Histologic image showing a section of epidermis. Stratum spinosum labeled slightly below center.
The stratum spinosum (or spinous layer) is a layer of the epidermis found between the stratum granulosum and stratum basale. This layer is also referred to as the "spinous" or "prickle-cell" layer. This appearance is due to desmosomal connections of adjacent cells. Keratinization begins in the stratum spinosum. This layer is composed of polyhedral keratinocytes, they have large pale staining nuclei as they are active in synthesizing fibrilar proteins, known as cytokeratin, which build up within the cells aggregating together forming tonofibrils. The tonofibrils go on to form the desmosomes allowing strong connections to form between adjacent keratinocytes.