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What are the divisions of the nervous system?
Understanding the divisions of the nervous system can help one to improve 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 of the central nervous system, such as stroke, cerebral palsy, or multiple sclerosis can cause symptoms that overlap with the symptoms of various neuromuscular diseases. These are not considered to be neuromuscular disease, however, as they do not directly affect the peripheral nervous system. For example, although cerebral palsy (CP) can affect one’s ability to use voluntary muscles, this disease directly affects the central nervous system (rather than the peripheral nervous system), so CP is not considered to be a neuromuscular disease.
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 often affects the muscles in the head, 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.
Some types of disease affect both the central and peripheral nervous systems. These diseases are considered to be neuromuscular disease. 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, (2010). What is Neuromuscular Disease? http://www.neurology.upmc.edu/neuromuscular/patient_info/what.html . Retrieved 1/5/11.
Web MD website (2009). Understanding Muscular Dystrophy – the Basics. http://www.webmd.com/parenting/understanding-muscular-dystrophy-basics . Retrieved 2/9/11.
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