The cellular irritability or cellular sensitivity is the ability of the cells of living beings to perceive one or more stimuli and respond to them. We can better understand this concept with a classic example: when an organism faces an external change such as, for example, an increase in temperature, the cells of its body react to this increase by moving away from this potentially dangerous condition.
When we refer to a "stimulus" we are talking about those changes in the cellular environment that modify the activity of cells. These cell changes are what we define as responses, internal or external.
The stimuli can be internal, due to changes inherent or inherent to the cell, or external, caused by biotic or abiotic factors, such as variations in light intensity, temperature and humidity, among others..
Although it is a not very "familiar" concept in scientific texts, cellular irritability can be considered as the way of living beings (or their cells) to maintain balance or internal "homeostasis" after receiving different types of stimuli.
Some authors describe irritability as the way cells have to prevent damage or destruction that their genetic material can suffer due to some internal or external element, which makes them capable of "feeling" them and responding to them..
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Irritability is a characteristic that all living beings have, be they unicellular or multicellular, animals, plants, fungi or bacteria. It has three components that we know by the name of sensitivity, coordination and responsiveness or responsiveness..
The sensitivity it is the ability of a cell or a group of cells in an organism to detect stimuli, which is often achieved through specialized sensory receptors.
Stimuli are any change in the internal or external environment of an organism, which tend to interrupt the state of balance or homeostasis, necessary for the maintenance of life.
- A stimulus can be physical: temperature, pressure, light and sound.
- It can also be chemical: changes in pH, in the concentration of water, in the ionic composition of body fluids, food or water, in the amount of oxygen, etc..
- Finally, a stimulus can also be biological, which means that it is caused by another living being, such as a predator, a potential partner, among others..
Receptors are cellular and / or bodily structures specialized in the perception or reception of stimuli, whatever their nature. These are different depending on the type of organism and even the type of cell under consideration..
Coordination has to do with the transmission of the stimulus, either by chemical or nervous means, up to what we could consider a “reaction center”. Coordination is, then, the joint work between receptors and effectors for the transmission of messages perceived as stimuli..
Responsiveness or responsiveness is the reaction of the cell or organism in question to the stimulus it has received, which usually involves some type of effector..
The responses in living beings are usually adaptive, as they seek to keep them alive and, in addition, adjust to the intensity of the stimuli that are received..
The reception of one or more stimuli induces different types of response in living beings, some of which are very evident to us humans, since they involve behavioral changes, either emotional or physical (in more complex animals) or of movement (in plants and other "simpler" organisms).
Among these types of response we find, for example, taxi, nastism and tropism. We will also describe some specific responses of complex organisms such as humans and other animals, such as instinct, learning, and reasoning, to name a few..
Taxiing involves the movement of an entire cell from one place to another in response to a certain stimulus. They are slow movements and, depending on the direction in relation to the stimulus, they can be positive (towards the source of the stimulus) or negative (in the opposite direction to the source of the stimulus).
They are common in single-celled organisms and invertebrate animals. The most representative example is that of the euglenas addressing the light.
This type of response refers to the movement of some parts of the body of plants, also in response to a certain stimulus. They differ from other responses in that they are rapid movements and do not necessarily have to do with growth movements.
An example of nastias in plants is the abrupt closing of the leaves of carnivorous plants or the closing of the leaves of Mimosa pudica after the brush of an animal.
These are directional movements that seek to move organisms away or closer in relation to the stimulus they receive. For some organisms, especially plants, tropisms are defined as growth “responses”, while for others they are just body movement..
These are involuntary responses that many animals have, since they do not require the processing of the nervous system (they occur in both invertebrates and vertebrates).
They have to do with changes in biological functions during a defined time interval. They include periods of sleep, changes in blood pressure and body temperature, etc. They occur in both plants and animals and are often related to day and night.
These responses are typical of complex ("superior") animals and depend on the interaction between sets of innate and predetermined responses that occur sequentially and which can vary between species and even between individuals of the same species..
We know, for example, the maternal instinct (which is not learned), the instinct for survival, for protection, and many others..
It is the change in the behavior patterns of animals that occur as a result of repeated (repeated) experiences, which many times has to do with the storage of some response patterns in the nervous system.
It is not a type of response exclusive to mammalian animals, as it has been observed both in invertebrates such as mollusks and arthropods, as well as in vertebrates such as fish, birds, amphibians and reptiles..
It consists of the ability of man to solve complex problems and respond to new situations "correctly".
Perhaps it is advisable to clarify that humans, as well as other mammals, have complex reception → transduction → response systems, which depend on processes that involve different organs, tissues and molecular signals..
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