Nervous System Development (don't need to study) Flashcards
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
Neural tube subdivisions
Spinal cord, rhombencephalon, mesencephalon, and prosencephalon
Pro to diencephalon and telencephalon
Rhumb to metencephalon and myelencephalon
Brainstem
Metencephalon and mesencephalon and myelencephalon
Forebrain
Diencephalon and telencephalon
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
Ependymal layer
When neuroepithelial see and ventricular layer forms into this layer which lines lumen of adult brain and choroid plexus of epithelium
Microglia
Mesenchymal derivatives that migrate into the CNS and function as macrophages
Oligodendroglia
Wrap myelin around CNS axons
Astroglia
Regulate extra cellular environment around neurons
Marginal zone
Future site of ascending and descending axons
Outer zone
Sulcus limitans
Longitudinal sulcus which delineates boundary between alar plate (dorsal horn) and basal plate (ventral)
Neural tube closure
Neural crest found between roof and overlying surface ectoderm
Transform into dorsal root ganglia neurons, autonomic ganglia neurons and Schwann cells
Dorsal root ganglion cells
Contain sensory neurons
Ventral roots
Axons of motor neurons exit spinal cord as this
Spinal nerves
Formed when ventral roots become bundled together with peripheral processes of dorsal root ganglia
Peripheral nerves mixed in a bundle
Ganglion
Collection of neuron cell bodies outside CNS
Nucleus
Collection of neuron cell bodies located inside CNS
Myelencephalon
Becomes medulla of adult brain
Neural tube closes and walls separate at the roof which then is Pia and ependyma
Sulcus limitans
Boundary between basal plate and alar plate which process motor and sensory respectively
Basal plate
Nearest to sulcus are visceral efferent and farthest are somatic efferent
Alar plate
Centra provesses of visceral afferent are nearest the sulcus and somatic afferents are furthest
Basal plate nerves
Trigeminal
Diencephalon
Original termination at lamina terminal is
Pineal gland
Develops as an outgrowth of the roof of the diencephalon
Telencephalon
Lateral outpocketing from either side of the lamina terminalis created paired lateral ventricles
Radial glial fibers guide migrations
Developing nervous system
Initial overproduction of neurons followed by cell death 50-80% same with synaptic connections
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
Neural crest
Peripheral nervous system and most of associated sensory structures derived from here and placodes
Olfactory placodes
Olfactory receptor cells are derived from here
Invaginate and integrate into the nasal mucosa
Trigeminal placodes
Induced to form metencephalon and develop into sensory cells of the trigeminal ganglion- touch of the face
Epibranchial placodes
Induced where pharyngeal pouches contact ectoderm
Form VII, IX, X
Sensory receptors
Touch, pain and temperature, vibration
Origin and derivatives of the neural crest
Neural crest from neural ectoderm
Cranial neural crest
Form cranioofacial mesenchyme that enters branchial arches and differentiates into cartilage, bone and connective tissue
V, VII, IX, X
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
Vagal and sacral neural crest
Generate parasympathetic ganglia associated with viscera and gut regulating peristalsis
Placodes
Ectodermal thickenings induced by underlying Brian regions
Neural crest germ
4th germ layer
Cardiac neural crest
Migrate to reach developing heart forming aorticopulmonary septum
Neural crest
Neuronal cells, Schwann and sheath cells, pigment cells, endocrine and paraendocrine cells, facial structures, muscle and connective tissue
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
Nasal region
Nasal placodes induced by telencephalon
Placodes sink inside nasal pits
Nasal placode never becomes vesicle
Optic vesicle
A diencephalic evagination
Induced lens placode
Optic cup is secondary invagination of the vesicle
Optic cup
Sensory part of retina is outer layer and inner layer forms pigment epithelium
Lens vesicle
Elongate in light transforming into lens fibers
Lens induces cornea to develop
Retinal ganglion cells
Travel from retina through optic stalk to reach the Brain and comprise optic nerves
Autonomic nervous system
Thoracic lumbar sympathetic and cranial-sacral parasympathetic components
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
Meningocele and meningoencephalocele
Soft swelling
Menigocele selling located outside skull defect, meninges and skin
If contains brain tissue is a meningoencephalocele
Cranioschisis
Skull defect
Inherited disorder in Burmese cats and associated with duplication of the face
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
Dicephalus
Two headed calves
Result from early splitting of the primitive streak
Prosencephalic hypoplasia
Partial failure of the outpocketing of the telencephalon from the neural tube
Midline defect involving neural tube
Hydranencephaly
Cerebral neocortex is absent
Hippocampus, pyriform lobe, and basal ganglia may be present
Due to viral infection during critical period for neurogenesis
Critical period brain development
Cerebral cortex and cerebellum have extended development and therefore extended critical periods
Cerebellar malformations
Usually due to viral infection or inherited progressive degeneration
Most common caused by BVD
Cerebellar abiotrophy
Postnatal degeneration of Purkinje neurons
Inherited condition, Kerry blue terriers
Produces late onset progressive ataxia
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
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
Cytoskeletal proteins
Crucial for normal migration
DCX
X linked, produces effects related to lissencephaly
Doublecortin gene
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
Holoprosencephaly
Telencephalon develops but incomplete bilateralization leading to facial deformation
Cyclopia, hypotelorism or hyper, ethmocephaly
Lambs, dogs and cats
Morphogenetic signaling
Non neural signaling centers: prechordal plate, Hensens node, visceral endoderm, epidermal ectoderm (sonic hedgehog)
Neural signaling from forebrain midline: SHH and Fgf8
Cyclopia
Single orbit
Hypotelorism
Eyes closer that normal, hyper is wider than normal
Ethmocephaly
Proboscis located dorsally between narrow set eyes
