NERVOUS SYSTEM I
A. Prosencephalon
1. Telencephalon - paired dorsolateral outgrowths which give rise to the cerebral hemispheres.
2. Diencephalon
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".
B. Mesencephalon - remains fairly simple and unchanged.
1. Lumen = aqueduct of Sylvia.
2. Region of cephalic flexure.
C. Rhombencephalon - resembles spinal cord in internal organization.
1. Metencephalon - 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.
2. Myelencephalon:
a. Gives rise to medulla oblongata.
b. Transition from brain to spinal cord.
c. Thin roof will form posterior choroid plexus.
II. SPINAL CORD
A. Morphology = tube with vertically elongated central canal, roof and floor plates, and thick lateral walls.
B. Neuroepithelium:
1. Not multilayered initially, but is pseudostratified.
2. High mitotic activity.
3. Mitotic cells line lumen.
C. Ventricular layer = cells that eventually line the central canal (also called ependyma).
D. Intermediate zone = layer of densely-packed postmitotic neuroblasts outside of pseudostratified layer.
Gray matter = tissue from central canal to outer margin of mantle.
E. Marginal zone = tissue surrounding gray matter, consisting of axons and other non-neuronal cells (neuroglia); = White matter because of myelination of axons.
F. Lateral plates = 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.
G. Ventral median fissure - formed by downward growth of lateral plates.
H. Dorsal median fissure - similar to ventral median fissure.