* Corpuscles, Pacinian, and Merkel cells are all types of sensory receptors in the skin. They are responsible for detecting different types of stimuli:

* Corpuscles: Detect pressure and vibration

* Pacinian: Detect deep pressure and vibration

* Merkel cells: Detect light touch and pressure

* Arrector pili are small muscles attached to hair follicles. They contract in response to cold or fear, causing the hair to stand on end (goosebumps).

While all these elements are found in the skin, only arrector pili are muscles, not sensory receptors like the others.