Nervous system (Forensic Science)
The basic units of the nervous system are specialized cells called neurons that are able to conduct stimuli. Neurons may be divided into three types: sensory neurons, which conduct sensations into the central nervous system; motor neurons, which conduct stimuli from the central nervous system to effector organs and muscles; and association neurons, which communicate stimuli between adjacent neurons.
Neurons are the only cells in the human body that can conduct stimuli. They exist in an electrical-chemical state that is said to be charged or polarized. When stimulated, the charge on the neuron is momentarily reversed in a process called depolarization or action potential. The action potential (stimulus) is initiated at one end of the neuron, the dendrites, and continues to the other end, the axons, from which neurotransmitters are released into the synapse between the neuron and the next neuron, effector gland, muscle, or organ. Arrival of sufficient quantities of neurotransmitters at the dendrites on the next neuron causes that neuron to exhibit an action potential along its length. In this way the stimulus is transmitted from neuron to neuron or from neuron to muscle.
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Three Nervous Systems in One (Forensic Science)
The human nervous system can be subdivided into the central nervous system, consisting of the brain and spinal cord; the peripheral nervous system, consisting of nerves that carry information to and from the central nervous system; and the autonomic nervous system, which monitors and maintains internal organs and their functions. The peripheral nervous system contains sensory receptors that respond to information from the external world and the individual’s internal environment and sensory neurons that transfer this information to the central nervous system. It also contains motor neurons that carry information from the central nervous system to voluntary muscles, allowing movement. The peripheral nervous system regulates the activities of the body that are under conscious control. It controls all voluntary systems within the body, with the exception of reflex arcs.
The autonomic nervous system monitors and maintains the body’s internal state. These maintenance activities are performed primarily without conscious control. The autonomic nervous system comprises two subdivisions with opposing functions: the parasympathetic division and the sympathetic division. Generally, the sympathetic division of the autonomic nervous system works to mobilize body activity to meet emergencies, whereas the parasympathetic division is responsible for maintaining body homeostasis at other times.
The central nervous...
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Forensic Toxicology and the Nervous System (Forensic Science)
As the nervous system is ultimately responsible for all behavior, physiological function, and reflexes, an analysis of the forensics of the nervous system can have far-reaching consequences and can raise concerns in a number of areas, including injury and sickness, especially as these may relate to accidents or deaths. Specialists in neuropsychiatry, psychopharmacology, and toxicology thus evaluate the nervous system for evidence in cases of traumatic brain injury, post-traumatic stress disorder, and similar disorders that may follow injury.
Forensic investigations regarding the nervous system generally focus on the types and concentrations of chemicals detected in neurological cells and tissue fluids that surround and protect the nervous system. Using techniques of toxicology, forensic analysts evaluate the possible role of toxins or drugs that may affect or impair the nervous system to determine whether any toxins present are related to the cause of death or bodily injury. Neuropsychologists are concerned with evaluating basic chemicals in the brain and nervous system to determine whether underlying or root causes of neurological or behavioral disorders may have contributed to the crime or accident being investigated.
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Further Reading (Forensic Science)
DiMaio, Vincent J. M., and Suzanna E. Dana. Handbook of Forensic Pathology. 2d ed. Boca Raton, Fla.: CRC Press, 2007. Comprehensive volume illustrates core aspects of modern forensic pathology.
Doerr, Hans O., and Albert S. Carlin, eds. Forensic Neuropsychology: Legal and Scientific Bases. New York: Guilford Press, 1991. Provides information on the legal system for neuropsychologists who may become involved in that system through participation as expert witnesses.
Dolinak, David, Evan W. Matshes, and Emma O. Lew. Forensic Pathology: Principles and Practice. Burlington, Mass.: Elsevier Academic Press, 2005. Reference volume covers all aspects of forensic pathology. Includes more than eighteen hundred color photographs.
Haines, Duane E. Fundamental Neuroscience. 2d ed. New York: Churchill Livingstone, 2002. Offers a thorough compendium of information about the structure and function of the human nervous system.
Kolb, Bryan, and Ian Q. Whishaw. An Introduction to Brain and Behavior. 2d ed. New York: Worth, 2005. Correlates brain structure and functions with the behaviors controlled or modified by the brain. Exquisitely written and highly detailed.
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Structure and Functions (Magill’s Medical Guide, Sixth Edition)
The nervous system serves as the major control system of the human body. It is responsible for the synchronization of body parts, the integration of physiologic activity, the interpretation of incoming stimuli, and all intellectual activity, including memory and abstract reasoning. The nervous system regulates these activities by communication between various nerve cells; by controlling the actions of skeletal, smooth, and cardiac muscle; and by stimulating the secretion of products from various glands of the body.
