17: Development Of The Brain Flashcards
When does brain start developing? From what?
3rd week, from neural tube
Primary vesicles
prosencephalon, mesencephalon, rhombencephalon
Secondary vesicles: in order from superior to inferior
Telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon
When do secondary vesicles and brain flexures appear?
5th week
Brain flexure
Space into which neural tube development is limited, but there is extensive growth -> NT bends
Two ventral flexures
Midbrain flexure, pontine flexure
1 dorsal flexure
Cervical flexure
What does the pontine flexure demarcate?
Metencephalon and myelencephalon
What does the cervical flexure demarcate
Hindbrain and SC
What types of fibers pass through the corpus striatum
Fibers of the internal capsule
Interthalamic adhesion
Thalamus fuses at midline in 70% of brains
Mammillary bodies are on the ventral surface of what structure?
Hypothalamus
Weeks 3-6 in hypophyseal diverticulum (pituitary) development
Week 3: diverticulum projects from roof of stomodeum
Week 4: constricts attachment
Week 5: passes through cranium, contacts infundibulum
Week 6: regresses from oral cavity
Three parts of the anterior pituitary + three parts of the posterior pituitary
Anterior: pars anterior, pars tuberalis, pars intermedia
Posterior: medial eminence, pars nervosa, infundibulum
Four tegmental nuclei (in mesencephalon)
Red, reticular, CN3, CN 4
Lamina terminalis
Most rostral commissure, extending from roof of diencephalon -> optic chiasm
Septum pellucidum formation
Forms from lamina terminalis stretching
Anterior commissure
Connects temporal lobes within each hemisphere
Hippocampal commissure
Interconnects hippocampi within each hemisphere
Corpus callosum
Largest commissure, connecting the two hemispheres
Volume of brain at birth
Only about 25% of adult volume
Two ways the post-natal brain grows
Neurons increase in size + myelination of axons
Laying down cortex layers
Lay down from deep to superficial; neurons migrate through deep layers to establish superficial layers
Holoprosencephaly
I’m complete separation of cerebral hemispheres
S/S of holoprosencephaly
Facial abnormalities: cyclopia, premaxillary agenesis, proboscis, single-nostril, hypotelorism, facial clefts
Biggest genetic contribution to holoprosencephaly
SHH
How does holoprosencephaly develop?
Impaired forebrain development, impacts FNP
Agenesis of corpus callosum: associated with…
More than 50 different congenital syndromes, seizures, mental deficiencies. Can be asymptomatic
Lissencephaly
Incomplete neuron migration during 3rd-4th month of gestation
Presentation of lissencephaly
Infant initially appears normal, but will develop profound mental deficiency, seizures, and mild spastic quadriplegia
Cerebral surface in lissencephaly
Can have pachygyria (broad, thick gyri) or agyria (lack of gyri)
Neuronal heterotopia
In lissencephaly, cells are in aberrant positions compared to normal brain
Microcephaly
Brain and calvaria are small, but face is normal size
What causes microcephaly physiologically?
Inadequate pressure from growing brain -> small neurocranium
Some potential causes for microcephaly
Autosomal recessive, ionizing radiation, maternal EtOH, infectious agents (cytomegalovirus, Zika, Rubella, Toxoplasma gondii)
