Nervous system development Flashcards
Steps in neural tube formation
- Ectoderm overlying notochord thickens = neural plate (neuroectoderm)
- Folding of neural plate
- Fusion of neural plate
- Cr. and cd. neural openings= neuropores
- Separation of neural tube from the overlying ectoderm
Neural crest cells formation
Before fusion, cells at both ends of neural tube separate and form neural crest cells
What do neural crest cells differentiate into?
PNS (sympathetic, motor neurons), melanocytes, odontoblasts, adrenal medulla, cr. and facial bones, CT of pharyngeal arches
What does the neural tube give rise to?
CNS
When does neuropores close for a human?
Cr. : 25 days
Cd. : 28 days
What are the 3 flexures of the neural tube?
Midbrain
Cervical
Pontine
Midbrain flexure
Level of mesencephalon (disappears in domestic animals)
Cervical flexure
Brain and SC (persist slightly in domestic animals)
Pontine Flexure
Junction of metencephalon and myelecenphalon but direction is opposite to midbrain and cervical
The ______ part of the ______ becomes spinal cord
- Distal
- neural tube
What are the 5 vesicles of the neural tube?
1& 2: Forebrain (prosencephalon)- telecephalon and diencephalon
3. Mid brain (Mesencephalon)
4 & 5: Hindbrain (rhombencephalon)- metencephalon and myelencephalon
Structures derived from the telecephalon (forebrain)
Cerebrum
Lateral ventricles
Olfactory (1) - sensory
Structures derived from the diencephalon (forebrain)
Thalamus and hypothalamus
3rd ventricles
Optic nerve (2)
Structures derived from the midbrain (mesencephalon)
Midbrain
Mesencephalic aqueduct
Oculomotor (3) and trochlear (4) nerves- motor
Structures derived from the metencephalon
Pons and cerebellum
4th ventricle
Trigeminal nerve (5)- sensory (mostly) and motor
Structures derived from the myelencephalon
Medulla oblongata
Fourth ventricle
C6-12
Terminal end of the SC in relation to the vertebral column
Dog: L 6 & 7
Ruminants: S1
Swine: S 1& 2
Horse: S2
Cat: L7- S3`
Myelencephalon cranial nerves
Abducent (motor)
Facial (motor mostly and sensory)
Vestibulocochlear (sensory)
Glossopharyngeal (sensory and motor)
Vagus (Sensory and motor)
Accessory (motor)
hypoglossal (motor)
What are the parts of the neural tube?
Ependymal
Mantle
Marginal
Dorsal (alar) plate:
Ventral (basal) plate
Roof
Floor
Ependymal
Line brain cavities, central canal of the SC, lines choroid plexus
Mantle
Neuroblast: neurons
Gliablast: glia cells
Gray matter of the CNS
Marginal
White matter of the CNS
Axons of neurons
Glia cells
Dorsal (alar) plate
Sensory neurons
Association neurons (form bulk of nervous system except motor neurons and dorsal root ganglion neurons)
Ventral (basal) plate
Extends up to the mesencephalon
Motor neurons innervating skeletal muscles
Sympathetic and parasympathetic neurons located in the lateral horn of the SC
Roof
Dorsal
Pathway for nerve fibers crossing from one side to the other
Floor
Ventral
Pathway for nerve fibers crossing from one side to the other
Where do nerves originate from?
Axons of neurons in ganglia or nuclei
What originates from neural crest cells?
Dorsal root ganglia
Autonomic ganglia
Schwann cells
Satellite cells
Where does sensory nuclei and motor nuclei of cr. nerves originate?
Alar plate
Basal plate 1
Where do sympathetic fibers originate?
Nuclei in the lateral horn of the thoraco-lumbar SC
Where do parasympathetic fiber originate?
Nuclei in brainstem (fibers in 3, 7, 9 and 10)
Nuclei in the lateral horn of the sacral SC
Where is gray matter?
Dorsal horn: association neurons (dorsal plate)
Ventral horn: alpha motor neurons (ventral plate)
Lateral horn: sympathetic (thoracolumbar) and parasympathetic (sacral)
Where is white matter
Axons of neurons
Neuroglia cells
Meninges
Dura mater: mesoderm
Pia-arachnoid: neural crest cells
4 ventricles: 2 later (cerebrum), 3 (thalamus), 4 (pons, medulla oblongata)
What connects the lateral ventricles with the 3rd ventricle?
Interventricular foramen
What connected the 3rd and 4th ventricles?
Cerebral aqueduct
Hydrocephalus
Accumulation of CSF in the ventricular system
Caused by excess fluid production, impaired drainage, blockage in the ventricles (cerebral aqueduct)
Hydranencephaly
Cerebral hemispheres are replaced by 2 fluid sacs
Caused by malformation of mantel layer of telencephalon
Cerebellar dyplasia and atrophy
Purkinje cells and granular neurons are affected
Common in kittens and calves
Caused by prenatal viral infection
Dysraphias
Results from defects in the normal closure of neural tube
Cr. Bifida
Cleft in neurocranium
Meningocele: meninges herniate
Meningoencephalocele: meninges in cerebal hemissphere herniate
Common in sheep and pigs
What causes cr. bifida?
Failure to close frontal/ parietal suture
Defect in the closure of cr. part of neural tube
Spinal bifida
Affects the SC
Meningocele: meninges herniate
Meningomyelocele: Meninges and SC herniate
What is spinal bifida caused by?
Defect in the formation and fusion of verteral arch which is related to the abnormal closure of nerual tube
Anencephaly
Absence of telencephalon and much of diencephalon
Cranium fails to develop which is caused by dysraphias of cr. neural tube
