BISC 307 Spring 2009 Exam 2 Answers 4 pts 1 Indicate whether each of the following statements is true or false by writing the word True or False in the blank Do not write T or F ANS a T b T c F d T a Dihydropyridine receptors are voltage sensors in the transverse tubule membrane b Type I skeletal muscle fibers contain large numbers of mitochondria c When a muscle fiber undergoes an isotonic contraction the spacing between z disks remains constant d Skeletal muscle fibers with more Ca2 pumps in the sarcoplasmic reticulum will relax more quickly following a twitch 4 pts 2 Write one number in each blank to best match each of the steps in skeletal muscle contraction on the left with its functional significance on the right a Ca2 pumping into SR 1 breaks the cross bridge b binding of ATP to myosin 2 terminates cross bridge cycling 3 causes depolarization of transverse tubules c release of Pi d binding of Ca2 to troponin 4 causes rigor mortis 5 change in myosin conformation causing filaments to slide 6 forms the cross bridge ANS a 2 b 1 c 5 d 7 7 trigger that initiates cross bridge cycling 6 pts 3 Briefly explain how a muscle can contract and lengthen at the same time and give an example of such a contraction ANS If the load placed on a muscle exceeds the force the muscle generates then the muscle will extend while contracting There are many possible examples but typical ones would be contractions of anti gravity muscles in the legs when walking downhill or landing from a jump off a platform note change in printing order 5 pts 5 Which one of the following comparisons between single unit and multiunit smooth muscle is correct d a Single unit smooth muscle receives mainly parasympathetic innervation and multiunit receives mostly sympathetic innervation b Single unit smooth muscle cells have only muscarinic cholinergic receptors and multiunit smooth muscle cells have only adrenergic receptors c In single unit smooth muscle neurotransmitter is released from varicosities along the length of axons and in multiunit smooth muscle neurotransmitter is released only at the terminals ends of axons d Single unit smooth muscle cells are coupled by gap junctions and multiunit smooth muscle cells are not coupled by gap junctions e Myosin light chain kinase activates contraction in single unit smooth muscle and troponin tropomyosin activates contraction in multiunit smooth muscles NAME 9 pts 4 In both skeletal muscle and smooth muscle Ca2 ions act as the trigger for contraction but the sources mechanisms and fate of Ca2 is different in some important ways Compare and contrast the following aspects of Ca2 dependent contraction in smooth muscle and skeletal muscle a sources of Ca2 ions that trigger contraction where do the Ca2 ions come from b mechanisms by which Ca2 ions trigger contraction Answer only within box Smooth Muscle Skeletal Muscle Sources of Ca2 1 IP3 mediated Ca release from the SR 2 influx through receptor activated Ca channels in the plasma membrane 3 influx through voltage gated Ca channels in the plasma membrane 3 pts Ca comes entirely from the SR following depolarization of the ttubules by the action potential 2 pts Ca2 triggering mechs Ca binds to calmodulin to activate a myosin kinase that phosphorylates myosin 2 pts Ca binds to troponin which causes a conformation change in tropomyosin that allows myosin to bind to actin 2 pts 5 pts 6 Indicate whether each of the following functions is more characteristic of insulin or glucagon by writing either I for insulin or G for glucagon in each blank a Stimulates glycogenesis I b Stimulates protein synthesis I c Stimulates gluconeogenesis G d Stimulates lipogenesis I e Stimulates glycogenolysis G 6 pts 7 Indicate whether each of the following characteristics applies best to epinephrine or cortisol by writing either Epi for epinephrine or Cort for cortisol in each blank a Hormone is released by exocytosis Epi b Cellular mechanism of action always requires protein synthesis Cort c Hormone has a short half life in the plasma Epi Page 2 of 5 NAME d Hormone has potent immunosuppressive effects Cort e Hormone release is directly controlled by cells in the anterior pituitary Cort f Hormone binds to both plasma membrane and intracellular receptors Cort 4 pts 8 Indicate whether each of the following statements is true or false by writing the word True or False in the blank Do not write T or F ANS a T b F c T d F a A person recovering from extensive surgery would do better with a diet high in protein compared to a diet high in carbohydrate assuming both diets were nutritious b When a person with type 1 diabetes contracts a serious infection his dosage of insulin should be decreased c Cortisol is required for glucagon to be fully effective d An increase in cortisol secretion typically triggers an increase in ACTH secretion 5 pts 9 A mother brings her 16 month old baby girl to a pediatrician because she thinks the baby is growing more slowly than normal The doctor notes that the baby s thyroid gland is greatly enlarged He orders some blood tests The results show that the baby s plasma levels of T4 are low and plasma levels of TSH are high Which one of the following is unlikely to be true e a The baby is usually lethargic b The baby has a low body temperature c The baby has not yet attempted to walk d The baby s brain development is retarded e The baby has bone structure typical of that of a 2 year old 10 pts 10 Two experts on Cushing s syndrome recently published the following statement Trying to diagnose mild Cushing s syndrome without measuring late night salivary cortisol may be like trying to diagnose mild primary hypothyroidism without obtaining a TSH Findling JW Raff HR 2005 Screening and diagnosis of Cushing s syndrome Endocrinol Metab Clin N Am 34 385 402 Briefly answer each of the following questions a What is Cushing s syndrome ANS Cushing s syndrome is a general term for hypercortisolism elevated levels of cortisol secretion b To detect Cushing s syndrome why would they recommend measuring salivary cortisol late at night ANS Cortisol secretion shows a circadian rhythm and is normally low late at night Thus measuring cortisol late at night would maximize the difference between the high level expected a person with Cushing s disease and the low level expected in a normal person c In primary hypothyroidism would you expect levels of TSH to be high or low Briefly explain your answer ANS Levels of TSH would be high In primary hypothyroidism