Motor Unit

Oxygen debt in the muscles is reached when oxygen levels are much lower than required during strenuous physical activity, causing lactate fermentation to occur in the cells leading to muscle fatigue. The results found in the experiment were the number of squeezes in the first trial for the dominant and non-dominant hands were significantly higher than the remaining ones. The results also showed as the trials continued, the number of muscle contractions decreased steadily which supported the hypothesis. However, there were some increased numbers for the dominant hand from trial 4 to 5 and trial 9 to 10. The non-dominant hand expressed similar unexpected results from trial 6 to 7 and trial 9 and 10. The reasons for these results might be due to the finger muscles being worked at the high intensity for a long period of time causing the muscles to consume higher amounts of oxygen thus producing more ATP production. This would cause the muscles to create more contractions towards the end of the trials. The unexpected results could also be caused by experimental errors such as faulty clothespins. The springs connecting the two ends of the clothespin was tight causing the number of contractions as the trials progressed having a more significant decrease. This is because the amount of energy required to open and close the clothespin would be higher, causing the lactate threshold to occur quicker. Due to this, the number of squeezes would decrease drastically as the trials progressed, in contrast to if the springs were normal. This would change the results by the difference between the trials not being evident therefore, not demonstrating the effects of muscle fatigue. Another factor that altered this experiment was the participant’s condition, Palmar Hyperhidrosis –excessive sweating on the palms – which

* Electromyogram- Measures electrical activity of muscles at rest and during contraction. These studies measure how well and fast the nerves can send electrical signals.

The more stimuli per second, the greater the force generated by the muscle due to a

The results in Figure 2. show that increasing the stimulus strength (V) from 0 to o.40V will result in an increase of Active Muscle force generated by the gastrocnemius muscle in the Buffo Marinus, confirming the hypothesis. The force generated plateaus when the stimulus is beyond o.40V.

Introduction: According to the “Human Physiology Laboratory Manual “,BIOL 282 ,page 31 , the reason of performing this experiment is to learn how the muscle contraction occurs based on the molecular level and what kind of factors are involved .As a matter of fact, skeletal muscles contain a lot of nuclei because of the cell fusion while being developed and are made of cylindrical cells that have myofibrils. The myofibrils contain sarcomeres and the

The contraction of the extent which the The direction which the bone of the joint move depends on the contraction of the muscle.

The power stroke is responsible for the contraction of the muscle and force generation. ATP binding to the myosin head detaches the myosin head from the actin filament and allows the cycle to repeat. The coordinated contraction and relaxation of many muscles in an antagonistic fashion is the basis for the kinematics of any movement.

EMG biofeedback: Can be utilized to receive information related to motor performance, kinesthetic performance or physiological response

The EMG signal that is observed through the placement of electrodes on the skin is closely coupled with the generation of muscle force. In normal conditions, the force-EMG relationship is either linear or the increase in EMG at low force levels is less than proportional (Semmler 2014). However, a different force-EMG relationship was observed following eccentric exercise,

Review Sheet Results 1. Describe how increasing the stimulus frequency affected the force developed by the isolated whole skeletal muscle in this activity. How well did the results compare with your prediction? Your answer: When the stimulus frequency was at the lowest the force was at its lowest level out of all of the experiments. As the stimulus frequency was increased to 130, s/s the force increased slightly but fused tetanus developed at the higher frequency. When the stimulus frequency was increased to the amounts of 146-150 s/s, the force reached a plateau and maximal tetanic tension occurred, where no further increases in force occur from additional stimulus frequency. 2. Indicate what type of force was developed by the isolated skeletal muscle in this activity at the following stimulus frequencies: at 50 stimuli/sec, at 140 stimuli/sec, and above 146 stimuli/sec. Your answer: At 50- Unfused

1. As you increase voltage to the muscle describe how it responds to the increased stimulus.

Another way that the nervous system can be perceived, is through motor unit recruitment. The measurement of how much motor unit recruitment that there is, it will then determine the contraction of a muscle. When a motor recruitment has less of a recruitment it will then cause a for a frailer muscle contraction. However, it is the same way if a motor recruitment has a bigger recruitment then it will have a better contraction a muscle, which is the third hypothesis. An example of motor unit recruitment is the heart, the muscle that is on the heart is the cardiac muscle, and it will have higher motor unit recruitment so that blood can circulate throughout the body.

EMG machines measure the contractions in forms of waves and then display them on a screen. The size and shape of the waves measured the electromyogram is the determining factor in a patient’s overall diagnosis. In some cases, an audio amplifier may be attached to the equipment as well; this may cause loud crackling noises during muscle

3. How can you explain the increase in force that you observe? the increase is how many volts went into the muscle.

Post-lab Quiz Results You scored 50% by answering 2 out of 4 questions correctly. 1. Which of the following is not one of the ways that the body can increase the force produced by a skeletal muscle? Your answer: b. application of high-frequency stimulation by a motor neuron Correct answer: d. application of higher voltages to the whole muscle 2. When a muscle receives a stimulus frequency that causes non-overlapping twitches to follow each other closely in time such that the peak tension of each twitch rises in a stepwise fashion up to a plateau value, the result is known as You correctly answered: c. treppe. 3. In this experiment the isolated skeletal muscle was repetitively stimulated such that individual twitches overlapped with each other and resulted in a stronger muscle contraction than a standalone twitch. This phenomenon is known as You correctly answered: c. wave summation. 4. Wave summation is achieved by Your answer: c. summating action potentials so that their depolarizing magnitude is greater. Correct answer: a. increasing the rate of stimulus delivery (frequency)