[E2T3] Ectodermal Derivatives Flashcards by Gianne Pagulayan

Level of Regional differentiation and change in the shape of the neural tube (oval)

Gross anatomical level

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Levels of differentiation of the neural tube - 3

Gross anatomical level
Tissue-level differentiation / Histogenesis
Cellular-level differentiation / Cytogenesis

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Changes in shape during the gross anatomical level

Lateral outpocketings or evagination: telencephalic vesicles and optic vesicles

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Three week embryo ?

Formation of neural tube

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Four week embryo

Formation of primary brain vesicles (prosen, mesen, rhomben)
Delineation of anteriormost and posteriormost regions of brain
Ballooning of early embryonic brain

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Six week embryo

Formation of secondary brain vesicles (telen, dien, mesen, meten, myelen)

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Seven week embyro

Formation of epithalamus, thalamus, hypothalamus, etc

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Prosencephalon divided into:

Telencephalon ➡️ cerebral hemispheres, basal ganglia, lateral ventricles
Diencephalon ➡️ thalamic/hypothalamic regions, optic vesicle, III ventricle, infundibulum, hypophysis (anterior pituitary, pars tuberalis, pars distalis, pars intermedia)

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Lumen and fate of mesencephalon?

Lumen ➡️ cerebral aqueduct / Aqueduct of Sylvius

Fate ➡️ optic lobes

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Rhombencephalon divided into:

Metencephalon ➡️ cerebellum, pons
Myelencephalon ➡️ medulla oblongata
** rhombomeres

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Level of organization of neurons into functional regions; entails migration, with neurons as spatial directors

Histogenesis/Tissue Level Differentiation

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Differentiation in structure and function of neurons (selective gene expression) and synthesis of luxury proteins (culminating phase in cell diff)

Cytogenesis/Cellular Level Diff

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Dorsal pattern induced by?

Ventral pattern induced by?

Epidermis

Notochord

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Initiate dorso-ventral axis specification

Paracrine factors

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Superfamily of proteins that establish the dorsal fates of the neural tube, originate in dorsal ectoderm

Transforming Growth Factor Beta / TGF-B

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Mediates the ventral specification of the neural tube through differential expression of transcriptional factors

Sonic Hedgehog protein / SHH

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One cell layer thick
Active in mitosis
Mother of all neurons and glia
Surrounds brain ventricle

Neuroepithelium

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Divisions of neuroepithelium (2)

Migrate and differentiate outside neural tube

Continue mitosis and return to germinal neuroepithelium

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Two kinds of mitosis

Vertical division - product: 2 stem cells

Horizontal division - product: apical cell (neuroblast) or basal cell (stem cell)

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Identity of neuron specified prior to migration but layer where it ends up is dependent on?

Time of birth

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What is the birthday of a neuron

Time of last horizontal division

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General model for development of CNS

Tripartite pattern

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3 zones of tripartite pattern

Marginal zone
Intermediate Zone / mantle
Ventricular germinal zone

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Stable secondary center of mitosis

Marginal zone

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Gray matter (aggregation of neurons) & color is caused by perikaryon/cytoplasm/soma cell body of neurons being highly pigmented

Mantle zone

Source of all stem cells, active in mitosis

Ventricular germinal zone

Migrating cells of neuroepithelium will form?

Mantle or intermediate zone

Germinal epithelium will become?

Ventricular zone and then ependymal layer

Mantle zone cells differentiate into:

Neurons and Glia

White matter is composed of:

Axons in marginal zone covered with myelin sheaths

Gray matter composed of:

Neuronal cell bodies

Order of layers from inner to outer:

Ventricular ➡️ mantle ➡️ marginal

Divides neural tube into dorsal and ventral halves

Sulcus Limitans

Migration of neurons to form nuclei in marginal zone ➡️ white matter Neuroblasts divide & form 2nd mitotic center: external granular/germinal layer

Cerebellar organization

Modifications in tripartite pattern due to? (3)

