Exam One - Neuroembryology Flashcards
The basic formation of the human CNS is complete by ________ of gestation
6 weeks
Following fertilization, cells divide to form a ________
morula
What day does a morula form?
3
Morula differentiates into:
trophoblast (outside cells - nourishment)
embryoblast (inside-baby)
embryoblast forms on day______
6
The fluid filled space between a trophoblast and an embryoblast is called __________-
blastocytic cavity
blastulation to gastrulation happens between what days?
8-14
The embryoblast differentiates into?
hypoblast and epiblast
_________ then epiblast, then hypoblast, then _________
amnionic cavity, primitive yolk sac
bilaminar blastocyst (disk) refers to what two layers?
epiblast and hypoblast
What day does the primitive streak form?
day 15
what marks the beginning of gastrulation?
the primitive streak
Gastrulation
inner cell mass is converted into the trilaminar ambryonic disk containing 3 layers: ectoderm, mesoderm, and endoderm
endoderm makes…
GI tract, liver, pancreas, respiratory lining, middle ear and bladder epithelium, thyroid, and parathyroid
mesoderm makes…
muscles, bone, connective tissue, urinary system, reproductive system, circulatory system, and dermis
ectoderm makes…
the nervous system!!
Day 16
notochord develops as a primitive beggining of backbone, it appears as a small flexible rod made from cells in mesoderm
Day 17
neuroectodermal tissue differentiates from ectoderm to form the neural plate (shallow groove and small fold)
Day 18
neural groove deepends to form neural folds with the crest
Day 21-22
the neural crest of each neural fold fuse to form the neural tube
primary neurulation
rostral portion of neural tube gives rise to the brain and the spinal cord through the lumbar levels
secondary neurulation
the caudal portion of neural tube gives rise to sacral and coccygeal levels of the cord
congenital malformations associated with defective neurulation are called_____-
dysraphic disordered
disruptions of rostral neurulation
anencephaly
disruptions of caudal neurulation
spina bifida
primary neurulation
forms neural tube on day____, continues both rostrally (and closes on day_____) and caudally (closure on day_______)
22, 24, 26
the neural tube differentiates into:
CNS:
- brain
-spinal cord
- ventricles
-neurons, glial cells, lower motor neurons, preganglionic autonomic neurons
the neural crest differentiates into:
PNS:
- sensory ganglia of cranial nerves
- dorsal root ganglia
- ganglia of ANS
- schwann cells
- melanocytes
- pia and arachnoid of the meninges
the precursor cell population for neurons and glia is
neuroepithelial cells
neuroblastic lineage
- from neuroepithelial cells
- generates neurons
glioblastic lineage
- from neuroepithelial cells
- generates glia (radial glia, astrocytes, oligodendrocytes)
totipotent stem cells
self renewing, unspecialized, can be anything
multipotent
self renewing, give rise to specific cell lineages
restricted
- GRP Glial restricted precursors: glioblastic lineage
- NRP Neuron restricted precursors: neuroblastic lineage
What are the 3 layers of the developing spinal cord?
- ependymal layer: lining of central canal
- mantle layer: alar plate = sensory, basal plate = motor
- marginal layer: white matter
the spinal cord develops from the ___________ of the neural tube
caudal portion
during the _____ a ____________ groove develops in the lateral wall of the developing spinal cord, and it is called ____________
4th week, longitudinal, suclus limitans
the suclus limitans separated the neural tube into a _______ (alar plate) and a ________ (basal plate)
dorsal, ventral
derivatives of the alar plate
sensory neurons that innervate skin, joints, tendons and muscles (somatic afferent), and sensory neurons that innervate visceral structures (visceral afferents)
derivatives of the basal plate
motor neurons that innervate skeletal muscle (somatic efferent), and lateral horm neurons that project to autonomic structures (visceral efferents)
Somites are…
blocks of mesoderm located on either side of the neural tube in the developing vertebrate embryo
somites are subdivided into…
sclerotomes (vertebrae)
myotomes (muscle)
dermatomes (skin sensation)
how many total somites and how are they divided?
