CAT 2 2014 — Physiology & Biochemistry MCQs OmpathStudy

CAT 2 2014 — Physiology & Biochemistry MCQs (Part 2 of 3) Continued from $1. Covers Papers 4–5 of this combined seven-paper set. PAPER 4: MBChB/BPharm/BDS Level I — CAT 3, June 2014 (Muscle Physiology, Autonomic Nervous System, Haematology) Q1. The following reflexes are mediated by the Golgi tendon organ: A. Reciprocal inhibition B. Inverse stretch reflex C. Cross extensor reflex D. Stretch reflex E. Flexor reflex Answer: b Explanation: Golgi tendon organs detect muscle tension and mediate the inverse (autogenic) stretch reflex , causing muscle relaxation to protect against excessive tension. --- Q2. Effector organs/structures in a typical reflex arc may include all EXCEPT: A. Secretory glands B. Extrafusal fibres C. Endocrine organs D. Skeletal muscles E. Intrafusal fibres Answer: e Explanation: Intrafusal fibres are the sensory (receptor) component of the muscle spindle, not an effector. --- Q3. The following statement is TRUE about the muscle spindle: A. It is also known as intrafusal fibres B. Is made up of contractile central portion C. Is a sense organ D. Is located at the central portion of the extrafusal fibres E. Is only innervated by efferent fibres Answer: c Explanation: The muscle spindle is a proprioceptive sensory organ detecting muscle length/stretch; its central portion is non-contractile, and it is innervated by both afferent (sensory) and efferent (gamma motor) fibres. --- Q4. Polysynaptic reflexes serve all of the following EXCEPT: A. Withdraw affected part of the body from danger B. Is protective in nature C. Translocate the entire organism from danger spot D. Keep the withdrawn part away from danger E. Regulate the rate of change of muscle fiber length Answer: e Explanation: Regulating muscle fiber length change rate is the role of the (monosynaptic) stretch reflex via muscle spindles, not polysynaptic withdrawal reflexes. --- Q5. Type Ia nerve fibres that innervate the muscle spindle: A. Are afferent in nature B. Are slow conduction fibres C. Travel to the spinal cord through the ventral route D. Are distributed to nuclear chain fibre only E. Synapse polysynaptically with the alpha motor neurone Answer: a Explanation: Type Ia afferents are large, fast-conducting sensory fibres that travel via the dorsal root and synapse monosynaptically with alpha motor neurones (stretch reflex arc). --- Q6. Extrafusal muscle contraction can be achieved by: A. Physical stretch of the extrafusal muscle B. Distorting the central non-contractile portion of the spindle C. Reducing the frequency of action potentials flowing through the gamma motor neurone to the spindle D. By mechanically relaxing the extrafusal fibres E. Contraction of the contractile ends of the spindle Answer: a Explanation: Extrafusal (ordinary skeletal) muscle fibres contract in response to alpha motor neuron stimulation, but physical stretch itself is a normal way tension is generated/activated via the stretch reflex — the other options describe intrafusal spindle mechanics, not extrafusal contraction directly. --- Q7. Concerning gamma motor neurone: A. Constitutes 90% of all fibres in the ventral root of the spinal cord B. It is distributed to the contractile ends of the muscle spindle C. Is also known to carry sensory information D. Directly supplies the extrafusal fibres with motor innervation E. Supplies the nuclear chain fibre only Answer: b Explanation: Gamma motor neurones innervate the contractile polar ends of intrafusal fibres within the muscle spindle, adjusting spindle sensitivity. --- Q8. True statement about withdrawal reflexes: A. Knee jerk is an example B. Are mediated by muscle spindle C. Are monosynaptic in nature D. Can sometimes be effected via secretory glands E. Exhibit the principles of reverberation (and divergence) Answer: e Explanation: Withdrawal (flexor) reflexes are polysynaptic, exhibiting divergence and reverberation circuits — unlike knee jerk, which is a monosynaptic stretch reflex. --- Q9. Adequate stimulus for muscle spindle is/are: A. Pressure B. Touch C. Stretch D. Stress E. Proprioception (modality, not stimulus) Answer: c --- Q10. The principle of divergence, with regard to reflex physiology, is where: A. There is only one synapse B. Many afferents directly synapse with many efferents C. Many efferents directly synapse on several end organs D. One interneurone is shared by many afferents E. One interneurone is shared by many afferents (duplicate distractor) Answer: c Explanation: Divergence describes one input (afferent/interneuron) spreading its influence to multiple output pathways/effector organs. --- Q11. The enzyme which determines the rate of Hb synthesis is: A. δ-ALA hydrase B. Oxidase C. Decarboxylase D. Co-synthetase E. δ-ALA synthetase Answer: e Explanation: δ-aminolevulinic acid (ALA) synthetase is the rate-limiting enzyme of haem synthesis. --- Q12. Normal daily requirement of cobalamin (B₁₂) is: A. 1 mg B. 1 µg C. 5 mg D. 10 mg E. 100 µg Answer: b Explanation: Daily B₁₂ requirement