Image of a fluorescently-labeled<unk>  extending from an axon F-actin (red) microtubules (green). A<unk>  is a large actin-supported extension of a developing or regenerating neurite seeking its synaptic target. It is the<unk>  that drives axon<unk> . Their existence was originally proposed by Spanish histologist Santiago Ramón y Cajal based upon stationary images he observed under the microscope. He first described the<unk>  based on fixed cells as "a concentration of protoplasm of conical form, endowed with amoeboid movements" (Cajal, 1890).<unk> s are situated on the tips of neurites, either dendrites or axons, of the nerve cell. The sensory, motor, integrative, and adaptive functions of growing axons and dendrites are all contained within this specialized structure.
Growth cone
Root sheath 
Germinal matrix
Cortical homunculus
Neuromatrix
Cortical minicolumn
Optic cup 
Neurosphere