NERVOUS SYSTEM I

I. NEURAL TUBE - modified by outgrowths and flexures.

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.