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
16
Q
What are the hindbrain derivatives?
A
- myelencephalon: medulla oblongata
- metencephalon: pons and cerebellum
- cavity of hindbrain: 4th ventricle (caudal) and central canal (medulla)
- associated flexures: cervical and pontine
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
21
Q
Describe the development of the median and lateral apertures of the 4th ventricle:
A
- roof of 4th ventricle evaginates, forming outpockets
- outpockets rupture to form median and lateral apertures
(similar plexuses form in roof of 3rd ventricle and medial walls of lateral ventricles)
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
Describe the development of the hypophyseal diverticulum:
1. projects from room of stomodeum (primordial oral cavity) by 3rd week (C and D)
2. constricts its attachment from oral cavity (D)
3. passes through cranium and contacts infundibulum by 5th week (E)
4. regresses from oral cavity by 6th week (E, F)
26
hypophyseal diverticulum from roof of stomodeum
- embryonic derivative:
- tissue type:
- gives rise to:
- lobe:
**hypophyseal diverticulum from roof of stomodeum**
- embryonic derivative: oral ectoderm
- tissue type: adenohypophysis (glandular tissue)
- gives rise to: **pars anterior, pars tuberalis**, pars intermedia
- lobe: anterior lobe
27
neurohypophyseal diverticulum from floor of diencephalon
- embryonic derivative:
- tissue type:
- gives rise to:
- lobe:
**neurohypophyseal diverticulum from floor of diencephalon**
- embryonic derivative: neuroectoderm
- tissue type: neurohypophysis (nervous tissue)
- gives rise to: **pars nervosa, infundibular stem (infundibulum), median eminence**
- lobe: posterior lobe
28
Describe the development of the telencephalon and associated structures:
- 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
- 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
holoprosencephaly (HPE)
30
- 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**
cerebral commissures
31
- 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
lamina terminalis
32
- one of the cerebral commissures
- interconnects the **temporal lobes** within each hemisphere
anterior commissure
33
- one of the cerebral commissures
- interconnects the **hippocampi** within each hemisphere
hippocampal commissure (fornix)
34
- 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
corpus callosum
35
- 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
agenesis of corpus callosum
36
Describe the growth of the cerebral hemispheres:
- 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
What are the differentiated cellular zones (layers) seen in the early neural tube?
How are the zones (layers) laid down during development?
- 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
- 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
lissencephaly
39
- 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
microcephaly
