لجنة الطب البشري رؤية تنير دروب تميزكم

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2 1) Hyperpolarization phase of the action potential: a. is due to the opening of voltage-gated Cl channels. b. is due to prolonged opening of voltage-gated K + channels. c. is due to closure of the Na + channels. d. is due to closure of Cl channels. e. is due to the opening of Ca 2 + 2) In nerve: a. the refractory period is caused by the hyperpolarization phase of the AP. b. during absolute refractory period a stronger stimulation will lead to the generation of new AP. c. during the absolute refractory period Na + channels change from open to inactive state. d. the relative refractory period allows the overlap of succeeding APs. e. summation is possible. 3. The following are statements about cell-to-cell transmission: a. an impulse in an axon that releases excitatory transmitter usually produces an AP in the postsynaptic neuron. b. the amount of neurotransmitter released from axon terminal depends on extracellular Na+ ion concentration c. inhibitory transmitter produces an increase in permeability of the postsynaptic membrane to Cl and K + ions. d. transmission across a synapse occur in both directions. e. chemically-gated channels transmits AP in cardiac muscle.

3 4. Which of the following characteristic is shared by simple and facilitated diffusion? a. occurs down an electrochemical gradient. b. is saturable. c. requires carrier protein. d. is competitive. e. requires a Na + gradient. 5. During the upstroke of the AP: a. there is net outward current and the cell interior becomes more negative. b. there is net outward current and the cell interior becomes less negative. c. there is net inward current and the cell interior becomes more negative. d. there is net inward current and the cell interior becomes less negative. e. the inward and outward currents are at equilibrium. 6. In the heart: a. contraction normally begins in the right atrium. b. S-A node depolarize at a faster rate at 37ºC than at 39ºC. c. Purkinje fibers conduct cardiac impulses from S-A node to A-V node. d. the spontaneous AP is generated at the same rate in all components of the conduction system of the heart. e. membrane potential in pacemaker cells becomes stable in denervated heart.

4 7. In the heart which of the following is the result of an inward Na + current? a. upstroke of the action potential in the S-A node. b. plateau of the AP in ventricular muscle. c. upstroke of the AP in ventricular muscle. d. repolarization of the AP in S-A node. e. repolarization of the AP in ventricular muscle. 8. The pacemaker potential is attributed to: a. an increase in K + permeability. b. an increase in Na + permeability. c. a decrease in Cl permeability. d. a decrease in Ca 2+ permeability. e. simultaneous increases in K + and Cl permeability. 9. The plateau phase of cardiac muscle AP: a. has the highest permeability to Cl ions. b. allows repeated excitations of cardiac muscle. c. contributes in the activation of contractile mechanism of the heart. d. keeps cardiac muscle in a very short state of depolarization. e. occurs also in skeletal muscles. 10. The summation of several EPSPs occurring closely in time that produced by successive firing of a single presynaptic neuron is called: a. total postsynaptic potential. b. temporal summation. c. spatial summation. d. total excitatory potential summation. e. total hyperpolarization potential.

5 11. If an excitatory presynaptic input is stimulated a second time after the first EPSP in the postsynaptic neuron died off: a. a second EPSP will add onto the first EPSP resulting in temporal summation. b. the postsynaptic neuron is brought to threshold by spatial summation. c. a second EPSP will occur. d. a second EPSP occurs during the refractory period of the post synaptic neuron. e. postsynaptic membrane potential reaches the threshold level. 12. ATP is used indirectly for the: a. accumulation of Ca 2+ by the sarcoplasmic reticulum. b. transport of Na + from intracellular to extracellular fluid. c. transport of K + from extracellular to intracellular fluid. d. transport of H + from parietal cells into the lumen of stomach. e. absorption of glucose by intestinal epithelial cells. 13. Resting membrane potential (RMP) of a nerve fiber: a. is largely determined by Ca 2+ concentration gradient across the cell membrane. b. Na + contribution to RMP is determined by permeability of cell membrane to Na +. c. is generated by the activity of Na + K + pump. 14. In the transport across the cell membrane: a. O 2 and CO 2 are transported by facilitated diffusion. b. Na + K + pump maintains a high intracellular Na +. c. glucose is transported in muscle cells by simple diffusion d. glucose is transported in renal tubules by secondary active transport.

6 15. Simple diffusion: a. is a carrier mediated. b. requires the activity of Na + - K + pump. c. indirectly requires metabolic energy. d. is governed only by the concentration gradient across the membrane. e. occurs down a concentration gradient until a state of equilibrium is reached. 16. A change in membrane potential from 90 mv to + 30 mv is due to: a. movement of Na + inside the cell. b. movement of Na + outside the cell. c. movement of Cl outside the cell. d. movement of K + into the cell. e. inhibition of the Na + - K which of the following would occurs as a result of inhibition of Na + - K + pump. a. decreased intracellular Na +. b. increased intracellular K +. c. increased intracellular Ca 2+. d. increased Na + - glucose cotransport. e. increased Na + - Ca 2+ exchange. 18. An inhibitory postsynaptic potential (IPSP) a. depolarize the postsynaptic membrane by opening Na+ channels. b. depolarize the postsynaptic membrane by opening K+ channels. c. hyperpolarize the postsynaptic membrane by opening Ca2+ channels. d. hyperpolarize the postsynaptic membrane by opening of Cl channels.

7 19. simple diffusion of a substance a. shows saturation properties. b. can occur against an electrochemical gradient. c. is not carrier mediated. d. requires metabolic energy. e. shows competition properties. 20. all the following about active transport of a substance are true Except: a. can occur against a concentration gradient. b. can occur against an electrochemical gradient. c. is a carrier mediated transport. d. shows saturation properties. e. does not require metabolic energy. 21. which of the following is an example of simple diffusion? a. movement of Na + by the Na + - K + pump. b. uptake of Ca 2+ by the sarcoplasmic reticulum of muscle. c. movement of O 2 through the cell membrane. d. the Na + - glucose cotransport. e. the Na + - Ca 2+ countertransport. 22. the resting potential across the nerve membrane: a. depends on the ratio of K+ concentration inside and outside the cell. b. is positive inside with respect to outside. c. is 50 mv. d. magnitude is not affected by inhibition of the Na+ - K+ pump. e. is grater in non-myelinated than myelinated fibers.

8 23. normally the pacemaker of the heart is: a. the S-A node. b. the A-V node. c. the A-V bundles. d. the Purkinji fibers. e. the cardiac muscle. 24. The plateau phase of cardiac muscle action potential is due to: a. inward movement of Na+. b. inward movement of K+. c. inward movement of Ca2+. d. outward movement of Cl. e. activity of Na+-K+ pump. 25. Na+ channels in a nerve membrane are: a. chemically gated channels. b. voltage gated channels. c. causing repolarization. d. producing hyperpolarization. e. present along the whole length of myelinated fibers.

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