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Nettle jelly. A nerve net consists of interconnected neurons lacking a brain or any form of cephalization.While organisms with bilateral body symmetry are normally associated with a condensation of neurons or, in more advanced forms, a central nervous system, organisms with radial symmetry are associated with nerve nets, and are found in members of the Ctenophora, Cnidaria, and Echinodermata ...
The plexus is the characteristic form of nervous system in the coelenterates and persists with modifications in the flatworms.The nerves of the radially symmetric echinoderms also take this form, where a plexus underlies the ectoderm of these animals and deeper in the body other nerve cells form plexuses of limited extent.
In radially symmetric animals such as the jellyfish and hydra, the nervous system consists of a nerve net, a diffuse network of isolated cells. [10] In bilaterian animals, which make up the great majority of existing species, the nervous system has a common structure that originated early in the Ediacaran period, over 550 million years ago.
It is hypothesized that the elementary biological unit is an active cell, called neuron, and the human machine is run by a vast network that connects these neurons, called neural (or neuronal) network. [5] The neural network is integrated with the human organs to form the human machine comprising the nervous system. [citation needed]
An action potential (or nerve impulse) is a transient alteration of the transmembrane voltage (or membrane potential) across the membrane in an excitable cell generated by the activity of voltage-gated ion channels embedded in the membrane. The best known action potentials are pulse-like waves that travel along the axons of neurons.
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The long thoracic nerve traverses this passageway in addition to axillary blood vessels and the brachial plexus. This complex nerve network arises in the neck from the fifth, sixth, seventh and eighth cervical roots, C5, C6, C7 and C8, together with the first thoracic root, T1. It then enters the canal in the axilla. [5] [6]