Animals without central nervous system

What is the function of the nervous system? Any of us could answer this question by saying that the central nervous system serves us primarily to think, have ideas, awareness and we would not be wrong, but the nervous system goes further.

The reason for its existence is to give animals the main characteristic that separates it from other groups of living beings, the locomotion .Animals are characterized among other things by our ability to move.

Animals without central nervous system are not non-sentient animals , we must differentiate between perception of the environment and its possible threats and the presence or absence of a central nervous system.

In this article of  Animals and Pets Online we will talk about animals without central nervous system , starting with the definition of the system itself and the adaptations of animals that do not possess it.

What is the central nervous system?

The central nervous system is one of the two subdivisions of the nervous system, which is responsible for many tasks, such as controlling all functions, organs and tissues of the body.The central nervous is composed of the brain and spinal cord .

The brain is found inside the skull in vertebrates and in the most anterior area of ​​the body in other invertebrate animals.It is formed by the brain , base of memory and learning, the cerebellum , responsible for the motor functions of the body and the brain stem , which leave a series of nerves that control organs located in the head, also takes care of heart rate, breathing and other primary functions.

How, then, animals without central nervous system control all these functions vital?

What do animals that have no central nervous system possess?

One of the main characteristics that animals possess is the capacity of locomotion , for this capacity to exist there must be a set of nerve cells or other system that allows them to react to the stimuli that occur in the middle, but would disappear.

Each group of animals has found the strategy most suited to their way of life, so, we show you a list of some of Animals that lack a central nervous system:

Sea sponges

These animals do not have any type of tissue itself, nervous, digestive or respiratory.Instead they have several cell types with specific functions:

• Pinacocytes: cells that cover the body, there is no communication between the cells.
• Coanocitos: flagellated cells responsible for digestion.
• Mesohilo: space between the layer of Pinacocytes and coanocytes.Here are the rudimentary skeleton of sponges and other less known cell types.

Sponges do not move, do not require a central nervous system, it is their own cells that detect changes in the environment and are reorganized according to function.of these stimuli.

Image: Axinella Damicornis

Jellyfish

The jellyfish, belonging to the edge of the cnidarians, if they have a capacity for locomotion, however, do not have a central nervous system, so how do they move?

It is true that jellyfish have little locomotion capacity, can move within a column of water, up or down, but to move laterally they need water currents.

The jellyfish nervous tissue is formed by a set of sensory cells that are embedded in the epidermis and gastrodermis (tissue that covers the gastrovascular cavity or "stomach" of jellyfish).These sensory cells are communicated with muscle cells and inform the animal if there is any danger nearby , a food source or any other change in the environment.

Discover which is the largest jellyfish in the world.

Image: Rhizostoma luteum

Acelomados

The acelomados are a group of very rudimentary animals but that are already beginning to show some cephalization, which is the evolutionary process by which the sensory organs agglutinate in a pole of the body.

These animals, very visually similar to a worm or slug, have a nervous ring at one of the poles of their body, branching into eight longitudinal nerves to the body.In addition, these animals appear for the first time about Rudimentary eyes called ocelos.

Image: Taenia saginata from http://bioweb.uwlax.edu/

Turbelarios

The turbelarios belong to the edge of the platelmintos.In this group of animals the cephalization process is even clearer, but it is very far from what more evolutionarily developed animals such as vertebrates present.

The nervous system model is very basic, its "brain" is ring-shaped subepidermic, with nerve cords (one or several pairs depending on the species) that extend along the body.Although, as we said , it has a more concentrated part (cephalization), it is still a diffuse set of nerve cells that run through the body.

Image: Dugesia japonica by Junji Morokuma | Tufts University

Anelids

The defining characteristic of these animals is that their body is divided into metameros or segments.Their nervous system is organized in such a way that we find a primitive brain in the segment corresponding to the head, from which two cords come out Ventral nerves that form a nerve ganglion in each segment.The nodes are sets of nerve cells.

Also discover which animals are boneless.

Image: Lumbricus terrestris at www.discoverlife.org/

Mollusks

It is in this group that we find the turning point between the primitive and the most modern nervous systems.The mollusks have a cephalic zone proper, with brain, mouth and sensory organs.

They have a periesophageal ring and two pairs of nerves (tetraneuro), two pedios (locomotors) and two visceral (digestive, reproductive, etc.) In less active animals, such as bivalves (clams), it is poorly developed, but in snails , octopus, cuttlefish and squid is very developed and has additional ganglia in the most active.

For all these reasons, we could say that mollusks have a central nervous system, as long as we talk about gasteropods and cephalopods, and at a level somewhat lower in development than fish or mammals.

Image: Helix aspersa

If you want to read more articles similar to Animals without nervous system c entral , we recommend that you enter our Curiosities section of the animal world.

Bibliography

• Avelina Tortosa i Moreno.NERVOUS SYSTEM: ANATOMY.Official College of nurses and nurses of Barcelona.
• Hickman Jr, CP (2009).Integral principles of zoology (No.591 HICp 14a.ed).
• Thibodeau, GA,&Patton, KT (1995).Anatomy and physiology.Mosby-Doyma Books.