3. a) The neurotransmitter that is responsible for âcommunicationâ at the neuromuscular junction between motor nerve cells and skeletal muscle fibers is acetylcholine (ACh). The ACh receptor protein is a channel that opens when ACh binds. Upon the opening of this channel, the membrane at the motor end plate region of the muscle cell becomes depolarized, resulting in the generation of an action potential in the muscle fiber membrane. The ACh receptor channel is equally permeable to both Na+ and K+ ions. Explain how opening a channel that allows both potassium and sodium to cross the membrane results in membrane depolarization. (2 points)
b) In normal individuals, a single end-plate potential (EPP) is always sufficient to elicit an action potential (and hence contraction) in a skeletal-muscle fiber. This is not the case in individuals suffering from myasthenia gravis (MG). MG is an autoimmune disorder in which antibodies are produced that attack the AChRs at skeletal-muscle endplates reducing their number. Patients suffering from the disease present with significant muscle weakness. Explain why patients with MG would exhibit muscle weakness. (2 points)
c) Treatment strategies for myasthenia gravis include thymectomy (removing the source of the antibody producing cells) or immunosuppressant drug therapy (inhibiting the synthesis and release of the antibodies). In addition, the drug neostigmine administered at carefully monitored doses is highly effective in treating myasthenia gravis. Investigate the actions of neostigmine, and discuss in detail why it may be an effective treatment. (2 points)
3. a) The neurotransmitter that is responsible for âcommunicationâ at the neuromuscular junction between motor nerve cells and skeletal muscle fibers is acetylcholine (ACh). The ACh receptor protein is a channel that opens when ACh binds. Upon the opening of this channel, the membrane at the motor end plate region of the muscle cell becomes depolarized, resulting in the generation of an action potential in the muscle fiber membrane. The ACh receptor channel is equally permeable to both Na+ and K+ ions. Explain how opening a channel that allows both potassium and sodium to cross the membrane results in membrane depolarization. (2 points)
b) In normal individuals, a single end-plate potential (EPP) is always sufficient to elicit an action potential (and hence contraction) in a skeletal-muscle fiber. This is not the case in individuals suffering from myasthenia gravis (MG). MG is an autoimmune disorder in which antibodies are produced that attack the AChRs at skeletal-muscle endplates reducing their number. Patients suffering from the disease present with significant muscle weakness. Explain why patients with MG would exhibit muscle weakness. (2 points)
c) Treatment strategies for myasthenia gravis include thymectomy (removing the source of the antibody producing cells) or immunosuppressant drug therapy (inhibiting the synthesis and release of the antibodies). In addition, the drug neostigmine administered at carefully monitored doses is highly effective in treating myasthenia gravis. Investigate the actions of neostigmine, and discuss in detail why it may be an effective treatment. (2 points)
