Chapter 11: Functional Organization of Nervous Tissue

Transcription

1 Chapter 11: Functional Organization of Nervous Tissue Multiple Choice 1. The nervous system A) monitors internal and external stimuli. B) transmits information in the form of action potentials. C) interprets or assesses information. D) maintains homeostasis. E) all of the above 2. Which of the following is responsible for problem-solving skills? A) central nervous system B) peripheral nervous system C) somatic nervous system D) autonomic nervous system E) none of the above 3. The central nervous system includes the A) ganglia. B) spinal cord. C) spinal nerves. D) cranial nerves. E) sensory receptors. 4. The peripheral nervous system includes the A) brain. B) spinal cord. C) cranial nerves. D) blood-brain barrier. E) cerebellum. 5. There are pairs of cranial nerves and pairs of spinal nerves. A) 10; 30 B) 31; 12 C) 12; 31

2 D) 30; 10 E) 12; Cell bodies of the peripheral nervous system are located in A) ganglia. B) Schwann cells. C) the motor division. D) the sensory division. E) nerves. 7. The sensory (afferent) division of the peripheral nervous system A) transmits action potentials to sensory organs. B) conveys action potentials to the CNS. C) stimulates glands to release hormones. D) stimulates muscle contractions. E) does not involve sensory receptors. 8. The motor (efferent) division of the peripheral nervous system A) is a division of the CNS. B) regulates the digestion of food. C) transmits impulses from the CNS to skeletal muscle. D) has nerve cell bodies located in ganglia near the spinal cord and brain. E) detects a stimulus. 9. The autonomic nervous system A) stimulates skeletal muscle contractions. B) has two sets of neurons in a series. C) is involved in problem solving. D) is under voluntary control. E) does not include the central nervous system. 10. Digestion of food is regulated by the A) sensory division. B) sympathetic division of the ANS. C) parasympathetic division of the ANS. D) somatic nervous system.

3 E) none of the above. 11. The central nervous system A) is the site for processing information. B) initiates visual and auditory stimuli. C) consists of 43 pairs of nerves. D) is totally involuntary. E) does not interact with the peripheral nervous system. 12. Which of the following is mismatched? A) central nervous system - brain B) autonomic nervous system - sympathetic and parasympathetic divisions C) peripheral nervous system - spinal nerves D) somatic nervous system - sensory division of PNS E) peripheral nervous system sensory and motor divisions 13. Protein synthesis in neurons occurs in A) axons. B) dendrites. C) cell bodies or soma. D) terminal boutons. E) node of Ranvier. 14. Nissl bodies are A) part of a dendrite. B) also called gemmules. C) lipid droplets. D) areas of rough endoplasmic reticulum. E) part of the Golgi apparatus. 15. Dendrites A) are the input part of the neuron. B) conduct action potentials away from the cell body. C) are generally long and unbranched. D) form synapses with the microglia. E) contain the trigger zone.

4 16. Axons A) contain the nucleus. B) are numerous extensions from each neuron. C) do not have a trigger zone. D) have a distal portion that branches to form the presynaptic terminals or terminal boutons. E) do not have a resting membrane potential. 17. Axons contain A) the trigger zone. B) foot processes. C) Nissl bodies. D) the soma. E) the rough endoplasmic reticulum. 18. Synaptic vesicles contain neurotransmitter are present in the A) dendrites. B) cell body. C) axolemma. D) presynaptic terminals or terminal boutons. E) trigger zone. 19. A neuron that carries action potentials from one neuron to another is called a(n). A) motor neuron B) sensory neuron C) afferent neuron D) efferent neuron E) interneuron 20. A neuron that conducts pain sensations to the central nervous system would be classified as a(n) A) motor neuron. B) sensory or afferent neuron. C) efferent neuron. D) association neuron.

