Development of the Brain Flashcards
Neural tube development
Neural plate and neural groove first develop from neuroectoderm, induced by notochord in week 3
Neurulation begins in week 4
Cranial end–>4th pair of somites-future brain
Caudal end- future spinal cord
Neural tube forms at 5th somite
Brain develops from the
Neural tube during the 3rd week, from cranial end to the 4th pair of somites
Forebrain gives rise to
Telencephalon, diencephalon - these are considered the secondary vesicles
Forebrain/prosencephalon, midbrain/mesencephalon, hindbrain/rhombencephalon are primary vesicles
Hindbrain gives rise to
Metencephalon, myelencephalon - also considered secondary vesicles
Telencephalon derivatives
Walls- Cerebral hemispheres
Cavities- Lateral ventricles, anterior 3rd ventricle
Diencephalon derivatives
Walls- thalami
Cavities- third ventricle
Mesencephalon derivatives
Walls- midbrain
Cavities- aqueduct
Metencephalon derivatives
Walls- pons, cerebellum
Cavities- upper part of fourth ventricle
Myelencephalon derivatives
Walls- medulla
Cavities- lower part of fourth ventricle
Cervical flexure
Demarcates the hindbrain from the spinal cord
Flexures form during the 5th week
Pontine flexure
Formed by unequal growth
Divides hindbrain into the metencephalon and myelencephalon
Alar plate neuroblasts
Form nuclei gracilus and cuneatus GVA SVA GSA SSA
Basal plate neuroblasts
Develop into motor neurons
GSE
SVE
GVE
Olivary nuclei
Formed from alar/basal plate neuroblasts
Cerebellum derived from
Dorsal parts of alar plates
Tela choroidea
Sheet of pia/ependymal roof covering lower 4th ventricle
Invaginates 4th ventricle to form choroid plexus
Epithelia and stroma of choroid plexus are derived from
Epithelial lining- neuroepithelium
Stroma- mesenchymal cells
Median and lateral apertures formed by
Evaginations of 4th ventricle, permit the CSF to enter subarachnoid space from 4th ventricle
Superior and inferior colliculi derived from
Neuroblasts of alar plates
Tegmental nuclei include what and are formed by
Include red, reticular, CN III, CN IV nuclei
Neuroblasts of basal plates
Epithalamus development
Roof and dorsal portion of the lateral wall of the 3rd ventricle form epithalamus
Pineal gland development
Formed by median diverticulum of the roof of diencephalon (epithalimus)
Pituitary gland development- hypophyseal and neurohypophyseal diverticuli
Hypophyseal diverticulum: forms anterior lobe, glandular tissue
- formed by upgrowth of roof of surface ectoderm from stomodeum (mouth)
Neurohypophyseal diverticulum: posterior lobe, nervous tissue
- formed by downgrowth of neuroectoderm from diencephalon
Hypophyseal diverticulum lies near floor of diencephalon in 3rd week, connection to oral cavity degenerates in 6th week
Telencephalon and formation of optic vesicles
As closure of rostral neuropore occurs, optic vesicles appear which form retinae and optic nerves
Cerebral hemispheres communicate with 3rd ventricle via interventricular foramina
Hemispheres become C-shaped because cortex rapidly proliferates while deeper nuclei do not
Falx cerebri formed by
Mesenchyme trapped in longitudinal fissure
Holoprosencephaly
Incomplete separation of cerebral hemispheres
Defects in forebrain development cause facial anomalies resulting from reduction of the forebrain FNP
-Clyclopia, premaxillary agenesis, proboscis, single-nostril, hypotelorism, facial clefts
- Many genes involved inhibit cholesterol synthesis- which leads to lack of sonic (Hedgehog?) signaling
Cerebral commissures
Groups of nerve fibers interconnecting the cerebral hemispheres
Anterior & hippocampal commissures form first
Anterior connects olfactory bulb w/hemispheres
Hippocampal connects hippocampal formations
Anterior corpus callosum forms before posterior
Lamina terminalis is stretched forming the septum pellucidum- thin plate of brain tissue dividing right and left lateral ventricles
Agenesis of corpus callosum
Complete or partial absence of corpus callosum
Condition may be asymptomatic, but seizures and mental deficiency are common
Associated with more than 50 congenital syndromes
Brain reaches final size at age
7
Histogenesis of the cerebral cortex
Cortical layers are laid down in a sequence from deep to superficial
Neurons migrate through deeper layers and exit, to establish more superficial layers
This causes earliest born neurons to be deepest in the brain
Lissencephaly
Incomplete neuronal migration to cerebral cortex during 3-4 months of gestation
Cerebral surface exhibits pachygyria (broad, thick gyri), agyria, neuronal heterotopia (cells in aberrant positions), enlarged ventricles and malformation of corpus callosum
Patient initially appears normal but later develops seizures, profound mental deficiency and mild spastic quadriplegia
Microcephaly
Calvaria and brain are small but face is normal size
Significant mental deficiency due to brain underdevelopment
Caused by autosomal recessive gene
Ionizing radiation
Cytomegalovirus, rubella, toxoplasma gondii
Maternal alcohol use
Cranial and caudal neuropores close when
At 25 and 27 days, respectively
Hypothalamus development
Arises from neuroblasts in the intermediate zone
Mamillary bodies form on ventral surface