42-44 total:
4 occipital
8 cervical
12 thoracic
5 lumbar
5 sacral
8-9 coccygeal
* 1st occipital and 5-7 coccygeal disappear
a dermatome is an…
area of skin that is supplied by a single spinal nerve
days _____ the neural tube forms these 3 primary vesicles and 2 flexures
day 27-28
prosecephalon
mesencephalon
rhombencephalon
cephalic flexure: in midbrain
cervical flexure: b/t rhomb and spinalcord
What week do 2 more flexures appear? What are these flexure? What are the 5 secondary vesicles that also form at this time?
5-6th week
- pontine flexure that divides rhobencephalon into metencephalon and myelencephalon
- telencephalic flexure that divides forebrain into diencephalon and telencephalon
what does the telencephalon derrive?
cerebral cortex and corpus striatum
what does the diencephalon derrive?
thalamus and hypothalamus
what does the mesencephalon derrive?
midbrain
what does the metencephalon derrive?
pons and cerebellum
what does the myelencephalon derrive?
medulla
holoprosencephaly
failure of the prosencephalon to form secondary vesicles
causes: genetic mutations of teratogens like alcohol, retinoic acid, and maternal diabetes
alobar holoprosencephaly
complete failure to divide into left and right hemispheres
semilobar holoprosencephaly
partial separation of hemispheres
hydrocephalus
excess csf building up within ventricles
dandy-walker syndrome
defect in development of cerebellum leading to expanded 4th ventricle
primary neurulation defects include
- anencephaly
- crania bifida (encephalocele): failured closeure of cranium
- spina bifida: failure in closure of vertebra
secondary neurulation defects include:
- open and closed spina bifida
- tethered cord syndrome: abnormal separation of neurotube from the surrounding tail bud tissues
anencephaly
- defects of anterior neuropore
- rostral end of tube fails to close usually between the 23-26 day of development
encephalocele (crania bifida)
- partial lack of bone fusion leaves a gap through which a portion of the brain protrudes
- csf or meninges may also protrude through
- protrusion usually covered by skin or thin membrane
- most often affects the occipital area
3 types of encephalocele
- meningocele: least severe, csf and meninges protrude
- meningoencephalocele: brain, csf, and meninges protrude
- meningohydroencephalocele: most severe, ventricle, brain, csf, and meninges protrude
chiari malform 1
structural defect in the base of the skull that results in the cerebellums extension below the foramen mag into the upper spinal canal
chiari malform 2
both the cerebellum and the brain stem tissue protrude into the foramen mag
chiari malform 3
some of the cerebellum herniate through an abnormal opening in the back of the skull
chiari malform 4
incomplete or underdeveloped cerebellum
What is the most common neural tube defect in the US?
spina bifida - “cleft spine” is due to incomplete development of the brain, SC, and/or meninges
spina bifida occulta
skin covers the affected area, can affect any level of the spine but it is usually found on the lower end. characterized by a hair patch
spina bifida cystica meningocele
cyst contains meninges and csf
spina bifida cystica meningomyelocele
cyst contains spinal cord and/or spinal cord roots
spina bifida cystica myeloschisis (myelocele)
spinal cord is often open because the neural folds failed to fuse during the 4th week, the spinal cord in the affected area is a flattened mass of nervous tissue
upper motor neuron signs
increased muscle tone
increased tendon reflexes
spasticity
lower motor neuron signs
decreased muscle tone
decreased tendon reflexes
muscle weakness or complete denervation
tethered cord syndrome
conus medullaris and filum terminate are abnormally fixed to the vertebral column
signs of tethered cord syndrome
lower extremity weakness
sensory loss
asymmetrical growth of legs/feet
bowel and bladder dysfunction
