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Development Of The Brain Flashcards

1
Q

When does the brain develop?

A

During the 3rd week from the NT, cranial to 4th pair of somites

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2
Q

Fusion of neural folds in the cranial region and closure of rostral neuropore form what?

A

Three primary vesicles (prosencephalon, mesencephalon and rhombocephalon)

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3
Q

What occurs during the 5th week of development?

A

Five secondary vesicles form
Forebrain divides into telencephalon and diencephalon
Midbrain -> mesencephalon
Hindbrain divides into metencephalon and myelencephalon

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4
Q

What does the prosencephalon (forebrain) divide into?

A

Telencephalon and diencephalon

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5
Q

What does the rhombocephalon (hindbrain) divide into?

A

Metencephalon and myelencephalon

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6
Q

What are brain flexures?

A

Space into which the NT is developing is limited but there is extensive growth
Causes the NT to bend or flex at two ventral flexures and a dorsal flexure
Includes midbrain, cervical and pontine flexures

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7
Q

When do flexures form?

A

As the primary vesicles -> into secondary vesicles (5th week)

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8
Q

Which flexures are in the hindbrain?

A

Cervical and pontine flexures

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9
Q

Describe the cervical flexure

A

Demarcates hindbrain from the SC

Arbitrarily defined at superior rootlet of C1 roughly at foramen magnum

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10
Q

What does the pontine flexure demarcate?

A

Metencephalon (rostral) from myelencephalon (caudal)

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11
Q

What does the myelencephalon become?

A

Medulla oblongata

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12
Q

What does the metencephalon become?

A

Pons and cerebellum

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13
Q

What does the cavity of the hindbrain become?

A

4th ventricle (caudal) and central canal (medulla)

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14
Q

Describe the caudal myelencephalon

A

In this region neuroblast in alar plates migrate into marginal zone and form nucleus gracilis and nucleus cuneatus
Dorsal sensory nuclei associates with afferent tracts of the DCML
Pyramids (ventral) consisting of CST fibers

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15
Q

Describe the rostral myelencephalon

A

Wide and flat
Pontine flexure causes walls of medulla to move laterally
Roof plate is greatly thinned
Cavity is part of future 4th ventricle (caudal)

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16
Q

In the myelencephalon the alar plates become lateral to the basal plates causing what?

A

Motor nuclei to be medial to sensory nuclei

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17
Q

Neuroblasts in the basal plate of the medulla develop into what?

A

Motor neurons and nuclei organize into cell columns

General somatic efferent, special visceral efferent and general visceral efferent

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18
Q

Neuroblasts in the alar plate of the medulla form what?

A

Neurons that are arranged in columns

General visceral afferent, special visceral afferent, general somatic afferent and special somatic afferent

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19
Q

Some neuroblasts from the alar plates of the medulla migrate more ventrally as compared to afferent columns and form what?

A

Neurons in the olivary nuclei

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20
Q

Describe the metencephalon

A

Walls form the pons and cerebellum
Cavity forms 4th ventricle (rostral)
Pontine flexure forces walls of pons laterally and spreads the gray matter in the floor of the 4th ventricle
Neuroblasts of basal plate develop into motor nuclei

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21
Q

What does the cerebellum develop from?

A

Dorsal parts of alar plates (of metencephalon)
Cerebellar swellings project into 4th ventricle and fuse in median plane, overgrow rostral 4th ventricle, pons and medulla
Alar plates will also form central nuclei, pontine, cochlear nuclei

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22
Q

The ependymal roof of the 4th ventricle is covered with what?

A

Pia mater derived from hindbrain mesenchyme

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23
Q

What is the tela choroidea?

A

Formed from pia mater and ependymal roof

Proliferates and invests into 4th ventricle -> forming the choroid plexus which secretes ventricular fluid

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24
Q

The roof of the 4th ventricle evaginates and forms what?

