Skeletal Muscle Physiology

Using electrodes on the bicep to record the motor unit recruitment during all four conditions: control, stretching, cardio, and aerobic stretching. As shown in figure 5, the control group and the stretching are similar in the amount of EMG amplitude (mV). However, when comparing stretching with both cardio and aerobic stretching there is an increase as the intensity of the warm-up. Moreover, aerobic stretching has the highest EMG amplitude, which shows that there is motor unit cycling. Motor cycling provides a more efficient performance on the bicep because more of the muscle is being used (Widmaier, et al.,

An increase in the strength of a muscle’s contraction is necessary to perform a task. Subsequently, the brain increases the number of simultaneously active motor units within the muscle by a process known as the motor unit recruitment. Physical muscle movement in humans involves movement of fibers which are hundreds of cylindrically shaped cells bound together by connective tissue. It is essential for individuals, mainly professionals who work to promote health, to understand the mechanisms in the body. Resting skeletal muscles in vivo exhibit a phenomenon known as tonus, a constant state of slight tension that serves to maintain the muscle by motor centers in the brain and spinal cord. However, muscle

* 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 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.

Next with a stimulation duration of 50us, the stimulus amplitude should be set to the maximal tolerable stimulus intensity. With stimulus frequency of 2Hz, observe and record the leg movement, increase it by 5Hz but should not exceed 50Hz. With the electrodes connected to the analogy output channel and ground of the DAQ board. With the corresponding LabVIEW program, the frequency and amplitude (voltage) of the stimulation supplied to the leg can be controlled. With this the “sweet spot” of the lowest amplitude and best frequency to cause evoked movement can be found and recorded. Now the stimulation frequency should be set to 10Hz and the duration of stimulation pulse to 5ms or less. The range if leg movement changes can be observed as amplitude changes. Electrical stimulation in increments of 0.01V should be delivered and the minimal voltage required to generate muscle twitch should be recorded. The pulse duration should then be increased by durations of 10ms and the minimum voltage should be recorded this should be repeated for a variety of pulse

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 lab chart was then stopped once the 5s contraction period had ended. Then the maximum force in Neutons (N) for that trial was calculated by the chart. The 5s MVC procedure was then repeated two more times and the MVC for each trial was calculated by the chart software and the highest MVC contraction and MVC for each trial was then identified and all the values were out into table 1.5. Then each participant 90% MVC was calculated by taking the 100% MVC and multiplying it by 0.9 which was then put into the second table, and the guideline of the participants 90% max was then put into the lab chart. The participant then prepared to hold their 90% MVC for 1 minute. With their knee already extended as far as they could without contracting with no slack in the line or chain the lab chart was started and the participant was instructed to kick out to achieve maximal force and tried to hold it for 1 minute to the best of their abilities and then relax when the minute has

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

While the impulse generated by a single motor unit is quite weak, the combination of several can be detected by surface electrodes (EMG) (Michell, 2011). This is coupled with the measurement of power (DYN). When all of the available motor units are recruited at maximum strength, the muscles will fatigue rather quickly. However, when only a few of the motor units are recruited, the muscles will take more time to fatigue as the motor units will use those that are in reserve whenever one reaches fatigue (MacIntosh, Gardiner & McComas, 2006).

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

The current tracing does not dip as much but gradually decreases as the muscle fatigues.

The skeletal muscle is under voluntary control and therefore gives room for essential activities like walking. The neuronal power and the movement form the primary function of the muscles. However, different groups categorize it regarding their functioning, location and their connection to various systems in the human body. These are the slow oxidative, fast oxidative and fast glycolytic (Tropomyosin, 2015). The reason for such grouping is because they are connected to the bones through the tendons and also makes up to a half of the total body mass. Skeletal muscles are thus the underlying type of ensuring active, conscious movement.

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)

Without the skeletal muscle in our body, we would be stick people; we would have no movement. Almost all of the movement in our body is a result of muscle contraction. Did you know that the skeletal muscle makes up 40% of someone’s body weight, and it forms more than 600 muscles. The muscles allow us to frown, laugh, smile and express many other emotions. But, the most important functions of the muscular system are movement, posture, joint stability and heat production. There are also three major different types of muscle in the body: skeletal, smooth, and cardiac. They all play an important role in maintaining homeostasis.

This is the “muscle – bone preparation” you will use for your muscle physiology experiments. Connect the femur to the femur clamp as shown in VI. Steps IV, V and VI can be done concurrently.