In order to understand how MATLAB interfaces with other programs, such as a music player, tutorials MATLAB were watched. Basic functions and applications of MATLAB were practiced during this week. General ideas about how the placement of electrodes on the face and how the electrodes will communicate with MATLAB through a data-aquisition system were discussed. Ideas of which muscle contractions would control the music player were also discussed, such as a forceful blink of the right eye will skip the song ahead and a forceful blink of both eyes will play or pause the song.
The instrumentation amplifier will not be available for another few weeks, therefore the preliminary testing of the electrodes will be delayed.
Research was done to find a suitable music player. A MATLAB generated graphical user interface (GUI) will be used to control Windows Media Player. This program will then be operated by the EMG signals, rather than with the GUI.
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| MATLAB generated GUI |
Research was also done to find what causes the electrical conduction in muscles. Neurons are cells that control all body functions, and motor neurons specifically control muscle movement. Motor neurons consist of the main cell body, dendrites that receives nerve impulses from other neurons, the axon, and the axon terminal that sends nerve impulses to other neurons. Nerve impulses are sent between neurons to tell the muscles when to contract. [11]
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| Motor Neuron [11] |
Action potential allows the cell to have a nerve impulse and is caused by the rapid change in charge of the axon of the cell. At its resting potential, the axon has more positive ions inside the membrane than outside the membrane, causing the axon to have a net negative charge. This change occurs because there are more Na+ ions outside than inside the membrane and more K+ ions inside than outside the membrane. The action potential begins when the Na+ ions flow into the membrane and causes depolarization. Depolarization is when the membrane to loses its negative charge to now have a positive charge. To repolarize the membrane, the K+ ions flow out of the membrane and the membrane regains its negative charge. The wave of the change in charge caused by the depolarization and repolarization travels down the axon and this change in charge is the change in voltage that is detected by the electrodes. More information about this can be found
here. [11]
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| The depolarization and repolarization of a neuron [11] |
The orbicularis oculi are muscles that are located around the eyes and cause the eyelids to close. The palpebral part is in the eyelids, and closes over the eyes. The orbital part is around the eye and contracts when the eye closes. The orbital part of the orbicular is oculi is more accessible and less obtrusive to the user, therefore this will be the muscle that the electrodes will be placed over. The electrodes will detect the voltage changes in the orbital orbicularis oculi when the user forcefully blinks. The voltage changes are caused by the neuron impulses in the muscle cells to tell the muscle to contract. These voltage changes will be interpreted by MATLAB so the music player can be controlled by the forceful blinks. [11]
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| The Orbicularis Oculi muscle [9] |
The EMG signals of the orbicularis oculi muscles are shown in the picture below. The signals vary in amplitude between +/- 0.5 mV. The peaks in the graph are when the neurotransmitter signals the receiving cells and tell the muscle to contract. The rising part of the peaks are caused by the depolarization of the axon and the downward part of the peaks are caused by the repolarization of the axon. The neuron impulses which tell the muscle to contract when blinking or squinting cause the continuous bioelectrical signals. [10]
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| Change in EMG Volts over time [10] |
