How is this possible ? #300084
Asked February 07, 2016, 9:44 PM EST
I was recently looking up different sea creatures. Some of them don't have brains, I was wondering how these creatures are considered animals or even to be living without a Nervous System. I understand for plants, but this I cannot grasp sadly.
Hennepin County Outside United States
While marine invertebrates do not have a central nervous system like you or me, they still have their own version of a nervous system. They have nerve and nerve-like cells that respond to things in their environment. For example, when a clam or oyster is exposed to air, these cells trigger the muscles to pull the shell closed to keep the animal from drying out. In humans, the nerve cells send a signal to the brain, which then tells other cells how to respond. In invertebrates without a brain, this still occurs. However mammals can sense something and choose a response. If you are cold, you might decide to go inside, get a coat, or do something else. For most of these creatures, they cannot make a choice. Their cells respond in a set manner. If they detect a predator, they flee, close up their shell, or retract. Here you can read about the jellyfish "nerve net" https://en.wikipedia.org/wiki/Jellyfish#Nervous_system, or starfish https://en.wikipedia.org/wiki/Starfish#Sensory_and_nervous_systems.