The skin contains a variety of specialized receptors that respond to different touch-related stimuli. The main types include Meissner's corpuscles, Pacinian corpuscles, Merkel's disks, and Ruffini corpuscles, each sensitive to specific aspects of touch like pressure, vibration, and stretch.

Receptors Involved in Touch

A person blindfolded is asked to identify an object placed in their hand. They describe feeling a smooth, cool, hard surface and can tell it is spherical. They are also aware of its weight as they hold it. Which of the following descriptions is exclusively the result of the sensory system responsible for perceiving contact with the skin?

Somatosensation, commonly known as the sense of touch, is the sensory system responsible for perceiving contact with the skin.

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The common idea that humans have only five senses is oversimplified. Along with vision, hearing or audition, smell or olfaction, taste or gustation, and touch or somatosensation, humans also have sensory systems for balance, body position and movement, pain, and temperature.

The Senses

A large part of our somatosensory system is responsible for our perception of touch.
- Sensory Organ: Skin
- Dorsal Column System
- Primary Sensory Cortex
- Secondary Sensory Cortex
- Skin sensory receptors

Somatosensory System: Touch

The body senses are a group of sensory modalities that provide information about the body itself and its interaction with the environment. This category includes touch (somatosensation), temperature perception (thermoception), pain (nociception), balance (vestibular sense), and the sense of body position and movement (proprioception and kinesthesia).

Body Senses

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

People tend to use a high amount of visual information to inform their daily activities. There is also a lot of sensory information coming in through the eyes, which makes the visual system a highly researched field of neuroscience. 

Vision

The vestibular sense is the sensory system responsible for maintaining balance and body posture. It operates through the response of specialized hair cells located in the utricle, saccule, and semi-circular canals of the inner ear, which detect changes in head position and gravity.

Vestibular Sense

Gustation (also known as "taste") is a chemical sense that allows individuals to sense and perceive five major flavors: sweet, salty, sour, bitter, and umami.

Gustation (Taste)

Audition, or hearing, is the process by which the auditory system converts pressure waves from the environment into meaningful sounds. This capability is fundamental for human experience, enabling communication through spoken language, the appreciation of music, and the perception of environmental sounds.

Audition (Hearing)

Proprioception is the sensory perception of the position of the body's parts. This sense allows an individual to understand their body's orientation in space without relying on visual cues.

Proprioception

Kinesthesia refers to the perception of the movement of the body through space.

Kinesthesia

Nociception is the sensory system that provides the brain with information related to pain, typically in response to potentially damaging stimuli.

Nociception (Pain)

Touch (Somatosensation)

The sensory modalities of taste (gustation) and smell (olfaction) are classified as chemical senses. This categorization is due to the fact that they rely on specialized sensory receptors designed to detect and respond to specific molecules present in the food consumed and the air inhaled.

Chemical Senses

Thermoception is the sensory system that enables an organism to perceive temperature. This process relies on specialized sensory receptors, known as thermoreceptors, which are primarily located in the skin and detect changes in temperature from the external environment.

Thermoception (Temperature)

Analyze the following scenario and explain the roles of three key sensory systems (other than vision) that are critical for the individual's performance.

Sensory Integration in Action

Nociception is a sensory system that provides information about pain.

Nociception

The senses function as the interface between the mind and the external environment. They receive environmental stimuli and translate them into nervous impulses, which are then transmitted to the brain for processing.

Sensory Interface with the External Environment

Thermoception is a sensory system that provides information about temperature.

Thermoception

Skin is the largest organ in the human body. It is responsible for receiving the environmental stimuli that we process when perceiving touch and pain. The skin is made up of three separate layers.
- Epidermis
- Dermis
- Hypodermis

Sensory Organ: Skin

The dorsal column system is the pathway in which the touch receptors that have sent their axons to the spinal cord, have entered the spinal cord through the dorsal horn and turn upward, traveling to the brain along the spinal cord's dorsal column of white matter.
- Dorsal column nuclei
- Dermatome

Dorsal Column System

The primary somatosensory cortex (S1) is located in both hemispheres and lies in the postcentral gyrus of the parietal cortex, just behind the central sulcus dividing the parietal lobe from the frontal lobe. Each S1 receives touch information from the opposite side of the body. 
- Topographic Mapping
- Plasticity of the Sensory Cortex

Primary Sensory Cortex

The secondary somatosensory cortex (S2) maps both sides of the body in registered overlay (ie. the left-arm and right-arm representations occupy the same part of the map and so forth). In recent studies, the S2 has been implicated in information integration, grounded essentially in spatial body maps, allowing humans to form complex relations between the body and the environmental space (establishing a body-in-world map). 

Secondary Sensory Cortex

Sensory neurons located in the skin that respond to various mechanical stimulations. There are 3 main groups of receptors, categorized by what type of stimulus they detect:
- Mechanoreceptors
- Thermoreceptors
- Nociceptors


Skin Receptors

There are anatomical and functional connections between auditory and somatosensory processing. For instance, hearing a rubbing sound and feeling sandpaper with the fingers activates the same part of the cortical area in the caudal auditory region.

Auditory and Somatosensory Processing

The pathway for sensory information begins at the skin's receptors and free nerve endings. From there, signals ascend the spinal cord and are relayed through the medulla and thalamus before reaching their final destination for processing in the somatosensory cortex, which is situated in the postcentral gyrus of the parietal lobe.

Somatosensory Information Pathway

Receptors located within the muscles, joints, skin, and tendons detect stretch and tension, gathering proprioceptive and kinesthetic information. This sensory data travels via the spinal column to the brain. There, the cerebellum and multiple other cortical regions process the information; additionally, these cortical areas transmit signals back to the proprioceptive and kinesthetic sensory organs.

Neural Basis of Proprioception and Kinesthesia

The perception of touch (somatosensation), temperature (thermoception), and pain (nociception) is made possible by a variety of specialized receptors and free nerve endings. These sensory structures are widely distributed throughout the skin and other bodily tissues.

Sensory Receptors for Touch, Temperature, and Pain

The proprioceptive and kinesthetic systems provide the brain with information regarding the body's position and movement. This is accomplished via specialized receptors that detect stretch and tension within the body's muscles, joints, tendons, and skin.

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