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1. What is the embryologic origin of the nervous system? - The nervous system develops from ectoderm as an elongated thickening (neural plate) that overlies the notochord and paraxial mesoderm. Develops a neural groove and neural tube (becomes the brain and spinal cord). Cells at the margins of the folds break away and form neural crest cells that become peripheral ganglia, enteric nervous system, the adrenal - Neuroepithelium is the progenitor for neurons and astrocytes, 2. What is the condition when the neural tube does not close and becomes - dysgraphia (general term for failure of the neural tube to close) - anencephaly (when the neural tube fails to close at the -exencephaly: protrusion of brain not covered by skin or meninges (occurs in rat fetuses due to excessive exposure to Vit A and - spina bifida (failure of the neural tube to close at the caudal extremity) - cranium bifidum= dorsal mid-line cranial defect through which - the protruded material forms a sac (-cele) is covered by skin and can be lined by meninges (meningocele) or meninges accompanied by a part of - hereditary in cats and pigs (can also occur with griseofulvin treatment in - menigomyelocle: associated with spina bifida, herniation of spinal cord and meninges through a defect in the neural tube 4. Hydromyelia: abnormal dilation of the central canal of the spinal cord, forms a cavity where CSF accumulates (infectious, genetic (congenital) injury causes damage to the ependymal cells lining the canal), can be acquired with obstruction of CSF flow by infection, inflammation and neoplasia 5. Meninges: What are the three layers that make up the meninges? - developmental anomaly that results in a part or the entire cerebrum having smooth surfaces lacking normal gyri and sulci - cortex is thicker than normal on transverse section and the normal - genetic and though to result from arrest or a defect in neuronal migration - porencephaly: formation of large, fluid filled cavities in the brain, typically communicates with the subarachnoid space or lateral ventricle - results from destruction of immature neuroblasts whose loss prevents normal development as a result of faulty or abhorrent neuroblast - hydrancephaly: formation of large, fluid filled cavities in the brain - can be associated with infection with Akabane visrus, BVD, blue tongue, border disease, Rift Valley fever and Wesselsbron disease in utero (destroy differentiating neuroblasts and neuroglial cells) 8. What are common causes of cerebellar hypoplasia? - parvoviruses (panleukopenia, canine parvovirus) - pestiviruses (BVD, classical swine fever) - results in cytolysis of dividing germinal cells of the external granular layer, so they cannot migrate to the inner layer and vasculitis and -especially if the calf is infected between 100-180 days gestation - cyst forms in the spinal cord (tubular cavitation=syrinx) is not lined by ependymal and is separate from the central canal - Weimaraner and calves - Syrinx can communicate with the central canal - Can also be acquired (trauma, infection or neoplasia) - Ataxia, urinary incontinence, respiratory difficulty, muscle weakness and - affects cells that form the ependymal and choroid plexus - caused by in utero injury following viral infection - congenital occurs in brachycephalic and toy breeds (poor motor skill development, delay in learned behavior, dullness, cirlcling, periodic - basic lesion is stenosis of the mesencephalic duct - virus causes destruction of ependymal cells lining the ventricular system, accompanied by inflammation and resolves in 2 weeks - Communicating hydrocephalus: communication with the subarachnoid - Noncommunicating: results from obstruction within the ventricular system at, or rostral to the lateral apertures of the fourth ventricle - An area of great vulnerability is the mesencephalic aqueduct - Bones of the calvarium are thin and the fontanelles are prominent - acquired: injury to the ependymal resulting in obstruction of the lateral apertures of the fourth ventricle, the cerebral aqueduct of the o abscesses, neoplasms, infectious/inflammatory disease resulting in ventriculitis, cholesteatomas (cholesterol granuloma) in the horse o hydrocephalus ex vacuo (compensating) occurs secondary to the los of neural tissue eg. Polioencephalomalacia, ceroid lipofuscinosis in sheep, aging and postradiation exposure 11. Spinal cord anatomy: dorsal funiculi, (ascending sensory axons) ventral funiculi (descending motor axons), lateral funucilu (mixture of sensory and motor axons), dorsal grey horn, ventral grey horn, central canal - hypothalamus (ACTH, GnRH, GHRH, corticotrophin releasing hormone and oxytocin) note: ADH is synthesized in the hypothalamus but stored in

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