Neural Development Flashcards
What tissue layer develops into neural components?
ectoderm
What organ system is developed first?
-Nervous system is the first organ system to be created (although it is not the first system to be functional)
Neurulation
-the process of ectoderm folding to become the central nervous system
Neural Crest vs. Neural Tube
-Neural crest: becomes PNS
-Neural tube: becomes CNS
Neuroectoderm development
-neural tissue develops from a small portion of ectoderm
-Notochord (central mesoderm) signals with Sonic the Hedgehog to ectoderm resulting in differentiation to become neuroectoderm
Neural crest development
-several layers of ectoderm migrate laterally to form neural crest which will become PNS
Neural Tube formation
-neural fold fuses at the midline (both dorsally and transversely), giving rise to the neural tube
-the neural tube then fuses and extends in a cranial and caudal fashion
-Neural tube becomes CNS
Somites
-lateral collection of specialized mesoderm (paraxial mesoderm)
- forms bones, muscles, and connective tissue of the vertebral column and the rib cage
Nutrients and vitamins for proper embryogenesis
-many are critical but folic acid (Vitamin B9) seems to be very important in preventing neural tube defects
**Failure of neural tube closure results in developmental abnormalities
Can viruses cause neural tube defects
yes
Common neural tube defects
-Anencephaly (no cranial closure of neural tube)
-Spinal bifida (incomplete closure of neural tube anywhere; lacking proper somites development/protection)
-Dermoid sinus (incomplete separation between skin and nervous system so no protection)
-tethered cord syndrome (incomplete separation from the nervous and connective tissue; additional ligaments that cause pulling and pain within)
Manx Cats and Neural tube closure failure
-Caudal neural tube defect (incomplete closure)
-Can result in no tail/vertebrae, no caudal spinal cord, pelvic limb dysfunction (mild/moderate/severe), death
Stumpies=short tail; Rumpies=no tail
Rumpies breeding
-if you breed 2 together, usually have offspring that have hind limb defect
**Note: need up to Saccral 3 to control bowels
Rhodesian Ridgebacks and neural tube failures
-incomplete closure of neural tube (dorsally) results in dermoid sinus formation
-ectoderm (skin) is incompletely separated from the neuroectoderm (spinal cord) and this causes abnormal hair growth (often longer, grows in opposite direction, or darker pigmented hairs)
-various depths of dermal sinuses (penetrations) are observed
Processes for developing CNS after neural tube formed and closed
1.cell division
2.cell migration and differentiation
3.axonal outgrowth and pathfinding
4.synapse formation and remodeling
5. myelination
Ependymal cells
-neural stem cells that have the ability to become all of the types of the cells within the nervous system
-line central canal and parts of the brain (present into adulthood and provide some regenerative ability)
Cell division and CNS development
-cells of the neuroectoderm are fated to be neural cells lining the wall of the ependyma
-the neural stem cells then have 2 characteristics: mitosis or multipotent
Mitosis of neural stem cells
-rapid expansion of cell numbers is required to build a functional nervous system
Multipotent neural stem cells
-multiple possible cell types originating from a single stem cell
Neurons, Glia
Cell division
-neural stem cells divide into neural progenitor cell (NPC) or glial progenitor cell (GPC). These make identical daughter cells (via mitosis) of the chosen specialized cells (eg. Neurons, astrocytes, oligodendrocytes)
Regenerative stem cells
Neural stem cells are retained in adult mammals, allowing for some regenerative capacity within the nervous system
Cell migration/differentiation
-various growth factors and signalling molecules are involved in differentiating neural stem cells and guiding their migration to final destinations
-cells push laterally as they grow/differentiate
Axonal outgrowth and pathfinding
-a highly complex process
-growth factors drive the direction of axon growth
-chemicals can act as both repellants and attractants to guide migration to neural cells to their final destination
-Ex. outgrowth and pathfinding guides the visual pathways. Need crossed and uncrossed pathways so that information is delivered to both sides of the brain
Synapse formation and remodeling
-early neural development creates an excess number of initial synapses BUT these are temporary and non-precise
-Then, “pruning” axonal connections occurs during maturation. Possibly selects for the most effective connections/stronger electrical activity (Use it or lose it)
»can be a link with pruning and disorders such as autism
Myelination
-performed by oligodendrocytes (which are derived from glial progenitor cells (GPCs))
- the process of myelination occurs late in development (post-natal and into adolescence)
»reason is because want correct/good pathway, and because myelination is inhibitory to growth
Development of the brain
-rapid cell growth continues and the neural tube changes shape
»internal canal becomes the central canal (spinal cord) and ventricles (brain)
»tissue expands laterally and dorso-ventrally from the alar, basal, roof, and floor plates
Rostral Neural tube (neuropore)
-gives rise to 3 vesicles (Prosencephalon, Mesencephalon, Rhombencephalon)
-3 vesicles then give rise to 5 brain regions
Three vesicles of rostral neural tube
1.Prosencephalon (forebrain)
2.Mesencephalon (midbrain)
3.Rhombencephalon (hindbrain)
5 brain regions created from 3 vesicles
1.Telencephalon (cerebrum)
2.Diencephalon (thalamus, hypothalamus)
3.Mesencephalon
4.Metencephalon (pons and cerebellum)
5. Myelencephalon (medulla)
Prosencephalon
-forms the forebrain:
1.Telencephalon (cerebrum)
2.Dienceohalon (thalamus, hypothalamus)
Mesencephalon
-forms the midbrain
Rhombencephalon
-forms hindbrain
1.Metencephalon (pons and cerebellum)
2.Myelencephalon (medulla)
Ventricular system
-internal lumen (ependymal layer) of the brain cavity is retained with the divisions of the brain and forms the ventricular system
-Function: acts as nourishment to the brain (oxygen and sugar), and to act as a cushion
Lateral ventricles
cerebrum
Third ventricle (III)
-diencephalon
Mesencephalic aqueduct
-midbrain
Fourth ventricle (IV)
-pons/medulla
Central canal
spinal cord
Development of the spinal cord
-spinal cord develops from the caudal neuropore (closure of the caudal neural tube)
-expansion of the alar and basal plates gives rise to the bilaterally symmetrical pattern of the dorsal and ventral grey matter
-the marginal layer becomes the surrounding white matter
