DBMCI eGurukul OFFICIAL

Answer2780. #EXPLANATION ⦁ Chromosomal abnormalities may involve changes in number (i.e., polyploidy and aneuploidy) or changes in structure (i.e., rearrangements such as translocations, rings, and inversions). ⦁ Extra material (i.e., extra chromatin) seen on chromosome 5 implies recombination of chromo some 5 DNA with that of another chromosome to produce a rearranged chromosome. ⦁ Since this rearranged chromosome 5 takes the place of a normal chromosome 5, there is no change in number of the autosomes (nonsex chromosomes) or sex chromosomes (X and Y chromosomes). ⦁ The question implies that all cells karyotyped from the patient (usually 11 to 25 cells) have the same chromosomal constitution, ruling out mosaicism. ⦁ The patient’s clinical findings are similar to those occurring in trisomy 13, suggesting that the extra material on chromosome 5 is derived from chromosome 13, producing an unbalanced karyotype called dup (13) or partial trisomy 13. Ans. D. Unbalanced rearrangement

Answer2799. #EXPLANATION ⦁ The oculomotor nerve innervates the levator palpebrae superioris, which elevates the eyelid. This nerve also innervates the inferior oblique muscles, as well as the superior, inferior, and medial rectus muscles. ⦁ The oculomotor nerve also contains preganglionic parasympathetic fibers that synapse, in the ciliary ganglion, on postganglionic parasympathetic nerve fibers that innervate the sphincter pupillae muscle, which constricts the pupil. A lesion of the oculomotor nerve may therefore result in both drooping of the eyelid (ptosis) and dilation of the pupil (mydriasis). ⦁ The cervical sympathetic chain contains preganglionic sympathetic nerve fibers, arising from the upper thoracic spinal cord, which ascend to the cervical sympathetic ganglia. A lesion of these nerves may result in Horner's syndrome, which includes a ptosis and miosis (pupillary constriction) and, often, anhidrosis (lack of sweating). ⦁ The facial nerve innervates the muscles of facial expression, including the orbicularis oculi muscle. A lesion of this nerve may therefore result in the inability to close the eye. ⦁ The superior cervical ganglion contains the cell bodies of postganglionic sympathetic nerves that innervate structures in the head. A lesion of this structure will cause Horner's syndrome. ⦁ The trigeminal nerve provides sensory innervation to much of the head. A lesion of this nerve may interfere with the corneal blink reflex. Ans. C. Oculomotor nerve

Answer2778. #EXPLANATION ⦁ As the gastric reservoir fills during a meal, mechanoreceptors signal the CNS. When the limits of adaptive relaxation in the reservoir are reached, signals from the stretch receptors in the reservoir’s walls account for the sensations of fullness and satiety. ⦁ Over distention is perceived as discomfort. Adaptive relaxation appears to malfunction in the forms of functional dyspepsia characterized by the symptoms described in this question. ⦁ If adaptive relaxation is compromised (e.g., by an enteric neuropathy), mechanoreceptors are activated at lower distending volumes and the CNS wrongly interprets the signals as if the gastric reservoir were full. ⦁ None of the other choices would be expected to activate mechanosensory signaling of the state of fullness of the gastric reservoir. Ans. A. Malfunction of adaptive relaxation in the gastric reservoir

Answer2776. #EXPLANATION ⦁ The slower cycling rate of the cross-bridges in smooth muscle means that a higher percentage of possible cross-bridges is active at any point in time. ⦁ He more active cross-bridges there are, the greater the force that is generated. Although the relatively slow cycling rate means that it takes longer for the myosin head to attach to the actin filament, it also means that the myosin head remains attached longer, prolonging muscle contraction. ⦁ Because of the slow cross-bridge cycling rate, smooth muscle actually requires less energy to maintain a contraction compared with skeletal muscle. Ans. D. Slower cycling rate of the smooth muscle myosin cross-bridges

Answer2777. #EXPLANATION ⦁ In both smooth and striated muscle, contraction is produced by the cross- bridge cycle in which the cross-bridge on the thick filament binds to the actin molecule on the thin filament. ⦁ In excitation-contraction coupling in striated muscle, calcium initiates contraction by binding to troponin. ⦁ The calcium-activated troponin then acts to remove the tropomyosin-mediated inhibition of the actin-myosin interaction. In excitation-contraction coupling in smooth muscle, calcium initiates contraction by binding to calmodulin. ⦁ The calcium-activated calmodulin then activates the myosin light chain protein kinase (MLCK) enzyme, which phosphorylates the myosin light chains. Actin-myosin interaction follows light-chain phosphorylation. Ans. D. Actin