Muscle Tissue and Physiology

Joseph Miller, a 52-year-old farmer, presents to the local Emergency Department accompanied by his spouse. Joe is unable to speak but is able to acknowledge yes and no questions with noticeably painful head gestures. His wife Marjorie explains that Joe's hand was cut badly while repairing a tractor attachment about nine days ago. The wound was quite deep and dirty, and Joe cleaned and bandaged it himself. Despite these measures, the wound became progressively more red, swollen, and painful. Three days ago, Joe began to experience muscle cramps, especially in the muscles around his jaw and neck. Eventually Joe began to have difficulty speaking and swallowing, at which point his wife insisted that he seek treatment. At first glance, some might dismiss this as a simple wound infection. After all, Joe did not seek medical care for a rather deep and dirty wound, which creates perfect conditions for an infection. But remember that Joe has also experienced cramps, or muscle spasms—painful, involuntary muscle contractions. Is this a separate problem, unrelated to his wound, or are the two related? 1. In Joe's case, which of the three types of muscle tissue would you expect to be affected? a. Smooth muscle tissue b. Skeletal muscle tissue c. Cardiac muscle tissue d. All three muscle tissue types would be affected. 2. Define the five common properties of muscle cells, and explain how each of these might be affected in Joe's case. Joe was examined by the nurse practitioner at the clinic. She notes that the wound is approximately 1 cm deep, and there is exposed muscle tissue with areas of apparent tissue death. In addition, Joseph’s head and neck muscles are in a continuous spasm, they resist passive flexion and extension, and there is increased tone in his muscles of mastication and muscles of facial expression The findings from the physical exam lead us to think that there may be more to this story than a simple wound infection. The continuous spasm of the muscles of the head, neck, and face indicates something potentially more serious. Remember that the muscular system is responsible for vital functions such as breathing, so any disturbance in skeletal muscle homeostasis must be closely monitored. 1. Describe the structural components of the myofibril. What are the different proteins associated with the thick and thin myofilaments? 2. What would you expect the different regions of the sarcomeres to look like in the muscles of Joe's jaw and neck? a. The I band would increase in length as the sarcomere increased in length. b. The A band and zone of overlap would increase in length as the sarcomere increased in length. c. The I band would decrease in length as the sarcomere decreased in length. d. The A band would decrease in length as the sarcomere decreased in length Due to the progression of Joe’s symptoms, the nurse practitioner admits Joe to the hospital with a severe wound infection. She consults with a physician, and they prescribe immediate therapy with muscle-relaxing agents to try to lessen Joe's muscle spasms. They also order tests to determine the cause of his illness and the best course of therapy. Based on Joe's recent medical history, the emergency room nurse practitioner diagnoses him with tetanus, a disease caused by the bacterium Clostridium tetani. C. tetani, which is a normal inhabitant of the soil, can easily contaminate dirty wounds, especially those due to farm implements, as with this case. In the body, these bacteria produce a toxin called tetanospasmin. The toxin enters the central nervous system (the brain and spinal cord) where it blocks the mechanisms that inhibit motor neurons from firing when a muscle relaxes. With this inhibition removed, the neurons fire repeatedly and continually stimulate the muscle, causing painful and increasingly stronger muscle spasms. The masseter (jaw) muscles are often the first muscles involved, and it is the spasm of these muscles that gives rise to tetanus’ common name: lockjaw, also called trismus. The muscles of the face, neck, back, and proximal limbs are also commonly affected. The contraction of the facial musculature leads to a characteristic facial expression with a teeth-baring grin and raised eyebrows. Contraction of the back muscles may cause the back to arch posteriorly. The worldwide incidence of tetanus is around one million cases per year. The mortality rate is nearly one hundred percent if no medical care is available. Fortunately, Joe is now in a hospital where his condition can be monitored and treated. The most serious complication of tetanus is respiratory failure, which is usually due to spasms of the muscles around the throat. When respiratory failure develops, the only treatment is mechanical ventilation: inserting a tube into the trachea (windpipe) and having a machine breathe for the patient. Will Joe face this potentially deadly complication? 1. Why would repetitive stimulation from a motor neuron lead to a sustained muscle contraction? (Hint: Think about the processes of excitation-contraction coupling and relaxation.) 2. Which component of the neuromuscular junction is directly affected by the toxin produced by the tetanus organism? a. The synaptic cleft b. The axon terminals c. The motor end plate d. The sarcoplasmic reticulum A potentially serious complication of tetanus is the destruction of the muscle fibers themselves, a condition known as rhabdomyolysis. The breakdown of muscle fibers releases myoglobin into the blood, which can put a strain on the kidneys and lead to a decline in their function. Joe's physician notes that his kidney function has declined. She suspects that this may be a result of this muscle fiber breakdown, because myoglobin was detected in Joe's urine. She initiates immediate therapy for the kidney dysfunction and orders additional tests to look at the level of myoglobin in his blood. This is a setback for Joe's recovery, and makes his prognosis more serious. Fortunately, his physician has discovered this complication early and has taken measures to protect his kidneys from the circulating myoglobin. 1. Joe’s skeletal muscles affected by the tetanus toxin would require an enormous amount of energy to continue to progress through repeated excitation-contraction coupling and relaxation cycles. (a) What is the role of myoglobin in muscle fiber energy production, and where is it normally found? (b) What would you expect to happen to the ATP level in Joe’s affected skeletal muscle fibers, given enough time? 2. Which of the following processes is/are used to regenerate ATP as it is consumed for energy during both muscle contraction and relaxation? a. The creatine phosphate reaction in the cytosol b. Glycolytic or anaerobic catabolism in the cytosol c. Oxidative or aerobic catabolism in the mitochondria d. Each of the above reactions is involved in ATP regeneration Joe has now had eleven days of therapy with muscle-relaxing drugs, and is showing slow but steady improvement. He continues to have spasms in his neck and back, but they are less severe. . Joe's physician feels that he should be able to go home soon, providing he continues to improve over the next few days. Although he is still symptomatic, it seems as if Joe has avoided the most serious complication of tetanus: respiratory failure. However, even with improvement, he will still need to remain hospitalized for a few days to ensure that his body continues to respond to treatment. 1. If you were to do a myogram of Joe’s muscles while in spasm, what do you think it would show: isolated twitches, unfused tetanus, or fused tetanus? Why? Considering this, explain why this disease is called tetanus. 2. What would you expect to see and feel if you examined Joe’s affected skeletal muscles? a. Flaccid or soft muscles with little muscle tone--hypotonia b. Flaccid or soft muscles with abnormally high muscle tone--hypertonia c. Rock hard muscles with little muscle tone--hypotonia d. Rock hard muscles with abnormally high muscle tone—hypertonia 1. Describe the effects of disuse on Joe's muscles if he was bedridden in the hospital for several months. 2. Damaged skeletal muscle fibers do not generally regenerate, because they are no longer capable of dividing by mitosis. Which of the following cells can assist in the repair of damaged skeletal muscle? a. Fibroblasts b. Satellite cells c. Chondroblasts d. Neurons      

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