EMG PSD Measures in Orthodontic Appliances

Abstract

The human body consists of different systems which include the nervous system, the cardiovascular system, the musculoskeletal system, etc. Each system performs some kind of vital task and carries on many physiological processes. For example, the primary functions of the musculoskeletal system can be summarized as generating forces, producing motion, moving substance within the body, providing stabilization, and generating heat. Physiological processes are multifaceted fact and most of them manifest themselves as signals that reflect their nature and activities. These types of signals may be hormonal, physical or electrical. The general name of the electrical signals taken from the related organ or physiologic process with invasive or non-invasive methods is called Biomedical Signals. This signal is normally a function of time and is definable in terms of its amplitude, frequency and phase (Rangayyan, 2002). The electromyography (EMG) signal is a biomedical signal that detects the electrical potential generated by muscle cells when these cells contract, and also when the cells are at rest. Three types of muscle tissue can be identified. One of them is the skeletal muscle, and the others are the smooth muscle and the cardiac muscle. The EMG is applied to the study of skeletal muscle (Reaz et al., 2006). Skeletal muscles are comprised by nearly parallel cells and the muscle fibers which constitute the contractile structural units. Muscle fibers are activated by the central nervous system through electrical signals transmitted by motoneurons. A single motoneuron together with the muscle fibers that it contacts is called a motor unit which is the smallest functional subdivision of the neuromuscular system (Moritani, et al. 2004) The central nervous system controls the activation of motor units to optimize the interaction between our body and the surrounding environment. When the motor units are activated by the central nervous system, they produce an action potential trains of the active motor units add together to generate the interference EMG signal. Surface and needle electrodes have been used to detect EMG of muscles. Surface electrodes have been widely used to investigate neuromuscular functions because of their several advantages, for example, it is noninvasive, easy to adhere to the skin and to detect the total activities of the muscle and it was called Surface EMG (SEMG). Bu the real advantage of this technique is that it is more beneficial in studies, in which simultaneous movement of many muscles is examined in vast muscle groups. On the other hand, surface electrodes have disadvantages as well. Due to the broad area for receiving signals on respective muscle