Development of the Brain Flashcards
The neural plate and neural groove develop on the posterior aspect of the trilaminer embryo beginning at 3 weeks. They are induced by the ______
The process of neurulation begins during the ____ week. The cranial 2/3 of the neural plate (4th pair of somites) becomes the future _______. The caudal 1/3 of the neural plate becomes the future _______
Notochord
4th; brain; spinal cord
The _____ _____ first forms at the 5th somite. Fusion proceeds cranially to caudally until only the cranial and caudal _______ remain, the former closes several days before the latter
Neural tube; neuropores
Describe epithelium of neural tube
Pseudostratified columnar neuroepithelium
The SC develops caudal to the 4th pair of somites. The lateral walls of the NT thicken, reducing the size of the neural canal until only a small ____ ____ exists (9-10 wks)
Central canal
3 defined zones of the developing SC
Ventricular zone = neuroepithelial cells closest to the lumen, will divide and migrate
Intermediate zone = differentiation into neurons and/or glia
Marginal zone = decreased cell bodies; contains axons that will eventually be myelinated (white matter — more superficial)
There are five total closure sites involved in formation of the neural tube.
Failure of site 1 results in what condition?
Spina bifida cystica
There are five total closure sites involved in formation of the neural tube.
Failure of site 2 results in what condition?
Meroencephaly (anencephaly)
There are five total closure sites involved in formation of the neural tube.
Failure of sites 1,2, and 4 results in what condition?
Craniorachischisis
There are five total closure sites involved in formation of the neural tube.
Nonfusion of which site is most rare?
Site 3
Differences between spina bifida occulta, w/ meningocele, w/ meningomyelocele, and w/ myeloschisis
SB Occulta = unfused neural arch, skin remains intact
SB w/meningocele = meninges extrude
SB w/meningomyelocele = meninges and neural tissue extends
SB w/myeloschisis = open neural tissue
Glioblasts differentiate from neuroepithelial cells. After neuronal formation ceases, they become _____ and ________
Astrocytes; oligodendrocytes
Once glial prodution stops, cells differentiate into _____ cells.
Microglia are not derived from neuroepithelium like the neuroblasts and glioblasts, but instead are derived from _______
Ependymal
Mesenchyme
_____ controls the proliferation and patterning of neuroepithelial cells via _____ transcription factors
SHH; GLI
Differentiation of SC produces thick walls but thin roof and floor plates
This produces a shallow, longitudinal groove on each side called the ____ _____
Sulcus limitans
The sulcus limitans separates what structures?
Alar plate (dorsal) Basal plate (ventral)
What forms from cell bodies of alar plates?
Dorsal gray columns (afferent nuclei)
Dorsal gray horns
Dorsal median septum also forms with enlargement of alar plates
What forms from cell bodies in basal plates?
Ventral and and lateral gray columns
Ventral and lateral gray columns that form from the basal plates then go on to form efferent nuclei. The ventral gray horns are _______ while the lateral gray horns are ________ (in terms of function)
Axons will also grow out to form the ventral roots of ____ ___
Somatic
Autonomic
Spinal nerves
As the basal plates enlarge, they bulge ventrally on each side to form what?
Ventral median septum
[a deep longitudinal groove (ventral median fissure) develops on the ventral surface]
Basal and alar cranial nerve nuclei are organized into what 7 columns?
[roof plate]
- Somatic efferents
- Branchial efferents
- Visceral efferents
- Visceral afferents
- Special visceral afferents
- General afferents
- Special somatic afferents
[floor plate]
The brain develops during the 3rd week from the neural tube, cranial to the 4th pair of somites.
Fusion of neural folds in cranial region and closure of rostral neuropore form the ____ ____ ____
Primary brain vesicles
What are the 3 primary brain vesicles?
Forebrain = prosencephalon
Midbrain = mesencephalon
Hindprain = rhombencephalon
During the 5th week, secondary brain vesicles form. the forebrain (prosencephalon) divides to form the _____ and _____.
The midbrain does not divide - so remains the mesencephalon.
