Embryology Flashcards
What week does gastrulation occur and therefore what week does CNS begin to appear
3
Neural tube initially remains open at its anterior and posterior ends as what
Anterior and posterior neuropores
What week do the 3 primary brain vesicles form
4
What week do the 3 primary vesicles subdivide into 5 secondary vesicles
5
What flexure divides the mesencephalon and rhombencephalon
Cephalic
What flexure divides the rhombencephalon and spinal cord
Cervical
What flexure divides the metencephalon and myelencephalon
Pontine
What week does CSF formation begin
5
What do neural crest cells form
PNS neurons and glia
What week does cortical folding occur to form sulci and gyri
26
Name 3 neural tube defects (due to failure of neural tube to close)
Anencephaly/exencephaly
Encephalocele
Spina bifida
What causes anencephaly
+ what is the resulting damage
Failure of anterior neuropore to close
Skull fails to form, brain tissue degenerates
What is craniorachischisis
Failure of neural tube to close along entire neuroaxis
What causes encephalocele
+ what is it
Failure of anterior neural tube to close
Herniation of cerebral tissue through a defect in the skull
What causes spina bifida
Failure of caudal neural tube to close
Non-fusion of the vertebral arches
Name the 2 types of spina bifida
Spina bifida occulta
Spina bifida cystica
Name other congenital brain abnormalities
Lissencephaly - smooth brain (no gyri or sulci)
Polymicrogyria
Microcephaly
Agenesis corpus callosum
Porencephaly
Schizenecephaly
Diastematomyelia (split cord malformation)
When does neural tube fuse/close
-when does it begin + when is it completed by
Begins day 18 and complete by end of 4th week
When the 3 germ layers (ectoderm, mesoderm, endoderm) have formed, cells from primitive streak continue to sink down to form what
Notochord (solid tube of cells in the midline)
What does the notochord do
sends out signals to ectodermal cells in the midline, causing the cells there to thicken and influencing a neural plate to form
Neural plate eventually sinks down and forms a dip in the midline of the ectoderm layer then…
Surface ectoderm comes together centrally and encloses the neural tube
Name the 3 primary brain vesicles
forebrain/rosencephalon,
midbrain/mesencephalon,
hindbrain/rhombencephalon
Name the 5 secondary brain vesicles
Forebrain:
Telencephalon,
Diencephalon,
Midbrain:
Mesencephalon,
Hindbrain:
Metencephalon, Myelencephalon
Optic vesicles grow laterally from which brain vesicle of the neural tube
Diencephalon
Optic vesicles eventually develop into what
Eyeballs
When the optic vesicles reach surface ectoderm, it sends signals to the surface ectoderm inducing what to happen
surface ectoderm to thicken –> forming the lens placode
Define placode
thickening of embryological tissue
Optic cup is connected to neural tube by what
Optic stalk (future CN II)
10th layer of retina is formed by inner or outer layer of optic cup
Other 9 layers of the retina are formed by inner or outer layer of optic cup
A potential space therefore sits between the inner 9 layers and the outer 10th layer which is important clinically because it gives rise to…
outer
inner
Diseases like retinal detachment
5 histological layers of the cornea
Epithelium Bowman's membrane Stroma Descemet's layer Endothelium
What type of epithelium covers the cornea
Stratified squamous non-keratinised
What is bowman’s membrane
Basement membrane of corneal epithelium
What is the stroma of the cornea made of
REGULARLY ARRANGED COLLAGEN FIBRES –> making cornea TRANSPARENT
What is descemet’s layer
Basement membrane of the endothelium
Endothelium v epithelium
Endothelium is just epithelium lining the inside of a surface
If cornea is avascular, where does it get its nutrition from
from AH and blood vessels at the side of it
Which of the 3 germ layers does the CNS develop from
Ectoderm
Telencephalon becomes the (3)
Cerebral hemispheres
Hippocampus
Basal ganglia
Metencephalon becomes the (2)
Cerebellum
Pons
Myelencephalon becomes the
medulla
Lumen of neural tube forms the
ventricular system
Name a genetic cause of hydrocephalus
Congenital aqueductal stenosis
Neural tube is lined with what epithelium
Pseudostratifed
Neural tube is initially a single layer of rapidly dividing neuroepithelial cells
Neuroepithelium goes on to produces most cells of the CNS including… (4)
Neurons
Astrocytes (glia)
Oligodendrocytes (glia)
Ependymal cells (glia)
Microglia ARE NOT derived from neuroepithelial cells, instead they’re derived from…
MESENCHYMAL CELLS that migrate into CNS
Neural tube also forms non-neuronal cells such as (2)
Melanocytes
Adrenal medulla
Neural crest cells are derived from… and break away from it by undergoing a what transition
neural ectoderm
epithelial to mesenchyme transition
Neural crest cells migrate through the neural tube to form things such as
DRG
Autonomic ganglia
Neural crest cells form the motor or sensory component of spinal nerves
sensory
Cortical folding (where the brain develops sulci and gyri) occurs at what week + purpose of this folding
26
Minimises brain volume and bring together brain regions that would otherwise be far apart
Describe spina bifida occulta (a type of spina bifida)
- failure of what to fuse
- usually occurs in which vertebral levels
- symptoms/signs
Most common but most minor
Failure of embryonic halves of vertebral arch to grow normally and fuse
Occurs in L5 & L6 vertebrae
No symptoms
SIGN SOMETIMES - dimple in back with a bushy growth of hair
Spina bifida cystica is what
protrusion of spinal cord through the defect in the vertebral arches
3 subtypes of spina bifida cystica
Spina bifida with meningocele
Spinda bifida with meningomyelocele
Myeloschisis (most severe)
Prenatal diagnostic investigations of spina bifida (3)
Maternal blood screening
Amniocentesis
Ultrasound
How can maternal blood screening diagnose spina bifida
Neural tube defect would be indicated by HIGH ALPHA FETOPROTEIN (AFP) in blood
How early can spina bifida be detected in utero
16-20 wks
How can amniocentesis diagnose spina bifida
high levels of alpha fetoprotein (AFP) in amniotic fluid (foetal liver leaks into amniotic fluid)
Pregnant women are advised to take what to prevent neural tube defects
FOLIC ACID SUPPLEMENTS
Risk factors of neural tube defects
Genetic predisposition, e.g. abnormal fold acid metabolism
Poor nutrition, e.g. too little folate, teratogens
Environmental, e.g. hypothermia, toxic drugs
What is lissencephaly
‘smooth brain’
- no formation of gyri or sulci
- -> severe mental impairment
What is polymicrogyria
excessive number of small gyri –> variable neuro problems
What is microcephaly
Head circumference smaller than usual
-usually have a small brain and intellectual disability
What isa genesis corpus callosum
Complete or partial absence of the corpus callosum
What is porencephaly
CSF FILLED CYSTS OR CAVITIES in the brain
extremely rare
What is schizencephaly
Loss of brain tissue –> large clefts/spaces in brain
often presents with seizures, mental retardation, hemiparesis
What is diastematomyelia
Split cord malformation
-spinal cord splits longitudinally into 2
Causes of brain defects
Genetic Infection - e.g. rubella Radiation Maternal alcohol abuse Drugs
