Final answer:
A third-degree burn fully extends into the epidermis and dermis, destroying tissue and affecting nerve endings and sensory function. A fourth-degree burn is even more severe, affecting the underlying muscle and bone.
Step-by-step explanation:
A third-degree burn fully extends into the epidermis and dermis, destroying the tissue and affecting the nerve endings and sensory function. These are serious burns that may appear white, red, or black; they require medical attention and will heal slowly without it. A fourth-degree burn is even more severe, affecting the underlying muscle and bone.