developing Nervous System
 

[SIZE="4"][COLOR="Red"]NERVOUS SYSTEM I[/COLOR][/SIZE]

[U][B][COLOR="Blue"]I. NEURAL TUBE[/COLOR][/B][/U] - modified by outgrowths and flexures.

[COLOR="blue"]A. Prosencephalon[/COLOR]

[I][COLOR="Blue"]1. Telencephalon [/COLOR][/I]- paired dorsolateral outgrowths which give rise to the cerebral hemispheres.

[COLOR="Blue"][I]2. Diencephalon[/I][/COLOR]

a. Thalamus

b. Hypothalamus

c. Infundibulum (posterior pituitary)

d. Anterior choroid plexus = thin roof which is pushed into neurocoel ahead of ingrowing blood vessels; source of nutrients and oxygen.

e. Pineal body (epiphysis) = "third eye".

[COLOR="Blue"]B. Mesencephalon [/COLOR]- remains fairly simple and unchanged.

1. Lumen = aqueduct of Sylvia.

2. Region of cephalic flexure.

[COLOR="blue"]C. Rhombencephalon[/COLOR] - resembles spinal cord in internal organization.

[U]1. Metencephalon[/U] - extensive growth which may continue after birth; characterized by complex series of folds.

a. Cerebellum - motor coordinating center.

b. Pons - ventral prominence; communication between cerebellum and rest of nervous system.

[U]2. Myelencephalon:[/U]

a. Gives rise to medulla oblongata.

b. Transition from brain to spinal cord.

c. Thin roof will form posterior choroid plexus.



[B][U][COLOR="blue"]II. SPINAL CORD[/COLOR][/U][/B]

[COLOR="blue"]A. Morphology[/COLOR] = tube with vertically elongated central canal, roof and floor plates, and thick lateral walls.

[COLOR="blue"]B. Neuroepithelium:[/COLOR]

1. Not multilayered initially, but is pseudostratified.

2. High mitotic activity.

3. Mitotic cells line lumen.

[COLOR="blue"]C. Ventricular layer [/COLOR]= cells that eventually line the central canal (also called ependyma).

[COLOR="blue"]D. Intermediate zone [/COLOR]= layer of densely-packed postmitotic neuroblasts outside of pseudostratified layer.

Gray matter = tissue from central canal to outer margin of mantle.

[COLOR="blue"]E. Marginal zone[/COLOR] = tissue surrounding gray matter, consisting of axons and other non-neuronal cells (neuroglia); = White matter because of myelination of axons.

[COLOR="blue"]F. Lateral plates [/COLOR]= thickened lateral walls.

1. Longitudinal sulcus = groove extending along inner surface of each lateral plate, dividing it into a dorsal afferent part (alar plate) and a ventral efferent part (basal plate).

2. Alar plate - sensory.

3. Basal plate - motor.

[COLOR="blue"]G. Ventral median fissure [/COLOR]- formed by downward growth of lateral plates.

[COLOR="blue"]H. Dorsal median fissure [/COLOR]- similar to ventral median fissure.