development of the brain Flashcards
when and where does the neural plate and neural groove form?
what is it induced by?
develop on the posterior aspect of the trilaminar embryo (3 weeks)
Induced by the notochord
When does Neurulation begin and what components develop into what?
Neurulation begins 4th week
-Cranial 2/3 = 4th pair of somites and becomes future brain
-Caudal 1/3 = Future spinal cord
Where does the neural tube form?
When does the neurotubes close
Neural tube first forms at the 5th somite
Cranial neurotube closes at 25 days
Caudal neurotube closes at 27 days
what are the three primary brain vesicles
Forebrain: Prosencephalon
Midbrain: Mesencephalon
Hindbrain: rhombencephalon
What are the 5 secondary brain vesicles and when do they develop?
5th week
Telencephalon and Diencephalon (via the forebrain division)
Mesencephalon (midbrain does not divide)
Metencephalon, and Myleencephalon (via division of the hindbrain)
What are the walls and cavities derived from the secondary vesicles: Telencephalon
Cerebral hemispheres
Lateral ventricles
What are the walls and cavities derived from the secondary vesicles: Diencephalon
Thalamus, etc
Third ventricle
What are the walls and cavities derived from the secondary vesicles: Mesencephalon
Midbrain
Cerebral Aqueduct
What are the walls and cavities derived from the secondary vesicles: Metencephalon
Pons, Cerebellum
Upper part of fourth ventricle
What are the walls and cavities derived from the secondary vesicles: Myelencephalon
Medulla
Lower part of fourth ventricle
What are the three flextures of the brain and when do they occur and what direction
Midbrain or mesencephalic flexure (towards trunk bend)
Cervical flexure (hindbrain/SC junction and flexes toward the trunk)
Unequal growth produces the pontine flexure (extension away from trunk) occurs at the Meten-myelencephalon junction
These occur at week 5 and lead to producing considerable variation position of the gray and white matter
what makes up the hindbrain
Cervical flexure to Pontine flexure
Myelencephalon - Medulla oblongta
Metencephalon - Pons and Cerebellum
Cavity: Fourth ventricle and central canal in the medulla
What makes up the caudal mylencephalon
Alar plates migrate into the marginal zone give rise to
nucleus gracilus, nucleus cuneatus
Pyramids consisting of corticalspinal tracts
What makes up the rostral myelencephalon
is wide and flat
Pontine Flexure: causes the walls of medulla to move laterally
Roof plate: greatly thinned
cavity becomes part of future 4th ventricle
Alar plates become lateral to the basal plates
motor nuclei develop medial to sensory nuclei
What do neuroblasts in the basal plate of the medulla develop to
columns motor neurons. efferent
General somatic efferent
special viscereal efferent
general visceral efferent
What do neuroblasts in the alar plate of the medulla develop to
columns of Afferent neurons
general visceral afferent
special visceral afferent
general somatic afferent
special somatic afferent
What develops out of the metencephalon
forms the pons and the cerebellum
superior part of the 4th ventricle
Cerebellum develops from dorsal parts of alar plates
- cerebellar swellings project into 4th ventricle
- fuse in median plane
- overgrows rostral 4th ventricle and overlap the medulla and pons
How is the choroid plexus formed
Ependymal roof of 4th ventricle is covered externally by pia mater
-these two together make up the tela choroidea
the tela choroidea will invaginate the 4th ventricle to form the choroid plexus
what is the epithelial lining of the choroid plexus derived from? the stroma?
neuroepithelium
stroma is the mesenchymal cells
how are the median and lateral aperatures formed
the roof of the 4th ventricle evaginates in three locations which will rupture making the apertures
-this allows for the CSF to enter the subarachnoidspace
What do the neuroblasts of the alar plate in the midbrain give rise to
Tectum which will form the superior and inferior colliculi
What do neuroblasts of basal plates of the midbrain give rise to
tegmental nuclei (red nuclei, reticular nuclei, CN III, and IV nuclei
What does the substantia nigra derive from
is still arguable could be basal plate or alar plate cells that migrate ventrally
how is the cerebral aqueduct formed
formed in the midbrain due to neural canal narrowing
What develops in the Diencephalaon
swellings of the lateral walls of the third ventricle will form the thalamus, hypothalamus and the epithalamus
Epithalamic sulcus seperates the thalamus and epithalamus
Hypothalamic sulcus seperates the thalamus and the hypothalamus
what does the the hypothalamus arise from?
