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Nervous System: Overview

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Knowledge of the nervous system in general and of the brain and human behaviour in particular are of paramount importance to those who are dedicated to a safe and healthy environment. Work conditions, and exposures that directly affect the operations of the brain, influence the mind and behaviour. To evaluate information, to make decisions and to react in a consistent and reasonable manner to perceptions of the world require that the nervous system functions properly and that behaviour not be damaged by dangerous conditions, such as accidents (e.g., a fall from a poorly designed ladder) or exposure to hazardous levels of neurotoxic chemicals.

Damage to the nervous system can cause changes in sensory input (loss of vision, hearing, smell, etc.), can hinder the capacity to control movement and body functions and/or can affect the brain’s capacity to treat or store information. In addition, altered nervous system functioning can cause behavioural or psychological disorders. Mood and personality changes are a common occurrence following physical or organic damage to the brain. As our knowledge develops, we are learning more about the way in which nervous system processes are modified. Neurotoxic substances can cross the brain’s natural barrier and directly interfere with its intricate workings. Although some substances have a particular affinity to certain areas of the nervous system, most neurotoxins have widespread effects, targeting cell processes involved in membrane transport, internal cellular chemical reactions, liberation of secretory substances, and so on.

Damage to the various components of the nervous system can occur in different ways:

  • direct physical injury from falling objects, collisions, blows or undue pressure on nerves
  • changes in the internal environment, such as insufficient oxygen due to asphyxiants and heat exposure
  • interference in the cellular processes through chemical action by substances, such as metals, organic solvents and pesticides

 

The insidious and multifaceted development of many nervous system disorders requires persons working in the field of occupational health to adopt different but complementary approaches to the study, understanding, prevention and treatment of the problem. Early alterations can be detected in groups of active, exposed workers using sensitive measures of impairment. Identification of initial dysfunction can lead to preventive actions. In the latter stages, a good clinical knowledge is required and differential diagnosis is essential to the adequate treatment and care of disabled workers.

Although chemical substances are mostly examined one by one, it should be remembered that in many workplaces mixtures of potentially neurotoxic chemicals are used, exposing workers to what can be called a “cocktail”. In processes such as printing, painting, cleaning, in poorly ventilated offices, in laboratories, pesticide application, microelectronics and many other sectors, workers are exposed to chemical mixtures. Although there may be information on each one of the substances separately, we have to consider the combined nocivity and possible additive or even synergistic effects on the nervous system. In some cases of multiple exposure, each particular chemical may be present in very small quantity, even below the detection level of exposure assessment techniques; however, when all are added together, the total concentration can be very high.

The reader should be aware of three major difficulties in reviewing facts about the nervous system within the scope of this Encyclopaedia.

First, the understanding of occupational diseases affecting the nervous system and behaviour has changed substantially as new approaches to viewing brain-behavioural relationships have developed. The main interest of characterization of gross morphological changes that occur due to mechanical trauma to the nervous system—particularly, but not exclusively to the brain—was followed by an interest in the absorption of neurotoxic agents by the nervous system; interest in the study of cellular mechanisms of nervous system pathology; and finally, the search for the molecular basis of these pathologic processes began to grow. These approaches coexist today and all contribute information for evaluating the working conditions affecting the brain, mind, and behaviour.

Second, the information generated by neuroscientists is staggering. The third edition of the book Principles of Neural Sciences edited by Kandel, Schwartz and Kessell which appeared in 1991—one of the most valuable reviews of the field—weighs 3.5 kg and is more than 1,000 pages long.

Third, it is very difficult to review knowledge about the functional organization of the nervous system as it applies to all niches of occupational health and safety. Until about 25 years ago, the theoretical views that gave support to those concerned health experts who specialize in the detection, monitoring, prevention, and the clinical treatment of a worker who has absorbed a neurotoxic agent sometimes did not overlap with theoretical views regarding workers’ brain trauma and the behavioural manifestations of minimal brain damage. Behavioural manifestations said to be the consequence of the disruption of specific chemical pathways in the brain were the exclusive territory of the neurotoxicologist; both structural tissue damage of specific regions of the brain, and distant neural structures linked to the area where the lesions occurred, were explanations invoked by neurologists. It is only in the past few years that converging views are appearing.

With this in mind, this chapter addresses issues important to the understanding of the nervous system and the effects of workplace conditions on its functioning. It begins with a description of the anatomy and physiology, followed by a section on neurotoxicity, which reviews exposure, outcomes and prevention.

