We explain what touch is, how it works and what organs it uses. Also, what are its characteristics and possible diseases.
What is touch?
Touch is one of the human senses, shared with other higher animals
. It allows to perceive the qualities of objects and media, such as texture, pressure, temperature and hardness. It is also the one that allows us to feel certain stimuli that later turn into pleasure and pain.
Touch is a key sense and as vital as sight or hearing, but much less visible and more difficult to study. This may be because it is a passive sense that we cannot use at will
, to the point that many times we do not even associate it with the specific sensations that it allows us, such as cold or pain.
The term tact is also used as a metaphor in interpersonal relationships
, to refer to empathic, delicate or considerate communication : "Saying things with tact", for example, means doing it in a good way, without hurting yourself.
How does touch work?
Touch is part of the sensory system
, which is permanently active in the human being .
It is a sense that would work even if we were deprived of others.
It operates based on the confluence of the nervous system and the skin
, our largest organ.
It uses an important and diverse number of receptors
that transmit to the parietal lobe of the brain , responsible for deciphering nerve stimuli and providing them with a response.
Touch also operates based on the internal sensations of the body
: movement, pressure, pain, everything is registered by the nervous system , which keeps us constantly alert to the state of our organism.
Organs involved in touch
Touch is not confined to one major organ, as is sight or hearing. On the contrary, it spreads throughout our skin
and our internal tissues.
The skin is extremely important for the body. First of all, it is a protective barrier that isolates us and selectively communicates with the outside
. On the other hand, it keeps us constantly informed about the environmental temperature, about the damage we suffer or about the objects that we trip over.
The skin has sensitivity throughout its surface
, but concentrates its specialized receptors in some specific areas. For example, the tongue or fingertips are particularly sensitive. On the other hand, the genitals are the most sensitive area, since they are responsible for the pleasant sensations of intercourse, necessary for reproduction .
The skin consists of several layers of specialized tissue
that is constantly renewed. Each has its own maintenance mechanisms. These layers are:
- Epidermis. The outer layer of the skin, where the pigments that give it its particular color (melanin) are found and where the pores that allow lubrication and cooling (sweating) are located.
- Dermis. The middle layer is abundant in nerve endings, blood vessels and glands of two types: sebaceous (responsible for secreting the sebum that lubricates the skin) and sweat (responsible for secreting sweat that cools and cleans the skin). There are also the hair follicles, from which the hairs come out.
- Hypodermis. The innermost layer, called the subcutaneous tissue ("under the skin"), consists of a set of fatty tissues that serve as reserve and defensive cells in the body.
The sense of touch is not located in the outer layers of the skin but in the intermediate layer, where the nerve receptors are found.
The skin has different nerve receptors, each one specialized in a type of sensation: touch, pressure and temperature.
- Mechanoreceptors. A series of specialized receptors that transmit the diverse variety of tactile sensations, either coming from outside (exteroceptors, such as Meissner's corpuscles, Merkel's receptors, Krause's corpuscles, and Ruffini's corpuscles) or from within the body ( interoceptors, such as Pacini's corpuscles and also Ruffini's).
- Thermoreceptors. Those receptors specialized in the perception of cold or heat from the environment .
- Nociceptors. Those receptors that perceive pain and transmit it to the brain as a feeling of urgency.
Each type of receptor in the skin transmits its nerve information to the brain through a specific type of nerve fiber.
Three types of sensations
The sensations perceived by touch are of three types and are transmitted to the brain in different ways:
- Protopathic sensitivity. The most primitive and little differentiated, it responds to the thickest and most extensive sensations, such as pain, extreme cold or heat. It is the first to reappear after nerve injuries.
- Epicritic sensitivity. The finest, localized and exact one allows us to appreciate low intensity stimuli, allowing us to recognize shapes and sizes.
- Thermoalgesic sensitivity. Those that are linked to temperature and pain.
Those responsible for registering the pressure on the skin are the Pacini corpuscles
. They tend to accumulate in areas near the joints, in deep tissues, and in the breasts and genitals. They are thick, onion-shaped, and very sensitive to vibration or variation. Its concentration on the face makes it particularly sensitive.
Those in charge of recording the temperature on the skin are the Ruffini corpuscles
. They are found under the skin and are able to report both rises and falls in temperature.
The tongue is the organ where they accumulate the most
. In addition, they are responsible for initiating actions to combat cold or heat, such as sweating, trembling or vasoconstriction or vasodilation.
Specialized pain receptors are called nociceptors
. They are widely distributed over the skin, with emphasis on the most vulnerable areas, since their mission is to alert the body of the injuries suffered as quickly and in a focused way as possible, to avoid the source of the pain.
Touch and the brain
The brain receives in each parietal lobe all the nerve emissions from the opposite side of the body. For this, it has two sensitive areas
, called somatosensory areas (I and II) that occupy different portions of the brain.
These areas allow two types of perception :
- Conscious self-perception. The one we actively notice and differentiate.
- Unconscious self-perception. It is a passive perception, which registers the world around us or the pain in some situation.
Why is touch important?
Touch is essential for life. It constantly alerts us to the situation in which we find ourselves
, the situation in our environment and gives us a danger signal in case we hurt ourselves: pain.
Without such stimuli, we could take actions without knowing that we are hurting ourselves, or it would be much more difficult to determine certain bodily stimuli. In addition to offering us the pleasures associated with touch, this sense allows us to communicate with other human beings
, through hugs, handshakes, etc.
Diseases that affect touch
Some common touch conditions are:
- Hyperesthesia . Exaggerated perception of tactile sensations, due to a perception disorder, which causes excessive reactions to the slightest stimulus.
- Hypoesthesia . The opposite of the previous one: a noticeable decrease in the ability to perceive tactile stimuli, making everything feel very mitigated or distant.
- Anesthesia . Total absence of tactile stimuli in any region of the body.
- Hyperalgesia . Disproportionate increase in the sensation of pain, making everything hurt more and responding disproportionately to the degree of damage inflicted.
- Hypalgesia . The opposite: absence of the perception of pain, which prevents the individual from realizing in time the damage that is caused or received, or causing it to be perceived as less than it really is.
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