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Somatosensory system
From Wikipedia, the free encyclopedia
The somatosensory system is a sensory system that detects experiences labelled as touch or pressure, temperature (warm or cold), pain (including itch and tickle), as well as proprioception, which is the sensations of muscle movement and joint position including posture, movement, visceral (internal) senses and facial expression. Visceral senses have to do with sensory information from within the body, such as stomach aches.
Touch may be considered one of five human senses; however, when a person touches something or somebody this gives rise to various feelings: the perception of pressure (hence shape, softness, texture, vibration, etc.), relative temperature and sometimes pain. Thus the term "touch" is actually the combined term for several senses. In medicine, the colloquial term "touch" is usually replaced with somatic senses, to better reflect the variety of mechanisms involved.
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The somatosensory system is spread through all major parts of the nervous system. In one study, the somatosensory cortex was found to be 21% thicker in 24 migraine sufferers, on average than in 12 controls.[1]
In the periphery, the somatosensory system detects various stimuli by sensory receptors, e.g. by mechanoreceptors.
In the spinal cord, the somatosensory system [2] consists of ascending pathways from the body to the postcentral gyrus in the cerebral cortex, namely the Dorsal Column Medial Lemniscal pathway, the Ventral Spinothalamic pathway, ventral and dorsal spinocerebellar tracts.
The primary somatosensory area in the human cortex is located in the postcentral gyrus of the parietal lobe. The postcentral gyrus is the location of the primary somatosensory area, the main sensory receptive area for the sense of touch. Like other sensory areas, there is a map of sensory space called a homunculus in this location. For the primary somatosensory cortex, this is called the sensory homunculus. Areas of this part of the human brain map to certain areas of the body, dependent on the amount or importance of somatosensory input from that area. For example, there is a large area of cortex devoted to sensation in the hands, while the back has a much smaller area.
A somatosensory pathway typically has three long neurons[3]: primary, secondary and tertiary (or first, second, and third).
- The first neuron always has its body in the dorsal root ganglion of the spinal nerve (if sensation is in head or neck, it will be the trigeminal nerve ganglia or ganglia of other sensory nerves).
- The second neuron has its body either in the spinal cord or in the brainstem, and will cross (or decussate) to the opposite side and terminate in the thalamus. In the case of the somatosensory system, the pathways all terminate in the ventral posterior nucleus (VPN) of the thalamus.
- The third neuron has its body in the VPN of the thalamus and ends in the postcentral gyrus of the parietal lobe.
The new research area of haptic technology allows to provide touch sensation in virtual and real environments. This exciting new area has started to provide critical insights into touch capabilities.
- Body image
- Cell signaling
- Special senses
- Mechanoreceptor
- Molecular Cellular Cognition
- Nociceptor
- Muscle spindle
- Proprioception
- ^ http://www.medicalnewstoday.com/articles/89286.php Migraine Sufferers Have Thicker Brain Cortex rate icon Featured Article Main Category: Headache / Migraine News Article Date: 20 Nov 2007 - 3:00 PST
- ^ Nolte J.The Human Brain 5th ed. 2002. Mosby Inc, Missouri.
- ^ Saladin KS. Anatomy and Physiology 3rd ed. 2004. McGraw-Hill, New York.
- Flanagan, J.R., Lederman, S.J. Neurobiology: Feeling bumps and holes, News and Views, Nature, 2001 Jul. 26;412(6845):389-91.
- Hayward V, Astley OR, Cruz-Hernandez M, Grant D, Robles-De-La-Torre G. Haptic interfaces and devices. Sensor Review 24(1), pp. 16-29 (2004).
- Robles-De-La-Torre G., Hayward V. Force Can OvercomFLARGUSe Object Geometry In the perception of Shape Through Active Touch. Nature 412 (6845):445-8 (2001).
- Robles-De-La-Torre G. The Importance of the Sense of Touch in Virtual and Real Environments. IEEE Multimedia 13(3), Special issue on Haptic User Interfaces for Multimedia Systems, pp. 24-30 (2006).