Development of the Brain Flashcards by Sarah Gillen

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

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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

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Describe epithelium of neural tube

Pseudostratified columnar neuroepithelium

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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

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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)

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There are five total closure sites involved in formation of the neural tube.

Failure of site 1 results in what condition?

Spina bifida cystica

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There are five total closure sites involved in formation of the neural tube.

Failure of site 2 results in what condition?

Meroencephaly (anencephaly)

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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

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There are five total closure sites involved in formation of the neural tube.

Nonfusion of which site is most rare?

Site 3

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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

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Glioblasts differentiate from neuroepithelial cells. After neuronal formation ceases, they become _____ and ________

Astrocytes; oligodendrocytes

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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

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_____ controls the proliferation and patterning of neuroepithelial cells via _____ transcription factors

SHH; GLI

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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

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The sulcus limitans separates what structures?

Alar plate (dorsal)
Basal plate (ventral)

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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

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What forms from cell bodies in basal plates?

Ventral and and lateral gray columns

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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

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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]

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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]

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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

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What are the 3 primary brain vesicles?

Forebrain = prosencephalon

Midbrain = mesencephalon

Hindprain = rhombencephalon

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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

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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

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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.