Anatomically, the nervous system is divided into the central nervous system, which is composed of the brain and the spinal cord, and the peripheral nervous system, which includes all nervous structures outside the central nervous system—primarily, nerve processes, sensory receptors, and a limited number of cells of the nervous system that are located in special structures known as ganglia. Ganglia are found at various locations throughout the body. They are the only locations of neurons outside the central nervous system. Information from incoming cells can be transmitted to the ganglion cells, which in turn can transmit that information to other locations.
Although the brain and the spinal cord contain several different types of cells that are morphologically unique, there is only one functional cell present, which by convention is always referred to as the neuron. The neuron is one of the few...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
Diseases of the nervous system can be arranged into several general categories: infections, congenital diseases, seizure disorders, circulatory diseases, traumatic injury, demyelinating diseases, degenerative diseases, mental diseases, and neoplasms.
Infections of the nervous system are described according to the tissues infected. If the meninges are infected, the disease is known as meningitis; if the brain tissue is infected, the disease is referred to as encephalitis. The development of abscesses in the nervous tissue can also occur. The conditions described can be caused by viruses, bacteria, protozoa, or other parasites.
In most cases, the organism that causes meningitis is spread via the bloodstream. It is also possible, however, for infections to be spread from an infected middle ear or paranasal sinus, a skull fracture, brain surgery, or a lumbar puncture. The infectious agent can usually be determined by analyzing the spinal fluid. Bacterial infections are treated with antibiotics, while viral infections receive only supportive treatment.
An abscess of nervous tissue is usually a complication resulting from an infection at some other anatomical site, particularly from middle-ear infections or sinus infections. Abscesses may also occur following penetrating injuries. The abscess can create pressure inside the skull, and, if left untreated, it may rupture and lead to death.
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
When the control system of the body experiences a malfunction, the effects are wide ranging. Since the nervous system has the responsibility of regulating so many diverse activities, nervous system injury or disease must be treated immediately if the patient is to survive. This problem is further complicated by the fact that the brain is a difficult organ to study, because of its location within the skull and because its cells are vital and can be studied only after they have died.
Disease or injury of the cells of the nervous system—especially the brain—creates problems that are unique to that organ for several reasons, including the facts that those cells cannot repair themselves and cannot divide. In addition, the cells of the brain are restricted to a limited area. The cells of the nervous system are unique in that they are so highly specialized that they are not capable of cell division. As a result, humans have the greatest number of neurons during early childhood. Any neural injury or disease that kills cells results in a decreased number of neurons. In addition, neurons are not very good at repairing themselves. Furthermore, the space in the skull is tightly packed with cells and cerebrospinal fluid. There is no room for the blood that might appear as the result of an injury or the fluid accumulation that might be caused by tissue infection or tumors. Any of these conditions will increase the pressure...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Afifi, Adel K., and Ronald A. Bergman. Functional Neuroanatomy: Text and Atlas. 2d ed. New York: Lange Medical Books/McGraw-Hill, 2005. Written by a physician and an anatomist, this book is designed to be an integrated neuroscience textbook and atlas covering the regions of the central nervous system. The peripheral nervous system, however, is not covered.
Barondes, Samuel H. Molecules and Mental Illness. New York: Scientific American, 1999. A well-written book that describes the chemistry and physiology of mental illness. Provides a good background for understanding the pathology of mental illness.
Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 3d ed. Philadelphia: Lippincott Williams & Wilkins, 2007. Undergraduate text that introduces the topics of neuroscience, neurobiology, neurodiseases, and physiological psychology.
Bloom, Floyd E., M. Flint Beal, and David J. Kupfer, eds. The Dana Guide to Brain Health. New York: Dana Press, 2006. An easy-to-understand health guide to the brain from neuroscience, neurology, and psychiatry perspectives. More than seventy psychiatric and neurological disorders, their diagnoses, and their treatments are covered.
McCance, Kathryn L., and Sue M. Huether. Pathophysiology: The Biologic Basis for Disease in Adults and Children. 6th ed. St. Louis, Mo.: Mosby/Elsevier,...
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Introduction (Psychology and Mental Health)
The functions of the human nervous system are in many ways analogous to that of a computer. The brain receives information in the form of stimuli from the senses open to the outside world. Within the brain are specific regions, analogous to programs, that interpret the stimuli and allow for a response. More specifically, such responses take the form of physiological or behavioral changes. Some of these stimuli result from activation of tissues or organs within the endocrine system, a network of glands that secrete hormones directly into the bloodstream for regulation of target organs.
