The somatosensory system is a diverse sensory system comprising the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception (body position), and nociception (pain). The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal organs, and the cardiovascular system.
While touch (also called tactile perception or tactual perception) is considered one of the five traditional senses, the impression of touch is formed from several modalities. In medicine, the colloquial term "touch" is usually replaced with "somatic senses" to better reflect the variety of mechanisms involved.
Somatic senses are sometimes referred to as somesthetic senses, with the understanding that somesthesis includes touch, proprioception and (depending on usage) also haptic perception.
The system reacts to diverse stimuli using different receptors: thermoreceptors, nociceptors, mechanoreceptors and chemoreceptors. Transmission of information from the receptors passes via sensory nerves through tracts in the spinal cord and into the brain. Processing primarily occurs in the primary somatosensory area in the parietal lobe of the cerebral cortex.
At its simplest, the system works when activity in a sensory neuron is triggered by a specific stimulus such as heat; this signal eventually passes to an area in the brain uniquely attributed to that area on the body—this allows the processed stimulus to be felt at the correct location. The point-to-point mapping of the body surfaces in the brain is called a homunculus and is essential in the creation of a body image. This brain-surface ("cortical") map is not immutable, however. Dramatic shifts can occur in response to stroke or injury.
Famous quotes containing the word touch:
“Its the boxers who attract the real women, after all, with their raw primeval strength, beautifully toned bodies and just a touch of vulnerability.”
—Eamonn McCabe (b. 1948)
“But what is Hope? Nothing but the paint on the face of Existence; the least touch of truth rubs it off, and then we see what a hollow-cheeked harlot we have got hold of.”
—George Gordon Noel Byron (17881824)
“One touch of nature makes the whole world kin,
That all, with one consent, praise new-born gauds.
And give to dust that is a little gilt
More laud than gilt oer dusted;
The present eye praises the present object.”
—William Shakespeare (15641616)