Cell migration Differential neuronal proliferation Selective cell death

Cluster of neurons in brain; a fxnl unit; relay station between outer layers of cerebellum and other brain parts /// cluster of neurons in CNS

Nucleus

Neuronal precursors cells that migrate away from the germinal neuroepithelium and into marginal layer to form a second mitotic center (external granular layer)

Neuroblasts

Produced by other postmitotic neuroblasts migrating back into white matter

Internal granular layer / cortex

Ciliated simple columnar cells lining the lumen which produce new neurons and glial cells

Ependymal cells

Produced by ependymal cells, impt in electrical transmission, supports granule neurons Secretes SHH

Purkinje neurons

Young cerebellar cells migrate along

Bergmann glial fibers

In adults, differentiate white and gray matter

White: medullar/inner, myelinated axons Gray: cortical/outer, 3 sub-layers, nuclei

Growth cone composed of

Actin filaments

Form nuclei and leads to formation of neopallial cortex

Vertical or radial migration

Form 40~ regions of brain which regulate different body processes

Horizontal or lateral migration

Continue mitosis until middle of childhood to complete layers

Ventricular cells

Which layer a cell migrates to

Laminar identity

Second zone of neurons at outer surface of brain formed by neuroblasts from mantle zone

Neurocortex / Cortical Plane

Contain columnar, ciliated cells

Ependymal zones

Most predominant neurons | Primary excitation units

Pyramidal cells

Postnatal growth rate

250,000 neurons per minute for the first 2 years

Cortex formation rate

30,000 synapses per second per centimeters

Actual human gestation occurs for

21 months

Differentiate: Nucleus vs Ganglion Tract vs Nerve

Aggregation of cell bodies in CNS - in PNS | Aggregation of nerve fascicles in CNS - PNS

Outgrowth or cytoplasmic processes of beginning neurons

Neurite

Parts of a neuron: 3

Cell body/soma/perikarya Nerve processes Terminal buttons

Main types of neurons:

Bipolar - sensory neurons Multipolar - motor neurons Pseudounipolar - PNS ganglia

Neural precursor, half undergo apoptosis, with 2 developmental pathways

Neural stem cells

2 developmental pathways of neural stem cells

Neuron | Glial cell

Resident macrophages of brain and spinal cord, first line of defense of CNS, from monocytes

Microglia

Star shaped cells important for cell repair | Contributes to blood-brain barrier

Astrocytes

2 types of astrocytes

Protoplasmic - bigger fell body, fewer and longer cell processes Fibrous - branched

Natural rejuvenation of neurons with help of glial cells

Postnatal neurogenesis

Site of neurogenesis, joins 2 cerebral hemispheres, for recognition of memory and past events

Dentate gyrus of hippocampus

Human brain can be divided into 4 interconnected areas:

Brainstem, diencephalon, limbic system, neocortex

Inside the human cerebrum... (4)

Frontal region Occipital region Cingulate gyrus Hippocampus

Neural growth factors: (7)

``` GNF/GGF: Glial nerve/growth factor BDNF: brain derived nerve factor IGF: insulin-like growth factor NT-3: neurotropine 3 EGF: epidermal growth factor GGF: glial growth factor FGF: fibroblast growth factor ```

Effect of alcohol on neurogenesis

Stem cells will not undergo mitosis ➡️ no neurons | Fetal Alcohol Syndrome

Conical structure at tip of axon, guides elongation of axon via molecular signals from extracellular envt, composed of actin and tubulin

Growth Cone

Microspikes components??

Filopodia | Lamellipodia & Lamellipodium (finger like vs palm like)

Membrane proteins serving as axonal growth cone guidance molecules

Semaphorin

Two axonal guidance types

Long range and short range cues

Involves diffusible substances, released from target cells and or substrate

Long range cues

Mediated by contact-dependent mechanism that bind cells and ECM

Short range cues

Examples of long range cues

Netrin, semaphorin

Example of short range cues

Cadherins, ephrins

For myelination, which cells are involved?

CNS: Schwann cells + axons PNS: oligodendrocytes + nerve fibers