Skeletal Muscle Contraction Questions 5gr1u

Skeletal muscle contraction Nerve-muscle activity Isolated Muscle Responses 1. Why is there a difference in these threshold voltages? The axon is more sensitive, therefore the axon has a lower threshold voltage than that of the muscle. What is meant by the independent irritability of muscle? This is the property that claims that irritability exists only in muscles and it is independent of nerves. It is activated by getting action potential from axon and motor neuron, and it stimulates muscle contraction. 2. How is the response obtained related to the all-or-none law of muscle fiber contraction? The all-or-none law of skeletal muscle contraction states that when action potentials travel down a single motor unit, all the individual muscle fibers of that muscle unit will contract with equal force, regardless if those fibers have been stimulated or not. The response obtained relates to this because all the muscle fibers must work together to contract the muscle. The contraction that is seen happens because of this. When you apply different voltage to skeletal muscle, you activate different muscle fibers, and they will contract differently. In skeletal muscle fibers, you can generate very precise contractions and different movements, unlike with cardiac muscle fibers. 3. Explain the mechanism responsible for summation of contractions and the increase in height of contraction when the stimulus frequency is increased. The release of Ca2+ ions from the sarcoplasmic reticulum is responsible for this summation of contractions. When an influx of Na+ produces end-plate potential in a muscle fiber, voltage-sensitive receptors cause channels on the sarcoplasmic reticulum (SR) to open. The stored Ca2+ inside the SR is released out into the cytosol. When you stimulate the muscle at increasing frequencies, action potential stimulates the muscle to contract. Contraction is not able to return to sarcoplasmic reticulum in time, thus producing greater contraction when stimulated again. What is tetanus? Why is it produced? Tetanus relates to the diffusion of a contraction without relaxation. It is the plateu that results when a muscle is stimulated frequently over a prolonged period of time. When calcium is released, it es through skeletal muscle without going back to storage, because before it has a chance to return, the muscle is stimulated again. 4. How is the contractile tension developed with increasing stretch related to the sarcomere structure of the muscle fiber? When skeletal muscle is stretched, it is used to contract strongly with greater strength and with greater efficiency.

Stimulation of Motor Points 6. What is the effect of curare on muscle contraction when the nerve is stimulated? Curare affects the synapse rather than nerve propagation. What is curare’s mechanism of action? Curare works by blocking synaptic transmissions so that neural impulses do not travel from neuron to neuron. How could a large dose of curare cause death? Curare causes paralysis which leads to asphyxiation then death 7. Describe and explain what happens to muscle contraction when the nerve is

stimulated or the muscle is stimulated directly while either is in a calcium-free bath. This does not induce contractions because AP is not received. Apply What You Know 1. Based on your knowledge of muscle physiology and the nature of motor units, how would the structure of muscles in your thigh differ from muscles controlling the movements of your eyeball (the extraocular muscle)? The thigh muscles are rich in capillaries and they the whole body. The extraocular muscle controls the movements of your eyeball, and it is also rich in capillaries. The extraocular muscle controls more than the thigh muscles, in of the region it controls. There are other leg muscles that may be employed if the thigh muscles is injured; however, if the extraocular muscle gets injured, the situation is worse because the other muscles do not control that. 2. Imagine holding a heavy object stationary in front of you with your arm fully extended at the elbow. Describe, at the level of a sarcomere in which actin/myosin interactions are taking place, how you maintain this position. Because no movement is taking place, are you using ATP? If yes, explain your answer. Yes, you are using ATP because it takes energy to hold the heavy object when your arms are not ed by anything; your arm muscles get tired.