IRRITABILITY IN ANIMALS: CHARACTERISTICS AND TYPES - BIOLOGY - 2024

The irritability in animals is the property to respond to physical and chemical changes of its internal and external environment. Thanks to this ability they can survive and adapt to the changes that occur in their environment.

Unlike unicellular organisms that generate simple responses, multicellular organisms such as animals have highly specialized receptor organs that receive stimuli and transmit them for the body to generate the response.

The nervous system and the endocrine system are in charge of receiving stimuli and coordinating their respective response.

Irritability has a homeostatic purpose in the body, that is, to maintain its constant internal conditions such as body temperature, the amount of circulating blood, the amount of oxygen received or the amount of water needed.

What distinguishes the irritability of living organisms from the reactions in inert beings is that the response of the latter will always be the same while (a metal corrodes in the presence of an acid) that the reaction of a living being differs.

Characteristics of irritability

The main characteristics of irritability are:

1- It is an adaptive response, not a static one. That is, it is adapted according to needs.

2- They can be different for the same type of stimuli.

3- They are calibrated according to their intensity.

Complexity in the manifestations of irritability

Single-celled organisms such as bacteria manifest their irritability by changing the rate of cell division and moving toward or away from the stimulus. Their responses are not very varied or complex because they lack organic coordination and integration systems.

For their part, plants slowly move away from or approach the stimulus (tropism) thanks to their hormonal coordination and integration system called phytohormones.

Animals are multicellular organisms and consequently, they have an endocrine and a nervous system that are composed of highly specialized organs linked through a complex communication network that delivers a response in a matter of seconds.

A stimulus is anything that an organism responds to or reacts to.

Types of irritability

The types of irritability in animals are tactisms, reflexes and instincts.

1- Tactisms

They are the innate, fixed and inevitable behaviors that lower animals such as invertebrates perform. They are fast, wide movements that move the individual to bring him closer to or away from the stimulus.

If the movement leads to an approach of the stimulus it is called positive tactism.

If the movement leads to a withdrawal from the stimulus, it is called Negative tactism.

The most common agents of tactism are light, gravity, water, and touch.

Phototacticism

It is the response to the variation of light, regardless of whether it is natural or artificial. If the answer is to go to the light source, it is a positive phototacticism but if it is remote it will be a negative phototacticism.

To illustrate the two previous phenomena, let us recall mosquitoes and other insects that fly around an illuminated light bulb; they are an exemplary case of positive phototacticism. On the other hand, the earth pigs look for dark and humid places, so their phototacticism is negative and hydrotacticism positive.

Gravitation

Reaction to gravity. It can also be positive or negative, following the logic of approaching or moving away from gravity, respectively.

Ladybugs or chinitas are beetles that, when placed on the palm of the hand, will direct them to the fingertips, presenting a negative gravitactism.

The case of earthworms that always seek to be on dry, dark, dry ground is our example of positive gravitation and negative phototacticism.

Hydrotacticism

Response to water or humidity. The approach to this stimulus constitutes positive hydrotacticism and its avoidance is negative hydrotacticism. Earthworms and piglets are hydrotactic positive insects. Spiders, on the other hand, try to stay away from water sources so their hydrotacticism is negative.

Thigmotacticism

Response to tactile stimuli. Centipedes or millipedes curl up when touched (negative thigmotacticism).

Chemotacticism

Reaction to chemical stimuli. All insects repel the effect of an insecticide, moving away from the place, therefore, the insecticide produces negative chemotacticism.

The case of positive chemotacticism is that of bees that approach certain trees for their pollen.

2- Reflections

They are involuntary, rapid and pre-established animal responses of a part of the organism to certain stimuli.

Most of the cases are about movements but it can also be exclusively or include hormonal secretion.

In this case, the stimulus does not travel through the neurons until it reaches the brain (central nervous system), but the receptor will send it to the spinal cord that will activate the motor neurons and these will produce the movement of the muscle (muscle tension) or hormonal secretion if the response is endocrine. This happens in a matter of fraction of seconds.

Reflexes can be innate or acquired. Breathing, swallowing saliva or blinking are innate or unconditioned reflexes that appear during or after birth and that are carried out automatically without the participation of the brain.

Instead, acquired reflexes or conditioned reflexes are adopted over time through a learning process in which the brain participates in establishing a relationship between a stimulus and a reinforcement.

When an innate reflex to an acquired one is exercised then it is reinforced but if the stimulus is not exercised, over time it weakens and finally disappears.

3- Instincts

They are more complex and elaborate innate reactions, in which various reflexes intervene. These are innate, fixed and specific behaviors that are genetically transmitted between individuals of the same species to respond in a certain way to certain stimuli.

Being a type of genetic animal irritability with adaptive purposes, in many cases they result from the evolutionary process of the species.

The vital instincts are present in all animals while the pleasure and social instincts are more common in more evolved species. The cultural ones are exclusive to the human being.

Vital instincts

They are commonly known as survival instincts whose purpose is to preserve the existence of the subject, his family or his species. The 4 most important are:

• Nutrition instinct: behavior acquired in the face of hunger and thirst to meet their need for food and water.
• Sexual instinct: erotic behavior to procreate and preserve the species.
• Fight and flight instinct: conduct of defending themselves physically against an external stimulus that they perceive as threatening.
• Den instinct and heat search: another behavior to protect their physical integrity against inclement weather.

Pleasure instincts

The pleasure instincts are usually the sophisticated version of the vital instincts to increase the degree of general well-being.

Sex is a vital instinct that turns into a pleasant one when the procreative purpose is abandoned and adopted exclusively for recreational purposes as occurs in humans and dolphins.

Social instincts

They are the behaviors of the individual within a community and the role they have within it. The solitary behavior of certain species, the collective instinct in others, the rank of authority of one (s) over another (s) within a group are examples of social instinct.

4- Learning

It is the adoption of a new pattern of behavior as a result of your interaction with the external world. It is common in complex vertebrates such as reptiles, birds, and mammals.

How to obtain food or how to fly are mandatory "lessons" of many youngsters that they learn from their parents.

5- Reasoning

It is the ability to solve complex problems or to give adequate responses to new situations not faced before.

This process involves using previously acquired knowledge in a new situation, minimizing the margin of error.

There is an academic debate about whether this ability is shared by more developed mammals or only human beings, since gorillas, chimpanzees and dolphins show patterns of "reasoning", only inferior to human beings.

References

1. Contreras Rivera, J. (15 of 7 of 217). Irritability and Nervous System. Obtained from Colegio San Sebastián de los Andes: ssla.cl
2. Deeptirekha, J. (15 of 7 of 2017). Response and Coordination in Plant and Animals. Obtained from Biology Discussion: biologydiscussion.com
3. EcuRed. Knowledge with everyone and for everyone. (15 of 7 of 2017). Instinct. Obtained from EcuRed. Knowledge with everyone and for everyone: ecured.cu
4. Ministry of Education Chile. (15 of 7 of 2017). Irritability, a fundamental property of living beings. Obtained from the Educational Platform of the Ministry of Education of Chile: ftp.e-mineduc.cl
5. Monge-Nájera, J., Patricia, GF, & Rivas Rossi, M. (2005). Irritability and homeostasis. In J. Monge-Nájera, GF Patricia, & M. Rivas Rossi, General Biology (pp. 47-49). San José: Editorial Universidad Estatal a Distancia.