neuroblasts in intermediate zone
- Endocrine and homeostatic nuclei develop
- Mamillary bodies form on ventral surface of the hypothalamus
How does the epithalamus develop?
develops from the roof and dorsal portion of the lateral wall
forms the epithalamic swellings which are large but then will become relatively small
How does the Pineal gland form
Develops as a median diverticulum of the caudal part of the roof of the diencephalon
-proliferation of cells in its walls converts it into the solid cone shaped gland
How does the Anterior lobe of the Pituitary gland develop
Oral ectoderm
Hypophyseal diverticulum (rathkes pouch) from the roof of the stomodeum migrates up gives rise to:
Pars anterior
pars tuberalis
pars intermedia
the tissue type: adenohypophysis
connection to the oral cavity degrades week 6
How does the Posterior lobe of the Pituitary gland develop
Neuroectoderm
Neurohypophyseal diverticulum from the floor of the diencephalon migrate down (connected to brain via the infundibulum (passes between developing bones of the cranium))
- Pars nervosa
- Infundibular stem
- Median eminence
What consists in the telencephalon and how does it form the cerebral hemispheres
median part and two telencephalic/cerebral vesicles, primordia of the cerebral hemispheres
the median cavity will form the anterior 3rd ventricle
communication of cerebral hemispheres with 3rd ventricle is done via the interventricular foramina
The hemispheres become C-shaped
-due to cortex rapidly proliferating but deeper nuclei do not
When do the optic vesicles appear on the telencephalon
as closure of the rostral neuropore occurs the optic vesicle will appear
Where does the choroid plexus form in the 3rd ventricle
the medial wall of the cerebral hemisphere which is continuous with the roof of the 3rd ventricle will develop the choroid plexus
How does the falx cerebri form
from mesenchyme trapped in the longitudinal fissure which occurs via the cerebral hemispheres expanding to meet each other in the midline causing the medial surfaces to flatten
Cavities of what secondary brain vesicles make up the 3rd ventricle
Telencephalon (anterior part)
Diaencephalon (the rest)
Holoprosencephaly
Incomplete separation of the cerebral hemispheres
Defectss in forebrain development often cause facial anomalies resulting from a reduction of FNP
Cyclopia, premaxillary agenesis, proboscis, single-nostril, hypotelorism, facial clefts
genetic that causes an inhibition of cholesterol syntesis
What are the Cerebral commissures and what are they connecting
groups of nerve fibers interconnecting the cerebral hemispheres
-lamina terminalis: rostral end of the forebrain
Anterior commisure and hippocampal commissure form first
- anterior interconnects the olfactory bulb with the hemispheres and temporal lobes
- Hippocampal connects the hippocampal formations
Posterior commisure: posterior to upper portion of the cerebral aqueduct and is important in the bilateral pupillary light reflex
Corpus callosum forms the hemispheres
-anterior portion forms first then the posterior portion in fetal life
Lamina terminalis forms the septum pellucidum which is a thin plate of brain tissue containing nerve cells and fibers
Agenesis of corpus callosum
complete or partial absence of the corpus callosum
the condition may be asymptomatic but seizure and mental deficiency are common
How does growth of the cerebral hemispheres occur
Cortex is initially ssmooth but growth gives the development of gyrus and sulci
has zones: ventricular, intermediate and marginal and subventricular
cortical layers are layed down deep to superficial
- neurons migrate through the deeper layer to establish superficial layers
- inside out development
Lissencephaly
incomplete neuronal migration to cerebral cortex during 3-4 months of gestation
smooth cerebral surface
- Pachygyria: broad thich gyri
- Agyria: lack of gyri
- Neuronal heterotopia: cells in aberrant positions compared to a normal brain
- enlarged ventricles and malformed corpus callosum
initially appear normal and then develop seizures, profound mental deficiencies, spastic guadriplegia
Microcephaly
calvaria and brain are small but face is normal sized
significant mental deficiencies due to brain underdevelopment
reduction in brain growth
Causes:
- Autosomal recessive primary microcephaly
- ionizing radiation
- infectious agents (cytomegalovirys, rubella virus, toxoplasma gondii)
- Maternal alcohol abuse
