Neurons can be categorized either by their structure or their function. Structurally, neurons are classified by the number of processes emerging from the cell body. Multipolar neurons, most abundant in the CNS, have one axon and multiple dendrites emerging from the cell body. Bipolar neurons have two processes, an axon and a main dendrite that branches distally. They are rare and are found in the retina, inner ear, and olfactory mucosa. Unipolar or pseudounipolar neurons have a single process consisting of an axon partially fused with dendrites. They are primarily sensory neurons in the PNS with axons extending over long distances and cell bodies in the spinal or cranial ganglia. Functionally, neurons are categorized as sensory neurons that deliver information from sensory receptors to the CNS, motor neurons that relay instructions from the CNS to peripheral effectors, and interneurons that transmit information between sensory and motor neurons. Sensory neurons are mostly unipolar and sometimes bipolar, while motor neurons and interneurons are multipolar.