Nervous System and Senses
Ctenophores have no brain or central nervous system, but instead have a nerve net (rather like a cobweb) that forms a ring round the mouth and is densest near structures such as the comb rows, pharynx, tentacles (if present) and the sensory complex furthest from the mouth.
The largest single sensory feature is the aboral organ (at the opposite end from the mouth). Its main component is a statocyst, a balance sensor consisting of a statolith, a solid particle supported on four bundles of cilia, called "balancers", that sense its orientation. The statocyst is protected by a transparent dome made of long, immobile cilia. A ctenophore does not automatically try to keep the statolith resting equally on all the balancers. Instead its response is determined by the animal's "mood", in other words the overall state of the nervous system. For example if a ctenophore with trailing tentacles captures prey, it will often put some comb rows into reverse, spinning the mouth towards the prey.
Read more about this topic: Ctenophores, Description, Common Features
Famous quotes containing the words nervous system, nervous, system and/or senses:
“A two-week-old infant cries an average of one and a half hours every day. This increases to approximately three hours per day when the child is about six weeks old. By the time children are twelve weeks old, their daily crying has decreased dramatically and averages less than one hour. This same basic pattern of crying is present among children from a wide range of cultures throughout the world. It appears to be wired into the nervous system of our species.”
—Lawrence Kutner (20th century)
“He was the finest of our happy men;
He had all joys, he never thought of death;
He fiddled sometimes with his mind, and then
Shook off the tremor like a nervous wren....”
—Allen Tate (1899–1979)
“Our system is the height of absurdity, since we treat the culprit both as a child, so as to have the right to punish him, and as an adult, in order to deny him consolation.”
—Claude Lévi-Strauss (b. 1908)
“We are all instruments endowed with feeling and memory. Our senses are so many strings that are struck by surrounding objects and that also frequently strike themselves.”
—Denis Diderot (1713–84)