Embryology of the Nervous System Flashcards
Which layer does the nervous system form from?
Ectoderm
At what point does the cranial neuropore close?
18-20 somite stage (25 days)
At what point does the caudal neuropore close?
27 days
At what point is the neural tube closure complete?
At the end of the 4th week
What is the consequence of the neural tube failing to close?
Neural tube defects: anencephaly, encephalocoele and spina bifida
What happens in exencephaly/anencephaly?
The anterior neuropore fails to close: skulls fail to form, brain tissue degenerates and it is incompatible with life
What is craniorachichisis?
Failure of the neural tube closure along the entire neuroaxis
What happens in encephalocoele?
Herniation of cerebral tissue through a defect in the skull: failure in closure of the rostral neural tube. Variable degree of neurological defects
What is the most common site of encephalocoele?
Occipital
What are the three primary brain vesicles?
Prosencephalon, mesencephalon and rhomboencephalon
What is formed by the prosencephalon?
Forebrain
What is formed by the mesencephalon?
Midbrain
What is formed by the rhomboencephalon?
Hindbrain
Which secondary brain vesicles are formed from the prosencephalon?
Telencephalon, diencephalon and mesencephalon
Which secondary brain vesicles are formed from the rhomboencephalon?
Metencephalon and myencephalon
Where is the cephalic flexure found and when does it develop?
Between the midbrain and hindbrain - end of 3rd week
Where is the cervical flexure found and when does it develop?
Between hindbrain and spinal cord - end of 4th week
Where is the pontine flexure found and when does it develop?
Hindbrain between metencephalon and myencephalon - 5th week
What structures are formed from the diencephalon?
Thalamus, hypothalamus, pituitary gland and pineal gland
What structures are formed from the telencephalon?
Cerebral hemispheres, hippocampus and basal ganglia
What structures are formed by the mesencephalon?
Superior and inferior colliculi
What structures are formed from the rhombencephalon?
Metencephalon - cerebellum and pons
Myencephalon - medulla
At what point in development does CSF begin to form and where is it produced?
5th week - choroid plexus
Where does the CSF drain?
Subarachnoid space via the 4th ventricle
What is hydrocephalus?
Accumulation of CSF which results in an enlarged brain and cranium
What are the causes of hydrocephalus?
Genetic, prenatal viral infection, intraventricular haemorrhage and spina bifida cystica
What type of cells line the neural tube?
Initially it is a single layer of neuroepithelial cells then it is pseudostratified epithelium
At what level does a newborns spinal cord end?
L2/3
Where are spinal nerves found in newborns and what happens to them?
Found at the level of origin - become elongated forming cauda equina
What is the function of cortical folding?
Space saving and brings together brain regions allowing optimisation of brain wiring and functional organisation
What is Lissencephaly and what is it caused by?
Failure of the gyri and sulci to develop - caused by defective neuronal development
What are the consequences of lissencephaly?
Severe mental impairment, failure to thrive, seizures and abnormal muscle gyri
What is polymicrogyria and what does it cause?
Excessive number of small gyri - varying neurological problems (e.g. mental retardation, seizures and motor deficits)
What are the causes of intellectual impairment with no obvious gross brain defects?
Genetic, radiation, infectious agents (rubella. toxiplasmosis etc.), birth trauma and postnatal insults (head injury, infecions etc.) and alcohol abuse
