens
oropharyngeal
At first the neural plate is longer in length than the underlying notochord.
T/F
F
At first the neural plate corresponds precisely in length to the underlying notochord.
Eventually the neural plate extends beyond the notochord.
T/F
T
NEURULATION
At approximately the __th day, neural plate invaginates along its central axis to form a longitudinal median- neural____, that has neural____ on each side.
18
groove; folds
NEURULATION
Neural folds become particularly prominent at the (cranial or caudal?) end of embryo
-By_____, neural folds have begun to move together & fuse, converting the neural plate into neural____, the primordium of the CNS.
Cranial
end of 3rd week
tube
first signs of brain development is ______?
Prominence of neural folds
Regarding the notochord
- As the notochordal process elongates, the primitive streak____
- At____ week the notochordal process is transformed into notochord
- Embryonic disc is originally_-shaped but soon becomes __-shaped & then ___-like
shortens
end of the 3rd
egg
pear
Slipper
The ____ functions as the primary inductor in the early embryo ;a prime mover in a sries of signal-calling episodes that ultimately transform unspecialized embyonic cells into definitive adult tissues & organs
notochord
The notochord is an intricate structure around which the _____forms.
- It extends from ______ membrane to the_____
- Notochord degenerates & disappears as the_____ form, but persists as the____ of _____
- Neurulation is completed during the___ week
vertebral column
oropharyngeal
primitive node
bodies of the vertebrae
nucleus pulposus of each IV disc.
4th
NEURAL CREST FORMATION
-As the neural folds fuse to form neural tube, some neuroectodermal cells on the crest of each fold lose their epithelial affinities & attachments to neighbouring cells.
T/F
T
As the neural tube separates from surface____, neural crest cells migrate_____ on each side of the neural tube .
-The neural crest is eventually formed between the _____ and ____
ectoderm
dorsolaterally
neural tube & the overlying surface ectoderm.
Derivatives of Neural Crest Cells
- ____ganglia (____ganglia)
- Ganglia of____
- Ganglia of cranial nerves___,___,__,___ (in part)
- ______of peripheral nerves
- _____of brain & spinal cord
Spinal
dorsal
ANS
V, VII, IX & X
Neurolemmal sheaths
Meninges
Embryological Origin of the Brain
- The brain develops from the____ end of the neural tube
- cranial to the___ pair of somites
anterior
4th
the anterior end of neural tube, at an early period becomes expanded into ___ vesicles, the primary cerebral vesicles.
-These are marked off from each other by intervening constrictions
-they are named the fore-brain or____, the mid-brain or____, and the hind-brain or_____—the last being continuous with the_____
3
prosencephalon
mesencephalon
rhombencephalon
medulla spinalis.
Secondary Brain Vesicles
- During the ____ week
- forebrain partly divides into 2 secondary vesicles-____ and ____
- hindbrain partly divides into ___ and ____
5th
telecenphalon & diencephalon
metencephalon & myelencephalon
Midbrain/ mesencephalon divides into ___ and ___ vesicles
Midbrain/ mesencephalon does not divide
HEAD FLEXURES
- As a result of unequal growth of these different parts 3 flexures are formed and the embryonic brain becomes_____ in a somewhat zigzag fashion
- The 2 earliest flexures are con___ ventrally and are associated with corresponding flexures of the whole head
bent on itself
cave
The first head flexure is the ____ flexure
Midbrain
Mid brain flexure
- aka _____ flexure
- By means of the midbrain flexure, fore-brain is bent in a (ventral or dorsal) direction around the _____ end of the notochord & fore-gut, with the result that the____
- This flexure causes the mid-brain to become, for a time, the most prominent part of the brain, since its (ventral or dorsal?) surface corresponds with the_____ of the curve.
ventral cephalic
Ventral
anterior
floor of the fore-brain comes to lie almost parallel with that of the hind-brain.
dorsal; convexity
Hind brain flexure
- The (2nd or 3rd) bend appears at the junction of the _____ and ___
- aka ____\ flexure
- the flexure increases from ____ to the end of ___ week, when the hind-brain forms nearly a___ angle with the _____
2nd
hind-brain and medulla spinalis
cervical
3rd;5th
right; medulla spinalis
After the 5th week, _______takes place & the cervical flexure diminishes & disappears.
erection of the head
Pons flexure
- The 3rd bend is named the pontine flexure
- Located in future pontine region; divides hindbrain into caudal- ____cephalon & rostral ____cephalon
- It differs from the other 2 in that (a) its_____, and (b) it______
myelen; meten
convexity is forward
does not affect the head
The lateral walls of the brain-tube, like those of the medulla spinalis, are divided by internal furrows into
___/____&___/_____ laminæ
alar; dorsal
basal; ventral
The Hind-brain
- Rhombencephalon
- The cavity of the hind-brain becomes the______
- Immediately behind the mid-brain it exhibits a marked constriction, the______
4th ventricle.
isthmus rhombencephali.
the length of the hind-brain once exceeded the combined lengths of the other 2 vesicles.
