Embryology Flashcards
What is gastrulation (occurs in 3rd week)?
The 3 primary germ layers form (ectoderm, mesoderm, endoderm)
What process does the notochord initiate?
Neuralation
- Induces overlying ectoderm to become neural plate
What does the notochord form into later?
Nucleus pulposus
The ectoderm forms a layer around the other germ layers, why is this?
It forms into the skin later
Somites are formed from what germ layer and then turn into what structures?
Formed from mesoderm and turn into bone muscle and cartilage
The neural plate (ectoderm) folds inwards to create what?
The neural plate folds inwards to create the neural fold it then folds in further to create the neural tube
What does the neural plate give rise to?
The neural tube and neural crest cells
At what day does the neural plate form and at what day does it become the neural tube?
- Day 18 = Neural plate
- Day 21 = Neural tube
The alar plate is located dorsally and relays what information?
Sensory
The basal plate is located ventrally and relays what information?
Motor
What is the alar (dorsal, sensory) plate regulated by?
TGF-B (including bone morphogenic protein, BMP)
What is the basal (ventral, motor) plate regulated by?
SHH
What are the 3 primary vesicles of the brain?
- Forebrain
- Midbrain
- Hindbrain
What are the 5 secondary vesicles?
- What primary vesicles are these derived from?
- Telencephalon (forebrain)
- Diencephalon (forebrain)
- Mesencephalon (midbrain)
- Metencephalon (metencephalon)
- Myencephalon (hindbrain)
What does the telencephalon become?
- Cerebral hemispheres
- Basal ganglia
- Lateral ventricles
What does the diencephalon become?
- Thalamus
- Hypothalamus
- Retina
- 3rd ventricle
What does the mesencephalon become?
- Midbrain
- Cerebral aqueduct
What does the metencephalon become?
- Pons
- cerebellum
- Upper part of 4th ventricle
What does the myelencephalon become?
- Medulla
- Lower part of 4th ventriclde
The neuroepithelia in the neural tube become what?
- CNS neurons
- CNS glial cells (astrocytes, oligodendrocytes and ependymal cells)
What cells/structures are derived from the neural crest?
- PNS neurons (DRG, autonomic ganglia [sympathetic, parasympathetic, enteric])
- PNS glial cells (schwann cells, satellite cells)
- Adrenal medulla
- Melanocytes
- Face/ brachia arch mesenchyme
What cells in the NS are derived from the mesoderm?
Microglia (like macrophages)
What is Holoprosencephaly?
Failure of embryonic forebrain (prosencephalon) to seperate into 2 cerebral hemispheres - 1 hemisphere
What gene mutation is thought to cause Holoprosencephaly?
SHH (usually occurs in weeks 3-4)
What other developmental defects and diseases are associated with Holoprosencephaly?
- Cleft lip/palate
- Cyclopia
- Pituitary dysfunction (diabetes insipidus)
- Patau syndrome
- Maternal alcohol use
What substance is associated with Holoprosencephaly?
Alcohol
What will be see o MRI in Holoprosencephaly?
- Monoventricle
- Fusion of basal ganglia
What is Lissencephaly and what is it caused by?
Smooth brain that lacks sulci and gyri
- Failure of neuronal migration
What conditions is Lissencephaly associated with?
- Microcephaly
- Ventriculomegaly
- Hydrocephalus
What are the 3 posterior fossa malformations?
- Chiari I malformation
- Chiari II malformation
- Dandy-Walker malformation
What is Chiari I malformation?
Ectopia of cerebellar tonsils inferior to foramen magnum
What can a Chiari I malformation present with?
- Asymptomatic often in childhood
- Headaches
- Cerebellar symptoms
- Spinal cavitations - syringomyelia
What structures are herniated in Chiari II malformation?
- Cerebellum (vermis and tonsils)
- Medulla
What can Chiari II malformation cause?
- Noncommunicating hydrocephalus
- Aqueductal stenosis
- Lumbosacral myelomeningocele (may present with paralysis/sensory loss at and below the level of the lesion)
What is a Dandy-Walker malformation?
Agenesis of cerebellar vermis -> cystoc enlargement of 4th ventricle that fills the enlarged posterior fossa
What conditions is Dandy-Walker malformation associated with / what does it cause?
- Noncommunicating hydrocephalus
- Spina bifida
What does the 1st pharyngeal arch form on the tongue?
Ant 2/3s (sensation via V3, taste via VII)
What do the 3rd and 4th pharyngeal arches form on the tongue?
Posterior 1/3 (sensation and taste via CNIX)
What does the Hyoglossus muscle do?
Retracts and depresses tongue
What does the Genioglossus do?
Protrudes tongue
What does the Styloglossus do?
Draws sides on tongue upwards to create a trough for swallowing
What are the muscles of the tongue?
- Hyoglossus
- Genioglossus
- Styloglossus
- Palatoglossus
What does the palatoglossus do and what is it innervated by?
Elevates posterior tongue during swallowing
What fails to fuse in a neural tube defect?
Neuropores
When are neuropores meant to fuse by (what week)?
4th
What are NT defects caused by (what incr risk from mother)?
Diabetes and folate deficiency
What will amniotic fluid show in NT defects?
`- Incr AFP (also in serum)
- Incr AChE (acetylcholinesterase)
Which type of neural tube defect will have a normal AFP level in mother?
Spina bifida occulta
What is spina bifida occulta and what are the unque features of it?
- Neuropore doesnt close but no herniation
- Dura is intact
- Lower vertebral levels
- Skin dimple or tuft of hair at level
What herniates through the bony defect in meningocele?
Meninges but not neural tissue
What herniates through the bony defect in myelomeningocele?
Meninges and neural tissue (eg caudia equina) herniate through boney defect
What is myeloschisis (rachischisis)?
Exposed, unfused neural tissue w/o skin/meningeal covering
What is anencephaly?
Failure of rostral neuropore to close -> no forebrain, open calvarium
What finding will the mother have if her child has anencephaly?
Polyhydramnios
