Observe a vertical section of human skin through a tattoo, using low-power magnification. Note the location of the dispersed ink granules within the upper portion of the dermis. From a thin vertical section of a tattoo, it is not possible to determine the figure or word of the entire tattoo as seen on the surface of the skin. Compare this to the location of melanin granules found in dark (heavily pigmented) skin. Suggest reasons why a tattoo is permanent and a suntan is not.

A tattoo is permanent because the pigments are applied into the dermis, while suntan is not permanent because it affects only the epidermis, which undergoes constant renewal

Explanation:

The epidermis is composed of cells located in the upper layers of the skin. The superficial epidermal layer is constantly being renewed by new cells by the processes of mitosis and keratinization, i.e., by cell division and accumulation of keratine in the cytoplasm of epidermal cells during their terminal differentiation. In consequence, a tan is not permanent because surface epidermal cells naturally exfoliate over time. Moreover, tattoos are permanent because tattoo pigments are injected into the dermis layer and dermal cells are not replaced. The dermis is a layer of the skin located between the epidermis and subcutaneous tissue.

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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