5. Development Flashcards
which process converts neural plate –> neural tube?
neurulation
steps to neurulation
- lateral edges of neural plate fold DORSALLY
- midline neural groove forms
- folded edges meet & fuse at midline
- fusion begins day 22 (cervical region, 5th somite)
- neural groove is converted to neural tube
which day does neural fusion start?
at which region and somite?
fusion begins day 22 (cervical region, 5th somite)
- direction of fusion during neurulation
- on day 23, neuropores are (closed/open)
- cranially and caudally
- both cranial and caudal neuropores are still open to the amniotic sac
which neuropore closes first?
*cranial neuropore first (day 25)
and then caudal neuropore (day 28)
neural crest cells (aka “fourth germ layer”)
- from what layer is it formed?
- where do they originate?
- migration patterns?
- from ectoderm –> forms neural crest cells
- originates from lateral edges of neural plate
- migration
- cephalic region - sheet-like mass migration; pharyngeal arches
- trunk - chain migration
neural crest derivatives
- cranial nerve ganglia
- spinal (dorsal root) ganglia
- sympathetic chain and pre-aortic ganglia
- parasympathetic ganglia of GI tract
- schwann cells
- glial cells
- meninges (forebrain)
what does the neural tube develop into?
CNS
what do differentiating neuroblasts develop into?
these are primitive nerve cells; which these are responsible for neurons.
These migrate and form in mantle layer
layers of the spinal cord
- ventricular
- develops into neuroepithelium (pseudostratified)
- differentiates into neuroblasts
- neuroblasts form mantle layer
- gray matter
- marginal layer forms as nerve fibers emerge from neuroblasts
- white matter
neuroblasts form mantle layer and develop into…
gray matter
marginal layer forms as nerve fibers emerge from neuroblasts and differentiate into…
white matter
what are the plates of the spinal cord
- basal plate
- alar plate
- roof
- floor
basal plate of spinal cord develops into:
- ventral horn w/
- motor cells
These are primary order sensory cells
alar plate of spinal cord includes, and develops into:
second order sensory cells
- dorsal horn
- sensory cells
intermediate horn of spinal cord develops into:
autonomic nervous system (gray matter)
central canal develops into
cerebrospinal fluid
where do the ventral root and dorsal root come from?
- ventral root/ motor nerve fibers arise from cells in basal plate
- dorsal root/ sensory nerve fibers arise from sensory nerve cells
process of forming dorsal root?
(neural crest derivatives –> form outside the spinal cord (dorsal root ganglion) –> processes extend centrally to alar plate, and peripherally to join ventral root –> form sensory nerve cells
axonal growth:
direction and details
- axons grow towards their target (end) organs
- growth cone at apical end of developing axon is guided by molecular signaling
- towards - chemoattractants,
- away from- chemorepellants)
synaptogenesis
- synaptic connection forms when axon interacts w/ target
- not precise
apoptosis w/ regards to axonal growth and synaptogenesis?
50% of neurons produced during development undergo apoptosis
somites:
precursor; and develops into
- develop from paraxial mesoderm
- differentiate into:
- sclerotome: the part of each somite in a vertebrate embryo giving rise to bone or other skeletal tissue
- dermomyotome: the remaining part of the somite left when the sclerotome migrates
sclerotome: define
the part of each somite in a vertebrate embryo giving rise to bone or other skeletal tissue
dermamyotome: define
the remaining part of the somite left when the sclerotome migrates
purpose of resegmentation of sclerotomes
- resegmentation allows passage of spinal nerves between vertebrae
- accounts for segmental nerve distribution
- myotomes - motor innervation
- dermatomes - sensory innervation
myotome: define
what does myotome split into?
- dorsal part of each somite in a vertebrate embryo, giving rise to the skeletal musculature
- divides into:
- epimere: dorsal; deep back muscles
- hypomere: ventral; develops into hypaxial muscles
epimere:
develops into
inn. by
- the dorsal portion of the mesodermal mass in the early development of chordate embryos that gives rise to the skeletal muscles
- develops into deep back muscles
- inn by dorsal rami
hypomere:
develops into
inn. by
hypaxial musculature
- lateral and ventral body wall musculature
- limb musculature
- inn by ventral ramus
3 primary brain vesicles
- prosencephalon
- mesencehalon
- rhombencephalon
which primary brain vesicle develops into:
future forebrain
prosencephalon
which primary brain vesicle develops into:
future midbrain
mesencephalon
which primary brain vesicle develops into:
future hindbrain
rhombencephalon
secondary brain vesicles
(and which primary vesicle they developed from)
- TELencephalon - prosencephalon
- DIencephalon - prosencephalon
- MESencephalon - mesencephalon
- METencephalon - rhombencephalon
- MYELencephalon - rhombencephalon
which 2 secondary brain vesicles develop from prosencephalon?
- telencephalon
- diencephalon
which 2 secondary brain vesicles develop from rhombencephalon?
metencephalon and myelencephalon
brain region at birth from the secondary brain vesicles?
- telencephalon - cerebrum
- diencephalon - diencephalon
- mesencephalon - mesencephalon
- metencephalon - cerebrum and pons
- myelencephalon - medulla oblongata
which secondary brain vesicles form the brain stem?
