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:
“... there is a lightness about the feminine minda touch and gomusic, the fine arts, that kind of thingthey should study those up to a certain point, women should; but in a light way, you know.”
—George Eliot [Mary Ann (or Marian)
“And yet we constantly reclaim some part of that primal spontaneity through the youngest among us, not only through their sorrow and anger but simply through everyday discoveries, life unwrapped. To see a child touch the piano keys for the first time, to watch a small body slice through the surface of the water in a clean dive, is to experience the shock, not of the new, but of the familiar revisited as though it were strange and wonderful.”
—Anna Quindlen (b. 1952)
“... they think that Miss America belongs to them! That they can touch her and give her a kiss on the cheekor even on the lips!”
—Ellie Ross, Travelling companion for Miss Americas. As quoted in Miss America, ch. 17, by Ann-Marie Bivans (1991)