Development of the Brain (Dennis) Flashcards
1
Q
- cells that differentiate and proliferate, eventially migrating into the intermediate zone and marginal zone
A
neuroepithelial cells
2
Q
- superficial to the marginal zone is sclerotomal mesenchyme that will become the _________
- in the SC, the neural canal will become the _____ ______, and is lined by _______ _____ derived from neural tube
A
- superficial to the marginal zone is sclerotomal mesenchyme that will become the meninges
- in the SC, the neural canal will become the central canal, and is lined by ependymal cells derived from neural tube
3
Q
this dividing line separates neuroepithelial cells that take on different roles depending on the division
A
sulcus limitans
4
Q
Describe the general process of neurulation:
A
- notochord forms from mesoderm cells soon after gastrulation is complete
- signals from notochord cause inward folding of ectoderm at neural plate
- ends of neural plate fuse and disconnect to form an autonomous neural tube
(tube is developed outward in the directions of the cranial and caudal neuropores)
5
Q
When does the brain start forming and where is it located in the developing embryo?
A
- develops during 3rd week from neural tube
- located cranial (superior) to 4th pair of somites
6
Q
What are the 3 primary vesicles and how are they formed?
A
- prosencephalon (forebrain)
- mesencephalon (midbrain)
- rhombencephalon (hindbrain)
- form from fusion of neural folds in cranial region and closure of rostral neuropore
7
Q
What are the 5 secondary vesicles and what do they form from?
A
(form during 5th week)
- prosencephalon (forebrain) divides and creates telencephalon and diencephalon
- mesencephalon remains the midbrain
- rhombencephalon (hindbrain) divides and creates metencephalon and myelencephalon
8
Q
What are the adult derivatives of the telencephalon?
A
- walls: cerebral hemispheres
- cavities: lateral ventricles
9
Q
What are the adult derivatives of the diencephalon?
A
- walls: thalamus, hypothalamus, epithalamus
- cavities: third ventricle
10
Q
What are the adult derivatives of the mesencephalon?
A
- walls: midbrain
- cavities: aqueduct
11
Q
What are the adult derivatives of the metencephalon?
A
- walls: pons and cerebellum
- cavities: upper part of fourth ventricle
12
Q
What are the adult derivatives of the myelencephalon?
A
- walls: medulla
- cavities: lower part of fourth ventricle
13
Q
What are the 3 brain flexures and how do they form?
A
- developing space for neural tube is limited, but there is extensive growth which causes neural tube to bend or flex which creates the flexures; they form w/ the primary vesicles and then into the secondary vesicles (5th week)
- the two ventral flexures are midbrain flexure and cervical flexure, while the dorsal flexure is the pontine flexure
14
Q
- flexure that demarcates hindbrain from SC
- arbitrarily defined at superior rootlet of C1, roughly at foramen magnum
A
cervical flexure
15
Q
- flexure that demarcates metencephalon (rostral) from myelencephalon (caudal)
A
pontine flexure
17
Q
Describe the structure of the caudal, rostral, and general myelencephalon:
A
- caudal: neuroblasts in alar plates migrate into marginal zone forming nucleus gracilis and nucleus cuneatus; dorsal sensory nuclei a/w afferent tracts of the DCML; pyramids (ventral) consist of CST fibers
- rostral: wide and flat; pontine flexure causes walls of medulla to move laterally; roof plate is thinned; cavity is part of future 4th ventricle (caudal)
- general: alar plates become lateral to the basal plates > motor nuclei are medial to sensory nuclei
18
Q
How does the alar and basal plate of medulla migration give rise to the adult structures of the medulla?
A
- fourth ventricle causes medulla to “open like a book” which causes alar plates to become lateral to basal plates
- neuroblasts in basal plate develop into motor neurons, organized into the following cell columns: general somatic efferent, special visceral efferent, and general visceral efferent
- neuroblasts in the alar plates of the medulla form sensory neurons that are arranged into the following columns: general visceral afferent, special visceral afferent, general somatic afferent, and special somatic afferent
- also, some neuroblasts from the alar plates migrate ventral to to afferent columns and the basal plates, forming the neurons in the olivary nuclei
19
Q
Describe the development of the metencephalon, what structures it gives rise to, and how the cerebellum develops from this area:
A
- walls: pons and cerebellum
- cavity: 4th ventricle (rostral)
- flexure: pontine flexure, forces walls of pons laterally, spread gray matter in floor of 4th ventricle, neuroblasts of basal plate develop into motor nuclei
- cerebellum develops from dorsal parts of alar plates: cerebellar swellings project into 4th ventricle and fuse in median plane, overgrowing rostral 4th ventricle, pons, and medulla; alar plates also form central (dentate, etc), pontine, and cochlear nuclei
20
Q
- the ependymal roof of the 4th ventricle that is covered w/ pia mater
- derived from hindbrain mesenchyme
- proliferates and invests into 4th ventricle forming choroid plexus (CSF prod)
A
tela choroidea
22
Q
Describe the development of the midbrain and associated structures:
A
- develops from the mesencephalon
- neuroblasts of alar plates migrate into the tectum forming superior and inferior colliculi
- neuroblasts of basal plates form tegmental nuclei (red, reticular, and CN III and IV nuclei)
- substantia nigra is either formed from basal or alar plate by cells that migrate ventrally
- neural canal narrows and forms cerebral aqueduct connecting 3rd and 4th ventricles
- fibers from cerebral cortex form cerebral peduncles (crus cerebri)
23
Q
Describe the development of the diencephalon and associated structures:
A
- swellings (3) in the lateral walls of 3rd ventricle form the thalamus, hypothalamus, and epithalamus
- thalamus: develops and bulges into cavity; fuses at midline in ~70% of brains, forming interthalamic adhesion
- hypothalamus: arises from neuroblasts in intermediate zone; endocrine and homeostatic nuclei develop, mammillary bodies form on ventral surface
- epithalamus: develops from roof and dorsal portion of lateral wall
- pineal gland: develops as a median outgrowth of roof of diencephalon
24
Q
What are the 2 embryonic sources for pituitary gland development?
