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Flashcards in Nervous System Development (don't need to study) Deck (67):
1

Neural tube formation

Neural plate becomes elevated forming neural folds around neural groove

Two folds meet and fuse forming the neural tube surrounding the ventricular lumen

2

Neural tube subdivisions

Spinal cord, rhombencephalon, mesencephalon, and prosencephalon

Pro to diencephalon and telencephalon

Rhumb to metencephalon and myelencephalon

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Brainstem

Metencephalon and mesencephalon and myelencephalon

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Forebrain

Diencephalon and telencephalon

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Spinal cord development

Neuroepithelial cells proliferate in walls of neural tube so ventricular lumen thins

Neurons, oligodendroglial, or astroglial cells within mantle layer

Ventricular zone is continued proliferation

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Ependymal layer

When neuroepithelial see and ventricular layer forms into this layer which lines lumen of adult brain and choroid plexus of epithelium

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Microglia

Mesenchymal derivatives that migrate into the CNS and function as macrophages

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Oligodendroglia

Wrap myelin around CNS axons

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Astroglia

Regulate extra cellular environment around neurons

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Marginal zone

Future site of ascending and descending axons

Outer zone

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Sulcus limitans

Longitudinal sulcus which delineates boundary between alar plate (dorsal horn) and basal plate (ventral)

12

Neural tube closure

Neural crest found between roof and overlying surface ectoderm

Transform into dorsal root ganglia neurons, autonomic ganglia neurons and Schwann cells

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Dorsal root ganglion cells

Contain sensory neurons

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Ventral roots

Axons of motor neurons exit spinal cord as this

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Spinal nerves

Formed when ventral roots become bundled together with peripheral processes of dorsal root ganglia

Peripheral nerves mixed in a bundle

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Ganglion

Collection of neuron cell bodies outside CNS

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Nucleus

Collection of neuron cell bodies located inside CNS

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Myelencephalon

Becomes medulla of adult brain

Neural tube closes and walls separate at the roof which then is Pia and ependyma

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Sulcus limitans

Boundary between basal plate and alar plate which process motor and sensory respectively

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Basal plate

Nearest to sulcus are visceral efferent and farthest are somatic efferent

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Alar plate

Centra provesses of visceral afferent are nearest the sulcus and somatic afferents are furthest

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Basal plate nerves

Trigeminal

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Diencephalon

Original termination at lamina terminal is

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Pineal gland

Develops as an outgrowth of the roof of the diencephalon

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Telencephalon

Lateral outpocketing from either side of the lamina terminalis created paired lateral ventricles

Radial glial fibers guide migrations

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Developing nervous system

Initial overproduction of neurons followed by cell death 50-80% same with synaptic connections

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Maturation of the Brain

Maturation of the Brain involves growth of neural tissue and reduction in size of the ventricles

Development of white matter occurs as axons extend and become myelinated organizing into tracts

Myelination creates white matter

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Neural crest

Peripheral nervous system and most of associated sensory structures derived from here and placodes

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Olfactory placodes

Olfactory receptor cells are derived from here

Invaginate and integrate into the nasal mucosa

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Trigeminal placodes

Induced to form metencephalon and develop into sensory cells of the trigeminal ganglion- touch of the face

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Epibranchial placodes

Induced where pharyngeal pouches contact ectoderm

Form VII, IX, X

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Sensory receptors

Touch, pain and temperature, vibration

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Origin and derivatives of the neural crest

Neural crest from neural ectoderm

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Cranial neural crest

Form cranioofacial mesenchyme that enters branchial arches and differentiates into cartilage, bone and connective tissue

V, VII, IX, X

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Trunk neural crest

Dorsolateral- pigment synthesizing melanocytes in skin, hair or feathers

Migrate ventrally and become sensory neurons of dorsal root ganglion, Schwann cells, chromaffin, and neurons around aorta

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Vagal and sacral neural crest

