Max S Voice Is Altered Because Myasthenia Gravis Has Impaired His Ability to Voluntarily

Chapter 12

1. Max’s voice is altered because myasthenia gravis has impaired his ability to voluntarily contract certain skeletal muscles, including those required to produce speech.
2. Holding the head erect requires that the head extensors (trapezius, splenius capitis, and semispinalis capitis) be contracted to some degree. As these muscles lose acetylcholine receptors due to myasthenia gravis, their ability to contract is decreased, thus impairing the patient’s ability to hold his or her head erect as well.
3. The amount of time required to reopen the eyes is due to changes in the available acetylcholine receptors present on the muscles that affect the eyes. Because these muscles have fewer receptors, they begin to receive decreased stimuli and become more susceptible to fatigue. Max experiences double vision for a similar reason. Late at night, the muscles regulating eye movement and the muscles responsible for focusing images on the retina are more susceptible to fatigue than earlier in the day. This effect is further exacerbated by reduced lighting at night.
4. Generalized myasthenia gravis affects all the muscles of the body, including those involved in swallowing. When asleep, the body relies on reflex actions to initiate swallowing, but if the muscles of swallowing have been affected, this action is impaired, resulting in an accumulation of saliva that could induce choking. This is less likely to occur during the day because the patient notices the salivary accumulation. However, as the disease progresses, patients lose their ability to control the muscles that affect swallowing even when awake and thus begin to drool due to salivary accumulation.
5. The thymus is one of the organs of the lymphatic system, the system that works in conjunction with the immune system to minimize infections. Specifically, the thymus is involved in the development and activity of T lymphocytes. Therefore, removing the thymus negatively affects the immune system’s ability to prevent disease.
6. Curare blocks acetylcholine receptors and prevents normal muscle contraction. As a result, animals struck by darts containing this chemical become paralyzed. Unable to grip the trees, they fall to the ground, and unable to flee the hunters, they can then be easily killed. A high enough dose of curare can also kill an animal outright by inducing respiratory arrest.
7. The muscles of Susan’s left calf underwent disuse atrophy because they were immobilized and did not perform the same amount of work as usual. This could have been prevented to some extent by direct electrical stimulation of the muscles to induce small contractions. These contractions, however, would have to be weak enough to not disrupt the alignment of the third metatarsal. Susan could also have been instructed to perform isometric muscle contractions while her foot was in the cast to minimize the loss of muscle mass.
8. The cholinesterase inhibitor would prevent the hydrolysis of any acetylcholine released. Thus, the acetylcholine would have a prolonged effect on the skeletal muscles and induce a spastic state that would be treated in a manner similar to treatment for tetanus. The primary difference is that treatment with tetanus antitoxin would not be necessary.
9. As part of her treatment, Carla may be using immunosuppressive agents and may have undergone a thymectomy as well. Both of these treatments decrease the immune system’s ability to mount an immune response. As a result, the tetanus boosters may not produce the same degree of response in Carla as they would in other people.
10. Fibromyalgia is difficult to diagnose because of its rather nonspecific symptomology. Patients present with chronic pain that is not localized to any given body region and is aggravated by excessive muscle activity. They also report fatigue, insomnia, headache, anxiety, cold insensitivity, and an irritable bowel. The results of most of their diagnostic tests (electromyelogram, muscle biopsy, and blood chemistry) are usually normal, making it very difficult for physicians to readily diagnose their disease.