The only multi-cellular animals without a nervous system are sponges. They do not have any nerve cells or sensory cells. Despite this, touch or pressure to the outside of a sponge will cause a local contraction of its body.
Cnidarians
The jellyfish and most all other forms of cnidarians, such as the hydra and sea anemone, are characterized by a nerve net. A nerve net is a series of interconnected nerve cells that conduct impulses around the jellyfish’s entire body. The strength of the jellyfish’s response is proportional to the strength by which the jellyfish is being stimulated. So, in other words, the stronger the stimulus is the stronger the reaction will be.
Platyhelminthes
The nervous system of the planaria, similar to that of many platyhelminthes, is only a step above the simple nerve net of the Cnidarians. In addition to the nerve net, the platyhelminthes have long nerve cords that connect the different sections of nerve nets. All of the nerve cords come together at a location near the head called the cerebral ganglion. The central nervous system has been described as ladder-like because of the nerves connecting the cords.
Nematoda
The nematoda have a simple nervous system. It consists of a ring of nervous tissue around the pharynx that gives rise to dorsal and ventral nerve cords running the length of the body. The dorsal nerve cord runs along the top of the intestine and the lateral nerve cord runs to the left of the intestine. When the nerve cords are stimulated they cause the longitudinal muscle, which runs all along the outside of the body, to contract.
The Term Paper on Main Body Systems
The respiratory system is one of the bodies most important systems, the main goal of the respiratory system is to provide gas exchange so the inhaling of oxygen and the exhaling of carbon dioxide. In the health and social care setting the words “respiratory rate” or “resps” are often used, this simply means how many times a person breathes in a minute this can help to diagnose problems such as ...
Annelida
The brain of most annelids is relatively simple in structure. In some, the brain is divided into a forebrain, midbrain, and hindbrain. Sensory nerves leave the brain and run forward into the prostomium and first segment. A single pair of circumesophageal connectives leaves the brain, surround the anterior gut, and connect with the ventral nerve cord.
The most primitive annelids have a pair of ventral nerve cords joined by transverse connectives; the most advanced forms have the cords fused to form a single cord. A ganglionic swelling of the cord is found in each body segment. Two to five pairs of lateral nerves leave each ganglion to innervate the body wall of that segment.
Giant axons, usually few in number, are found running the length of the cord. They may belong to one cell or be composed of many neurons. These axons are capable of rapidly conducting impulses to the segmental muscles; their main function is to permit the worm to contract very quickly as a defense against predators. Impulses are carried over sensory nerves to the cord, causing motor neurons to send impulses to the longitudinal muscles, which then contract.
Mollusca
Within the phylum Mollusca there are two different types of nervous system formats, I will break them up into two sections. First there are primitive mollusks, which include snails, clams, and oysters. Then there is a second section called complex mollusks that are scientifically called cephalopods; this group will include the octopus and squid.
The nervous systems of the more primitive mollusks conform to the basic annelid plan, but are modified to conform to the strange anatomy of these animals. In snails, a pair of cerebral ganglia constitutes the brain, which overlies the esophagus. Nerves leave the brain and go forward to enter the eyes, tentacles, and a pair of ganglion. Nerve cords called the pedal cords leave the cerebral ganglion ventrally and end in a pair of pedal ganglion, which stimulate the foot muscles. Another pair of nerve cords, called the visceral cords, leave the brain and run back to the visceral ganglion.
The Essay on Nervous System 2
The Nervous System is the system of cells, tissues, and organs that regulates the body’s responses to internal and external stimuli. In vertebrates it consists of the brain, spinal cord, nerves, ganglia, and parts of the receptor and effector organs. Your nervous system is composed of the central nervous system, the cranial nerves, and the peripheral nerves. The brain and spinal cord ...
In the bivalves, a cerebral ganglion is situated on either side of the esophagus. An upper pair of nerve cords leave this ganglion and run posterior to the visceral ganglia. The visceral ganglia supply the mantle, adductor muscles (which close the shell), and internal organs. A second pair of nerve cords run ventrally to the pedal ganglion. Most of the sense organs are found at the edge of this mantle.
The elaborate nervous system of the complex mollusks is correlated with the active movement and voracious habits of these animals. Most of the ganglions typical of mollusks are concentrated in a brain that encircles the esophagus. Nerves extend from the brain to ganglion at the base of the arms or tentacles and from the ganglia the length of the arms. A pair of large pallial nerves connect the brain with a pair of stellate ganglia on the inner surface of the mantle.
