Nt1310 Unit 2 Lab Report

• Once your muscles have been studied at rest, your health care provider will ask you to contract or flex your muscles. The electrodes will send a signal that tells the electrical activity of your muscles.

The objective of this experiment was to record electromyograms of the Achilles tendon and use this information to determine the time between when the tendon stretches and when the motor impulse will arrive at the muscle. Using this information, the conduction velocities and times will be calculated and compared with different stimulus strengths.

An electrode is the sensor, which can recognize the voltage or electricity produced from the contraction of a muscle. Electromyography signals are measured in microvolts.1 The stronger a contraction is, the higher the voltage amplitude reaches. This voltage recognition information is then sent, either through wires or wirelessly, depending on the chosen type of electrode, to the microprocessor,which is a powerful microcomputer. The microprocessor has full computing capability, this allows for the integration of data quickly and commands are formed based on the incoming EMG signals. The microprocessor organizes the data received from the electrodes by origin of signal, meaning which electrode the signal came from, using an algorithm that is pre-programmed into the computer.17 The microprocessor also contains filter methods, programmed into the computer to enable the microprocessor to use only the desired signals. The signals must make it through these filters in order to be integrated and understood. Commonly, the filters screen any signals too low or high in amplitude, ensuring the movement is not inadvertent or too exaggerated, respectively.18 The algorithm, a mathematical matrices equation programmed into the microprocessor, allows for the integration of the incoming data and enables the microprocessor to translate received data into a command that

This is an exercise designed to demonstrate some properties of skeletal muscle using the gastrocnemius muscle of a frog. A muscle organ, such as the gastrocnemius muscle, is composed of many individual muscle fibers. A twitch is a muscle contraction the occurs in response to a single, rapid stimulus that evokes a single, isolated action potential in a muscle fiber. The contraction of a muscle fiber in response to a single action potential is likewise an all or none response. There is a minimum stimulus strength that must be applied to the muscle fiber in order to reach threshold, evoke the action potential and, in turn induce the contraction. The threshold is that intensity (voltage) of stimulus which brings response. The experiment will note

The maximum twitch tensions recorded for increasing stimulus voltages starting at V_(threshold) and ending at V_maximum (Figure 1.1). Threshold voltage is the lowest voltage that produced an observable twitch that was recorded at .2375V. As stimulus intensity increased, so did twitch tension until this contractile activity plateaued. The lowest stimulus voltage to produce the first twitch to plateau was recorded as .275V. As seen in Fig 1.1, there was a 26-fold increase in tension from the threshold value to the maximum as stimulus intensity increased. To take into account possible sources of error, changes in baseline tension were recorded at certain stimulus voltages (Fig 1.2). As stimulus intensity increases, baseline tension decreases from the starting baseline tension, giving a loss of

Nerve and muscle twitch recruitment: External electrode stimulation of a nerve or muscle can lead to a twitch so long as the stimulus voltage is above the muscle or nerve’s threshold value. Electrical stimulation works to open ion channels without the muscle cells, leading to the firing of action potentials. After some time, however, a maximal stimulus voltage will be found. Voltages above this lead to no significant increase in the amplitude of the twitch. Our expectation was that twitch amplitude would increase steadily starting at threshold stimulus and level off at the maximal stimulus. These expectations were based on the results we obtained in previous labs as well as a basic understanding of action potentials, and they were met in this

However, current research is looking into the myoelectric prosthesis, which takes electric (and chemical) signals from the patient’s original muscles on their residual limb and then has those signals control the movement of the artificial limb. In 2013, the researchers at the Rehabilitation Institute of Chicago developed a leg that takes those neural impulses from the patient’s thigh muscles into movement. With the research that is currently being done, soon it will be commonplace for users to control their bionic devices with solely their mind. (114

Skeletal muscle contraction and relaxation is vital for voluntary body movements to occur. Skeletal muscles contract when myofibrils composed of actin and myosin slide past each other, which contracts the muscle by altering its length. The gastrocnemius muscle in Rana pipiens, which is attached to the sciatic nerve, can be stimulated to find threshold and maximal stimulus voltage. Once threshold is reached, contraction amplitude increases with stimulus voltage until the maximal voltage is reached, at which point it levels off. Altering the interstimulus interval can induce twitch summation in the gastrocnemius, leading to one combined contraction with a high amplitude. Increased stimulus frequency can be used to induce a tetanic

This experiment used a surface Electromyography (EMG) which is a non- invasive technique to confirm electrical signals produced by muscles and the nerve cells that control them. Furthermore, this experiment shows a visual confirmation of the neuromuscular relationship as well as showing the dependent relationship between body systems. If this experiment shows the difference in voltage produced by skeletal muscle contractions with that then a maximal grip versus a submaximal might show difference in force and relaxation.

These results indicate that there was more electrical activity in the muscle, as more motor units were required to produce a greater amount of force and resist the weight placed on the arm. As the weight increased, a greater amount of force was needed.

For the twitch recruitment, I believe that while a muscle will be more likely to flex when it is provided with electricity, the muscle will not keep flexing at a continuous rate, even if the electricity

In the Myoelectric hand prosthetic like the Bebionic3 by RSL Steeper the EMG activity is captured through the use of electrode pads placed over the muscle bulk of the existing musculature in the residual limb.7 Typically there are two electrodes used with one placed over the flexor muscle bulk and the other placed over the extensor muscle bulk. The muscle contraction itself is not the only thing used to control the various movements of the Bebionic3. Contraction intensity, pattern of contractions in a series, object held, and pre-positioning of the manually placed thumb in either opposition or non-opposition are all variables used by the prosthetic to create the desired and appropriate movement pattern for the user.8,9

The relationship between stimulus voltage and muscle response is demonstrated in Figure 1a and 1b. Force of contraction is used to measure the muscle response due to stimulation. In figure 1b, the mean maximum muscle response is calculated by averaging the maximum amplitudes in grams from the 3 single stimuli, then converting force of contraction from gram to Newton using F=ma, where a=9.8m/s2. Above figures show that as the voltage of the stimulus increases, the strength of the twitch increases. The threshold voltage required to produce a twitch response is 0.4 V. The minimum voltage required to give a maximal response is 5 V. There is an increase in muscle response from 0.4 V to 5V. Increasing voltage of the stimuli beyond 5 V does not further increase the twitch response significantly.

Possible changes Potential differences are recorded from a small volume of the muscles in the immediate neighbuorhood of the tip of the needle tip . Thus, it is has been observed that most of the electrical activity is from the active fibers near the electrodes. Sometimes, surface electrodes is are used in stead of coaxial deep muscle electrodesdeep muscle coaxial electrode. In this recording method, two surface electrodes are placed on the skin overlying the muscle, which is to be studied, over the to be studied muscle’s at a reasonable distance.

Isometric contraction tests were conducted on a knee extension equipment (HUR Oy, Kokkola, Finland). All the tests were performed in a seated position where the knee angle was fixed at 120°, and there was a force transducer attached to the lever arm at ankle. The force data were displayed real-time on a computer screen so the participants had feedbacks on their force exertion. Each participant performed maximum voluntary contraction (MVC) tests 3 times. Whereafter, 25% MVC tests were performed 5 times in each participant. A one-minute break was guaranteed between each trial to avoid muscle fatigue. The tests were executed twice: the ones measured by textile electrodes, and the ones with traditional Ag/AgCl electrodes, which were placed exactly at the same area as the textile electrodes.