5 E) interneuron. 21. The motor neurons responsible for making a fist are A) unipolar. B) bipolar. C) multipolar. D) pseudopolar. E) none of the above 22. Neurons that have a single axon and a single dendrite are A) unipolar. B) bipolar. C) multipolar. D) pseudopolar. E) monopolar. 23. Neurons in the skin that are responsible for detecting pain are A) apolar. B) unipolar. C) bipolar. D) multipolar. E) pseudopolar. 24. Which of the following statements regarding neuroglia is false? A) Neuroglia serve as the major supporting tissue in the CNS. B) Neuroglia form part of the blood-brain barrier. C) Neuroglia produce action potentials for skeletal muscles. D) Neuroglia form myelin sheaths around some axons. E) Neuroglia produce cerebrospinal fluid. 25. The blood-brain barrier A) permits passage of foreign substances from the blood to neurons. B) prohibits the transport of amino acids and glucose to the neurons. C) prohibits the removal of waste materials from the neurons. D) protects neurons from toxic substances in the blood. E) does not prevent fluctuations in the composition of the blood from affecting the functions

6 of the brain. 26. A neuroglial cell that is a major component of the blood-brain barrier is the A) astrocyte. B) microglial cell. C) oligodendrocyte. D) ependymal cell. E) macrophage. 27. Which of the following substances must pass through the blood-brain barrier in order for neurons to survive? A) nicotine B) collagen C) glucose D) dopamine E) insulin 28. Overproduction of cerebrospinal fluid could be the result of overactivity of the A) astrocytes. B) microglial cells. C) oligodendrocytes. D) macrophages. E) ependymal cells. 29. Microglia A) are part of the blood-brain barrier. B) are phagocytic cells in the CNS. C) produce cerebrospinal fluid. D) form myelin sheaths. E) are part of the choroids plexus. 30. Multiple sclerosis is a neurological disorder in which myelin sheaths in the CNS are destroyed. Which of the following neuroglial cells is being damaged in multiple sclerosis? A) astrocyte B) microglial cell C) oligodendrocyte

7 D) ependymal cell E) Schwann cells 31. Schwann cells differ from oligodendrocytes in which of the following ways? A) Schwann cells form myelin; oligodendrocytes do not. B) Oligodendrocytes are only found in the PNS; Schwann cells are only found in the CNS. C) Schwann cells form sheaths around several axons, while oligodendrocytes form sheaths around only one axon. D) Schwann cells form a myelin sheath around a portion of only one axon, while oligodendrocytes can surround portions of several axons. E) None of the above are true differences. 32. Which of the following is mismatched? A) microglia - provide support for the neuron cell body B) astrocytes - blood-brain barrier C) oligodendrocytes - form myelin sheaths D) ependymal cells - produce cerebral spinal fluid E) ependymal cells choroid plexus 33. Which of the following is true? A) In saltatory conduction, electrical charges flow from node to node. B) Myelination will not influence the speed of conduction of action potentials. C) The myelin sheath inhibits the flow of electrical charges at nodes. D) The myelin sheath is a protein wrapping. E) The myelin sheath does not electrically insulate the axons from one another. 34. Gaps or interruptions in the myelin sheath are called A) internodes. B) tight junctions. C) neurofilaments. D) nodes of Ranvier. E) gap junctions. 35. Action potentials are conducted more rapidly when transmission is A) from node to node on a myelinated axon. B) on a small diameter axon.