T/F
T
At the time when the ____flexure makes its appearance, the length of the hind-brain exceeds the combined lengths of the other 2 vesicles.
ventral cephalic
From that constriction the _____ and _____ are formed
anterior medullary velum & the superior peduncle of the cerebellum
Olivary nuclei are formed from neuroblasts from the ___ lamina of the ____brain and its _____
alar
Hind
rhombic lip
Cerebellum
- The cerebellum is developed by a thickening of ___ of the ___cephalon.
- The fissures of the cerebellum appear first in the____ and _____ region, and traces of them are found during the ____ month
roof; meten
vermis & floccular; 3rd
Fissures on the cerebellar hemispheres do not appear until the_____ month.
5th
The primitive fissures of the cerebellum are developed in the order of their relative size in the adult
T/F
F
The primitive fissures of the cerebellum are not developed in the order of their relative size in the adult—thus the horizontal sulcus in the fifth month is merely a shallow groove.
The best marked of the early fissures of the cerebellum are: (a) the ____between the developing____and_____, and (b) the____ between the_____ and _____
fissura prima
culmen and declive
fissura secunda
future pyramid and uvula.
The flocculus & nodule are developed from the ____
rhombic lip
____ and ____ are recognizable as separate portions before any of the other cerebellar lobules.
Floculus
Nodule
On the ventricular surface of the cerebellar lamina a transverse furrow, the _____, appears, and deepens to form the ____ recess of the____ of the____ ventricle
tent-like
Roof;4th
As the cerebellar rudiments enlarge & fuse in the median plane, they overgrow the____ half of 4th ventricle & overlap ____ and ___
- Some neuroblasts in intermediate zone of the____ plates migrate to marginal zone & differentiate into neurons of the cerebellar cortex
- Other neuroblats from these plates give rise to the _____ nuclei
rostral
pons & medulla
alar
central
Pons
-pons is developed by a thickening in the ____ and ____ walls of the ____cephalon.
floor & lateral; meten
Medulla
Summary
-The ___ and ____walls of the ____cephalon are thickened to form the medulla oblongata.
floor & lateral
myelen
- Each lateral wall of myelencephalon consists of an alar and a basal lamina, separated by an _____, the remains of which are represented in the adult brain by the ____ on the_____
- The contained cavity is more or less____ in outline, the base being formed by the ___-plate, which is thin and greatly expanded transversely.
internal furrow
sulcus limitans
rhomboid fossa
triangular; roof
Neuroblasts are developed in the alar & basal laminæ of myelencephalon & their narrow stalks are elongated to form the _____of the nerve fibres.
axis-cylinders
Opposite the furrow or boundary between the alar & basal laminæ a bundle of nerve fibres attaches itself to the outer surface of the alar lamina -_______, & is formed by the sensory fibres of the ______ and _____ nerve.
tractus solitarius
glossopharyngeal & vagus n
Within a few days the rhomboid lip of myelencephalon becomes applied to, and unites with, the outer surface of the main part of the alar lamina, and so covers in the tractus solitarius & also the _____ root of _____ nerve
spinal root of the trigeminal
From the alar lamina and its rhombic lip, neuroblasts migrate into the basal lamina, and become aggregated to form the ____ nuclei, while many send their axis-cylinders thru the floor-plate to the _____ side, and thus constitute the rudiment of the ___ of the medulla oblongata.
olivary
opposite
raphe
(a) the development of the pyramids of medulla which are formed about the ____ month by the ___ward growth of the (sensory or motor?)fibres from the cerebral cortex
4th; down
Motor
On the rhomboid fossa a series of 6 temporary furrows appears- rhombic____.
•They bear a definite relationship to some of the cranial nerves; thus, from before backward the 1st & 2nd grooves overlie the nucleus of the____; the 3rd, the nucleus of the____; the 4th, that of the ____; the 5th, that of the____; and the 6th, that of the____
grooves
trigeminal
facial
abducent
glossopharyngeal
vagus
Mid Brain
- Cells from the ___ plates give rise to the ___ nuclei,___ and___ nuclei,____ nuclei of trigeminal nerve
- Its cavity becomes relatively (increased or reduced?) in diameter, and forms the_____ of the adult brain.
alar
pontine
cochlear & vestibular
sensory
Reduced; cerebral aqueduct
cerebral peduncles develop from ____ and are are at first of small size, but rapidly enlarge after the ____ month.
