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The Comparison of Nervous Systems in Humans, Cnidarians, Flatworms, and Annelids Essay

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Biology II 30 March 2012 The Comparison of Nervous Systems in Humans, Cnidarians, Flatworms, and Annelids The nervous system is one of the most important organ systems in the body. It is in charge of all of the things that happen within the body. Being responsible for receiving sensory input from internal and external stimuli, integrating and processing information, and generating output, it would be hard to survive without a nervous system; however, there are different types of nervous systems in various organisms. Humans, cnidarians, flatworms, and annelids all have very diverse nervous systems.

There are similarities and differences in each of these beings. Of the fours organisms listed, the nervous systems in humans in the most complex. Their nervous system is divided into two parts, central and peripheral. The central nervous system includes the brain and spinal cord, which is protected by bone and guarded by cerebrospinal fluid to help prevent injury. The brain is separated into four different parts: the cerebrum, the cerebral cortex, the cerebellum, and the medulla oblongata. The cerebrum is the biggest section of the brain (Understanding the Basic Anatomy and Physiology of the Human Body).

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There are two sections of the cerebrum, the right and left hemispheres. The right side controls the left side of the body and the left side controls the right side of the body. As well as being the center for thought and intelligence, the cerebrum also contains control of sensory and motor areas. The cerebral cortex is on the outside of the cerebrum, and it is responsible for learning, language, memory, and reasoning. The cerebellum is at the rear of the skull beneath the cerebrum, and it controls voluntary muscle, balance, and muscle tone.

Finally, the medulla oblongata is in control of heart rate, breathing, swallowing, coughing, vomiting, and all other involuntary muscle functions. Also, the medulla oblongata forms the brainstem needed to connect the cerebrum to the spinal cord (Understanding the Basic Anatomy and Physiology of the Human Body). The spinal cord, connected by the medulla oblongata, runs down the spine to the second lumbar vertebrae. The spinal cord is the route that nerve impulses take when traveling to the specific organ or muscle systems.

The impulse will travel down the spinal cord and branch out at the appropriate time to arrive at the necessary organ or muscle (Understanding the Basic Anatomy and Physiology of the Human Body). The spinal cord also has white matter and gray matter. The white matter possesses the zones that connect the brain and the spinal cord. The gray matter has the interneurons that hold the motor and sensory neurons (The Nervous System: Organization). The central nervous system also has four lobes: frontal, parietal, occipital, and temporal. Each lobe has a different responsibility.

The frontal lobe is in control of the motor functions, skeletal muscles, and conscious thought. It also holds the primary motor cortex. The parietal lobe, which holds the primary sensory cortex, is responsible for the sensory parts of the epidermis. The occipital lobe has the primary vision cortex. Finally, the temporal lobe is responsible for hearing and smell (The Nervous System: Organization). The peripheral system is what connects the central nervous system to the remainder of the body through three different sections: the autonomic nervous system, the somatic nervous system, and the nerves.

The autonomic nervous system controls the heart, organs, and glands. It has two systems called the “flight-or-flight” system and the “resting and digesting” system. The somatic system, which has twelve cranial nerves and thirty-one spinal nerves, is what allows humans to intentionally control our skeletal muscles. The nerves are made of neurons (Understanding the Basic Anatomy and Physiology of the Human Body). In the nerves, messages transfer from one neuron to the next across a synapse. There are neurotransmitters at each synapse that facilitate communication.

There are sensory neurons that transport messages to the brain from a receptor where the brain will interpret it. The brain then will send motor neurons to the correct affecter in muscles and glands (Understanding the Basic Anatomy and Physiology of the Human Body). The nervous system of cnidarians is called a nerve net. This is the simplest nervous system found in any organism (The Nervous System: Organization). It is called a nerve net because there is no center point of the system, and the nerve cells are spread throughout the body in a net like system (The Nervous System: Organization).

Within the nerve net of cnidarians you will find sensory neurons, motor neurons, and intermediate neurons. The intermediate neurons carry messages from the sensory neurons to the motor neurons, and some of these could possibly be organized into ganglia. In the body there are two layers of cells: nerve cells and body cells. The nerve cells help to coordinate the actions of some body cells that are within the net. For instance, if the body is touched, the whole body will react (Cnidarians). Flatworms, which have bilateral symmetry, have a nervous system that is arranged like a ladder that includes two nerve cords and a brain at the head end.

