According to the sliding-filament theory, which of the following statements i A.

Question

According to the sliding-filament theory, which of the following statements i A. B. C. D. E. Calcium is required to disengage the interactions between Thin filaments move away from the M-line Skeletal muscle contractions will always occur Thick filaments rema ATP myosin & actin molecules since these contractions do not require ATP in stationary (or do not move) during cross-bridge formation is required to interact with troponin before myosin & actin molecules can interact with one Which of the following responses is caused by a release of ENDOTHELIN-1 A. Vasodilation B. Vasoconstriction C. Vasodilation D. A&B; E. A, B&C; at low concentration; vasoconstriction at high concentration The PLATEAU phase of action potentials from pacemaker cells is maintained by. A. sodium influxes B. chloride effluxes C. potassium influxes D. bicarbonate effluxes E. calcium influxes Which of the following would be produced by the LOWESI frequency of stimulation? A. Unfused tetanus B. Summation C. Twitch D. A& B E. A, B&C; Which of the following is a benefit resulting from a EEVER? A. Activities of interleukin-1 (IL-1) are decreased B. Production of cytokines is prevented C. Tachycardia is induced (or promoted) D. Production of interferons is inhibited E. Activities of transfrrins are increased Axons of UPPEB motor neurons are contained within A. pyramidal tracts B. cranial& spinal nerves C. spinothalamic pathways D. A&B; E. A, B&C; Pacinian corpuscles respond to stimuli by generating_potentials A. excitatory postsynaptic B. generator C. action D. receptor E. inhibitory postsynaptic Which of the following factors affects the force generated by WHOLE skeletal muscles? A. Recruitment B. Size principle C. Presence of gap junctions D. A& B E. A, B&C;

Explanation / Answer

1. Calcium is required to expose binding sites in actin. It binds to troponin, allowing trophomyosin to move away, thereby exposing the binding sites. ATP will bind to myosin. It is hydrolyzed to ADP and Pi, which allows cross-bridge formation. The M line is the attachment site of thick filament. The actin filaments (thin filaments) move towards the M line during muscle contraction, thereby shortening the sarcomeres. It is the thick filaments that remain stationery during cross bridge formation, as per the Sliding theory of Muscle Contraction.

Option D.

2. Endothelin-1 is a 21 amino acid potent vasoconstrictor. It is produced by endothelial cells and binds to two receptors ETA and ETB. Binding to ETA in smooth muscle will cause vasoconstriction. Binding of ET-1 to ETB in endothelial cells will cause vasodilation, while in smooth muscle will cause vasoconstriction.

Option D.

3. During the plateau phase, K+ move out of the cell. L-type calcium channels are activated and allow calcium to move into the cell. In this phase, the membrane starts to repolarize.

Option E.

4. A twitch is a single stimulus that is delivered. It causes the muscle to contract and relax once. In wave summation, stimuli are delivered frequently. Hence, the muscle cannot relax completely. Unfused tetanus will cause complete twitch fusion. Due to rapid stimuli.

Option C.

5. Fever induces tachycardia or increased heart rate in an attempt to maintain stability. Faster heart rate will increase respiration. As a result, oxygen will be carried more to tissues.

Option C.

6. The upper motor neurons in the cerebral cortex reside are present in highly interconnected areas in the frontal lobe. They mediate the planning and initiation of complex temporal sequences of voluntary movements. The axons of upper motor neurons are contained within the pyramidal system of corticospinal (pyramidal) and corticobulbar tracts.

Option A.

7. The Pacinian corpsucles is a receptor located in the skin. Pacinian corpuscles have two component: the tip of a sensory neuron that conducts action potentials towards the brain and numerous lamellae, wrapped around the neuron tip.

Option C.

8. Skeletal muscle slack gap junction as their presence may have propogated muscle contraction. Higher the recruitment of the muscle fiber, stronger will be the muscle contraction. It will therefore affect the force of whole muscle. Smallest units are first recruited followed by larger motor units in muscle contraction. This is known as Hennemen size principle. Size principle governs the force generated by the whole skeletal muscle.

Option D.

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