Thickened basal lamina of midbrain
4th
The cerebral peduncles are the anterior part of the midbrain that connects the remainder of the_____ to the _____
brainstem
thalami
The neuroblasts of these basal laminæ of midbrain constitute the nuclei of the____,___,and______.
III & trochlear n. & of the mesencephalic root of the trigeminal n
By a thickening process, alar laminæ of midbrain are developed into the _____ lamina.
quadrigeminal
Neuroblasts migrate from the alar plates of midbrain into the tectum & aggregate to form-________
sup & inf colliculi
Neuroblasts from basal plates of midbrain may give rise to groups of neurons in the tegmentum (___nuclei, nuclei of ____and___ cranial nerves, & _____ nuclei of thalamus
red
3rd & 4th
reticular
The Fore-brain
- Prosencephalon
- At a very early period 2 lateral diverticula, the____, appear, one on either side of the fore-brain
- The (central or peripheral?) parts of the vesicles expand, while the (proximal/distal?) parts are reduced to______, called the____
optic vesicles
Peripheral
Proximal
tubular stalks; optic stalks.
for a time the optic vesicles communicate with the cavity of the fore-brain by relatively narrow openings.
T/F
F
Wide openings
The optic vesicle gives rise to the___ and the epithelium on the back of the_____ and ____
-The optic stalk is invaded by nerve fibres to form the ____ nerve
retina
ciliary body and iris.
optic
A 2nd pair of diverticula soon arise from forebrain , more dorsally& rostrally-_____ vesicles- primordia of_____
-The cavities of these diverticula are the rudiments of the_____; they communicate with the median part of the fore-brain cavity by relatively wide openings, which ultimately form the _____
cerebral/telencephalic
cerebral hemispheres.
lateral ventricles
interventricular foramen
The (median or lateral) portion of the wall of the fore-brain vesicle consists of a thin lamina, the____, which stretches down from the____ to the recess at the base of the______
Median
lamina terminalis
interventricular foramen; optic stalk.
The anterior part of the fore-brain, including the rudiments of the cerebral hemispheres, is named the_____, & its posterior portion is termed the_____
telencephalon
diencephalon
Only the telencephalon contributes to form the lateral ventricles
T/F
F
both telencephalon and diencephalon contribute to the formation of the third ventricle.
Diencephalon
-From the (alar or basal?) lamina of the diencephalon, the___,___,____ are developed.
Alar
thalamus, metathalamus, and epithalamus
Thalamus separated from epithalamus by ____ sulcus & from hypothalamus by____ sulcus
epithalamic
hypothalamic
Thalamus
-Develops (slowly or rapidly?) on each side & bulges into cavity of___ ventricle, reducing it to a narrow cleft
Rapidly
3rd
Thalami meet & fuse in midline in ~___% of brains, forming a bridge of gray matter across the 3rd ventricle-_______(______)
70
interthalamic adhesion
massa intermedia
Metathalamus
-The metathalamus comprises the ______which originate as_______ of the ____ lamina
geniculate bodies
slight outward bulgings
alar
Epithamus
- The epithalamus includes the pineal body, the posterior commissure, & the trigonum habenulæ.
- The pineal body arises as an (upward or downward?) evagination of the (cranial or caudal?) part of roof-plate of diencephalon, immediately in front of the____
- this evagination becomes solid with the exception of its (proximal of distal ?) part, which persists as the ______
Upward
Caudal
midbrian
Proximal
recessus pinealis.
In lizards the pineal evagination is elongated into a stalk, and its peripheral extremity is expanded into a vesicle, in which a rudimentary ___ and ___ are formed. The stalk becomes solid and nerve fibres make their appearance in it, so that in these animals the pineal body forms a____
lens and retina
rudimentary eye.
The posterior commissure is formed by the ingrowth of fibres into the depression (infront or behind?) & (above or below?) the___ evagination
Behind
Below
pineal
the trigonum habenulæ is developed (in front of or behind?) the pineal recess
In Front of
Hypothalamus
-From the (alar or basal?) laminæ of the diencephalon
basal
the pars mamillaris hypothalami is developed and this comprises the_____ & the (anterior or posterior?) part of the_____
corpora mamillaria
Posterior
tuber cinereum.
The corpora mamillaria arise as a (single or double ?) thickening, which becomes divided into __ by a median furrow during the 3rd month.
Single
2
Telecephalon
- Consists of a median portion & 2 lateral diverticulae.
- The median portion forms the (anterior or posterior ?) part of the cavity of the 3rd ventricle, and is closed below and in front by the______
- The lateral diverticulae consist of outward pouchings of the (alar or basal ?) laminæ
- the cavities represent the____ ventricles, and their walls become thickened to form the nervous matter of the cerebral hemispheres.
Anterior
lamina terminalis.