Generate parasympathetic ganglia associated with viscera and gut regulating peristalsis

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Placodes

Ectodermal thickenings induced by underlying Brian regions

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Neural crest germ

4th germ layer

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Cardiac neural crest

Migrate to reach developing heart forming aorticopulmonary septum

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Neural crest

Neuronal cells, Schwann and sheath cells, pigment cells, endocrine and paraendocrine cells, facial structures, muscle and connective tissue

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Peripheral nervous system

Motor nerves- somatic and visceral

Special visceral efferents innervate branchial arch muscles

Visceral afferent in dorsal root ganglia

Afferents from placodes- special afferents

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Nasal region

Nasal placodes induced by telencephalon

Placodes sink inside nasal pits

Nasal placode never becomes vesicle

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Optic vesicle

A diencephalic evagination

Induced lens placode

Optic cup is secondary invagination of the vesicle

44

Optic cup

Sensory part of retina is outer layer and inner layer forms pigment epithelium

45

Lens vesicle

Elongate in light transforming into lens fibers

Lens induces cornea to develop

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Retinal ganglion cells

Travel from retina through optic stalk to reach the Brain and comprise optic nerves

47

Autonomic nervous system

Thoracic lumbar sympathetic and cranial-sacral parasympathetic components

48

Choroid plexus and granulomas

Choroid plexus within ventricles and produce CSF

In older horses cholesterol crystals accumulate in choroid plexus due to chronic bleeding which block CSF

49

Meningocele and meningoencephalocele

Soft swelling

Menigocele selling located outside skull defect, meninges and skin

If contains brain tissue is a meningoencephalocele

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Cranioschisis

Skull defect

Inherited disorder in Burmese cats and associated with duplication of the face

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Exencephaly

Brain tissue that protrudes outside the cranial vault and is covered by meninges- exencephaly

Less common than meningocele or meningoencephalocele t also includes cranioschisis

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Dicephalus

Two headed calves

Result from early splitting of the primitive streak

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Prosencephalic hypoplasia

Partial failure of the outpocketing of the telencephalon from the neural tube

Midline defect involving neural tube

54

Hydranencephaly

Cerebral neocortex is absent

Hippocampus, pyriform lobe, and basal ganglia may be present

Due to viral infection during critical period for neurogenesis

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Critical period brain development

Cerebral cortex and cerebellum have extended development and therefore extended critical periods

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Cerebellar malformations

Usually due to viral infection or inherited progressive degeneration

Most common caused by BVD

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Cerebellar abiotrophy

Postnatal degeneration of Purkinje neurons

Inherited condition, Kerry blue terriers

Produces late onset progressive ataxia

58

Lissencephaly

Cerebral hemispheres not convoluted, appear smooth

Lis-1 (autosomal) gene mutation leads to generalized migration defect in males and females, microtubule dynamics implicated

Seizures common

Autosomal gene, DCX is x linked

59

Migration using radial glia

As cells leave mitosis cycle that migrate to their final destinations using radial glia as guides

Cytoskeletal proteins are crucial for normal migration

60

Cytoskeletal proteins

Crucial for normal migration

61

DCX

X linked, produces effects related to lissencephaly

Doublecortin gene

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Normal cortical development

Preplate from first postmitotic cells to leave ventricular zone

Inside out migration of ventricular zone cells in successive waves

Crates 6 layers

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Holoprosencephaly

Telencephalon develops but incomplete bilateralization leading to facial deformation

Cyclopia, hypotelorism or hyper, ethmocephaly

Lambs, dogs and cats

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Morphogenetic signaling

Non neural signaling centers: prechordal plate, Hensens node, visceral endoderm, epidermal ectoderm (sonic hedgehog)

Neural signaling from forebrain midline: SHH and Fgf8

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Cyclopia

Single orbit

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Hypotelorism

Eyes closer that normal, hyper is wider than normal

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Ethmocephaly

Proboscis located dorsally between narrow set eyes