Embryology Flashcards
When do the 3 layers of embryonic tissue appear? When does Neural Plate give rise to Neural Tube? When is neural tube development complete?
Week 3
Day 18–> Neural Plate gives rise to Neural Tube.
Day 28–> Neural Tube development completed
When does the Nervous System develop?
3rd trimester
What does the Notochord form in the adult? What problems can it create?
Nucleus Pulposus, which lies within the vertebral column. It can herniate through the annulus fibrosus and impinge on spinal root–> PAIN.
Describe Neuralation (4 steps)
1) Notochord (which comes from Prenotochordal cells) induces overlying ectoderm to form Neural Plate. Notochord becomes nucleus Pulposus.
2) Nerual plate invaginates–> Neural Groove (Day 18)
3) Neural Groove–> forms Neural Tube and Neural Crest Cells
4) Neural Tube closes, starting in center and expanding rostrally and caudally.
What does the PNS develop from?
Neural Crest cells
What forms from the exterior and interior of the Neural Tube?
Exterior–> CNS
Interior–> ventricles and spinal canal
What is Anencephaly? What are the characteristic features?
Failure of the ROSTRAL neuropore to close
Features: absence of scalp, skull, and portions of cortex. FROG EYE appearance.
What is Spina Bifida?
Failure of caudal neuropore closure
What is the main cause of anencephaly and spina bifida?
Low folate levels
What clinical findings/tests can indicate fetal neural tube defects?
Elevated alpha-fetoprotein in maternal serum OR amniotic fluid. Can also be elevated with hepatocellular carcinoma and yolk sac tumors.
Describe the different forms of Spina Bifida
Spina Bifida Occulta: No herniation, but failure of vertebral archto clouse. Tuft of hair.
Meningiocele: Failure of vertebral arch to close with Herniation of meninges (subarachnoid space). Form lumbosacral cyst.
Meningomyocele: Failure of vertebral arch to close with Herniation of meninges AND spinal cord. Associate with Arnold-Chiari syndrome. Can result in loss of reflexes and sensation, paralysis.
What defines the severity of Spina Bifida?
-location and degree of closure
What is Meningoencephalocele?
Herniation of meninges and brain–> Mental Retardation
What is Meningohydrocephalocele?
Herniation of meninges, brain, and CSF-containing ventricles–> Mental Retardation
What are the Alar and Basal Plates? What is the Sulcus Limitans?
Alar Plate: gives rise to Sensory neurons
Basal Plate: gives rise to Motor neurons
Sulcus Limitans: separates two plates
What do the Neural Crest cells give rise to? (Possible defects)
MOST IMPORTANT: PNS and Schwann Cells
Aortic arch/ Aorticopulmonary Septum (Great vessel deformities)
Parafollicular Cells/ C-cells
Tissue of sclera. cornea, ciliary muscle
Connective/skeletal tissue of pharyngeal arches (DiGeorge–> pharyngeal pouches)
Enterochromaffin cells of intestines (Hirschprung Disease and achalasia
PNS
Schwann cells
Chromaffin cells of Adrenal Medulla
Odontoblasts
Melanocytes (Albinism)
Leptomeninges
What is Arnold-Chiari? (Type I and II)
Congenital herniation of cerebellum through foramen magnum
Type I: Herniation of cerebellar tonsils ONLY.
Type II: Herniation of tonsils and vermis, breaking of tectal plate, aqueductal stenosis, stretching cranial nerves. May also have cervical syringomyelia and lumbar meningomyocele.
What are the clinical presentations of Arnold-Chiari Types I and II? Prognosis?
Type I: Or cerebellar ataxia, hydrocephalus, etc. May have not symptoms or not until adolescence/adulthood.
Type II: diff swallowing, loss of sensation-with/out pain (back of neck, shoulders), mental retardation, hydrocephalus. Usually die (cranial nerve dysfcn or respiratory failure)
What is Dandy-Walker Syndrome? Prognosis?
Occurs far less than Arnold-Chiari. Cerebellar vermis hypoplasia–> dilation of 4th ventricle due to failure of foramina of Luschka and Magendie to open. Posterior fossa cyst/ hydrocephalus.
Prognosis varies.
What is the most common cause of hydrocephalus? Treatment
Aqueductal stenosis
Treatment: axtraventricular shunt, cauterize ependymal cells, endocscopic ventriculostomy
Define: Microencephaly. Prognosis?
small brain size with decreased head circumference
50% mental retardation
Define: Holoprosencephaly. Possible causes?
Failure of midline cleavage of forebrain. Forebrain may lack midline features.
Fetal Alcohol Syndrome or Trisomy 13 (Patau syndrome)
What is the most common cause of mental retardation?
Fetal Alcohol Syndrome
Which of the meninges is vascular?
Pia mater
Where does the subarachnoid space terminate?
S2 vertebrae.
What is contained in the Epidural Space?
Fatty areolar tissue, lymphatics, venous plexus, meningeal arteries
Describe clinical features of Epidural Hematoma
Due to traumatic injury
Biconvex shape–> does not cross Dural Attachments
“Talk and die” syndrome (temporarily improve and then die)
Middle Meningeal artery most commonly ruptures
Describe the clinical features of Subarachnoid Hemorrhage
Ruptured Berry Aneurysm
“Worst Headache of my life”
Sudden Onset headache
Increased Risk: HTN, smoking, increased age, polycystic kidney disease, Marfan, Ehlers-Danlos Type 4
Describe Intracerebral/Parenchymal Hemorrhage
Trauma, infarct, angiopathy, diabetes, HTN (Charcot-Bouchard aneurysm)
Basal ganglia and thalamus common areas
Describe clinical features of Subdural Hematoma
More common than epidural hematoma
Does NOT cross midline
Crescent-shaped
Elderly at risk due to atrophy of cortex–> increased tension on bridging veins
May be assoc. with contusion, subarachnoid, and other hemorrhages.
What does Neuroectoderm give rise to?
CNS neurons, ependymal cells, oligodendrocytes, astrocytes
What does Mesoderm five rise to in Nervous System?
Microglia
Which drugs are strongly associated with neural tube defects?
Carbamazepine and Valporic Acid
Which germ layer gives rise to Microglia?
Mesoderm
Which nerve covering is re-ligated in surgery?
Perineurium
