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

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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). 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...
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