Daily questions for Session 4

  1. Information from the nociceptors in the tissue is transmitted to the brain where information is interpreted as pain. Using your knowledge of how action potentials occur, and in particular the role of cell membrane channels, suggest how local anaesthetics could exert their effect.
  2. Using your knowledge of neurotransmitters, suggest how general anaesthetics may exert their effect.
  3. Myasthenia gravis is a disease caused when acetylcholine (Ach) receptors on the post synaptic side of the neuromuscular junction are destroyed. What is the role of acetylcholine in muscle function? Insecticides kill insects by blocking the enzyme acetylcholinesterase which breaks down acetylcholine. As a result the insects have uncontrolled muscle contractions and effectively dive exhaustion. How could acetylcholinesterase inhibitors people with myasthenia gravis?
  4. Cholera is an important cause of infectious diarrhoea and death. The disease is caused by a toxin produced by the bacterium Vibrio cholerae. The toxin exerts its effect by binding to receptors on small intestinal cells, stimulating production of the second messenger cAMP inside the cells. This opens a chloride channel in the membrane and as a result negatively charged chloride ions are able to move out of the cell. Cholera causes severe diarrhoea which results in severe dehydration and hyponatraemia. Treatment for cholera involves the administration of fluids which replace both water and electrolytes. Use your knowledge of SGLTs to explain why patients do better with oral fluids that contain sodium and glucose than fluids that contain only sodium.
  5. Many Australian snake toxins block post-synaptic acetylcholine receptors and therefore cause paralysis. Red Back spider venom depletes presynaptic stores of acetylcholine, meaning that neuromuscular transmission cannot occur. Funnel Web Spider toxin prevents the closure of Na+ channels resulting in ongoing action potentials in autonomic and motor neurones. Funnel-web spider toxin affects mammals, but primates are especially susceptible. No one is really sure why, but it may be due to differences in the structure and function of ion channels between different animals. In insects, which are the intended target of toxin, it exerts its effect by binding to K+ and Ca2+ channels. Blue ringed octopus toxin blocks Na+ channels to prevent action potential transmission, especially in in peripheral nerves, resulting in muscle paralysis. When the muscles of the diaphragm and the chest wall are affected, respiratory failure develops. The toxin is not produced by the octopus itself; it comes from bacteria that live in the salivary glands of the octopus in a symbiotic relationship. The toxin in blue ringed octopus saliva is the same as the toxin in puffer fish which has killed many people in Japan.