Physiolab 9.0 Exercise 2

* 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

Skeletal Muscle Structure.The cells of skeletal muscles are long fiber-like structures. They contain many nuclei and are subdivided into smaller structures called myofibrils. Myofibrils are composed of 2 kinds of myofilaments. The thin filaments are made of 2 strands of the protein actin and one strand of a regulatory protein coiled together. The thick filaments are staggered arrays of myosin molecules.

3. Considering your answers to Questions 1 and 2, why did activity in Annie’s motor nerves produce a skeletal muscle response that fatigued during repetitive stimulation?

types of muscle tissues : skeletal, cardiac, smooth. Each of these different tissues has the ability

What are the different levels of organization of a muscle down to myofilaments? What is a “sarcomere” and how are its proteins organized?

Smooth muscle contraction occurs when calcium is present in the smooth muscle cell and binds onto calmodulin to activate myosin light chain kinase (Wilson et al., 2002). Phosphorylation of myosin light chains result in myosin ATPase activity thus cross-bridge cycling occurs causing the muscle to contract (Horowitz et al., 1996). There are two known models of excitation and contraction in smooth muscle, electromechanical coupling (EMC) and pharmomechanical coupling

As a result of the contractions in the Muscle- Skeletal Longitudinal Section cells and the Muscle- Skeletal Cross Section cells, it allows your muscle to be able to contract in response to nerve stimuli. This means that the movements of most of these muscles are not involuntary, you can control them. Therefore, once the stimulation stops, the muscles relax.

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

In this exercise, you examined the effect of increasing stimulus intensity on the nerve. What other stimulus parameter

Rationale, Significance and Hypothesis. An extrinsic factor, which exerts a dominant influence on skeletal muscle fiber phenotype, is the nervous system. Buller et al. (1960) elegantly demonstrated the plastic nature of skeletal muscle fibers in response to changes in innervation type. Later, Lφmo and Westgaard (Lφmo and Westgaard, 1974; Westgaard and Lφmo, 1988) demonstrated that depolarization of muscle with specific patterns and frequencies of electrical activity are sufficient to cause changes in mature muscle fiber phenotypes. However, how myofibrillar gene expression and structural organization is affected by the frequency of impulses during activity, the amount of activity over time, or other characteristics of patterned activity is essentially unknown. To answer these questions will require the isolation and study of subsets of muscle-specific proteins in relation to different electrical activation patterns in vivo, an issue that cannot be easily addressed in preparations currently used in the study of muscle development and maintenance. However, using novel in vivo approaches can, in part, circumvent this difficulty.

2. What is a force-EMG relationship and why is there a tight coupling of these two parameters?

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

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

• pacemaker cells- are specialized cells that cause involuntary muscles and tissues to contract or dilate.