This constitutes about 2.4% of the body weight of man viz. Brain-1400 gram Spinal nerve-150 gram Spinal cord-30 gram Cranial nerve-10 gram C.S.F. is altogether not present in nervous tissue. About half of the solid nervous tissue is lipid and 40% is constituted by proteins. Nervous tissue is composed of two dissimilar types of cells- (1) The excitable cells are nerve cells /neuron. (2) The non-excitable cells are neuroglial cells.