The hindbrain (rhombencephalon) divides to form the ____ and ____.
Telencephalon; diencephalon
Metencephalon; myelencephalon
During the 5th week, the embryonic brain grows rapidly and bends ventrally with the head fold.
Bending produces the ______ flexure and _____ flexure.
Unequal growth produces the _______ flexure in the opposite direction, which is the metencephalon-myelencephalon junction.
Midbrain; cervical
Pontine
[brain flexures produce considerable variation in position of gray and white matter
The cervical flexure demarcates the ____ from the _____
The junction is arbitrarily defined as the level of superior rootlet of C1 (roughly located at foramen magnum)
Hindbrain; SC
Major derivative of myelencephalon
Medulla oblongata
Major derivatives of metencephalon
Pons
Cerebellum
The cavity of the hindbrain forms what 2 structures?
Fourth ventricle
Central canal
[in medulla]
In the caudal myelencephalon, neuroblasts in alar plates migrate into the marginal zone to form nucleus _____ and nucleus ________
The rostral myelencephalon is wide and flat, the ____ flexure causes the walls of the medulla to move laterally and the roof plate is greatly thinned.
Alar plates become _______ to the basal plates, which corresponds to motor nuclei developing medially to sensory nuclei.
Gracilis; cuneatus
Pontine
Lateral
Neuroblasts in the basal plate deevelop into _____ neurons, nuclei organize into what 3 cell columns on each side?
Motor
General somatic efferent
Special visceral efferent
General visceral efferent
Neuroblasts in the alar plates of the medulla form neurons that are arranged in what 4 columns on each side?
General visceral afferent
Special visceral afferent
General somatic afferent
Special somatic afferent
Some neuroblasts from the basal plate will migrate ventrally and form neurons in the ____ nuclei
Olivary
The ________ develops from the dorsal parts of the alar plates in the metencephalon when swelllings project into the 4th ventricle and fuse in the median plane, eventually overgrowing the rostral 4th ventricle and overlapping the pons/medulla
Cerebellum
T/F: Histogenesis of the cerebellum is still widely debated, but it is important to note that some cells migrate out to differentiate into different sorts of neurons in the cerebellum, while some migrate back in to form deep cerebellar nuclei
True
Structures that form in the midbrain
Superior and inferior colliculi (from neuroblasts of alar plate that migrate into the tectum)
Tegmental nuclei (from neuroblasts of basal plate)
Substantia nigra
Cerebral peduncles (aka crus cerebri)
Cerebral aqueduct (within narrowed neural canal)
Structures derived from diencephalon, particularly in lateral walls of 3rd ventricle
Epithalamus
Thalamus
Hypothalamus
[also boundaries = epithalamic sulcus and hypothalamic sulcus]
The hypothalamus arises in the diencephalon from neuroblasts in the _____ zone of the neural tube. ______ ____ form on the ventral surface of the hypothalamus
Intermediate; mammillary bodies
Embryonic sources for the 2 components of the pituitary gland: hypophyseal diverticulum and neurohypophyseal diverticulum
Hypophyseal diverticulum (rathke’s pouch) — upgrowth of roof of stomodeum (oral ectoderm)
Neurohypophyseal diverticulum — downgrowth of diencephalon
[hypophyseal connection to oral cavity degenerates by 6th week]
Adult derivatives of hypophyseal diverticulum vs. neurohypophyseal diverticulum
Hypophyseal diverticulum —> pars anterior and pars tuberalis
Neurohypophyseal diverticulum —> median eminence, infundibulum, pars nervosa
Components of telencephalon
Median part + 2 telencephalic/cerebral vesicles (primordia of cerebral hemispheres)
Median cavity forms the anterior 3rd ventricle
Optic vesicles (appear with closure of rostral neuropore)
interventricular foramina (communication pt between hemispheres and 3rd ventricle)
Choroid plexus
Falx cerebri (from mesenchyme trapped in longitudinal fissure)
Why do the hemispheres become C-shaped with development of the telencephalon?
Cortex rapidly proliferates but deeper nuclei do not
Cavities of what 2 brain primordia form the 3rd ventricle?
