Touch

The somatosensory system (also somatosensory nervous system) is a complex system of nerve cells that responds to changes to the surface or internal state of the body. Nerve cells called "sensory receptors" (including thermoreceptors, mechanoreceptors, chemoreceptors and nociceptors) send signals along a chain of nerve cells to the spinal cord where they may be processed by other nerve cells and then relayed to the brain for further processing. Sensory receptors are found in many parts of the body including the skin, epithelial tissues, skeletal muscles, bones and joints, internal organs, and the cardiovascular system.

Somatic senses are sometimes referred to as somesthetic senses, with the understanding that somesthesis includes the sense of touch, proprioception (sense of position and movement), and (depending on usage) haptic perception.

The mapping of the body surfaces in the brain is called a cortical homunculus and plays a fundamental role in the creation of body image. This brain-surface ("cortical") map is not immutable, however. Dramatic shifts can occur in response to stroke or injury.

The somatosensory system is spread through all major parts of a mammal's body (and other vertebrates). It consists both of sensory receptors and sensory (afferent) neurons in the periphery (skin, muscle and organs for example), to deeper neurons within the central nervous system.

...
Wikipedia