Touch

Somatic sensation consists of the various sensory receptors that trigger the experiences labelled as touch or pressure, temperature (warm or cold), pain (including itch and tickle), and the sensations of muscle movement and joint position including posture, movement, and facial expression (collectively also called proprioception).

A more complex concept comes into play when the term is used in reference to human beings. The sense of touch is mediated by the somatosensory system. 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.

The somatosenses include: Cutaneous (skin), kinesthesia (movement) and visceral (internal) senses, of which the first two are better known. Visceral senses have to do with sensory information from within the body, such as stomach aches.

Anatomy

Human brain localization

The somatosensory systemconsists 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 (Parietal Lobe). It is the location of the primary somatosensory cortex, 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. This somatosensory map is termed the homunculus.

Psychology

A somatosensory pathway typically has three long neurons: 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 ventro-posterior nucleus of the thalamus.
• The third neuron has its body in the VP nucleus of the thalamus and ends in the postcentral gyrus of the cerebral cortex, which is the primary somatosensory area in the human cortex.

Technology

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.

See also

• Cell signaling
• Special senses
• Mechanoreceptor
• Molecular Cellular Cognition
• Nociceptor
• Muscle spindle
• Proprioception

References

ISBN links support NWE through referral fees

• 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).

External links

• 'Somatosensory & Motor research' (Informa Healthcare)
• Overview
• Somatic vs. Special senses

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