Which epidermal layer contains living cells with intact membranes and interlocking fibrils?

• A. Stratum Germinativum
• B. Stratum Granulosum
• C. Stratum Corneum
• D. Stratum Spinosum

Answer: (D)

This question focuses on how the epidermal layers differ in the living state of the cells and how they connect to each other. The spinous (prickle cell) layer contains living keratinocytes whose membranes are intact and are held together by strong intercellular junctions called desmosomes. These desmosomes, along with the surrounding keratin filaments (tonofilaments), form interlocking fibrils between neighboring cells, which gives that characteristic “spiny” appearance when viewed under a microscope. So the living cells with intact membranes and networks of intercellular fibrils fit best in this layer, which lies above the basal layer and below the granular layer.

In contrast, the outermost layer is made of dead, flattened cells with no nuclei and no functioning membranes; the granular layer shows keratohyalin granules and cells beginning to keratinize; and the basal layer is where cells actively divide and attach to the basement membrane, not where those intercellular fibrils between living cells are most prominent.