The giant fiber system is very well developed in the squid. Giant neurons in the brain send fibers to the retractor muscles of the head and the funnel to the stellate ganglion. Fibers from the stellate ganglion fuse to form giant fibers that stimulate the covering. Because of their large size, these fibers are capable of rapid conduction, which, in turn, permits extremely rapid movement.
Echinoderms
Echinoderms do not have a brain, and there aren’t any ganglions to coordinate movement. Their nervous system is based on the same principals as their water vascular system. A nerve ring that surrounds the mouth and radial nerves that extends from it into each arm of their nervous system. All echinoderms follow the same format for their nervous system. The only difference is the number and placement of the radial nerves.
Arthropoda
The arthropoda’s brain consists of three main regions: the protocerebrum, deutocerebrum, and tritocerebrum. The ventral nerve cord, connected to the brain by the circumesophageal connectives, is composed of a double row of ganglia connected longitudinally by connectives and transversely by commissures. Different groups of arthropods exhibit different degrees of fusion of the ganglia. In spite of the small size of some arthropods, some of their nerve cells and axons are larger in diameter than any neuron in the human nervous system. The number of insect neurons is relatively small; so each neuron must be capable of dealing with a maximum amount of information.
The Essay on Nervous System Neuron Nerve Cord
Nervous System The two types of the nervous system are the Central nervous system and the peripheral nervous system. They are responsible for integrating, processing, and coordinating Sensory data and motor commands the central nervous system, which interprets sensory input and carry information to maintain homeostasis. CNS can^aEURTMt be regenerate because a CNS consists of the spinal cord that ...
In fact, the quick evasion of predators has probably influenced the evolution of the giant-fiber systems of worms and squid as well as crustaceans, insects and other arthropods. These giant fibers conduct impulses at much higher conduction velocities than do smaller axons, while the information-handling capacity of many small axons acting together is far greater than that of giant axons. Under these circumstances it is clear that different systems evolved in the invertebrate nervous system in response to different qualities of stimuli in the environment to which the organism had to react for survival and the other for information.
Chordata
There are several subphylums of chordata and most are very closely related as far as the nervous system goes. However, there is a group of chordata that are very different from the others. For the explanation of the chordate’s nervous system I will differentiate them by calling one section vertebrates, and the other invertebrate.
All vertebrates, at some time in their life history, have a rod like bar called the notochord running the length of their body. Lower vertebrates such as acorn worms, tunicates, and amphioxus, which lack a vertebral column, illustrate the most primitive features of the vertebrate nervous system. In these animals the nerve cord is a rather uniform-appearing dorsally placed tube with a hollow cavity, which corresponds roughly to the spinal cord of the vertebrates, suggesting that the spinal cord is the most primitive component of the central nervous system.
The brain of vertebrates was developed by the accumulation of nerve cells at the cephalic end of the nerve cord. This diffused the collection of nerve cells and regulated the reflex activity of spinal motor neurons. These cells are comparable to the reticular formation occupying the brain stem of higher vertebrates. Thus the brain stem is the oldest portion of the brain.
All of this information concerning the brain and notochord pertain to the nervous systems two main divisions. The central nervous system has the most to do with these two body parts. The central nervous system is the body’s main processing center. It sends and receives information through the passages that the peripheral nervous system is made of.
The Term Paper on Relationship and Differences Between the Central and Peripheral Nervous System
... the body via ventral nerves, dorsal roots receive information from the PNS via dorsal nerves and send it to the brain. The peripheral nervous system is ... with bilateral symmetry) which includes most vertebrates and invertebrates all have a central and peripheral nervous system, although they vary greatly in the ...
The other part of the vertebrates nervous system is the peripheral nervous system. The peripheral nervous system consists of two types of nerves: sensory nerves and motor nerves. Sensory nerves gather information about your environment and deliver it to your body’s central nervous system. Motor nerves transmit certain commands from the central nervous system to glands and muscles all over your body. This is the way vertebrates the nervous system works, some on a lower end of the scale, such as a bony fish, and some work on a higher more complex level, such as humans and other mammals.
The other sections of chordata have nervous systems that show very few chordate characteristics. In fact the only nervous system characteristics these creatures have are a nerve cord and a notochord.