Alar
lateral
Pituitary Gland
- The hypophysis cerebri is ___dermal in origin
- Develops from 2 sources
- An upgrowth from _____ of _____
- A downgrowth from neuroectoderm of diencephalon- the______
ecto
ectodermal roof of stomodeum
neurohypophysial bud
______ , a person divides each cerebral hemisphere into 3 fundamental parts, viz., the ____, the _____, and the _______
Elliott-Smith
rhinencephalon; corpus striatum; neopallium
The_____ represents the oldest part of the telencephalon
rhinencephalon
The Rhinencephalon
- forms almost the whole of the hemisphere in ___,___,and____
- In man it is ____ developed in comparison with the rest of the hemisphere
- comprises the following parts, viz., the___ lobe, the___ perforated substance, the septum pellucidum, the___and__calossal, and ____gyri, the fornix, the hippocampus, and the uncus.
fishes, amphibians, and reptiles.
feebly
olfactory; anterior; subcallosal, supracallosal; dentate
olfactory lobe consists of the____ and____ and the______
olfactory tract
bulb
trigonum olfactorium
Corpus Striatum
- The corpus striatum appears in the ___ week as a __shaped thickening of the (roof or floor?) of the telencephalon between the____ and _____, and continuous behind with the ____ part of the diencephalon
- It increases in size, and by the ____ month is seen as a swelling in the floor of the future___ ventricle
4th
triangular
Floor
optic recess and the interventricular foramen
thalamic
2nd; lateral
The neopallium
-The neopallium forms the remaining, and by far the greater, part of the cerebral hemisphere.
T/F
T
The neopallium Consists, at an early stage, of a relatively large, more or less hemispherical cavity—the primitive ___ ventricle—enclosed by a thin wall from which the____ of the hemisphere is developed.
-The vesicle expands in all directions, but more especially ____ and ____
lateral; cortex
upward and backward
by the ____ month the cerebral hemispheres cover the diencephalon, by the __ month they overlap the mid-brain, and by the___ month the hind-brain
3rd
6th
8th
Abnormal development of the brain is common or rare
_per __ births
And why?
Common
3 per 1000 births Because of the complexity of its embryological history
Neural Tube Defects: Rostral
(1) Exencephaly : large amount of ___and absence of____. It is considered to be an embryological precursor of____
(2) Meroanencephaly
- 1 /1000 births;
- ___ and ___ partially or totally absent
- perinatal mortality
protruding brain tissue ;calvarium; anencephaly
skull & brain
Meroanencephaly occurs more in males
T/F
F
Females
About 2-4x than in males
Meningocele
- aka____ or ____
- parts of ____/___/____system protrude outside skull
- mental disability depends on____
Microcephaly
-calvaria & brain are ____
Meningocencephalocele or Meningohydroencephalocele
meninges
brain
ventricular
extent; small
Those with microcephaly are not mentally retarded
T/F
F
They are
Infact they are grossly mentally retarded
In Agenesis of corpus callosum seizures & mental are rare
T/F
F
Common
Patients with Agenesis of corpus callosum may be asymptomatic
T/F
T
Holoprosencephaly
-having _____ leading to ___ ventricles merging to 1 large ventricle
Hydranencephaly
-____hemispheres are absent/represented by_____
small forebrain
lateral
cerebral; membranous sacs
Arnold-Chiari Malformation- 1/1000 births
-condition in which brain tissue extends into the_____, present at birth.
It occurs when part of the skull is abnormally___ or ___
spinal canal
small or misshapen.
Mental Retardation
-from _____ abnormalities/_____
chromosomal
mutant gene
______is the commonest cause of mental retardation
Maternal alcohol abuse
Abnormal histogenesis of cerebral cortex can result in ____ & various degrees of mental retardation
seizures
Submental intellectual development may result from exposure of embyo/foetus during ____ to____week period of development to certain ___ & high levels of____
8- to 16-
viruses; radiation
Prenatal factors may be involved in the development of cerebral palsy
T/F
T
General Causative factors of neural tube disorders
•_____,_____,_____
Genetic
Nutritional
Environmental
Stages of Cellular Activity
-6 distinct stages
List them
Neurogenesis
- Cell migration
- Differentiation
- Synaptogenesis
- Neuronal cell death
- Synaptic rearrangement
In Cell migration
- they go to specific ____along radial glia
- later: along____
“brain” locations
other neurons
In Differentiation
- into specific neuron types
- either by ____:influenced by surrounding cells
- or ______
induction
cell-autonomous
In Neuronal cell death
- apoptosis: programmed cell death
- ____% of neurons in a region die
- it is genetically programmed
- due to lack of _____ factors
20-80
neurotrophic
Alpha motor neurons are derived from alar plates
T/F
F
Basal
Spinal trigeminal nucleus is derived from alar plates
T/F
T