The functional unit of the nervous system is the neuron, a cell that receives or sends information in the form of electrical impulses. The major component of the neuron is the cell body, the portion that contains the nucleus and most of the internal organelles. Two major forms of neurons are found within the nervous system: sensory neurons, which transmit the impulse toward the central nervous system (brain and spinal cord), and motor neurons, which receive impulses from the brain or spinal cord and transmit the impulse to muscles or other tissues.
Depending on the type of neuron, a variety of processes may emanate from the cell body. Axons transmit the impulse away from the cell body and toward the target cell or tissue. Dendrites receive the impulse from other neurons or other sources of stimuli. The actual nerve consists of bundles of...
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Central Nervous System (Psychology and Mental Health)
The central nervous system is composed of two principal structures: the brain and the spinal cord. The brain is one of the largest organs in the body, weighing on average about three pounds and consisting of one trillion neurons by early adulthood.
The brain is subdivided into four major functional areas. The cerebrum, the largest portion of the brain, regulates sensory and motor functions. The convolutions characteristic of the human brain represent the physical appearance of the cerebrum. The brain stem connects the brain with the spinal cord, carrying out both sensory and motor functions. The diencephalon consists of the thalamus, the relay center for sensory functions entering the cerebrum, and the hypothalamus, which controls much of the peripheral nervous system activity and regulates endocrine processes. The fourth portion of the brain is the cerebellum, the rear of the brain where voluntary muscle activity is controlled.
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Peripheral Nervous System (Psychology and Mental Health)
The peripheral nervous system consists of the sensory receptors, such as those that recognize touch or heat in the skin or visual stimuli in the retina of the eye, and the nerves that communicate the stimuli to the brain. The peripheral nervous system is often subdivided into two parts, according to function: the somatic portion, which recognizes stimuli in the external environment such as on the skin, and the autonomic portion, which recognizes changes in the internal environment, such as hormone or mineral concentrations in the bloodstream.
The somatic portion of the peripheral nervous system in humans consists of twelve pairs of nerves that originate in the brain and that transmit sensory input from the body. For example, nerve endings in the retina of the eye transmit images to the brain; sensory fibers in the face transmit impulses affecting the skin or teeth. An additional thirty-one pairs of nerves emerge from the spinal cord, subdivide into branches, and innervate various regions of the body.
The autonomic nervous system maintainshomeostasis, or constancy, within the body. For example, receptors measure heart rate, body temperature, and the activity of hormones within the bloodstream and tissues. Any abnormality or change results in a signal sent to the brain.
The most notable of the functions of the autonomic nervous system occur in the sympathetic and parasympathetic systems. The...
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Role of Neurotransmitters (Psychology and Mental Health)
Neurons communicate with one another through the release of neurotransmitters, chemical substances that transmit nerve impulses between nerve cells. Numerous types of neurotransmitters have been identified. Some of these transmitters act to excite neurons, while others inhibit neuronal activity. The particular type of transmitter is synthesized within the cell body of the neuron, travels along the axon, and is released into the space between neurons, known as the synapse.
Among the most prominent neurotransmitters involved in the excitation of neurons is acetylcholine. The same transmitter bridges the junctions between nerves and skeletal muscles as well as glandular tissues in the body. In the brain, acetylcholine bridges the synapses between neurons throughout the central nervous system. The amino acids glutamic acid and aspartic acid are also known to be involved in excitation of some neurons within the brain. The neurotransmitter serotonin is released mainly within the brain stem, where it appears to regulate activities such as sleep, moods, and body temperature.
Certain neurotransmitters serve in the inhibition of neuronal activity. The most common of these is gamma-aminobutyric acid (GABA), found primarily in the diencephalon region of the brain. Here GABA acts to reduce the activity within the region. Antianxiety drugs such as Valium or Librium appear to work by enhancing the activity of GABA,...
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Endorphins and the Placebo Effect (Psychology and Mental Health)
People who receive treatments with agents that possess no pharmacological activity for various illnesses or conditions have often been known to show improvement. Such a reaction is called the placebo effect. Whether the placebo effect is real has long been controversial. A 1955 study published in the prestigious Journal of the American Medical Association was the first significant report that the effect was real. More recent work has suggested the placebo effect may be sometimes more myth than reality. Nevertheless, there is evidence that such an effect may indeed occur and may be associated with forms of neurotransmitters called endorphins (endogenous morphines) and enkephalins. Endorphins and enkephalins represent a class of neurotransmitterlike chemicals called neuropeptides, small molecules that consist of between two and forty amino acids.
