1 MCDB 111 Midterm (90 points) Name_________Key______________________________ 8/21/2017 Perm___________________________________________ Answer questions 1-10 on your Scantron answer form. Each multiple choice question is worth 3 points. 1. When a muscle develops tension but does not shorten or lengthen, the type of contraction is a. Isometric contraction b. Isotonic contraction c. Eccentric contraction d. Isomorphic contraction e. None of the above 2. At the synaptic knob, the arrival of an action potential opens voltage gated Ca2+ channels. What must be true for Ca2+ to enter the knob under these conditions? a. The force of the Ca2+concentration gradient must exactly balance out the electrical repulsive force b. The force of the Ca2+concentration gradient must be greater than the electrical repulsive force c. The force of the Ca2+concentration gradient must be less than the electrical repulsive force d. Ca2+cannot flow against a repulsive electrical force e. Ca2+must be pumped into the knob by an active transport mechanism 3. Which of the following is not an example of steady state behavior? a. The movement of K+ ions out of a neural cell by means of K+ leak channels b. The process that generates the resting potential of an afferent neuron c. The movement of protons out of a kidney collecting duct cell by means of a Na+/H+ antiport d. The movement of Ca2+ ions into the sarcoplasmic reticulum via a Ca2+ATPase e. Both a and c 4. Which of the following conditions could induce a state of tetanus? a. A deficiency of acetylcholinesterase b. A mutant ryanodine receptor that increases the amount of time a channel stays open for each action potential c. A drug that blocks the binding of acetylcholine to motor end plate receptors d. a and b e. a, b, and c 5. Which of the following substances will diffuse across a biological membrane without the aid of a transport protein or membrane channel? a. Na+ b. O2 c. glycerol d. H2O e. c and d 6. The primary function of secondary messengers such as cAMP, which are downstream of many hormone and neurotransmitter pathways, is that of a. signal amplification b. transcriptional activation c. receptor activation d. receptor inactivation e. transport of hormone-receptor complexes into the nucleus2 7. The drug rohypnol is an allosteric enhancer of the binding of GABA to its receptor. Which would describe the effect of this drug on a neuron with postsynaptic GABA receptors? a. It would elicit inhibitory postsynaptic potentials b. It would produce an afterhyperpolarization c. It would generate an absolute refractory state d. It would hyperpolarize the postsynaptic neuron e. Both a and d 8. A patient has a mutation that results in decreased deiodinase production. Which of the following would be a consequence of this mutation? a. A decrease in total thyroid hormone production b. All of the thyroid hormone would be in the form of T4 c. All of the thyroid hormone would be in the form of T3 d. hyperthyroidism e. both c and d 9. Which of the following neuronal changes is associated with short term synaptic strength? a. Increased buildup of Ca2+ in the terminal knob of the presynaptic axon b. Increased production of neurotransmitter vesicles in the presynaptic cell c. Increased expression of postsynaptic neurotransmitter receptors d. Changes in the shape of neural spines e. Changes in the size of neural spines 10. Acromegaly can result from a. elevated levels of cortisol as a result of adrenal gland tumors b. hypothyroidism due to a diet deficient in iodine c. a pituitary tumor that results in elevated levels of growth hormone d. hypopituitariasm e. a deficiency of vasopressin 11. (3 points) True or False, endocrine distruptors are peptide hormone mimics. 12. (6 points) Why does an increased frequency of action potentials cause a skeletal muscle fiber to contract more strongly? (Include in your answer any molecules and ions that are involved in this process). Repeated stimuli causes the ryanodine receptor channel to stay open longer, overwhelming the ability of the Ca2+-pump to send Ca2+ back in to the sarcoplasmic reticulum. The rise in cytoplasmic Ca2+ results in more Ca2+ binding to troponin, increasing the amount of myosin that is able to bind to actin (or efficiency of the myosin-actin interaction, increasing the force generating capacity of the myosin crossbridge, resulting in stronger muscle contractions.3 13. (5 points) Describe the physical state of a muscle fiber in rigor mortis and the molecular interactions responsible for this state. Rigor mortis, the stiffening of skeletal muscles following death, is caused by the depletion of ATP (2 points. In the absence of ATP, the thick (myosin) and thin (actin) filaments remain bound to each other in an immobile state (3 points). 14. a (6 points) Briefly describe the mechanisms that give rise to the relative vs. absolute refractory period. A relative refractory period results from the opening of voltage gated K+ channels and closure of Na+ channels during the repolarization stage of an action potential with the result that the outflow of K+ exceeds the inflow of Na+ ions. An absolute refractory period is caused by the closure of Na+ channel inactivation gates. 15. (6 points) Depolarization of the synaptic terminus will cause voltage gated Ca2+ channels to open. If the extracellular concentration of Ca2+ is 1 mM, the intracellular concentration of Ca2+ is 0.1 M, what is the driving force on Ca2+ when the membrane is depolarized to +50 mV? Begin your answer by writing out appropriate formulas and don’t forget units. ECa2+ = 61 log [ out ] = 61 log 1 mM = 122 mV z [ in ] 2 0.1 M Driving force = membrane potential – ion potential = 50 mV – 122 mV = -72 mV One point for each formula, 2 points for correctly plugging in the data, 1 point for correct final answer and 1 point for including units in answer. b. (5 points) At this driving force, will Ca2+ enter or leave the synaptic terminus? Explain your answer. Enter (2 points). The negative value of the driving force will attract the positively charged calcium ions facilitating their entry into the cell (3 points). [The 3 points will be given for a correct explanation even if the choice is “leave”].4 16. a (3 points) Your body develops a fever as a result of a viral infection. What feature of the homeostatic mechanism