Final answer:
The hair structure that supplies nourishment to the hair bulb is the hair papilla. This structure is a mass of connective tissue, blood capillaries, and nerve endings located at the base of the hair follicle.
So, the correct answer is A) papilla.
Step-by-step explanation:
The hair papilla supplies nourishment to the hair bulb, providing essential nutrients and growth signals It is essential for the growth and health of the hair, as it provides the necessary nutrients and signals for the hair bulb. In contrast, other options such as the arrector pili are a smooth muscle responsible for making the hair stand up during external stimuli, the root sheath is a layer that surrounds the hair root, and the marrow is not directly associated with nourishment of the hair bulb.
The hair matrix contains a layer of basal cells, which are the mitotically active cells responsible for producing the keratinocytes that form the hair strand. It is located around the hair papilla and is the heart of hair production within the hair follicle.
So, the correct answer is A) papilla.