Since the nervous system is central to the body’s well-being, many non-chemical hazards can likewise affect its normal functioning. Many of these are considered in different chapters dealing with these hazards. Traumatic head injuries are included in First Aid, heat stress is considered in the article “Effects of heat stress and work in the heat”, and decompression sickness is reviewed in the article “Gravitational stress”. Hand-arm vibration (“Hand-transmitted vibration”) and repetitive movement (“Chronic outcomes, musculoskeletal”) in the chapter Musculoskeletal System, which are risk factors for peripheral neuropathies, are likewise considered in these sections of the Encyclopaedia.

The chapter ends with a review of special issues and the outlook for future research avenues.

 

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Contents

Nervous System References

Amaducci, L, C Arfaioli, D Inzitari, and M Marchi. 1982. Multiple sclerosis among shoe and leather workers: An epidemiological survey in Florence. Acta Neurol Scand 65:94-103.

Anger, KW. 1990. Worksite neurobehavioral research: Result, sensitive methods, test batteries and the transition from laboratory data to human health. Neurotoxicology 11:629-720.

Anger, WK, MG Cassitto, Y Liang, R Amador, J Hooisma, DW Chrislip, D Mergler, M Keifer, and J Hörtnagel. 1993. Comparison of performance from three continents on the WHO-recommended neurobehavioral core test battery (NCTB). Environ Res 62:125-147.

Arlien-Søborg, P. 1992. Solvent Neurotoxicity. Boca Raton: CRC Press.
Armon, C, LT Kurland, JR Daube, and PC O’Brian. 1991. Epidemiologic correlates of sporadic amyotrophic lateral sclerosis. Neurology 41:1077-1084.

Axelson, O. 1996. Where do we go in occupational neuroepidemiology? Scand J Work Environ Health 22: 81-83.

Axelson, O, M Hane, and C Hogstedt. 1976. A case-referent study on neuropsychiatric disorders among workers exposed to solvents. Scand J Work Environ Health 2:14-20.

Bowler, R, D Mergler, S Rauch, R Harrison, and J Cone. 1991. Affective and personality disturbance among women former microelectronics workers. J Clin Psychiatry 47:41-52.

Brackbill, RM, N Maizlish, and T Fischbach. 1990. Risk of neuropsychiatric disability among painters in the United States. Scand J Work Environ Health 16:182-188.

Campbell, AMG, ER Williams, and D Barltrop. 1970. Motor neuron disease and exposure to lead. J Neurol Neurosurg Psychiatry 33:877-885.

Cherry, NM, FP Labrèche, and JC McDonald. 1992. Organic brain damage and occupational solvent exposure. Br J Ind Med 49:776-781.

Chio, A, A Tribolo, and D Schiffer. 1989. Motorneuron disease and glue exposure. Lancet 2:921.

Cooper, JR, FE Bloom, and RT Roth. 1986. The Biochemical Basis of Neuropharmacology. New York: Oxford Univ. Press.

Dehart, RL. 1992. Multiple chemical sensitivity—What is it? Multiple chemical sensitivities. Addendum to: Biologic markers in immunotoxicology. Washington, DC: National Academy Press.

Feldman, RG. 1990. Effects of toxins and physical agents on the nervous system. In Neurology in Clinical Practice, edited by WG Bradley, RB Daroff, GM Fenichel, and CD Marsden. Stoneham, Mass: Butterworth.

Feldman, RG and LD Quenzer. 1984. Fundamentals of Neuropsychopharmacology. Sunderland, Mass: Sinauer Associates.

Flodin, U, B Söderfeldt, H Noorlind-Brage, M Fredriksson, and O Axelson. 1988. Multiple sclerosis, solvents and pets: A case-referent study. Arch Neurol 45:620-623.

Fratiglioni L, A Ahlbom, M Viitanen and B Winblad. 1993. Risk factors for late-onset Alzheimer’s disease: a population-based case-control study. Ann Neurol 33:258-66.

Goldsmith, JR, Y Herishanu, JM Abarbanel, and Z Weinbaum. 1990. Clustering of Parkinson’s disease points to environmental etiology. Arch Environ Health 45:88-94.

Graves, AB, CM van Duijn, V Chandra, L Fratiglioni, A Heyman, AF Jorm, et al. 1991. Occupational exposure to solvents and lead as risk factors for Alzheimer’s disease: A collaborative re-analysis of case-control studies. Int J Epidemiol 20 Suppl. 2:58-61.

Grönning, M, G Albrektsen, G Kvåle, B Moen, JA Aarli, and H Nyland. 1993. Organic solvents and multiple sclerosis. Acta Neurol Scand 88:247-250.

Gunnarsson, L-G, L Bodin, B Söderfeldt, and O Axelson. 1992. A case-control study of motor neuron disease: Its relation to heritability and occupational exposures, particularly solvents. Br J Ind Med 49:791-798.

Hänninen, H and K Lindstrom. 1979. Neurobehavioral Test Battery of the Institute of Occupational Health. Helsinki: Institute of Occupational Health.

Hagberg, M, H Morgenstem, and M Kelsh. 1992. Impact of occupations and job tasks on the prevalence of carpal tunnel syndrome. Scand J Work Environ Health 18:337-345.

Hart, DE. 1988. Neuropsychological Toxicology: Identification and Assessment of Human Neurotoxic Syndromes. New York: Pergamon Press.

Hawkes, CH, JB Cavanagh, and AJ Fox. 1989. Motorneuron disease: A disorder secondary to solvent exposure? Lancet 1:73-76.

Howard, JK. 1979. A clinical survey of paraquat formulation workers. Br J Ind Med 36:220-223.

Hutchinson, LJ, RW Amsler, JA Lybarger, and W Chappell. 1992. Neurobehavioral Test Batteries for Use in Environmental Health Field Studies. Atlanta: Agency for Toxic Substances and Disease Registry (ATSDR).

Johnson, BL. 1987. Prevention of Neurotoxic Illness in Working Populations. Chichester: Wiley.

Kandel, ER, HH Schwartz, and TM Kessel. 1991. Principles of Neural Sciences. New York: Elsevier.

Kukull, WA, EB Larson, JD Bowen, WC McCormick, L Teri, ML Pfanschmidt, et al. 1995. Solvent exposure as a risk factor for Alzheimer’s disease: A case-control study. Am J Epidemiol 141:1059-1071.

Landtblom, A-M, U Flodin, M Karlsson, S Pålhagen, O Axelson, and B Söderfeldt. 1993. Multiple sclerosis and exposure to solvents, ionizing radiation and animals. Scand J Work Environ Health 19:399-404.

Landtblom, A-M, U Flodin, B Söderfeldt, C Wolfson and O Axelson. 1996. Organic solvents and multiple sclerosis: A synthesis of the cement evidence. Epidemiology 7: 429-433.

Maizlish, D and O Feo. 1994. Alteraciones neuropsicológicas en trabajadores expuestos a neurotóxicos. Salud de los Trabajadores 2:5-34.

Mergler, D. 1995. Behavioral neurophysiology: Quantitative measures of sensory toxicity. In Neurotoxicology: Approaches and Methods, edited by L Chang and W Slikker. New York: Academic Press.

O’Donoghue, JL. 1985. Neurotoxicity of Industrial and Commercial Chemicals. Vol. I & II. Boca Raton: CRC Press.

Sassine, MP, D Mergler, F Larribe, and S Bélanger. 1996. Détérioration de la santé mentale chez des travailleurs exposés au styrène. Rev epidmiol med soc santé publ 44:14-24.

Semchuk, KM, EJ Love, and RG Lee. 1992. Parkinson’s disease and exposure to agricultural work and pesticide chemicals. Neurology 42:1328-1335.

Seppäläinen, AMH. 1988. Neurophysiological approaches to the detection of early neurotoxicity in humans. Crit Rev Toxicol 14:245-297.

Sienko, DG, JD Davis, JA Taylor, and BR Brooks. 1990. Amyotrophic lateral sclerosis: A case-control study following detection of a cluster in a small Wisconsin community. Arch Neurol 47:38-41.

Simonsen, L, H Johnsen, SP Lund, E Matikainen, U Midtgård, and A Wennberg. 1994. Evaluation of neurotoxicity data: A methodological approach to classification of neurotoxic chemicals. Scand J Work Environ Health 20:1-12.

Sobel, E, Z Davanipour, R Sulkava, T Erkinjuntti, J Wikström, VW Henderson, et al. 1995. Occupations with exposure to electromagnetic fields: A possible risk factor for Alzheimer’s disease. Am J Epidemiol 142:515-524.

Spencer, PS and HH Schaumburg. 1980. Experimental and Clinical Neurotoxicology. Baltimore: Williams & Wilkins.

Tanner, CM. 1989. The role of environmental toxins in the etiology of Parkinson’s disease. Trends Neurosci 12:49-54.

Urie, RL. 1992. Personal protection from hazardous materials exposures. In Hazardous Materials Toxicology: Clinical Principles of Environmental Health, edited by JB Sullivan and GR Krieger. Baltimore: Williams & Wilkins.

World Health Organization (WHO). 1978. Principles and Methods of Evaluating the Toxicity of Chemicals, Part 1 and 2. EHC, No. 6, Part 1 and 2. Geneva: WHO.

World Health Organization and Nordic Council of Ministers. 1985. Chronic Effects of Organic Solvents On the Central Nervous System and Diagnostic Criteria. EHC, No. 5. Geneva: WHO.

Zayed, J, G Ducic, G Campanella, JC Panisset, P André, H Masson, et al. 1990. Facteurs environnementaux dans l’étiologie de la maladie de Parkinson. Can J Neurol Sci 17:286-291.