- mesencephalon (midbrain)
- cerebrun and pons
- medulla oblongata
why can’t we think about the brain stem as a layered ice cream cone?
because the cephalic flexure (as a result of cranial/caudal folding) affects the orientation
why do we have a cephalic flexure?
bc humans assume an upright stance which affects orientation of visual, auditory, and vestibular systems oriented accordingly
curves the axis of rotation
forebrain development - end structures
- telencephalon -
- future cerebral hemispheres (right and left)
- cortical structures develop (gyri, sulci, fissures)
- diencephalon - assoc. w/ 3rd ventricle
- eyes +
- subthalamus
- epithalamus
- thalamus (R/L)
- hypothalamus (R/L)
when the telecephalon (R/L hemispheres) growing most rapidly?
rapid growth during final 2 months of fetal period
diencephalon is assoicated w/ which ventricle?
3rd ventricle
from which layer does the pituitary gland develop?
from ectoderm
- starting wk 5, pituitary forms in dorsal midline above thyroid gland
- ectodermal pocket in dorsal midline of pharynx
- pocket loses connection w/ pharynx –> creating hollow ball of cells inf to floor of diencephalon (posterior to optic chiasm)
- cells divide and central chamber disappears –> endocrine mass becomes adenohypophysis
- neurohypophysis of pituitary gladn begins as depresion adn grows towards adenohypophysis
define the following:
gyri
sulci
fissures
gyri: folds
sulci: grooves
fissures: deep sulci
cephalic flexure is between which 2 secondary brain vesicles?
diencephalon and mesencephalon
changes directional orientation
somatotopic organization
organized into tracts/ based on region of the body; allows us to determine where the lesion is based on a map like the humunculus
*more complex rostrally
pituitary gland develops from which 2 things?
- oral ectoderm
- diencephalon
pharyngeal arches:
made of what?
how many?
covered by what?
- bars of mesenchyme derived from the mesoderm and neural crest cells
- form in 4 pairs around pharynx
- covered by ectoderm externally and endoderm internally
what is a synonym for branchial?
pharyngeal arches
difference between pharyngeal pouch vs. cleft?
cleft is externally between arches (ectoderm)
pouch is internal between arches (endoderm)
which pharyngeal arch tends to disappear betwen 5 weeks and 5 months
pharyngeal arch 2 seems to disappear
epiglottis forms from which pharyngeal arch?
pharyngreal arch 4 (Green)
which cranial nerve matches with each arch?
V3 , VII, IX, X
which cranial nerve is assoc. w/
arch 1
trigeminal nerve (V3) mandibular division
which cranial nerve is assoc. w/
arch 2
facial nerve (CN 7)
-involved in part of taste sensation
which cranial nerve is assoc w/
arch 3
glossopharyngeal (CN 9)
which cranial nerve is assoc w/
ARCH 4 (&6)
vagus nerve (CN 10)
CC: holoprosencephaly,
and mechanism
failure of prosencephalon (& sometimes other bilateral structures) to divide into right and left counterparts;
*injury to anterior midline of germ disc
can cause cyclopia
CC: hydrocephalus
(definition, causes, effects)
- build-up of cerebrospinal fluid w/in the brain ventricles –>taking up space in the fixed cavity, compressing other material)
- causes
- overproduction of CSF
- diminished reabsorption of CSF
- blockage of CSF circulation
- effects
- brain damage due to compression of CNS structures
CC: neural tube defects
spectrum of defects related to incomplete neurulation
during which stage of development is body plan refined?
gastrulation
(early on in development, we know where cranial and caudal ends are)
which CNS congential abnormality results from :
injury to anterior midline of germ disc (due to alcohol or genetics)
holoprosencephaly
tx for hydrocephalus
catheterize the enlarged ventricle –> subcutaneous catheter –> loop of catheter in peritoneum to accomodate growth (diverts to abdominal cavity where it is then absorbed)
meninges review: what layers are they and what do they cover?
- dura (externally)
- arachnoid
- pia
These cover both the brain and spinal cord
CC: anencephaly
- failure of cranial neuropore to close
- therefore, neural tissue is exposed to amniotic fluid –> necrosis
CC: spina bifida
- failure of caudal neuropore to close
CC: meningocele vs. meningomyelocele**
- meningocele: protrusion of the meninges through a gap in the spine due to a congenital defect
- meningomyelocele: *most severe; also CNS structures that have buldged out into the cyst
tx to prevent neural tube defects
effects of such tx
mandate to fortify cereals w/ folic acid to prevent neural tube defects
the rate of spina bifida has decreased & has now been relatively maintained at lower rate
significance of 1st pharyngeal cleft
where external auditory meatus forms
which is interior?
(pharyngeal pouch or cleft)
pharyngeal POUCH
which is exterior?
(Pharyngeal pouch or cleft)
Pharyngreal CLEFT
cc: where is the most common blockage of CSF, leading to hydrocephalus?
blockage of the cerebral aqueduct
CC: what structure is most likely damaged during hydrocephalus?
why?
brain material can be herniated through foramen magnum and damaging CNS (respiratory centers are here)
CC: Rachischisis
The vertebrae overlying the open portion of the spinal cord do not fully form and remain unfused and open, leaving the spinal cord exposed
Incompatible w/ life
