Development of the Brain Flashcards
Secondary Vesicles
5th Week = 5 Vesicles
Forebrain: Telencephalon + Diancephalon
Midbrain: Mesencephalon
Hindbrain: Metencephalon and Myelencephalon
Primary Vesicles
Forebrain, Midbrain, Hindbrain form from neural folds in cranial region
CNS Regions of Neural Tube
- Brain develops during 3rd week from neural tube above 4th pair of somites
- Fusion of neural folds cranial region and closure of rostral neuropore form primary vesicles
Telencephalon Derivatives
Cerebral hemisphere and Lateral Ventricles
Diancephalon Derivatives
Thalami and Third Ventricle
Mesencephalon Derivatives
Midbrain and Aqueduct
Metencephalon Derivatives
Pons, cerebellum, and upper part of fourth ventricle
walls = form pons and cerebellum
cavity = forms rostral fourth ventricle
Myelencephalon Derivatives
Medulla and lower part of fourth ventricle
most inferior part of developing tube/brain
Brain Flexures
- initial spaces where NT folds on itself to fit in calvarium
- midbrain flexure, cervical flexure, pontine flexure
- flexures form as primary vesicles into secondary vesicles
Cervical Flexure
- separates hindbrain from spinal cord
- superior root of C1 at foramen magnum
Pontine Flexure
-separates metencephalon (rostral) from myelencephalon (caudal)
Agenesis of Corpus Collosum
absence of corpus collosum
can have no sx but seizures and mental deficiency
Growth of Cerebral Hemispheres
cortex initially smooth
growth results in sulci
gyri form from infoldings
sulci and gyri increase surface area without increasing volume of neurocranium
brain increase postnatally is from neurons increasing in size and axon myelination
Alar Plate of Medulla
lateral to basal plate form columns of neurons: 1. GVA 2. SVA 3. GSA 4. SSA also forms olivary nucleus on surface of medulla
Basal Plate of Medulla
medial to alar plate form motor neurons motor nuclei medial to sensory nuclei 1. GSE 2. SVE 3. GVE
Myelencephalon Development
Caudal:
- Neural blasts in alar plate move to marginal zone = form nucleus gracilis and cuneatus of the PCML tract
- pyramids of corticospinal tract
Rostral:
- pontine flexure moves walls of medulla laterally
- roof plate thins
- cavity becomes part of 4th ventricle
Metencephalon Development
- walls form pons and cerebellum
- cavity forms 4th ventricle
- pontine flexure forces walls of pons laterally to spread grey matter on floor of 4th ventricle
- neuroblasts of basal plate become motor nuclei
Cerebellum Development
- from dorsal parts of alar plates
- cerebellar swellings project into 4th ventricle and fuse in median plane; overgrow rostral 4th ventricle, pons, and medulla
- alar plates also form central nuclei, pontine, cochlear nuclei
Choroid Plexus Development
- ependymal roof of 4th ventricle is covered with pia mater from hindbrain mesenchyme
- pia + ependyma = tela choroidea
- tela choroidea proliferates and invests in 4th ventricle to form choroid plexus
- roof of 4th ventricle invaginates and forms media + lateral apertures
Midbrain Development
- neuroblasts of alar plates migrate to tectum
- form inferior and superior colliculi
- neuroblasts of basal plates form tegmental nuclei of red, reticular, CN III and IV nuclei
- substantia nigra forms from either basal or alar plate
- neural canal narrows and forms cerebral aqueduct
- fibers from cerebral cortex form cerebral peduncles
Diencephalon Development
- swellings in lateral walls of third ventricle form thalamus, hypothalamus, epithalamus, subthalamus
- Thalamus: bulges into a cavity and fuses at midline
- Hypothalamus: neuroblasts in intermediate zone form endocrine and homeostatic nuclei; mamillary bodies form on ventral surface
- Epithalamus: from roof and dorsal lateral wall
- Pineal Gland: median outgrowth of roof of diencephalon
Pituitary Gland Development
2 embryo sources
- Hypopophyseal Diverticulum: upgrowth of stomodeum of oral ectoderm
- neurohypophyseal Diverticulum/Rathke’s Pouch: downgrowth of diencephalon of neuroectoderm; also forms infundibulum between developing bones of cranium
Hypopophyseal Diverticulum
- Projects from stomodeum by 3rd week
- constricts its attachment from oral cavity
- passes through cranium and contacts infundibulum by 5th week
- regresses from oral cavity by 6th week
Pituitary Gland Derivation: Oral Ectoderm
- hypophyseal diverticulum from roof of stomodeum
- Tissue Type: adenohypophysis (glandular)
- Part: pars anterior, tuberalis, and intermedia
- anterior lobe
Pituitary Gland Derivation: Neuroectoderm
- neurohypophyseal diverticulum from floor of diencephalon
- tissue type: neurohypophysis (nervous tissue)
- Part: pars nervosa, infundibular stem, median eminence
- posterior lobe
Telencephalon Development
- median part and two cerebral vesicles which become hemispheres
- cavity forms anterior 3rd ventricle
- hemispheres expand over diencephalon, midbrain, and hindbrain to meet in midline
- mesenchyme trapped in longitudinal fissure becomes falx cerebri
Corpus Striatum
- appears in 6th week as swelling in each hemisphere floor
- separates and defines caudate and lentiform nuclei (putamen and globus pallidus)
- medial wall of cerebral hemisphere thins and joins third ventricle roof to become choroid plexus
Holoprosencephaly (HPE)
incomplete separation of cerebral hemispheres with facial abnormalities
Cerebral Commissures
- Lamina Terminalis: largest and most rostral bundle connecting hemispheres - from roof of diencephalon to optic chiasm
- Anterior Commissure: connects temporal lobes within hemispheres
- Hippocampal Commissure: connects hippocampis within hemispheres
- Corpus Collosum: largest commissure linking hemispheres along their length; grow beyond lamina terminalis, ant portion forms first
- Septum pellucidum: thin plate of brain tissue containing nerve cells and fibers; formed from rest of lamina terminalis
Histogenesis of Cerebral Cortex
cerebral early zones: ventricular, intermediate, marginal
later subventricular zone appears
cortical layers: youngest neurons are outer surface and older neurons are deeper
Lissencephaly
- “smooth” brain containing pachygyria (thick gyri), agyria (lack of gyri), neuronal heterotopia (cells in abnormal places)
- incomplete neuronal migration during 3-4 months gestation
- infant appears normal but later develops seizures, mental deficiency
Microcephaly
- small brain and calvaria but normal face
- results from reduced brain growth and insufficient pressure from growing brain
