MOTOR UNIT
EMG begins with the body. To understand EMG signal acquisition and generation, it is first necessary to understand the basics of how the body generates signals, starting with the Motor Unit. The Motor Unit (MU) is the smallest functional unit that can be used in the understanding of the neural control necessary when a muscle contracts. The motor system within a human body must be equipped to cope with a diverse array of both internal and external demands and constraints including, but not limited to: regulation of force output, upright posture, locomotion, and smaller gestures or facial expressions. Delineating the complex specific control features that make up this array of motor systems, the focus in EMG understanding is placed
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This highlights the control of force and movements in humans, paralleling the use of EMG and specifying the details of only the most simple and applicable concepts behind the central motor system and motor unit. A hierarchy dictates the organization of the central nervous system with motor programming at the top (premotor cortex, supplementary motor area, and various other locations in the cortex), the outputs of which along with outputs primarily from the cerebellum converging in the primary cortex where they either excite or inhibit the various neurons located in the primary cortex, the outputs of which influence the interneurons and motoneurons of the brain stem and spinal cord, linked through the corticospinal tract and alpha-motoneurons of the spinal cord to have direct control of muscle activity. The motor unit[Figure Motor Unit] consists of the dendrites – or short branch-like extensions of nerve cells along which impulses are received from other cells at synapses (junctions between two nerve cells- gap that impulses pass by diffusion of a neurotransmitter) are transmitted to the cell body – that make up the alpha-motoneuron, the branches of its axon, and the muscle fibers it innervates (supplies with nerves). The alpha-neuron is at the bottom of the hierarchy, acting as the endpoint for all descending and …show more content…
In ionic equilibrium, a resting potential exists with the inside of the muscle cell approximately 70mV less than the outside. When an alpha-motoneuron is activated, it can result in the conduction of the excitation that acts along the nerve. Once the transmitter is released at the motor endplates, a potential is formed at muscle fiber that was innervated by the motor unit, the diffusion characteristics of which change as positively charge sodium ions flow in, causing a depolarization. The depolarization zone then moves along the muscle fiber and passes the electrode side [Figure signal A]. If the influx of positively charged sodium ions exceed a certain threshold, the depolarization causes an action potential, the outside becoming approximately 30mV greater than the inside. The depolarization is immediately restored by an exchange of ions resulting in repolarization. It’s followed by phase called the ‘after hyperpolarization’ period of the membrane. During this phase, the action potential spreads from the motor endplates, along the muscle fiber, and inside the muscle fiber. The excitation causes calcium ions to be released and the contractile elements of the muscle cell become shortened. This process describes the mechanisms that follow the contraction of a healthy muscle
In the beginning phases of muscle contraction, a “cocked” motor neuron in the spinal cord is activated to form a neuromuscular junction with each muscle fiber when it begins branching out to each cell. An action potential is passed down the nerve, releasing calcium, which simultaneously stimulates the release of acetylcholine onto the sarcolemma. As long as calcium and ATP are present, the contraction will continue. Acetylcholine then initiates the resting potential’s change under the motor end plate, stimulates the action potential, and passes along both directions on the surface of the muscle fiber. Sodium ions rush into the cell through the open channels to depolarize the sarcolemma. The depolarization spreads. The potassium channels open while the sodium channels close off, which repolarizes the entire cell. The action potential is dispersed throughout the cell through the transverse tubule, causing the sarcoplasmic reticulum to release
In order for a body to move, a muscle has to be activated by an electrical impulse. The electrical impulse sends a message to the parietal lobe, frontal lobe, and cerebellum. The message then works its way through the spinal cord next to nerve pathways to the muscles which activate movement. Kinesthetic arts to stimulate motor activity. Motor activity is followed by swift thought processes that set goals, predict outcomes, analyze variables and complete movements.
The production of physical movement in humans requires a close interaction between the central nervous system (CNS) and the skeletal muscles. Understanding the interaction behind the mechanisms of these two forces, and how they are activated to provide the smooth coordinated movements (such as walking or picking up a pencil) of everyday life is essential to the study of motor control. Skeletal muscles require the activation of compartmental motor units that generate their own action potentials, and produce a voltage force within the muscle fibers that can be detected and recorded with the use of a electromyography (EMG). Therefore, the purpose of this lab was to determine the differences between the timing of force production
When a muscle contracts and relaxes without receiving signals from nerves it is known as myogenic. In the human body, the cardiac muscle is myogenic as this configuration of contractions controls the heartbeat. Within the wall of the right atrium is the sino-atrial node (SAN), which is where the process of the heartbeat begins. It directs consistent waves of electrical activity to the atrial walls, instigating the right and the left atria to contract at the same time. During this stage, the non conducting collagen tissue within the heart prevents the waves of electrical activity from being passed directly from the atria to the ventricles because if this were to happen, it would cause a backflow. Due to this barrier, The waves of electrical energy are directed from the SAN to the atrioventricular node (AVN) which is responsible for transferring the energy to the purkyne fibres in the right and left ventricle walls. Following this, there is a pause before the wave is passed on in order to assure the atria has emptied. After this delay, the walls of the right and left ventricles contract
The pump exchanges three sodium molecules for two potassium molecules. In doing so an electrical gradient is formed across the basolateral membrane of the cell due to the imbalance of charge generated. The interior of the cell is negative by about 80mV in relation to the outside...