The nerve cords, which are a simple peripheral nervous system, have commissural nerve fibers that make the rungs of the ladder. The brain, which is the central nervous system, is not truly a brain, but is more a collection of two ganglia that acts like one. The ganglia integrate signals from the sensory organs such as eyespots (The Nervous System: Organization). Eyespots are pigmented cups with photoreceptor nerve ending, and are used to detect light. There are also sensory nerves in the anterior end of the flatworm that are responsible for detecting molecules in the water.

Auricles are widely spaced on the body and permit direction and intensity of the source of these molecules (Flatworms – Info and Games). There are sensory nerves in the anterior end of the flatworm that are responsible for detecting molecules in the water. There are also two ganglia at the head end of the flatworm. These two structures, the sensory nerves and the two ganglia, send nerve signals down the length of the body through the nerve cords, and these signals coordinate activity (Dolphin). The nervous system of annelids includes an anterior brain, repeating segments that each possesses a ganglion, and a ventral nerve cord.

These make up the central nervous system. The ganglion communicates with the muscles in each segment and controls these muscles. Annelids also have a nerve cord that runs down the whole length of the body and the brain is the most important organ in that it controls the animals entire body (The Nervous System: Organization). The ventral nerve cord is connected to the brain by a ring of nerves. The lateral nerves and ganglia within each segment are branched off of the ventral nerve cord (Annelid Characteristics). In earthworms, bundles of nerves make up the peripheral nervous system.

These nerves contain sensory and motor neuron fibers and they connect the rest of the body with parts of the nervous system. The sensory neurons, or afferent neurons, carry messages to the central nervous system while motor neurons, or efferent neurons, carry messages away from the central nervous system (Johnson 426). There are similarities and differences between the nervous systems of cnidarians, flatworms, and annelids. Cnidarians differ from flatworms and annelids in that they do not have a brain or anything that acts as one; meanwhile, the other two have brains.

Another difference is that some cnidarians and some annelids have ocelli, small eyes that detect the direction from which light is coming, while flatworms only have eyespots, which only detect light. One similarity that all three organisms share is their nerves. Each animal listed has nerves and also sensory and motor neurons that send impulses through their body to perform specific functions. There are some similar nerve pathways in humans and annelids. The human spinal cord and the ventral nerve cord of the annelid are similar because they both have a nerve cord running down the center of their body.

Also, the flatworms have similarities with the humans as well as the annelids because they all have a brain or something similar to a brain, whereas cnidarians have no brain at all. Another difference is the lobes of the human brain. Humans have four lobes that are held accountable for different actions. Cnidarians, annelids, nor flatworms have any lobes in their brain. This makes the human nervous system much more complex than any of the other three. In conclusion, without the nervous system, the body would not react to its environment the way it should in order to survive.

Although, the nervous systems of humans, cnidarians, flatworms, and annelids have many differences, they all serve the same purpose within the body of the organism. From the complexity of the human brain and spinal cord to the simplicity of the nerve net in cnidarians, these organisms all share similar traits within the nervous system. The nervous system is a vital part in the lives of every animal. Works Cited “Annelid Characteristics. ” Annelida: Annelid Characteristics a?? FactMonster. com. 2007. Web. 30 Mar. 2012. <http://www. actmonster. com/ce6/sci/A0856624. html>. “Cnidarians. ” Saddleback Valley Unified School District. Web. 29 Mar. 2012. <http://www. svusd. k12. ca. us/schools/rsm/teachers/bedelld/invertebratephyla/cnidarians. html>. Dolphin, W. D. “Phylum Platyhelminthes. ” Web. 30 Mar. 2012. <http://www. biology. iastate. edu/Courses/211L/Platyhelm/%20Platyhelminindx. htm>. “Flatworms – Info and Games. ” Sheppard Software: Fun Free Online Learning Games and Activities for Kids. Web. 29 Mar. 2012. <http://www. sheppardsoftware. om/content/animals/animals/invertebrates/flatworm. htm>. Johnson, Leland G. Biology. Dubuque, IA: W. C. Brown, 1983. 426-27. Print. “The Nervous System: Organization. ” Web. 29 Mar. 2012. <http://faculty. clintoncc. suny. edu/faculty/michael. gregory/files/bio%20102/bio%20102%20lectures/nervous%20system/nervous1. htm>. “Understanding the Basic Anatomy and Physiology of the Human Body. ” – The Nervous System. 2008. Web. 28 Mar. 2012. <http://lrrpublic. cli. det. nsw. edu. au/lrrSecure/Sites/LRRView/7700/documents/5657/5657/5657_05. htm>.