A coenzyme that functions in cell respiration.

The reduced form of NAD (Nicotinamide adenine dinucleotide).

(Nicotinamide adenine dinucleotide phosphate). An electron acceptor/donator system that functions, primarily, in biosynthetic processes.

The process in nature by which, according to Darwin\'s theory of evolution, only the organisms best adapted to their environment tend to survive and transmit their genetic characters in increasing numbers to succeeding generations while those less adapted tend to be eliminated.

See feedback inhibition.

The structural and functional unit of the kidney, numbering about a million in the renal parenchyma, each being capable of forming urine.

A cordlike structure comprising a collection of nerve fibers that convey impulses between a part of the central nervous system and some other body region.

A wave of physical and chemical excitation that moves along a nerve fiber in response to a stimulus.

A dorsal tubular structure in the vertebrate embryo that develops into the brain and spinal cord.

Nerve cell; any of the conducting cells of the nervous system, consisting of a cell body, containing the nucleus and its surrounding cytoplasm, and the axon and dendrites.

A substance released from the axon terminal of a presynaptic neuron on excitation, which diffuses across the synaptic cleft to either excite or inhibit the target cell.

The function or position of an organism or population within an ecological community.