A

Out pockets which then rupture to form median and lateral apertures

25
Neuroblasts of the alar plates of the midbrain migrate into what?
The tectum and form the superior and inferior colliculi
26
Neuroblasts of basal plates of the midbrain form what?
``` Tegmental nuclei (red nuclei, reticular nuclei, CN III and IV nuclei) Substantia nigra could be basal or alar plate cells that migrate ventrally ```
27
The neural canal of the midbrain narrows and forms what?
Cerebral aqueduct which connects the 3rd ventricle to the 4th
28
Fibers growing from the cerebal cortex form what?
Cerebral peduncles (crus cerebri)
29
Within the diencephalon there are swellings in the lateral walls of the 3rd ventricle which forms what?
Thalamus, hypothalamus and epithalamus
30
Describe the thalamus
Develops and bulges into cavity | Fuses at midline in 70% of brains forming interthalamic adhesion
31
Describe the hypothalamus
Arises from neuroblasts in intermediate zone Endocrine and homeostatic nuclei develop Mammillary bodies form on ventral surface
32
The epithalamus develops from what?
Roof and dorsal portion of the lateral wall of 3rd ventricle
33
The pineal gland develops as a median outgrowth of the what?
Roof of the diencephalon
34
What are the two embryonic source of the pituitary gland?
1. Hypophyseal diverticulum (Rathke’s pouch): upgrowth of roof of stomodeum (oral ectoderm) 2. Neurohypophyseal diverticulum: downgrowth of diencephalon (neuroectoderm)
35
What is the infundibulum?
Derived from neurohypophyseal diverticulum Will pass between developing bones of the cranium Stalk of the pituitary gland connecting it to the brain
36
Describe the hypophyseal diverticulum
Projects from roof of stomodeum by 3rd week Constricts its attachment from oral cavity Passes through the cranium and contacts infundibulum (5th week) Regresses from oral cavity (6th week)
37
What does the hypophyseal diverticulum form?
Pars anterior and pars tuberalis | Forms anterior lobe of pituitary gland
38
What does the neurohypophyseal diverticulum form?
Median eminence, infundibulum and pars nervosa | Forms posterior lobe of pituitary gland
39
Describe the telencephalon
Consists of a medical part and two cerebral vesicles, primordia of cerebral hemispheres Cavity forms anterior 3rd ventricle Telen and diencephalon contribute to 3V
40
What gives rise to the falx cerebri?
Mesenchyme trapped in longitudinal fissure
41
When does the corpus striatum of the telencephalon appear?
In the 6th week as a swelling in the floor of each hemisphere Fibers of IC will pass through Separates and defines caudate and lentiform (putamen and globus pallidus) nuclei
42
Medial wall of the cerebral hemisphere becomes very thin and is continuous with the roof of the 3rd ventricle and forms what at this site?
Choroid plexus
43
What is holoprosencephaly?
Incomplete separation of the cerebral hemispheres and most cases are associated with facial abnormalities (cyclopia, premaxillary agenesis, proboscis, single nostril, hypotelorism, facial clefts) Impaired forebrain development -> impacts FNP development -> facial anomalies
44
What is the lamina terminalis?
The largest and most rostral end of commissures Extends from roof of diencephalon to optic chiasm Within the lamina, other commissions will form
45
What does the hippocampal commissure interconnect?
The hippocampi within each hemisphere
46
What is the corpus callosum?
Largest commissure, links hemispheres along their length Will growth and extend beyond the lamina terminalis Anterior portion forms first; posterior portion forms in fetal life
47
Remainder of lamina terminalis is positioned between what?
Corpus callosum and fornix | Will stretch and form the septum pellucidum which is a thin plate of brain tissue containing nerve cells and fibers
48
Describe agenesis of the corpus callosum
Complete or partial absence of the corpus callosum The condition may be asymptomatic but seizures and mental deficiency are common Associated with more than 50 human congenital syndromes
49
Describe growth of the cerebral hemispheres
Cortex is initially smooth but growth results development to sulci and gyri Gyri result from infolding of the cortex Both increase surface area without increasing volume of neurocranium
50
Postnatal growth of the brain is from what?
Neurons increasing in size and myelination of axons
51
Describe the histogenesis of the cerebral cortex
Unique process of migration and differentiation Cerebral hemispheres initially have zones seen in early NT: ventricular, intermediate and marginal zones A 4th layer also appears (subventricular zone) Cortical layers are laid down in a sequence from deep to superficial Neurons migrate through deeper layer and exit to establish more superficial layers -> “inside out” development
52
What is lissencephaly?
Incomplete neuronal migration during 3-4 months of gestation Infant will initially appear normal but later develops seizures, profound mental deficiency and mild spastic quadriplegia
53
Describe the smoothness of the cerebral surface that can be exhibited with lissencephaly
Pachygyria, broad thick gyri Agyria, lack of gyri Neuronal heterotopia: cells in aberrant positions compared to a normal brain Enlarged ventricles and malformation of the corpus callosum are common
54
Describe microcephaly
Neurodevelopment disorder where calvaria and brain are small but face is normal sized Results from a reduction in brain growth Inadequate pressure from the growing brain leads to a small neurocranium Accompanied mental deficiencies
55
What are the causes of microcephaly?
Autosomal recessive primary microcephaly Ionizing radiation Infectious agents (cytomegalovirus, Zika virus, rubella virus, toxoplasma Gondii) Maternal alcohol abuse
56
What does the telencephalon form?
Cerebral hemispheres, lateral ventricle and part of 3rd ventricle
57
What does the myelencephalon form?
Medulla and lower part of 4th ventricle
58
What does the metencephalon form?
Pons and cerebellum | Upper part of 4th ventricle

NE Exam 2 (19 decks)

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