Nervous System Embryology and Congenital Malformations Flashcards
From what part of the embryo does the nervous system develop?
The embryonic ectoderm
When does the CNS start to appear?
At the beginning of the third week
How does the CNS initially form?
The ectoderm thickens to form the neural plate and the edges thicken and move upwards to form the neural folds
How does the neural tube form?
The neural folds migrate towards each other and fuse at the midline
When do the anterior and posterior neuropores close?
Anterior neuropore closes ~ day 25
Posterior neuropore closes ~ day 27
What defects can be caused by failure of the neural tube to close properly?
Anencephaly
Encephalocoele
Spina bifida
What causes anencephaly/exencephaly?
Failure of the anterior neuropore to close
What is the result of anencephaly/exencephaly?
Skull fails to form
Brain tissue degenerates
Incompatible with life
What is the cause of encephalocoele?
Herniation of cerebral tissue through a defect in the skull due to failure in closure of rostral neural tube
Most frequent in occipital region
What is the cause of spina bifida?
Defective closure of the caudal neural tube
What are the risk factors for spina bifida?
Genetic predisposition
Nutritional- too little folate, too much vitamin A
Environmental- hyperthermia
When do the brain vesicles begin to develop?
With the closure of the anterior neuropore
What are the names of the brain vesicles present in the fourth week?
Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)
What are the names of the brain vesicles present in the fifth week?
Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon
What does the prosencephalon form?
Forms diencephalon and telencephalon which form: Diencephalon: -Thalamus -Hypothalamus -Pituitary gland -Pineal gland Telencephalon: -Cerebral hemispheres -Hippocampus -Basal ganglia
What do the mesencephalon form?
Superior and inferior colliculi
What does the rhombenecephalon form?
Forms metencephalon and myelencephalon, which form: Metencephalon: -Cerebellum -Pons Myelencephalon: -Medulla
What does the caudal neural tube form?
The spinal cord
What does the lumen of the neural tube form?
The ventricular system
What do the neural crest cells form?
The peripheral nervous system neurons and glia
What is lissencephaly?
Rare brain disorder caused by defective neuronal migration meaning that the gyri and sulci fail to develop
Results in severe mental impairment, failure to thrive and abnormal muscle tone
Many affected die before 10
What is polymicrogyria?
Excessive number of small gyri
Variable degree of neurological problems
What is microcephaly?
Small head and brain
Caused by genetics, drugs or infection (Zika virus)
Causes intellectual impairment, delayed motor functions, hyperactivity, seizures, balance problems etc
What is porencephaly?
CSF filled cysts or cavities
Usually from postnatal stroke or infection
Causes delayed growth and development, seziures, hypotonia and intellectual impairment
What is shizencephaly?
Large clefts of slits in brain
Caused by genetics, in utero stroke, infection
Causes paralysis, seizures, intellectual impairment and developmental delay
What is diastematomyelia?
Spinal cord split longitudinally into two parts
Causes scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation
What are the causes of intellectual impairment?
Genetics Radiation Infectious agents Birth trauma Postnatal insults Maternal alcohol abuse