A
- hypophyseal diverticulum: upgrowth of roof of stomodeum (oral ectoderm)
- neurohypophyseal diverticulum: downgrowth of diencephalon (neuroectoderm); infundibulum is derived from this, will pass between developing bones of carnium
25
Q
Describe the development of the hypophyseal diverticulum:
A
- projects from room of stomodeum (primordial oral cavity) by 3rd week (C and D)
- constricts its attachment from oral cavity (D)
- passes through cranium and contacts infundibulum by 5th week (E)
- regresses from oral cavity by 6th week (E, F)
28
Q
Describe the development of the telencephalon and associated structures:
A
- consists of median part and two cerebral vesicles, primordia of cerebral hemispheres
- cavity forms anterior 3rd ventricle, contributed by telen- and diencephalon
- two hemispheres expand over diencephalon, midbrain, and hindbrain, meeting each other in the midline where the medial surfaces flatten
- mesenchyme trapped in longitudinal fissure gives rise to falx cerebri
- corpus striatum appears in 6th week as a swelling in the floor of each hemisphere: fibers of internal capsule pass through this area, separating and defining the caudate and lentiform (within putamen and globus pallidus) nuclei
- medial wall of cerebral hemispheres becomes thin and is c/w roof of 3rd ventricle, forming the choroid plexus
29
Q
- incomplete separation of cerebral hemispheres
- most cases a/w facial abnormalities: cyclopia, premaxillary agenesis, proboscis, single-nostril, hypotelorism, facial clefts
- severe, relatively common; 1:250 fetuses and 1:15,000 neonates
- 12+ genetic loci implicated: SHH, GLI, IHH, SIX3, TGIF, ZIC, PTCH
- impaired forebrain development > impacts FNP development > facial anomalies
A
holoprosencephaly (HPE)
30
Q
- groups of nerve fibers interconnecting cerebral hemispheres
- 4 groups of fibers: anterior commissure, posterior commissure, corpus callosum, commissure of fornix (hippocampal commissure), and habenular commissure
- some of the commissures form within the lamina terminalis
A
cerebral commissures
31
Q
- part of the cerebral commissure network
- the largest structure toward most rostral end of the commissure bundles
- extends from the roof of the diencephalon to the optic chiasm
- some of the commissures form within this structure
- throughout development, the remainder of this structure will become positioned between corpus callosum and fornix (hippocampal commissure)
- will stretch and form the septum pellucidum, a thin plate of brain tissue containing nerve cells and fibers
A
lamina terminalis
32
Q
- one of the cerebral commissures
- interconnects the temporal lobes within each hemisphere
A
anterior commissure
33
Q
- one of the cerebral commissures
- interconnects the hippocampi within each hemisphere
A
hippocampal commissure (fornix)
34
Q
- one of the cerebral commissures
- largest commissure, links hemispheres along their length
- will grow and extend beyond the lamina terminalis
- anterior portion forms first, posterior portion forms in fetal life
A
corpus callosum
35
Q
- complete or partial absence of the corpus callosum
- may be asymptomatic, but seizures and mental deficiency are common
- a/w more than 50 human congenital syndromes
A
agenesis of corpus callosum
36
Q
Describe the growth of the cerebral hemispheres:
A
- cortex is initially smooth, but growth results in development of sulci and gyri: gyri results from infolding of cortex, both increase surface area without increasing volume of neurocranium
- brain at birth is ~25% of adult volume
- postnatal growth is from neurons increasing in size and myelination of axons
37
Q
What are the differentiated cellular zones (layers) seen in the early neural tube?
How are the zones (layers) laid down during development?
A
- zones (layers): ventricular, intermediate, and marginal zones; a 4th layer, the subventricular zone, appears late on in development
- 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)
38
Q
- incomplete neuronal migration during 3-4 months of gestation
- 1:100,000 live births
- infant will appear normal but later develops seizures, profound mental deficiency, and mild spastic quadriplegia
- clinical appearance: “smooth” cerebral surface, pachygyria (broad, thick gyri), agyria (lack of gyri), neuronal heterotopia (cells in aberrant positions compared to a normal brain), enlarged ventricles and malformation of corpus callosum are common
A
lissencephaly
39
Q
- neurodevelopmental disorder where calvaria and brain are small, but face is normal sized
- results from: inadequate pressure from growing brain leads to small neurocranium
- 1:25,000 infants/year in US
- sx: mental deficiencies
- causes: autosomal recessive primary microcephaly, ionizing radiation, infectious agents (cytomegalovirus, Zika virus, rubella virus, Toxoplasma gondii), maternal alcohol abuse
A
microcephaly
