Touch

Touch (or tangoreception) is the physiological sense by which animals perceive an object in their environment when it comes into contact with the body surface. It belongs to a variety of closely connected mechanisms or faculties (collectively known as the senses) by which a living organism receives information about its external or internal environment.

There are two main types of sensory receptors related to touch: tactile hairs and subcutaneous receptors (receptors below the skin’s surface). Many animals, ranging from insects and other anthropods to birds and mammals, have hairs or hairlike projections richly supplied with nerves. Some hairs, such as whiskers, may be specially modified in certain areas of the body to provide more sensitive discrimination among sensory stimuli.

Sensory receptors below the skin are a second means of perceiving touch, which is a type of mechanoreception, or sensitivity to mechanical stimuli. Like other sensory cells, mechanosensors associated with touch convert physical stimuli into signals that are transmitted to specific areas of the central nervous system (i.e., the spinal cord and brain) for processing and interpretation. Stimuli create a temporary physical distortion in the membranes of these specialized receptors, causing ion channels to open and altering the resting potential of the cell, which in turn leads to the generation of action potentials, the message system of the nervous system. Density of tactile sensors varies across the body, but tends to be particularly concentrated in hairless skin like lips and fingertips. Particularly sensitive, exposed body parts are sometimes called organs of touch—e.g., the tentacles of the octopus, the beak of the sandpiper, the snout of the pig, or the human hand.

section on Braille example – exteroreception; The sense of touch is very closely related to the other four sensations received by the skin: pain, pressure, heat, and cold. It often combines with other senses to give the organism complex feedback about the external environment (exteroreception). Other features of the animal work in conjunction with touch receptors to enhance ability, like getting information about spatial position proprioreception) – i.e., external feedback helps the organism to understand its own positionality

how interconnected the skin’s sense perceptions are, why it’s difficult to divorce touch from other senses 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. closely linked with other somatic senses

Anatomy

objects touching our skin generate diverse sensations because our skin is packed with a variety of mechanosensors:

the outer layers of skin, esp hairless skin like lips and fingertips, contain whorls of nerve endings enclosed in connective-tissue capsules: they are Meissner’s corpuscles – respond to objects that touch the skin even lightly

expanded-tip tactile sensors also located in outer regions; differ from M’s corpuscles in that they adapt only partly and slowly; useful for providing steady-state information about objects that continue to touch the skin

density of tactile sensors varies across the surface of the body

Pacinian corpuscle senses pressure (deep in skin; made up of concentric layers of connective tissue that encapsulate an extension of a sensory neuron); respond esp well to vibrations applied to the skin, but adapt rapidly to steady pressure

Krause’s end bulb senses touch; Ruffini’s corpuscle senses touch and pressure

How touch works

mechanosensors: specialized cells that are sensitive to mechanical forces; stimuli that distort membranes; different kinds in skin include perception of touch, pressure, and tickle

physical distortion of a mechanosensor’s plasma membrane causes ion channels to open and alters the resting potential of the cell, which in turn leads to the generation of action potentials

Sensory cells convert physical or chemical stimuli into signals that are transmitted to other parts of the nervous system for processing and interpretation

Most sensory cells are modified neurons

Sensors are specialized for particular types of stimuli – chemical, mechanical, and light

In general, the sensor possesses a membrane protein that detects the stimulus and responds by altering the flow of ions across the cell membrane; therr esulting change in membrane potential causes the sensor to fire action potentials itself or to secrete neurotransmitter onto an associated cell tahat fires action potentials; ultimately, the stimulus is converted into the action potential, the universal message system of the nervous system; the stimulus’s intensity is coded as the frequency of action potentials

mechanosensor – sensory signals modify receptor proteins in the membranes of sensors, which in turn modify ion channels; pressure opens an ion channel

messages from sensors arrive at different places in the central nervous system (CNS)

adaption – defined in this context as enabling an animal to ignore background or unchanging conditions while remaining sensitive to new changes or to new information (example 930)

Functions of touch and its associated senses

location of object localize with some precision points of tactual stimulation at the body surface.

Sensory contact with the ground below often informs animals about their spatial position. Nocturnal animals (for example, some eels) find shelter during the day by keeping as much of their skin as possible in contact with solid objects in the surroundings (thigmotaxis). Animals that live in running water usually maintain their position as they turn and swim head-on against the current (rheotaxis). Study of rheotaxic behaviour reveals that the sensory basis almost exclusively depends on visual or tactile stimuli (or both) arising from the animal's movements relative to the solid bottom or surroundings. The long antennae of many arthropods (e.g., crayfish) and the lengthened tactile hairs (vibrissae) on the snouts of nocturnally active mammals (e.g., cat, rat) serve in tactually sensing objects in the vicinity of the animal's body, extending and enriching the adaptive function of the sense of touch.

Simulated touch

Haptic, from the Greek αφή (Haphe), means pertaining to the sense of touch (or possibly from the Greek word haptesthai meaning “contact” or “touch”).

Haptic technology refers to technology which interfaces the user via the sense of touch by applying forces, vibrations and/or motions to the user. This mechanical stimulation is used to create haptic virtual objects. This emerging technology promises to have wide reaching applications. In some fields, it already has. For example, haptic technology has made it possible to investigate in detail how the human sense of touch works, by allowing the creation of carefully-controlled haptic virtual objects. These objects are used to systematically probe human haptic capabilities. This is very difficult to achieve otherwise. These new research tools contribute to our understanding of how touch and its underlying brain functions work (See References below).

Although haptic devices are capable of measuring bulk or reactive forces that are applied by the user it should not to be confused with touch or tactile sensors that measure the pressure or force exerted by the user to the interface.

References

ISBN links support NWE through referral fees

• Flanagan, J.R. and S.J. Lederman. 2001. Neurobiology: Feeling bumps and holes. Nature 412(6845):389-91.
• Hayward, V., Astley, O.R., Cruz-Hernandez, M., Grant, D., and G. Robles-De-La-Torre. 2004. Haptic interfaces and devices. Sensor Review 24(1):16-29.
• Purves, W., D. Sadava, G. Orians, and C. Heller. 2004. Life: The Science of Biology, 7th edition. Sunderland, MA: Sinauer. ISBN 0716766728.
• Robles-De-La-Torre, G. and V. Hayward. 2001. Force Can Overcome Object Geometry in the Perception of Shape through Active Touch. Nature 412(6845):445-8.
• Robles-De-La-Torre, G. 2006. The Importance of the Sense of Touch in Virtual and Real Environments. IEEE Multimedia 13(3):24-30.

External links

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

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

• Touch  ^history

The history of this article since it was imported to New World Encyclopedia:

• History of "Touch"

Note: Some restrictions may apply to use of individual images which are separately licensed.