What is the appendage to the hair follicle that is attached midway between the bulb and the sebaceous gland?

The appendage to the hair follicle that is situated midway between the bulb and the sebaceous gland is known as the arrector pili. This small, smooth muscle is responsible for causing the hair to stand erect (commonly referred to as "goosebumps") in response to cold temperatures or emotional stimuli. When the arrector pili muscle contracts, it pulls on the hair follicle, which can enhance insulation in colder conditions or create a defensive posture in response to stress.

Understanding the role of the arrector pili is essential in the context of skin physiology and hair anatomy. The muscle's contraction can also lead to the secretion of sebum from the sebaceous glands, thereby playing an indirect role in maintaining skin and hair health. This anatomical relationship highlights the interconnectedness of hair follicle components and their physiological functions.