The basic cellular units of nervous tissue … The basic cellular units of nervous tissue. Neurons are polarized cells with defined regions consisting of the cell body, an axon, and dendrites, although some types of neurons lack axons or dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Neurons can be classified a number of different ways: anatomical, physiological, and developmental. Anatomical classes are defined first by the location of the neuron in the nervous system. Neurons are further distinguished from each other by features which include dendritic and axon morphology. Anatomical features also include synaptic connectivity (inputs and outputs) and molecular phenotype(the particular neurotransmitters, receptors, and ion channels expressed by a neuron). Neurons can be classified by their physiological properties. This includes their general function (Sensory, motor, interneuron). Functions can also include whether the neuron is a relay neuron or a local interneuron or whether it is involved in sensory processing or correction of motor responses. Physiological actions can also include the firing properties of the neuron (bursting, tonic, quiescent). Developmental classifications of neurons are based upon the lineage that the cell derives from. The number of neurons in a particular class can vary over orders of magnitude from individual neurons in some classes to millions of neurons in other classes. s to millions of neurons in other classes.