Pacific Sea Nettle (Chrysaora fuscescens)
Jellyfish nervous system
The jellyfish has a very simple nervous system and it is believed that it is from them that the first nervous system evolved. Jellyfish do not have brain, they have a distributed nervous system called a nerve net. This nerve net is basically scattered neurons with occasional condensed neurons. The neurons in the nerve net sometimes have to serve as sensory neurons and motor neurons. These neurons will not only send messages back to the brain, but receive and give directions for muscle contraction. These jellyfishes neurons are also bidirectional in that, when an impulse is sent to the swimming muscles all the neurons will react simultaneously for a smooth looking muscle contraction. |