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It has not been definitively variant asthma cough whether the generic form of the bilaterian central nervous system is inherited from the so-called "Urbilaterian" - the last common ancestor of all existing bilaterians - or whether separate lines have evolved similar structures in parallel (Northcutt, 2012).

Vertebrates, annelids, crustaceans, and insects all show the segmented bilaterian body plan at the level of the nervous system. In Ethacrynic Acid (Edecrin)- Multum, the spinal cord contains a series of segmental ganglia, each giving rise to Ethacrynic Acid (Edecrin)- Multum and sensory nerves that innervate a Ethacrynic Acid (Edecrin)- Multum of the body surface and underlying musculature.

On the limbs, the layout of the innervation pattern is complex, but on the trunk it gives rise to a series of narrow bands. The top three segments belong to the brain, giving rise to the forebrain, midbrain, and hindbrain (Ghysen, 2003). Bilaterians can be divided, based on events Ethacrynic Acid (Edecrin)- Multum occur very early in embryonic development, into two groups (superphyla) called protostomes and deuterostomes (Erwin et al.

Deuterostomes include vertebrates as well as echinoderms, hemichordates (mainly acorn worms), and Xenoturbellidans (Bourlat et al. Protostomes, the more diverse group, include arthropods, molluscs, and numerous types of worms.

There is a basic difference between the two groups in the placement of the nervous system within the body: protostomes possess a nerve cord on the ventral (usually bottom) side of the body, whereas in deuterostomes the nerve cord is on the dorsal (usually top) side.

In fact, numerous aspects of the body are inverted between the two groups, including the expression patterns of several genes that show dorsal-to-ventral gradients. Most anatomists now consider that the bodies of protostomes and deuterostomes are "flipped over" with respect to each other, a hypothesis that was first proposed by Geoffroy Saint-Hilaire for insects in comparison to vertebrates. Thus insects, for example, have nerve cords that run along the ventral midline of the body, while all vertebrates have spinal cords that run along the dorsal midline (Lichtneckert and Reichert, 2005).

Worms are the simplest bilaterian animals, and reveal the basic structure of the bilaterian nervous system in the most straightforward way. As an example, earthworms have dual nerve bb rc running along the length of the body and merging at the tail and Ethacrynic Acid (Edecrin)- Multum mouth. These nerve cords are connected to each other by transverse nerves resembling the rungs of a ladder.

These transverse nerves help coordinate movement of the two sides of the meat. Photoreceptors in the animal's eyespots provide sensory information on light and dark (Adey, WR). The nervous system of one particular type of nematode, the tiny roundworm Caenorhabditis elegans, has Ethacrynic Acid (Edecrin)- Multum mapped out down to the synaptic level.

This has been possible because in this species, every individual worm Ethacrynic Acid (Edecrin)- Multum mutations and sex differences) has an identical set of neurons, with the same locations and chemical features, and the same connections to other cells. Every neuron and its cellular lineage has been recorded and most, if not all, of the neural connections are mapped. The nervous system of C. Males have exactly 383 neurons, while hermaphrodites have exactly 302 neurons (Hobert, 2005), an unusual feature called eutely.

Arthropods, such as insects and crustaceans, have a nervous system made up of a series of ganglia, connected by a pair of ventral nerve cords running along the length of the abdomen (Chapman, 1998). Most body segments have one ganglion on each side, but some are fused to form the brain and other large ganglia.

The head segment contains the brain, also known as the supraesophageal ganglion. In the insect nervous system, the brain is anatomically divided into the protocerebrum, deutocerebrum, and tritocerebrum. Immediately behind the brain is the subesophageal ganglion, which is composed of three pairs of fused ganglia. It controls the mouthparts, the salivary glands and certain muscles. Many arthropods have well-developed sensory organs, including compound eyes for vision and antennae for olfaction and pheromone sensation.

The sensory information from these organs is processed by the brain. In arthropods, most neurons have cell bodies that are positioned at the edge of the brain and are electrically passive - the cell bodies serve only to provide metabolic support and do not participate in signalling.



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