In human skin, receptors that respond to external stimuli such as pressure, pain, and temperature are classified as which type of sensory receptors?

Introduction / Context:
The human nervous system uses specialised receptors to detect different types of stimuli. These receptors can be classified based on the type of stimulus they detect, such as mechanical, thermal, or chemical, and also based on the location of the stimulus source, such as external or internal. This question focuses on receptors in the skin that sense pressure, pain, and temperature, asking how they are classified with respect to the source of the stimuli.

Given Data / Assumptions:

• The receptors mentioned are located in the skin.
• They detect pressure, pain, and temperature changes.
• Options include exteroceptors, proprioceptors, interoceptors, and mechanoreceptors.
• We assume basic knowledge of receptor classification in physiology.

Concept / Approach:
Receptors that detect stimuli from outside the body, such as touch, pressure, pain due to external injury, or temperature changes in the environment, are called exteroceptors. They are commonly located in the skin and some special sense organs. Proprioceptors, on the other hand, are located in muscles, tendons, and joints, providing information about body position and movement. Interoceptors, also called visceroceptors, monitor internal conditions in organs such as blood pressure, pH, and stretch of internal walls. Mechanoreceptors are a functional category based on the type of stimulus (mechanical deformation) and can be present in exteroceptors and proprioceptors. Because the question emphasises skin receptors dealing with external stimuli, the correct classification is exteroceptors.

Step-by-Step Solution:
Step 1: Note that the receptors under discussion are located in the skin, which is exposed to the external environment. Step 2: Recognise that pressure, external injury causing pain, and environmental temperature are all external stimuli. Step 3: Recall that receptors that respond to external stimuli are classified as exteroceptors. Step 4: Understand that proprioceptors mainly provide information from muscles and joints about body position, not about external temperature or surface pressure on skin. Step 5: Recognise that interoceptors monitor internal organ conditions such as blood pressure, not external contact with the environment. Step 6: Mechanoreceptors describe receptors responding to mechanical stimuli, but the question includes pain and temperature as well, so the broader location based class exteroceptors is more appropriate.

Verification / Alternative check:
Physiology textbooks classify receptors based on location into exteroceptors, interoceptors, and proprioceptors. Under exteroceptors, examples given include tactile receptors in skin for touch, pressure, vibration, pain, and temperature. Diagrams show free nerve endings, Meissner corpuscles, and Pacinian corpuscles in the dermis as exteroceptors. Interoceptors are shown in internal organs, and proprioceptors such as muscle spindles are in muscles. This classification confirms that skin receptors detecting pressure, pain, and temperature should be called exteroceptors.

Why Other Options Are Wrong:

• Proprioceptors that inform the brain about body position and movement: These are located in muscles and joints and do not primarily detect skin surface pressure or external temperature.
• Interoceptors that monitor internal organ conditions: These respond to internal stimuli such as distension of the stomach or changes in blood pressure, not external contact.
• Mechanoreceptors that respond only to mechanical deformation: This term does not include pain and temperature receptors and is a functional rather than location based category, so it does not best answer the question asked.

Common Pitfalls:
A common confusion is between classification by location and classification by stimulus type. Mechanoreceptors, thermoreceptors, and nociceptors refer to the type of stimulus, whereas exteroceptors, interoceptors, and proprioceptors refer to the source or location of the stimulus. Students may incorrectly choose mechanoreceptors because pressure is a mechanical stimulus, but the question also mentions pain and temperature in the skin and emphasises a unified class. Remember that for skin sensing the outside world, the umbrella term is exteroceptors.

Final Answer:
Receptors in the skin that detect pressure, pain, and temperature are classified as exteroceptors that detect stimuli originating from outside the body.