Touch
The somatosensory system mediates touch, pain, temperature, and body position.
The somatosensory system is part of the sensory nervous system. Its main jobs are to detect external stimuli, sense internal stimuli, and help regulate body position and balance—a function known as proprioception. It is thought to serve as a bridge between different sensory modalities in the body. As of 2024, researchers were still debating how this system actually works, whether the current model is correct and valid, and whether it influences emotions.
The system is often divided into two parts. One handles mechanosensory information related to touch—such as light touch, vibration, pressure, and tension in the skin. This is part of the general somatic sense of touch, as opposed to the special senses like sight, smell, taste, hearing, and balance. The other part deals with nociception, which detects pain and temperature. Nociceptors are specialized receptors for signals of pain, while thermoreceptors handle normal temperature information.
Touch uses special sensory receptors in the skin called cutaneous receptors. These include mechanoreceptors (like tactile corpuscles, which relay information about pressure and vibration), nociceptors, and thermoreceptors. When these receptors are stimulated, they activate peripheral sensory neurons that send signals to the spinal cord. These signals may trigger a reflex or continue to the brain for conscious perception. For the face and head, somatosensory information enters the brain through cranial nerves, such as the trigeminal nerve.
The neural pathways to the brain are arranged so that information about where a stimulus occurs is preserved. Neighboring neurons in the somatosensory cortex represent nearby spots on the skin or body, creating a map known as the sensory homunculus.
Touch is also used for communication. Tactile signing is a common method for people with deafblindness, based on sign language or other manual communication systems. Humans can also communicate specific emotions through touch alone—including anger, fear, disgust, love, gratitude, and sympathy—at rates much better than chance.
There are two types of mechanoreceptors in the skin: low-threshold and high-threshold. Low-threshold mechanoreceptors respond to harmless stimuli and are found in glabrous skin, innervated by four different afferent fibers. High-threshold mechanoreceptors respond to harmful stimuli. Merkel cell nerve endings, located
- field
- Sensory nervous system
- known_for
- Perception of touch, pain, temperature, and proprioception
- subdivisions
- Mechanosensory (touch) and nociception (pain and temperature)
- key_receptors
- Merkel cell nerve endings, tactile corpuscles, Pacinian corpuscles, bulbous corpuscles
- cortical_areas
- Primary somatosensory cortex (S1) and secondary somatosensory cortex (S2)
Lore & Background
The somatosensory system is spread through all major parts of the vertebrate body, consisting of sensory receptors and sensory neurons in the periphery (skin, muscle, and organs) and deeper neurons within the central nervous system. The sense of touch uses special cutaneous receptors, including mechanoreceptors such as tactile corpuscles for pressure and vibration, nociceptors for pain, and thermoreceptors for temperature. Stimulation of these receptors activates peripheral sensory neurons that convey signals to the spinal cord, potentially driving a reflex, and may also be conveyed to the brain for conscious perception.
Reader's Guide
The somatosensory system's significance lies in its role as the primary interface for tactile interaction with the environment. It enables the perception of light touch, vibration, pressure, and tension in the skin, as well as the detection of harmful stimuli through nociception. The system's neural pathways preserve the location of physical stimuli, creating a sensory homunculus in the somatosensory cortex. Humans can communicate specific emotions through touch alone, including anger, fear, disgust, love, gratitude, and sympathy, at much-better-than-chance levels. The system also supports tactile signing, a common means of communication for people with deafblindness. Ongoing debate as of 2024 about the model's mechanisms and validity underscores its complexity and importance in understanding sensory processing and its potential links to emotion.
Did You Know?
- The four mechanoreceptors in glabrous skin are low-threshold and respond to harmless stimuli, while high-threshold mechanoreceptors respond to harmful stimuli.
- Pacinian corpuscles react to vibrations around 250 Hz and have been implicated in detecting the location of touch sensations on handheld tools.
- The insular cortex plays a role in the sense of bodily-ownership, bodily self-awareness, and perception, as well as conveying info about sensual touch, pain, temperature, itch, and local oxygen status.
- Tactile corpuscles are responsible for the ability to read Braille and feel gentle stimuli.
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