Published online by Cambridge University Press: 08 February 2010
Introduction
The five sensory systems, hearing, vision, tactile (somatosensory), smell and taste, provide conscious perceptions of physical stimuli from the environment. In addition to these five senses, temperature receptors in the skin and the mouth mediate the sensations of warmth and cool. These senses, together with motor systems, serve the purpose of communications between an organism and the environment. In fact, all input that the central nervous system (CNS) receives from the environment comes through sensory systems. Several disorders are directly associated with sensory systems. Some disorders are caused by various kinds of insults such as trauma and inflammation. Age-related changes are perhaps the most important cause of disorders of sensory systems. The symptoms of many of these disorders are caused by functional changes in the CNS induced by expression of neural plasticity.
The vestibular system that monitors head movements and proprioceptive systems that monitor motor activity may also be regarded as sensory systems, but many authors include these systems in their description of motor systems. The balance system and proprioception, together with vision and somesthesia, contribute to our perception of our body position. (The vestibular system, and disorders associated with it, is covered separately in Chapter 6.) Proprioceptive somatosensory systems, the receptors of which are found in muscles, tendons and joints, monitor the motor systems and other bodily functions. The role of the vestibular system in control of posture and walking is discussed in Chapter 5 where other forms of proprioception are also discussed.
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