Skeletal Muscle Physiology Lab Report

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

2. Discuss the biological processes that explain why peak contractile force changes with different stimulus strengths.

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.,

According to the results, the time of prior exercise and the average number of cycles after the exercise were inversely proportional. The time of prior exercise assumed to be approximately proportional to the amount of exercise. Also, the number of cycles presumed to be inversely proportional to muscle fatigue. This is because greater muscle fatigue would prevent faster rate of muscle contraction, this would result in performing a lower number of cycles during a given period. Hence, based on the graph, it was inferred that the amount of previous exercise and muscle fatigue would have a positive linear relationship. This implies that as the amount of previous exercise increased the macule fatigue increased accordingly.

During an eccentric contraction, the muscle lengthens under tension due to an opposing force that is greater than the force being produced by the muscle (Lindstedt et al. 2001). Eccentric contractions require little metabolic energy, however they are characterized by a high production of force (Semmler 2014). Fick observed that a lengthening muscle contraction could exert more force than a shortening muscle contraction, while Hill later observed that the body has a lower energy demand when contracting eccentrically compared to concentrically (Lindstedt et al. 2001). When the force applied is larger than the force that is created, work is done on the lengthened muscle and mechanical energy is absorbed – this is called “negative work” (Lindstedt et al. 2001). This absorbed energy can either be dissipated as heat, or it can be temporarily stored as elastic recoil potential energy for later use (Lindstedt et al. 2001).

A twitch is a contraction caused by one action potential. HYPOTHESIS!!!!!!!!!!!!!!!! In experiment 2, we measured muscular twitch in the thumb by using a finger pulse transducer and attaching a stimulus electrode to send shock through the ulnar nerve in the wrist. In experiment 3, we observed summation and tetanus by opening a new chart window, and placing the bar stimulus on the left wrist to send impulses to. In experiment 4, we measured the electrical activity of the median nerve stimulation by using the Bio Amp and the bar stimulus to stimulate the median nerve in the wrist and elbow.

This activity is the critical driving force of muscle contraction. The stream of action potentials along the muscle fiber surface is terminated as Acetylcholine at the neuromuscular junction is broken down by acetyl cholinesterase. The release of Calcium ions is ceased. The action of the myosin molecule heads is obstructed because of the change in the configuration of troponin and tropomyosin due to the absence of calcium ions. This will eventually cause the contraction to be ceased. Together with these physical processes, an external stretching force such as gravity pulls the muscle back to its normal length.

Exercise 2: Skeletal Muscle Physiology: Activity 4: Tetanus in Isolated Skeletal Muscle Lab Report Pre-lab Quiz Results You scored 100% by answering 3 out of 3 questions correctly. 1. Stimulus frequency refers to You correctly answered: b. the rate that stimulating voltage pulses are applied to an isolated whole skeletal muscle. 2. Which of the following distinguishes a state of unfused tetanus from a state of complete (fused) tetanus? You correctly answered: d. Muscle tension increases and decreases during a state of unfused tetanus. 3. When the stimulus frequency reaches a value beyond which no further increases in force are generated by the muscle, the muscle has reached its You correctly answered: a. maximal tetanic tension.

Their standing reach is determined by reading the Vertec’s set height and then adding the vanes – red vanes are every six inches, white vanes are every half inch, and blue vanes are every inch. Next you determine the subjects jump height giving them one preparation squat

Exercise 2: Skeletal Muscle Physiology: Activity 3: The Effect of Stimulus Frequency on Skeletal Muscle Contraction Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. During a single twitch of a skeletal muscle You correctly answered: b. maximal force is never achieved. 2. When a skeletal muscle is repetitively stimulated, twitches can overlap each other and result in a stronger muscle contraction than a stand-alone twitch. This phenomenon is known as You correctly answered: c. wave summation. 3. Wave summation is achieved by You correctly answered: a. increasing the stimulus frequency (the rate of stimulus delivery to the muscle). 4. Wave summation increases the force produced in the muscle.

A 2.99 kg textbook was placed in the subjects’ flat hand and held at shoulder height until instructed to extend their arm in the vertical

| |Contraction amplitude |Contraction amplitude with the |Effect of nerve stimulation on the contraction amplitude |

Activity 1: Investigating the Refractory Period of Cardiac Muscle Results: Briefly describe what happened when you applied the electrical stimuli to the heart. (1 mark) RESULTS: Applying single shocks in succession or multiple stimuli to deliver shocks at 20 stimuli/sec led to the formation of successive double peaks with a period of pause between them. This doublet is the normal systole closely followed by the extrasystole resulting from external stimulation, and then compensatory pause so the heart may resume normal beating afterwards if there is no further stimulus. Question 1: The refractory period of cardiac muscle cells is significantly longer than the refractory period of skeletal muscle cells.

2. What was the smallest voltage required to produce a contraction (the threshold voltage)? What proportion of the fibers in the muscle do you think were contracting to produce this small response?

During the lab I measured the length (in msec) of the latent period of a muscle reaction. The latent period is the time that is taken in order to generate an action of a muscle cell into a muscle contraction, during this time there is almost zero change in the muscle. I tested if there would be any change in the length of the latent period based on a change in stimulus voltage. My hypothesis is that even with an increase in stimulus voltage the latent period will stay constant.