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= Nervous Systems Among Different Animals =

It is certain that different species will hold different body structures. Therefore, their different body mechanisms and systems are sure to vary depending on the animal. By comparing the nervous systems of different animals to those of humans and other animals, we can find similarities and differences that will help us understand and learn more about the nervous system in the future. For example, Leonid Moroz has been studying comb jellies for many years, and they most recently discovered that the comb jelly is missing many considered essential genes involved in the nervous system for its development and function. On the other hand, you have sponges that clearly do not have any nerve- or muscle-like things yet they do have genes involved with the development and function of the nervous system. Obviously, there are still many secrets of the nervous system that we are trying to discover.

** Comb Jellies **


The above photo is a picture of a comb jelly. These interesting creatures, as mentioned before, have a very different nervous system than us. It is shown in a recent study about ctenophores (the comb jelly’s scientific name). In opening their research to all 150 species of comb jelly, they were able to find some interesting and mysterious things. First of all, as mentioned before, they were able to discover the fact that the comb jelly is missing many essential genes for nerve function. Therefore, this means that comb jelly embryos must fabricate their neurons from a completely different set of instructions – instructions no one have come to understand yet.

Comb jellies also don’t hold the standard neurotransmitters other animals may have. In the comb jelly, the genes of these neurotransmitters are either missing or inactive aside from glutamate. Instead of the neurotransmitters, it has been discovered that comb jellies have a diverse amount of receptors on their neurons. What the receptors are for is yet to be discovered, but Moroz believes they are picking up neurotransmitters.

**Video**
Here is a video explaining how these comb jellies, usually without a full nervous system, survive in their environment.

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As seen, the species of comb jelly that was mentioned first, the beroe, has no brain or specialized senses like we do. It only possesses a neural net around the mouth which is able to detect prey. It simply wraps its extremely large mouth around the prey until it is inside of it completely. The next one does not have a large mouth like the beroe. It has adhesive tentacles that are able to latch on to prey and then pull it into its gut to be digested. This video just gives an idea of the different species of comb jellies and how they are able to survive and consume prey with little to no neurons or neurotransmitters.

Spiders
Next, we will look at another, more familiar, organism which holds an interesting nervous system. The spider’s brain is so large compared to its body that it actually spills out of its head and then down its through its legs. Shown below is a diagram of a basic spider:



Compared to the human nervous system, which can respond to mechanical stimuli, external and internal chemicals and electromagnetic stimuli, spiders can respond to most types of stimuli. However, the receptors they use are structured very differently compared to vertebrae ones.

Japanese Sea Catfish
Another animal that uses their unique nervous system in an interesting fashion is the Japanese sea catfish. Below is a photo of this animal:



These fascinating creatures use their strong senses of smell, taste, hearing and vibration to hunt and see their prey in the dark. Another interesting talent they possess is being able to detect the pH levels of the water. John Caprio and his Colleagues at Kagoshima University in Japan discovered this ability. It lets the fish zero in on the breathing patterns of their prey hiding in the seafloor. It’s connected to the pH because when the hiding fish breathe out, the water around them becomes slightly more acidic. They are able to detect this because of nerve fibres in the fish’s whiskers or barbels.

Sponges
Finally, we must consider an animal with no nervous system whatsoever. The sponge is the simplest of the multi-cellular animals. One may ask: “how is an animal able to acquire their own food with no brain?” This type of animal is able to do so through pores. The tiny pores called ostia lead into a series of canals that eventually lead to larger holes called oscula. To receive their nutrients, they beat their flagella back and forth to make water go through the sponge. They then are able to filter nutrients and oxygen in through their pores. The photo below is a diagram of a sponge and its basic parts. This is just to show how an animal can work without a nervous system altogether, as opposed to just having a different one.