Enkephalins, discovered in 1975, block pain impulses within the central nervous system in ways similar to the drug morphine. The second class of molecules, subsequently called endorphins, was discovered soon afterward. They appear to act through suppression of pain impulses through suppression of a chemical called substance P. Substance P is released by neurons in the brain, the result of pain impulses from receptors in the peripheral nervous system. By inhibiting the release of substance P, these neuropeptides suppress sensory pain mechanisms. In support...
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Limbic System and Emotions (Psychology and Mental Health)
The limbic system is the label that applies to regions of the diencephalon such as the thalamus and hypothalamus that are associated with behaviors such as emotions, learning, and sexual behavior. Stimulation of various areas within the limbic system during surgery has resulted in the patient feeling a variety of conflicting emotions, such as happiness and pleasure or fear and depression, depending on the area being tested.
Some of these emotions or behaviors are associated with survival. For example, stimulation of certain areas results in feelings of rage or sexual excitement. Such patterns of behavior, accompanied by increased heart rate and blood pressure, have suggested that the limbic system plays a role in the fight-or-flight phenomenon.
Neurotransmitters such as serotonin and dopamine are believed to play roles in these behaviors. The effects of recreational drugs on behaviors and emotions may in part be due to the similarity of action between these drugs and neurotransmitters. For example, the high associated with amphetamine use or abuse may result from stimulation of these neurotransmitters. Cocaine blocks the movement of dopamine, resulting in the continual activation of neurons that use dopamine as a neurotransmitter. The addiction associated with cocaine results from alterations in the affected neurons, resulting in an increase in need for stimulation by these pathways.
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Sources for Further Study (Psychology and Mental Health)
Becker, J., S. Breedlove, and D. Crews. Behavioral Endocrinology. 2d ed. Cambridge, Mass.: MIT Press, 2002. Emphasis is on the role of the endocrine system and neurotransmitters on physiology of the nervous system, as well as effect on behaviors.
“The Brain.” Scientific American 241 (September, 1979). The issue was devoted entirely to the nervous system. Though new information has subsequently become available, the issue remains an excellent general source for the subject. Excellent photographs and diagrams are included in the articles.
Kolb, Bryan, and Ian Q. Whishaw. An Introduction to Brain and Behavior. 2d ed. New York: Worth, 2006. Textbook on the subject. In addition to thorough coverage of brain structure and function, the authors describe the role of neurophysiology and behavior.
Sherwood, Lauralee. Human Physiology: From Cells to Systems. 6th ed. Pacific Grove, Calif.: Brooks/Cole, 2009. Drawing on recent experimentation, the author provides extensive background material for those chapters that explain the function of the nervous system. The text includes comprehensive details, but tables and diagrams clarify the material and provide numerous examples.
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Nervous System (Encyclopedia of Science)
The nervous system is a collection of cells, tissues, and organs through which an organism receives information from its surroundings and then directs the organism as to how to respond to that information. As an example, imagine that a child accidentally touches a very hot piece of metal. The cells in the child's hand that detect heat send a message to the child's brain. The brain receives and analyzes that message and sends back a message to the child's hand. The message tells the muscles of the hand to pull itself away from the heat.
The basic unit of the nervous system is a neuron. A neuron is a nerve cell capable of passing messages from one end to the other. In the example above, the "hot" message was passed from one neuron to the next along a path that runs from the child's hand to its brain. The "move your hand" message then passed from one neuron to the next along another path running from the child's brain back to its hand.
Types of nervous systems
The complexity of nervous systems differs from organism to organism. In the simplest of organisms, the nervous system may consist of little more than a random collection of neurons. Such systems are known as a nerve net. An example of an animal with a nerve net is the hydra, a cylinder-shaped freshwater polyp. Hydra respond to stimuli such as heat, light, and touch, but their nerve net is...
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Nervous System (Encyclopedia of Psychology)
An electrochemical conducting network that transmits messages from the brain through the nerves to locations throughout the body.
The nervous system is responsible for the perception of external and internal conditions and the body's response to them. It has two major divisions: the central and peripheral nervous systems. The central nervous system (CNS), consisting of the brain and the spinal cord, is that part of the nervous system that is encased in bone; the brain is located in the cranial cavity of the skull, and the spinal cord in the spinal column, or backbone. Both are protected by cerebrospinal fluid and a series of three membranes called meninges. The CNS receives information from the skin and muscles and sends out motor commands as well.
The brain functions as the center of instinctive, emotional, and cognitive processes. It is composed of three primary divisions, the forebrain, midbrain, and hind-brain, and divided into the left and right hemispheres. The first division, the forebrain, is the largest and most complicated...
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