8 C) on an unmyelinated axon. D) from internode to internode. E) from internode to node on a myelinated axon. 36. White matter is composed of A) ganglial sheaths. B) bundles of myelinated axons. C) collections of nerve cell bodies. D) bundles containing both myelinated axons and nerve cell bodies. E) collections of unmyelinated axons. 37. If you cut bundles of axons and their myelin sheaths in the PNS, you cut A) ganglia. B) nuclei. C) nerves. D) gray matter. E) nerve tracts. 38. The plasma membrane of a neuron is more permeable to potassium ions because A) of its positive electrical charge. B) there are more non-gated channels for K+ than Na+. C) protein molecules cannot exit through the cell membrane. D) calcium ions block Na+ and Cl- channels. E) there are more non-gated channels for Na+ than K Which of the following is true? A) The resting plasma membrane is more permeable to Na+ than K+. B) The resting membrane potential never reaches an equilibrium point. C) The resting membrane potential is proportional to the tendency for K+ to diffuse out of the cell. D) Negatively charged Cl- ions are attracted by negative charges in the cell. E) The purpose of the sodium-potassium exchange pump is to create the resting membrane potential. 40. Mr. Miller has been hospitalized for the flu. The flu virus increases membrane permeability to potassium. You would expect his cells to

9 A) depolarize. B) repolarize. C) isopolarize. D) hyperpolarize. E) hypopolarize. 41. For the resting membrane potential, increasing the sodium ion concentration in the ECF results in A) hyperpolarization B) depolarization C) hypopolarization D) little change in membrane potential E) not enough information to tell 42. A change in the resting membrane potential has the following characteristics (nonpropagated, graded, can summate). This type of change can A) be a local potential B) be an action potential C) be a consequence of an increase in the permeability to Na+ D) result in repolarization E) A and C 43. Which of the following statements accurately describe events that occur as a result of a local potential reaching threshold? A) activation gates of Na+ ion channels begin to close B) inactivation gates of Na+ ion channels begin to open C) A positive feedback cycle develops in which depolarization causes activation gates of Na+ ion channels to open. D) K+ ion channels begin to close E) B and C 44. Which of the following events will lead to depolarization? A) an increase in K+ ions in the extracellular fluid B) a decrease in K+ ions in the extracellular fluid C) an increase in the rate of diffusion of K+ ions from cells D) an increase in Na+ ions in the extracellular fluid E) none of these cause depolarization

10 45. In hyperpolarization A) K+ ions tend to diffuse out of the cell. B) the plasma membrane's permeability to K+ decreases. C) the resting membrane potential moves closer to zero. D) Na+ ions enter the cell in large numbers. E) the resting membrane potential becomes more positive. 46. If the charge difference across the plasma membrane is decreased, A) the potential difference across the plasma membrane does not change. B) the membrane potential is more positive. C) the change is called hyperpolarization. D) negative proteins can leave the cell. E) the membrane potential is more negative. 47. Which of the following situations occurs in electrically excitable cells? A) When Na+ ion channels open, K+ ion channels close. B) The sodium-potassium exchange pump moves sodium into the cell. C) Depolarization causes voltage-gated sodium ion channels to open. D) Ligand-gated sodium ion channels are opened by high extracellular calcium levels. E) Proteins tend to diffuse out of the cell. 48. Voltage-gated sodium channels are sensitive to changes in the extracellular concentration of A) potassium ions. B) proteins. C) sodium ions. D) chloride ions. E) calcium ions. 49. A local potential A) does not occur until threshold. B) transmits information from one cell to another. C) might be a depolarization event but cannot be a hyperpolarization event. D) increases or decreases in direct proportion to the stimulus strength E) does not alter resting membrane potential.

11 50. A change in resting membrane potential confined to a small area is called a(n) A) local potential. B) action potential. C) summated potential. D) after potential. E) resting membrane potential. 51. Which of the following situations will lead to hyperpolarization? A) increase the permeability of the plasma membrane to Na+ ions B) decrease the permeability of the plasma membrane to K+ ions C) decrease the permeability of the plasma membrane to chloride ions D) any positive ion entering the cell E) none of these will lead to hyperpolarization 52. Depolarization of the nerve cell membrane occurs when there is a rapid influx (inflow) of A) potassium ions. B) chloride ions. C) calcium ions. D) sodium ions. E) proteins. 53. An action potential A) occurs when the local potential reaches threshold level. B) propagates across the plasma membrane in a decremental fashion. C) has no repolarization phase. D) is an example of negative feedback. E) cannot transmit information. 54. Which of the following events is not a characteristic of an action potential? A) The plasma membrane becomes highly permeable to sodium ions and depolarization results. B) As sodium ions enter, the inside of the plasma membrane becomes more negative. C) At the peak of depolarization, sodium channels begin to close and potassium channels open. D) In repolarization, potassium ions flow out of the cell. E) Action potentials occur according to the all-or-none principle.

12 55. A stimulus either causes an action potential or it doesn't. This is called A) an all-or-none response. B) a graded response. C) a latent period response. D) a relative refractory response. E) a local response. 56. In some cells, an afterpotential occurs because A) the sodium ions continue to enter the cell after depolarization is finished. B) there is prolonged, elevated permeability to potassium during repolarization. C) the sodium-potassium pump is actively exchanging ions across the membrane. D) the extracellular Na+ ion concentration is reduced. E) the permeability to sodium continues longer than necessary. 57. When repolarization of a neuron is complete, the A) neuron dies. B) neuron regenerates. C) cell no longer has a potential difference across its membrane. D) original polarity of the neuron is restored. E) neuron is no longer excitable. 58. The opening of more and more Na+ ion channels during depolarization A) is the result of the sodium-potassium exchange pump. B) is an example of a positive feedback cycle. C) is possible only if K+ channels remain closed. D) is the cause of the afterpotential. E) is an example of a negative feedback cycle. 59. Which of the following statements regarding voltage-gated K+ channels is true? A) These channels have only one gate. B) These channels open more slowly than Na+ channels. C) Once open, these channels remain open until repolarization is complete. D) These channels are specific for potassium. E) All of these are true.

13 60. During depolarization of the plasma membrane, A) sodium ions move rapidly into the cell. B) potassium ions move rapidly out of the cell. C) membrane permeability to sodium ions decreases. D) the outside of the cell becomes positively charged relative to the inside. E) sodium ions move rapidly out of the cell. 61. Each voltage-gated Na+ ion channel has two voltage sensitive gates: an activation gate and an inactivation gate. Which of the following would occur during depolarization? A) Activation gates are open; inactivation gates are closed. B) Activation gates are closed; inactivation gates are open. C) Both activation and inactivation gates are open. D) Both activation and inactivation gates are closed. E) None of the above occurs during depolarization. 62. Burn patients experience the destruction of cells and the release of cellular contents into the ECF. Burn patients are more likely to suffer from which of the following conditions? A) action potentials with exaggerated amplitudes B) tachycardia (a rapid heart rate) C) hyperpolarization of nerves and muscle fibers D) inability of neurons to stimulate muscle fibers E) A and B Level: If the ECF around a nerve cell is replaced with an isotonic saline solution that contains potassium ions and other solutes at concentrations very close to the ECF concentrations of a normal cell, the result is A) no resting membrane potential B) hyperpolarized membrane C) depolarized membrane D) a resting membrane potential close to its normal value E) none of the above Level: During the absolute refractory period, the cell A) generates many local potentials. B) is insensitive to further stimulation. C) responds to even weak stimuli.

14 D) reverses the direction of the action potential. E) is very sensitive. 65. The absolute refractory period assures A) prolonged depolarization during the action potential. B) completion of repolarization before another action potential. C) that no after-potential occurs. D) reversal of the direction of propagation of the action potential. E) that the stimulus is strong enough to elicit a response. 66. The absolute refractory period ends when A) inactivation gates of voltage-gated Na+ ion channels reopen. B) activation gates of voltage-gates Na+ ion channels reopen. C) the sodium-potassium exchange pump stops. D) voltage-gated K+ channels open. E) none of the above occurs. 67. Chemical synapses are characterized by A) the release of neurotransmitter by the presynaptic terminal. B) protein channels that connect the pre- and postsynaptic cells. C) the presence of receptors for neurotransmitters on the presynaptic terminal. D) the absence of gap junctions. E) receptors located only on the presynaptic terminal. 68. Gap junctions are functional synapses. A) chemical B) electrical C) potential D) intracellular E) neuromuscular 69. Local hyperpolarization in a synapse is called a(an) A) excitatory postsynaptic potential. B) resting membrane potential. C) inhibitory postsynaptic potential. D) gap junction potential.

15 E) action potential. 70. Arrange the events of synaptic transmission in correct sequence. 1. sodium ions diffuse into the cell and cause a local potential 2. neurotransmitter binds with receptor on postsynaptic cell 3. neurotransmitter diffuses across the synaptic cleft 4. membrane permeability to sodium ions on postsynaptic cell increases 5. action potential causes release of neurotransmitter A) 5, 2, 3, 4, 1 B) 5, 2, 3, 1, 4 C) 5, 3, 4, 1, 2 D) 5, 4, 3, 2, 1 E) 5, 3, 2, 4, A stimulus that results in a local potential that does not reach threshold is called a A) threshold stimulus. B) maximal stimulus. C) subthreshold stimulus. D) supramaximal stimulus. E) local stimulus. 72. As the strength of a stimulus is increased, the A) amplitude of the action potential increases. B) duration of the action potential increases. C) frequency of occurrence of action potentials increases. D) resonance of action potentials increases. E) height of the action potentials increases. 73. When the local potential returns quickly to resting membrane potential even though the stimulus continues, is occurring. A) an afterpotential B) ligand gating C) accommodation D) a sodium influx E) acclimation.

16 74. The junction between two neurons is a A) ganglia. B) synapse. C) fascicle. D) node of Ranvier. E) neuromuscular junction. 75. Neurotransmitters are released from the A) epineurium. B) synaptic cleft. C) presynaptic terminal. D) postsynaptic membrane. E) calcium channels. 76. Damage to a postsynaptic membrane would A) increase neurotransmitter release. B) decrease the release of neurotransmitter. C) increase neurotransmitter production. D) interfere with the ability to respond to neurotransmitter. E) destroy vesicles containing neurotransmitter. 77. Why isn't an action potential transmitted from a postsynaptic membrane to a presynaptic terminal? A) Presynaptic terminals have no acetylcholine receptors. B) Presynaptic neurons do not have a resting membrane potential. C) Acetylcholine can only diffuse in one direction across the synaptic cleft. D) Synaptic vesicles in the postsynaptic membrane are inactive. E) Acetylcholine is destroyed too fast. 78. Neurotransmitters A) stimulate presynaptic terminals. B) remain in the synaptic cleft for long periods of time. C) bind irreversibly to the receptor molecules of the postsynaptic membrane. D) cause the production of action potentials in the postsynaptic membrane. E) do not affect membrane channels in the postsynaptic membrane.

17 79. Neurotransmitter is being released at a synapse. Which of the following occurs last? A) Calcium ions enter the presynaptic terminal. B) Synaptic vesicles release neurotransmitter by exocytosis. C) An action potential is produced in the postsynaptic membrane. D) Neurotransmitter flows rapidly across the synaptic cleft. E) Neurotransmitter binds with the receptor on the postsynaptic membrane. 80. Rapid removal or destruction of neurotransmitter in the synaptic cleft A) may affect the ability of the postsynaptic membrane to generate action potentials. B) generates local potentials in the presynaptic terminal. C) is necessary for synaptic transmission. D) may lead to action potentials. E) may stop exocytosis. 81. Monamine oxidase inhibitors (MAO inhibitors) A) prevent synaptic transmission. B) enhance the breakdown of norepinephrine. C) enhance the binding of norepinephrine to its receptors. D) prevent the release of norepinephrine by the presynaptic terminal. E) have no effect on the action of norepinephrine. 82. Receptor molecules in synapses A) tend to concentrate on presynaptic terminals. B) bind irreversibly with neurotransmitter. C) have a high degree of specificity. D) serve as channel proteins. E) can bind to any molecule in the synapse. 83. Receptor molecules A) are nonspecific. B) are always lipids. C) attach to the synaptic cleft. D) determine whether a neurotransmitter will be excitatory or inhibitory. E) are not attached to ligand-gated channels. 84. A neuromodulator

18 A) acts as a neurotransmitter. B) inactivates neurotransmitters. C) is a receptor site for a neurotransmitter. D) has no influence on the amount of neurotransmitter released. E) is a substance released from neurons that influences the sensitivity of neurons to neurotransmitters. 85. When a neurotransmitter binds to its receptor and increases the permeability of the postsynaptic membrane to sodium ions, A) the membrane will be hyperpolarized. B) more chloride ions will also diffuse into the cell. C) an excitatory postsynaptic potential (EPSP) will result. D) the membrane will become impermeable to potassium ions. E) the sodium ions diffuse out of the cell. 86. The same neurotransmitter may produce different effects on neurons because of differences in the A) type of receptors on the postsynaptic membranes of neurons. B) strength of the action potential. C) amount of neurotransmitter. D) size of the neurons. E) potassium channels. 87. Action potentials at a chemical synapse travel A) from presynaptic terminal to postsynaptic membrane. B) from postsynaptic membrane to presynaptic terminal. C) back and forth from presynaptic terminal to postsynaptic membrane. D) from presynaptic terminal to presynaptic membrane. E) from postsynaptic terminal to postsynaptic membrane. 88. A decrease in the number of voltage-gated Ca++ ion channels in the presynaptic terminal would A) enhance transmission across the synapse. B) reduce or inhibit transmission across the synapse. C) have no effect on transmission across the synapse. D) alter receptors on the postsynaptic membrane. E) increase exocytosis.

19 89. A person who has seizures might have a deficit of which of the following? A) GABA B) dopamine C) glutamate D) serotoninp E) histamine 90. In an EPSP (excitatory postsynaptic potential), there is a A) net movement of sodium ions out of the cells. B) net movement of chloride ions into the cells. C) decrease in action potential amplitude. D) local hyperpolarization. E) local depolarization. 91. An inhibitory postsynaptic potential (IPSP) can result from the influx of A) calcium ions. B) sodium ions. C) chloride D) potassium ions. E) C or D 92. Enkephalins produce presynaptic inhibition in neurons transmitting pain signals. Increased levels of enkephalins will A) increase awareness of pain. B) decrease awareness of pain. C) increase amount of pain. D) decrease amount of pain. E) have no effect on awareness or amount of pain. 93. A local anesthetic such as Novocaine decreases membrane permeability to Na+ ions. The use of this anesthetic will A) block sensory input into the CNS. B) enhance the development of EPSPs. C) cause RMP to move closer to threshold. D) cause Cl- ions to enter cells instead of Na+ ions. E) depolarize the cell.

20 Level: An IPSP is inhibitory because it A) changes the threshold of the neuron. B) hyperpolarizes the postsynaptic membrane. C) prevents Ca++ entry into the presynaptic terminal. D) reduces the amount of neurotransmitter released by the presynaptic terminal. E) depolarizes the postsynaptic membrane. 95. When two action potentials arrive simultaneously at two different presynaptic terminals that synapse with the same postsynaptic neuron, A) the direction of the action potential is reversed. B) temporal summation occurs. C) spatial summation occurs. D) hyperpolarization occurs. E) threshold is never reached. 96. If five action potentials arrive at the same synapse in very close succession, which of the following would occur? A) The direction of the action potential is reversed. B) Temporal summation occurs. C) Spatial summation occurs. D) Hyperpolarization occurs. E) Depolarization always occurs. 97. Suppose both excitatory and inhibitory neurons synapse with a single postsynaptic neuron. What determines if an action potential is initiated in the postsynaptic neuron? A) the kind of neuron involved B) the size of the neuron involved C) whether the neuron is myelinated or non-myelinated D) the number of EPSPs in relation to the number of IPSPs E) This situation is not possible in humans. 98. When two or more presynaptic neurons synapse with a single postsynaptic neuron in the CNS, a(n) pathway is formed. A) convergent B) divergent