Telencephalon
Diencephalon
Cerebral hemispheres initially have zones in neural tube: ventricular, intermediate, and marginal. These are followed by development of subventricular zone. How do these contribute to histogenesis of the cerebral cortex?
Proliferating cells of the ventricular layer undergo series of regulated divisions to produce waves of neurons that migrate peripherally
Cortical layers are laid down from deep to superficial (inside—>out development)
During histogenesis of the cerebral cortex, the 1st neurons (from ventricular zone) form the ______ which underlies developing pia.
Axons extend on the inner side of the above structure, establishing an intermediate zone. The next set of neurons migrate into the above structure and split it to produce the ______ _____ in between the marginal zone (future lamina 1) and subplate
Preplate
Cortical plate
During histogenesis of the cerebral cortex, Neurons migrate on processes of ____ ____ cells that span the cortex. Axons from neurons in the cortical plate and subplate join those in the intermediate zone, which will later form the ____ ___ of the cortex
Early neurons form the deepes layers of the cortex: 5 and 6.
The ________zone consists of new neurons in an extra germinative layer
Radial glial; white matter
Subventricular
Groups of nerve fibers interconnecting the cerebral hemispheres = cerebral commissures.
The lamina terminalis is in the rostral end of the forebrain which forms the first of these cerebral commissures: the ____ and ____
Anterior commissure; hippocampal commissure
The anterior commissure interconnects what?
Olfactory bulb with hemispheres
Describe formation of corpus callosum
Anterior portion forms first, posterior portion forms in fetal life
Links hemispheres along their length
During cerebral commissure development, the lamina terminalis is stretched, forming the ____ _____, a thin plate of brain tissue containing nerve cells and fibers
Septum pellucidum
Complete or partial absence of corpus callosum which may be asymptomatic but seizures and mental deficiency are common. Also associated with more than 50 congenital syndromes
Agenesis of corpus callosum
Lack of sulci and gyri due to incomplete neuronal migration to cerebral cortex during 3-4 months gestation
Lissencephaly
Lissencephaly may be characterized by:
______ = broad, thick gyri
______ = lack of gyri
_____ _____ =cells in aberrant positions compared to normal brain
Pachygyria
Agyria
Neuronal heterotopia
[enlarged ventricles and malformation of the corpus callosum are also common]
Symptoms of lissencephaly
Initially appear normal but later develop seizures, profound mental deficiency, and mild spastic quadriplegia
Neurodevelopmental disorder where calvaria and brain are small but face is normal sized
Microcephaly
Causes of microcephaly
Autosomal recessive primary microcephaly
Ionizing radiation
Infectious agents (CMV, rubella, toxoplasma gondii)
Maternal alcohol use
Hydrocephalus can result from ________ where the cerebral aqueduct is narrow or consists of several minute channels
Congenital aqueductal stenosis (rare)
Incomplete separation of the cerebral hemispheres, usually associated with facial abnormalities like cyclopia, premaxillary agenesis, proboscis, hypertelorism, and/or facial clefts
Holoprosencephaly (HPE)
Over 12+ genetic loci have been associated with HPE, most of which involving downstream targets or receptors for what TF?
SHH
HPE is associated with genetic loci concerned with inhibition of _____ synthesis. Defects in forebrain development often cause facial anomalies resulting from reduction of the ______
Cholesterol; FNP
Structural defect of the cerebellum resulting in tongue-like projection of the medulla and inferior displacement of the cerebral tonsil through the foramen magnum into the vertebral canal
Chiari malformation
Which cranial fossa is usually small in chiari malformation?
Posterior cranial fossa — results in pressure on cerebellum and brainstem
Chiari malformation may lead to what type of hydrocephalus?
Noncommunicating
Primary 2 types of chiari malformation
Type I = inferior part of cerebellum herniates through foramen magnum. Most common. Usually asymptomatic and detected in adolescence.
Type II = Arnold-Chiari. Cerebellar tissue and brainstem herniate through foramen magnum. Often accompanied by occipital encephalocele and lumbar myelomeningocele.
