Which one of the following sensory receptors is found in epidermisa) Merkel discb) Meissner’s corpusclesc) Ruffini endingd) Pacinian corpuscles
First, I need to recall the locations of these receptors. Merkel discs are associated with the epidermis. They're for light touch and are found in the basal layer of the epidermis. Meissner's corpuscles are in the dermis, specifically in the papillary layer. They detect fine touch and vibrations. Pacinian corpuscles are in the deeper dermis or subcutaneous tissue and respond to deep pressure and vibration. Ruffini endings are in the dermis too, sensing skin stretch.
So the correct answer should be Merkel discs (option A). The other options are all in the dermis, not the epidermis. Let me double-check. Yes, Merkel cells are indeed in the epidermis. Meissner's and Pacinian are definitely deeper. Ruffini is in the dermis. So the answer is A. Need to explain each option clearly why they are wrong. Also, the clinical pearl would be remembering that Merkel discs are the only ones in the epidermis. That's a key point for exams.
**Core Concept**
Sensory receptors are specialized structures that detect stimuli and transmit signals via afferent nerves. The question tests knowledge of **cutaneous receptor localization**, specifically distinguishing epidermal from dermal/subcutaneous receptors like Meissner’s and Pacinian corpuscles.
**Why the Correct Answer is Right**
**Merkel discs** (Merkel cell-neurite complexes) are **slow-adapting type I tactile receptors** located in the **stratum basale** of the epidermis. They detect **light touch and texture** via direct contact with the skin surface. Their epidermal location differentiates them from dermal receptors like Meissner’s or Pacinian corpuscles, which require deeper tissue integration for their mechanosensory functions.
**Why Each Wrong Option is Incorrect**
**Option B:** **Meissner's corpuscles** reside in the **papillary dermis** and detect **low-frequency vibrations and discriminative touch**. They are not epidermal.
**Option C:** **Ruffini endings** are **slow-adapting stretch receptors** in the **reticular dermis**, sensing skin tension and joint position.
**Option D:** **Pacinian corpuscles** are **deep subcutaneous** receptors for **high-frequency vibrations and pressure**, not located in the epidermis.
**Clinical Pearl / High-Yield Fact**
Merkel discs are the **only epidermal tactile receptors**; all other primary mechanoreceptors (Meissner’s, Pacinian, Ruffini) are dermal or subcutaneous. Remember: **"Merkel in the epidermis, Meissner in the papillary dermis, Pacinian deep."**
**Correct Answer: A. Merkel disc**