For muscles to contract then there must be a presence of calcium within the fibers as it connects with troponin protein and orders tropomyosin to clear the binding sites to allow myosin to attach to these sites, which allows the muscle to contract and produces movement. Without all of these elements working in sync then the function of skeletal muscle would no longer work or even exist.
...ter screen an arm that was placed onto his stump. When Ture Johanson saw his arm on the computer screen, he was able to control his own movements using his own neural command. In this particular study, Johanson was asked to perform numerous movements with his phantom hands such as driving a racecar. By driving a racecar, Catalan found that the subject moved muscles at the end of his existing arm to show the intent of moving his missing hand. From this study, subjects who had been experiencing PLP for several years had longer periods without pain and had shorter periods of intense pain. In addition, the phantom hand was relaxed from a tight fist to a half-open position. This study is different from others because the control signals are retrieved from the arm stump, and thus the affected arm is in charge. Moreover, it uses the signals from the damaged limbs itself.
Let’s say that there is a mechanical sense. If someone touched your hand, your somatosensory system will detect various stimuli by your skin’s sensory receptors. The sensory information is then conveyed to the central nervous system by afferent neurons. The neuron’s dendrites will pass that information to the cell body, and on to its axon. From there it is passed onto the spinal cord or the brainstem. The neuron's ascending axons will cross to the opposite side either in the spinal cord or in the brainstem. The axons then terminates in the thalamus, and on into the Brodmann Area of the parietal lobe of the brain to process.
The occurrence of action potential is a very short process. When action potential occurs in the neuron the sodium channels open along the axon and sodium comes in. Because the sodium is positive it make the inside of the axon positive. When both the inside and outside are comparative in charge the sodium storms rushing in and starts the depolarization of the action potential. After this happens the sodium channels begin to close and the potassium channels begin to ...
When a message comes to the brain from body parts such as the hand, the brain dictates the body on how to respond such as instructing muscles in the hand to pull away from a hot stove. The nerves in one’s skin send a message of pain to the brain. In response, the brain sends a message back dictating the muscles in one’s hand to pull away from the source of pain. Sensory neurons are nerve cells that carry signals from outside of the body to the central nervous system. Neurons form nerve fibers that transmit impulses throughout the body. Neurons consists of three basic parts: the cell body, axon, and dendrites. The axon carries the nerve impulse along the cell. Sensory and motor neurons are insulated by a layer of myelin sheath, the myelin helps
Manto, M., Bower, J.M., Conforto, A.B., Delgado-Garcia, J.M., da Guarda, S.N., Gerwig, M., Habas, C., Hagura N., Ivry, R.B., Mariën, P., Molinari, M., Nairo, E., Nowak D.A., Oulad, B.T., Pelisson, D, Tesche, C.D., Tilikete, C., & Timman, D. (2012). Consensus Paper: Roles of the Cerebellum in Motor Control – The Diversity of Ideas on Cerebellar Involvement in Movement. Cerebellum, 11, 457-487.
Action potentials are started at one end of the node, flow passively through the myelinated axon, and pop out the other side to jump to the next node. This jumping of action potentials is called saltatory.
Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the sliding filament model of muscle contraction. Actin and myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped heads that project toward the actin filaments.
Synaptic transmission is the process of the communication of neurons. Communication between neurons and communication between neuron and muscle occurs at specialized junction called synapses. The most common type of synapse is the chemical synapse. Synaptic transmission begins when the nerve impulse or action potential reaches the presynaptic axon terminal. The action potential causes depolarization of the presynaptic membrane and it will initiates the sequence of events leading to release the neurotransmitter and then, the neurotransmitter attach to the receptor at the postsynaptic membrane and it will lead to the activate of the postsynaptic membrane and continue to send the impulse to other neuron or sending the signal to the muscle for contraction (Breedlove, Watson, & Rosenzweig, 2012; Barnes, 2013). Synaptic vesicles exist in different type, either tethered to the cytoskeleton in a reserve pool, or free in the cytoplasm (Purves, et al., 2001). Some of the free vesicles make their way to the plasma membrane and dock, as a series of priming reactions prepares the vesicular ...
The contraction of a muscle is a complex process, requiring several molecules including ATP and Cl-, and certain regulatory mechanisms [1]. Myosin is motor protein that converts chemical bond energy from ATP into mechanical energy of motion [1]. Muscle contraction is also regulated by the amount of action potentials that the muscle receives [2]. A greater number of actions potentials are required to elicit more muscles fibers to contract thus increasing the contraction strength [2]. Studied indicate that the larger motor units, which were recruited at higher threshold forces, tended to have shorter contraction times than the smaller units [3]. The aims of the experiment were to reinforce the concept that many chemicals are required for skeletal muscle contraction to occur by using the rabbit muscle (Lepus curpaeums) [2]. In addition, the experiment was an opportunity to measure the strength of contraction and to observe the number of motor units that need to be recruited to maintain a constant force as the muscles begin to fatigue [2]. Hypothetically, the rabbit muscle fiber should contract most with ATP and salt solution; and the amount of motor units involved would increase with a decreasing level of force applied until fatigue stage is reached.