A
nerve net is a type of simple
nervous systemThe nervous system is a network of specialized cells that communicate information about an organism's surroundings and itself. It processes this information and causes reactions in other parts of the body. It is composed of neurons and other specialized cells called glial cells that aid in the...
that is found in members of the
cnidariaCnidaria is a phylum containing over 10,000 species of animals found exclusively in aquatic, mostly marine, environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey...
and echinodermata phyla . Nerve nets consist of interconnected
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
s lacking a
brainThe brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all...
or any form of
cephalizationCephalization is an evolutionary trend, whereby nervous tissue, over many generations, becomes concentrated toward one end of an organism. This process eventually produces a head region with sensory organs....
. This nervous system allows cnidarians to respond to physical contact. They may then detect food and other chemicals in a rudimentary way. Although the nerve net allows the animal to respond to its environment, it has trouble alerting the animal from where the
stimulusIn physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity. When a stimulus is applied to a sensory receptor, it elicits or influences a reflex via stimulus transduction...
is coming.
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A
nerve net is a type of simple
nervous systemThe nervous system is a network of specialized cells that communicate information about an organism's surroundings and itself. It processes this information and causes reactions in other parts of the body. It is composed of neurons and other specialized cells called glial cells that aid in the...
that is found in members of the
cnidariaCnidaria is a phylum containing over 10,000 species of animals found exclusively in aquatic, mostly marine, environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey...
and echinodermata phyla . Nerve nets consist of interconnected
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
s lacking a
brainThe brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all...
or any form of
cephalizationCephalization is an evolutionary trend, whereby nervous tissue, over many generations, becomes concentrated toward one end of an organism. This process eventually produces a head region with sensory organs....
. This nervous system allows cnidarians to respond to physical contact. They may then detect food and other chemicals in a rudimentary way. Although the nerve net allows the animal to respond to its environment, it has trouble alerting the animal from where the
stimulusIn physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity. When a stimulus is applied to a sensory receptor, it elicits or influences a reflex via stimulus transduction...
is coming. For this reason, simple animals with nerve nets, such as
hydraHydra is a genus of simple fresh-water animal possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa. They can be found in most unpolluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a...
, will typically respond in the same way to contact with an object, regardless of where the contact occurs.
Hydra, which are cnidarians, have a nerve net throughout their body. On the other hand, Sea stars, which are echinoderms, have a nerve net in each arm, connected by a central radial nerve ring at the center. This is better suited to controlling more complex movements than a diffuse nerve net .