Frog muscle - lab report PDF

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Skeletal Muscle Activity in Rana pipiens
lab report required for gen phys lab, due at the time of the final exam ...

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--General Physiology Lab Thurs @ 1:00 Skeletal Muscle Activity in Rana pipiens Introduction Skeletal muscles are voluntarily controlled and attached to the skeletal system in vertebrates. This muscle type allows us to move our limbs and other body parts with conscious control by means of the somatic nervous system. Skeletal muscles are often contrasted to smooth and cardiac muscle types, which are involuntarily controlled by the autonomic nervous system. Skeletal muscles are innervated by motor neurons, and the location at which they meet is termed the neuromuscular junction. A motor unit describes a single motor neuron and the group of muscle cells it innervates. An action potential travelling down the axon of the presynaptic motor neuron must communicate with the muscle fibers by way of chemical communication (neurotransmitters). A neuron releasing acetylcholine, for example, would stimulate skeletal muscle contraction (BIOPAC). Just as a contraction can be stimulated by neurotransmitter release, drugs and fatigue can instead hinder muscle contraction. Fatigue can be caused by increased levels of lactic acid, and fatigue can occur at the sites of the central nervous system, neuromuscular junction, or muscle itself (Putnam). Examples of altering drugs include tubocurarine (curare), which inhibits synaptic transmission at the neuromuscular junction. It is a nicotinic antagonist, meaning it blocks acetylcholine binding. This results in relaxation of the muscle. Conversely, an example of an enhancer of transmission is neostigmine, which acts by inhibiting acetylcholinesterase (Cooper). This lab examined the activity of skeletal muscle in a frog model, Rana pipiens . The gastrocnemius, or calf muscle, of the frog was excised along with the sciatic nerve. We were able to observe the effects of muscle stimulation on contractile force. We were especially interested in summation, tetanus, and certain drugs. Results Exercise 1 aimed to determine the threshold stimulus (Figure 1). The muscle was directly stimulated with single pulses. Following the protocol, a low frequency of stimuli was used to avoid muscle fatigue. Figure 1 also shows that there is a greater contraction in the muscle with increasing voltage.

Figure 1. Stimulation of frog skeletal muscle over time. Threshold stimulus was determined (under resting and control conditions).

Figure 2 shows direct stimulation of the sciatic nerve. Frequency was increased until tetanus occurred.

Figure 2. Frequency trials conducted directly to nerve. Threshold of 0.3 V.

Exercise 3 tested the effect of stimulus frequency on twitch amplitude. Increasing frequencies were stimulated for short periods at 0.30 V. Incomplete tetanus was induced at 15 Hz frequency until complete tetanus at 50 Hz.

Figure 3. Effect of increasing stimulus frequency on twitch amplitude.

Exercise 5 involved myoneural block. Tubocurarine was injected into the frog skeletal muscle, inhibiting contraction (Figure 4). There was an observed decrease in contraction force over time.

Figure 4. Tubocurarine, nicotinic antagonist, injected into muscle.

Figure 5. Elapsed time after tubocurarine injection. Muscle does not respond to stimulation, regardless of voltage. Discussion This set of experiments allowed for the observation of skeletal muscle activity. Figure 1 displays the normal activity of this muscle. When directly stimulating the muscle, a threshold voltage of 0.3 V is noted. This acted as a control of sorts. Figures 2 and 3 depict fatigue to the point of tetanus. Figures 4 and 5 show the effect of tubocurarine on muscle contractions to be inhibitory. We were able to observe the effects of frequency and tubocurarine on muscle contraction, and the results matched our expectations and prior knowledge. Sources of error include incorrect dissection of the frog muscle and nerve, improper electrode placement, improper attachment of muscle to the force transducer, and incorrect dosage or location injection of tubocurarine into the muscle. References BIOPAC Systems, Inc. “BSL PRO Lesson A02: Contractility of Skeletal Muscle Using Frog Gastrocnemius Muscle.” Biopac.com , 4 Feb. 2014, pp. 1–23., www.biopac.com/wp-content/uploads/a02.pdf. Cooper, R.J., et. al. “Experiment AM-10: Summation, Tetanus, and Fatigue in an Intact Nerve-Muscle Prep.” Adapted from Experimental Physiology (1965). Putnam, R. W. "The Role of Lactic Acid Accumulation in Muscle Fatigue of Two Species of Anurans, Xenopus laevis and Rana pipiens." The Journal of Experimental Biology, vol. 82, pp. 35-51....