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

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

Touch (Somatosensation)

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

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

Johns Hopkins University

University of Rochester

Sensory receptors such as eyes or taste buds develop differently in different species. Sensory processing refers to the ways the brain integrates information received from sensory receptors in order to process appropriate behavioral or cognitive response. 

- Sensory organs
- Stimuli
- Receptor Cells
- Touch and the skin
- Pain
- Sensory processing disorder
- Synesthesia

Sensory processing, touch and pain

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Sensory receptor organs act as filters of the environment by responding to certain stimuli (ie. eyes for vision, ears for hearing). These organs, often times body parts, are particularly sensitive to some forms of energy.
- Receptor cells
- Hierarchy of Sensory Systems

Sensory Organs

A stimulus (plural: stimuli) is an event that affects the sensory organ. Stimuli can be sound waves, light entering the eye, or food touching the tongue.
- Adequate stimulus
- Labeled Lines
- Stimulus localization
- Selection and analysis along sensory pathways
- Selectivity and Range of Response to Stimuli

Stimuli

A condition in which a stimulus in one modality can trigger experiences in another or multiple other modalities. For example, to someone with this condition (a synesthete), the letter could be seen as green, or a particular musical tone could evoke a particular taste sensation. 
For the colored letters and numbers, some studies have pointed to this association with popular toys that depict these figures in the same colors. 

Synesthesia

Somatosensory System: Touch

The somatosensory system is partly responsible for detecting painful stimuli. Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
- Importance of Pain
- Congenital Insensitivity to Pain
- Classifying Pain
- Biological Basis of Pain

Somatosensory System: Pain

Sensory processing, touch and pain references

A condition where the brain has trouble receiving and responding to sensory input. May affect one or multiple senses. Symptoms could include over-sensitivity to certain stimuli, difficulties with coordination, or failure to respond to outside stimuli. This disorder is often seen in individuals on the Autism spectrum. It is not currently recognized as a distinct medical diagnosis.

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