Muscle Contraction Experiment

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

Muscle contraction can be understood as the consequence of a process of transmission of action potentials from one neuron to another. A chemical called acetylcholine is the neurotransmitter released from the presynaptic neuron. As the postsynaptic cells on the muscle cell membrane receive the acetylcholine, the channels for the cations sodium and potassium are opened. These cations produce a net depolarization of the cell membrane and this electrical signal travels along the muscle fibers. Through the movement of calcium ions, the muscle action potential is taken into actual muscle contraction with the interaction of two types of proteins, actin and myosin.

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.

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

The Purpose of this exercise is to understand how muscle twitch, contract and react to different activities.

A simple spinal reflex is a reflex—involuntary, graded, patterned response to a stimulus—that is produced via a single synapse between sensory axons and motor neurons and confined to the spinal cord. In this experiment, two simple spinal reflexes—the myotactic reflex and the H-reflex—were stimulated. We compared a) the latency period—the amount of time between a stimulus and the effector response— and the amplitude—magnitude of an electrical signal—of each reflex; then, b) the effect of the Jendrassik Maneuver (JM) upon the latency period and amplitude of each respective reflex. For the myotactic response, a mechanical stimulus, a sharp strike of the patellar tendon, was utilized to elicit a signal in stretch receptors; however, to trigger the H-reflex, an electrical impulse was applied. These reflexes originate from an action potential produced by a sensory neuron when a stimulus is applied. Sensory neurons transmit the action potentials to an integrating center—the spinal cord—where a response is determined. Then, this response is taken back to the effector organ via motor neurons. The reflex occurs while the brain is becoming aware of the stimulus. Furthermore, the myotactic reflex is

Current research suggests that trigger points are caused by a dysfunction in the nerves that signal the muscles to contract (Simons, Travell, & Simons 1999). When the neural activity becomes unsynchronized, it can cause muscles to contract without relaxing (Simons et al. 1999; Ge, Fernandez-de-las-Penas, & Yue 2011). This constant contraction results in a trigger point, which restricts blood flow to the taut muscle area and causes both localized and referred pain (Ge et al. 2011). Researchers theorize that DN interferes with the malfunctioning nerve signals and resets them to their normal function (Simons et al. 1999; Giamberardino, Affaitati, Fabrizio, & Costantini 2011).

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.

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

To fully understand the events taking place and the data collected, a brief but thorough review of muscles on a physiological level is needed. Muscles are responsible for producing force and motion in the both the external world and within the body. Locomotion of the body and its organs is achieved via the contraction of three types of muscles: skeletal muscle, cardiac muscle, and smooth muscle. Our lab focuses on the effects of stimulation of skeletal muscle and more specifically, the relationship between a motor neuron and muscle contraction.

This is because once a contraction has started, the action potential has already fired, stimularing the muscle fibers. Once they

A motor unit is made up of a motor neuron and the muscle fibers that it supplies depending on its size. The motor neuron controls the amount of force that is exerted by muscle fibers. There are two principles that control the relationship between motor neuron and muscle force, the size principle and rate coding. The size principle decides which motor units are recruited first. For example, recruitment is seen in larger muscles that have mixed fiber types such as the latissimus dorsi. Rate coding, which is also referred as motor unit firing rate, allows muscles to generate greater tension forces by producing high frequencies at which the signals are sent to the muscles telling them to contract. As the intensity of stimulus increases, the firing

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.