Embryology and Congenital Defects Flashcards
From which embryological tissue layer does the nervous system develop and at what week of development does it start?
Ectoderm
Week 3 during gastrulation
Neural Plate > Neural Fold > Neural Tube
What are the two openings of the neural tube called and which one closes first?
Anterior (cranial/rostral) and Posterior (caudal) neuropores
Anterior shuts first
They both should be shut at end of fourth week
What does the condition anencephaly involve?
Failure of the anterior neuropore to close leading to the brain being exposed to amniotic fluid. The brain degenerates and the skull doesn’t form.
Incompatible with life
What does the condition of encephalocele involve?
Failure of the rostral neuropore tube to close leading to a herniation of cerebral tissue through a defect in the skull. Occipital lobe is common which would mean visual defects (presentation varies depending on where on the skull is affected)
What is spina bifida?
Defective closure of the caudal neural tube affecting tissues overlying the spinal cord.
Non fusion of the vertebral arches.
What does spina bifida occulta involve?
Failure of embryonic halves of vertebral arches to fuse properly.
Mildest form and is usually asymptomatic.
Name the three types of spina bifida cystica and what they involve.
Meningocele is the rarest form and is when the meninges and CSF protrude out.
Meningomyolocele has the spinal roots or the spinal cord in the sac and the neurological deficits depend on where this is.
Myeloschisis is the most severe form as the spinal cord is involved.
What are four things that have decreased the incidence of spina bifida?
Folic acid supplementation
Maternal Blood Screening- high levels of AFP can indicate spina bifida
Amniocentesis
Ultrasound
What are the three flexures of the neural tube during development?
Cephalic
Cervical
Pontine
What is hydrocephalus and what is it caused by?
It is a build up of CSF frequently due to a blocked aqueduct so it cant drain from the third/lateral to the fourth ventricle, causing enlargement of the cranium and skull.
Caused by genetics, spina bifida cystica or prenatal viral infection.
What tissue makes up the cells of the nervous system?
Neuroepithelium makes up all of the cells apart from microglia which is made from mesenchyme which migrates into CNS.
What do neural crest cells form?
PNS and adrenal medulla
What are the dorsal and motor components of the spinal root formed from?
Dorsal-neural crest cells
Motor-neural tube
What is lissencephaly?
‘Smooth Brain’
Defective neuronal migration causes the gyri and sulci to fail to develop. Causes mental impairment, seizures, abnormal muscle tone and failure to thrive.
What is polymicrogyria?
Abnormal number and smallness of gyri resulting in neurological problems.
