The nervous system is built from two broad categories of cells, neurones and glial cells. The glial cells outnumber the neurones and the two cell types occupy a comparable amount of space in nervous tissue.The main glial cell types are, in the central nervous system, astrocytes and oligodendrocytes and, in the peripheral nervous system, Schwann cells, enteric glial cells and satellite cells.lia also maintain appropriate concentrations of ions and neurotransmitters in the neuronal environment. Increasing body of evidence indicates that glial cells are essential regulators of the formation, maintenance and function of synapses, the key functional unit of the nervous system.
Any of the pairs of nucleotides connecting the complementary strands of a molecule of DNA or RNA and consisting of a purine linked to a pyrimidine by hydrogen bonds. The base pairs are adenine-thymine and guanine-cytosine in DNA, and adenine-uracil and guanine-cytosine in RNA or in hybrid DNA-RNA pairing.
1 Nitrogenous bases can form hydrogen bonds. 2  Adenine, Thymine, and Uracil can form TWO hydrogen bonds. 3  Guanine and Cytosine can form THREE hydrogen bonds. 4  In nucleic acids (DNA and RNA), nitrogenous bases can bind to each other by hydrogen bonding. In DNA, Adenine binds to Thymine. 2  In RNA, Adenine binds to Uracil. 3  These hydrogen-bond interactions between nucleotides C-G and A-T or A-U are referred to as base-pairing or complementary base-pairing. 4  Base-pairing holds the double-stranded DNA molecule together.