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Divisions of the Nervous System
Gaining a basis understanding the basic divisions of the nervous system can improve your understanding of neuromuscular disease. The nervous system can be divided into two broad categories – the central nervous system and the peripheral nervous system.
Central Nervous System: The central nervous system can be divided further into the brain and the spine. Diseases that primarily affect the central nervous system without having a primary effect on the peripheral nervous system are not considered to be neuromuscular diseases (but are neurological disease). These neurological diseases, such as stroke, cerebral palsy, and multiple sclerosis (MS), often have overlapping symptoms with neuromuscular diseases. For example, multiple sclerosis is a disease of the central nervous system, affecting the white matter in the brain and/or spinal cord. MS is not a neuromuscular disease, although its symptoms can overlap.
Peripheral Nervous System: The nerves that run from the spinal cord out to the body make up the peripheral nervous system. The nerves of the peripheral nervous system communicate information from the brain throughout a person’s body. The peripheral nervous system can be further divided into two parts, the somatic system and the autonomic system.
The somatic system carries messages to and from the spine and the skeletal muscles, including to the muscles, the junction between the nerves and the muscles, and the motor-nerve cells in the spinal cord. Various types of neuromuscular diseases affect the somatic nervous system. For example, Myasthenia gravis affects the muscles in the head through causing a problem in the transmission of nerve signals in the somatic system leading to the facial muscles. The somatic system also carries messages from the spine to and from the sensory organs (i.e., the eyes and ears). Some neuromuscular diseases affect sensory organs, as well. For example, Charcot Marie Tooth sometimes causes hearing loss.
The autonomic system relays information between the spine and the internal organs and glands throughout the body. The term autonomic means “self-governing.” The autonomic nervous system governs activities such as respiration, digestion, perspiration, and heart rate. Some forms of neuromuscular disease, such as Myotonic Muscular Dystrophy, affect the autonomic nervous system, as well as affecting the somatic nervous system.
The autonomic nervous system can be further broken down into the sympathetic system, which functions as the body’s “fight or flight” system, and the parasympathetic branch, which quiets the body after arousal and keeps various body systems functioning at moderate levels. The balance between these two systems determines whether a person feels tense or relaxed.
Neuromuscular diseases directly affect the peripheral nervous system. Diseases that do not directly affect the peripheral nervous system are not considered to be neuromuscular disease. Examples of neuromuscular disease include the Myophathies, Charcot Marie Tooth, Friedreich’s Ataxia, and Amytrophic Lateral Sclerosis. Part of the differential diagnosis of neuromuscular disease often includes determining which part of the peripheral nervous system is affected and how.
Some types of disease directly affect both the central and peripheral nervous systems. These diseases are considered to be neuromuscular diseases, as well. For example, some types of muscular dystrophy, such as Duchenne Muscular Dystrophy, affect the central nervous system, sometimes causing cognitive deficits, as well as affecting the peripheral nervous system, causing problems such as muscle weakness and deterioration.
Coon, D., and Mitterer, J. (2007). Introduction to Psychology: Gateways to the Mind and Behavior. Thompson Wadsworth: Belmont, CA.
Department of Neurology, University of Pittsburg (2012). What is Neuromuscular Disease? Retrieved on 7/31/15 from http://www.neurology.upmc.edu/neuromuscular/patient_info/what.html .
NIH.gov (2014.) What are the parts of the nervous system? Retrieve on 7/31/15 from http://www.nichd.nih.gov/health/topics/neuro/conditioninfo/Pages/parts.aspx .
Web MD website (2015). Understanding Muscular Dystrophy – the Basics. Retrieved 7/31/15 from http://www.webmd.com/parenting/understanding-muscular-dystrophy-basics .
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