21 C) oscillatory D) somatic E) sensory 99. Sensory neurons carrying action potentials from pain receptors synapse within the spinal cord with interneurons. These interneurons synapse with motor neurons leading back to an effector and ascending neurons that carry action potentials toward the brain. This is an example of a(n) pathway. A) convergent B) divergent C) oscillatory D) sensory E) bifurcated Level: Neurons arranged in a circular pathway form A) neuromotor junctions. B) oscillatory circuits. C) spatial pathways. D) temporal circuits. E) circulating pathways. Refer to the following figure for questions Identify structure A on the neuron. A) Schwann cell B) Node of Ranvier C) neuron cell body (soma) D) dendrites E) axon

22 102. Identify structure B on the neuron. A) Schwann cell B) Node of Ranvier C) neuron cell body (soma) D) dendrites E) axon 103. Identify structure C on the neuron. A) Schwann cell B) Node of Ranvier C) neuron cell body (soma) D) dendrites E) axon 104. Identify structure D on the neuron. A) Schwann cell B) Node of Ranvier C) neuron cell body (soma) D) dendrites E) axon 105. Identify structure E on the neuron. A) Schwann cell B) Node of Ranvier C) neuron cell body (soma) D) dendrites E) axon Fill in the Blank 106. The nervous system has two subdivisions - the central nervous system and the nervous system. Answer: peripheral 107. are collections of neuron cell bodies located outside of the central nervous

23 system. Answer: ganglia 108. Nerve fibers are also called. xons 109. are processes that conduct electric signals toward the cell body. endrites 110. A neuron with several dendrites and a single axon would be called a neuron. Answer: multipolar 111. Most unipolar neurons are neurons. Answer: sensory 112. are neuroglia cells that are macrophages. Answer: microglia 113. Cerebrospinal fluid is produced by cells. pendymal 114. Action potentials are conducted rapidly from one node of Ranvier to the next in a process called conduction. Answer: saltatory Essay Questions 115. Why are mature neurons unable to give rise to brain tumors? What cells do give rise to the tumors of the nervous system? Answer: Mature neurons do not multiply and are unable to give rise to brain tumors. The great majority of tumors of the nervous system arise from glial cells or the proliferation of other tissue cells found in conjunction with the brain, such as the epithelial cells of the pituitary gland. Very rarely, immature neurons will give rise to tumors knows as neuroblastomas. Level: Distinguish between a neuron, a neurofilament, and a nerve.

24 Answer: A neuron is a nerve cell. Neurofilaments are intermediate filaments found inside the cell body of a neuron. Bundles of axons and their sheaths are known as nerves. Level: A virus causes damage to the sodium channels of the postsynaptic neuron such that they open very slowly in response to a neurotransmitter. How does this modify the generation of an action potential in the postsynaptic neuron? Answer: Because the sodium channels are opening slowly, depolarization of the cell membrane of the post-synaptic neuron takes longer. The overall speed of action potential conduction is slowed, as transmission takes longer at the synapse. In fact, the channels could open so slowly that depolarization does not occur at all and the action potential would not be transmitted across the synapse. Level: What is the survival advantage of the blood-brain barrier? Answer: The blood-brain barrier protects the delicate neurons from toxic substances in the blood, while allowing the exchange of nutrients and waste products between the blood and neurons Multiple sclerosis is a disease characterized by degeneration of the myelin sheath of nerve fibers in the brain and spinal cord. Why is the ability to control skeletal muscles affected in this disease? Answer: The motor neurons that carry information from the central nervous system to skeletal muscles are myelinated. Loss of myelin will adversely affect rate of nerve impulse conduction on these neurons. Nerve impulse conduction slows or may be stopped, resulting in difficulties controlling or moving these muscles. