Final answer:
Neurons are the adult cells most susceptible to cytotoxic agents because of their limited regeneration and specialized functions, which make them more vulnerable to damage than other cell types like osteoblasts, cardiomyocytes, and skin keratinocytes.
Step-by-step explanation:
Among the adult cells listed, neurons are the most sensitive to cytotoxic agents. They have a limited capacity to regenerate and are highly specialized cells. Neurons are highly specialized cells that are crucial for transmitting signals throughout the nervous system. Unlike other cells in the body, neurons do not readily divide or regenerate, making them particularly vulnerable to damage from cytotoxic agents. Osteoblasts, cardiomyocytes, and skin keratinocytes have greater regenerative capabilities or are not as highly specialized as neurons, and thus, they can better withstand the effects of cytotoxic agents.
Neurons, due to their complex structure, essential function, and limited regeneration ability, are most susceptible to damage. Cytotoxic agents can disrupt the delicate balance of neural functions, leading to significant, often irreversible consequences for an organism.