Development of the Brain Flashcards
When does the brain develop?
During the 3rd week
What does the brain develop from?
From the neural tube, cranial to 4th pair of somites
How do the primary brain vesicles form?
Fusion of neural folds in cranial region and closure of rostral/cranial neuropore
What are the primary brain vesicles?
Forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon)
What secondary vesicles does the prosencephalon give rise to?
Telencephalon and diencephalon
What secondary vesicles does the mesencephalon give rise to?
Mesencephalon
What secondary vesicles does the rhombencephalon give rise to?
Metencephalon and myelencephalon
What does the telencephalon give rise to?
Cerebral hemispheres and lateral ventricles
What does the diencephalon give rise to?
Thalami (hypothalamus, epithalamus, thalamus) and 3rd ventricle
What does the mesencephalon give rise to?
Midbrain and aqueduct
What does the metencephalon give rise to?
Pons and cerebellum and upper part of 4th ventricle
What does the myelencephalon give rise to?
Medulla and lower part of 4th ventricle
What causes brain folding/flexures?
Unequal proliferation in different brain vesicles
What is the first flexure to fold?
Midbrain flexure (mesencephalic flexure). Flattening/face down forward motion of telencephalon and diencephalon at junction with mesencephalon
What is the second flexure to fold?
Cervical flexure. Forward bending at hindbrain/spinal cord junction creates positioning of brainstem underneath brain
What is the third flexure?
Pontine flexure. Folds backward at metencephalon/myelencephalon junction. Positions cerebellum over/posterior to pons
What forms in the caudal myelencephalon?
Nuclei gracilus and cuneatus (from alar plate)
Pyramids (basal plate)
What forms in the rostral myelencephalon?
Alar plates (sensory/afferent inputs) and basal plates (motor/efferent outputs)
How does the pontine flexure move the alar and basal plates?
Alar plate moves lateral to basal plate
Neuroblasts in the basal plate develop into what?
Efferent neurons
Neuroblasts in the alar plate develop into what?
Afferent neurons
How are the olivary nuclei formed?
Alar neurons migrate anteriorly
How does the cerebellum develop?
From the dorsal parts of alar plates. Cerebellar swellings arise which fuse over the median plate, overgrowing the posterior side of the 4th ventricle
How does the choroid plexus form? (specifically in 4th ventricle)
Initially has a basic organization (pia + ependymal roof) without invaginations/layering called tela choroidea on roof of 4th ventricle. Then invaginates into 4th ventricle to form choroid plexus
How do the median/lateral apertures form?
The roof of the 4th ventricle ruptures/evaginates in 3 locations to permit CSF to enter subarachnoid space
In the midbrain, what is the tectum?
Forms from neuroblasts of the alar plate migrating together. Then forms superior (vision) and inferior (auditory) colliculi
In the midbrain, what are tegmental nuclei?
Form from neuroblasts of basal plates (red nuclei, reticular nuclei, CN III/IV nuclei)
What are the cerebral peduncles in the midbrain?
Also known as the crus cerebri, extensions of white matter. Fiber tracts from cortex to rest of body.
How is the cerebral aqueduct formed?
Narrowing of neural canal in the midbrain
What is the substantia nigra?
Nucleus important for movement, unsure whether alar or basal derivative
How are the thalami formed?
Swellings in lateral walls of 3rd ventricles form the thalamus, hypothalamus, and epithalamus
What separates the thalamus and epithalamus?
Epithalamic sulcus
What separates the thalamus and hypothalamus?
Hypothalamic sulcus
What structure is present in people whose thalamus have fused?
Massa intermedia (interthalamic adhesion/mass) connects R and L thalamic structures in 70% of people
How is the hypothalamus formed?
Arises from neuroblasts in intermediate zone. Mammillary bodies form on the anterior surface
Where does the pineal gland come from?
From the epithalamus
How does the epithalamus form?
From roof/posterior portion of lateral wall of 3rd ventricle
What does the pineal gland do?
Regulates sleep/wake cycles
What is the infundibulum?
Attaches the posterior pituitary to the hypothalamus
How is the anterior pituitary made?
Upgrowth of surface ectoderm from roof of stomodeum called the hypophyseal diverticulum (Rathke’s pouch)
How is the posterior pituitary made?
Downgrowth of diencephalon (neuroectoderm) called the neurohypophyseal diverticulum
When does the pituitary gland develop?
3rd week
When does the connection of the anterior pituitary to the oral cavity degenerate?
6th week
What does the telencephalon divide into?
Two telencephalic/cerebral vesicles which then make the cerebral hemispheres
What happens after rostral neuropore closes?
Optic vesicles appear
Where does the falx cerebri come from?
Mesenchyme is trapped in the longitudinal fissure when cerebral hemispheres expand and meet each other in the midline
What is holoprosencephaly?
Failure of telencephalon to divide into R/L cerebral vesicles (single-lobed brain). Impairs cholesterol synthesis and therefore SHH signaling
What are commissures?
White matter tracts that connect different brain regions to each other (ex: corpus callosum)
Where do commissures form?
In the lamina terminalis (rostral/inferior end of forebrain)
What do anterior commissures connect?
R and L olfactory areas
What do hippocampal commissures connect?
R and L hippocampi
What do posterior commissures connect?
R and L temporal lobes
What does the corpus callosum connect?
R and L hemispheres
What is the septum pellucidum?
A thin plate of brain tissue that separates R and L lateral ventricles
How does postnatal growth of the brain occur?
Neurons increasing in size and myelination of axons
How does the cortex grow?
New neurons migrate through deeper layers to exit to the surface and establish more superficial layers (‘inside out’ development)
What is lissencephaly?
Abnormal migration of new neurons onto surface. Smooth brain = decreased gyration of brain. Developmental and mental abnormalities and seizures
What is microcephaly?
Calvaria and brain are underdeveloped
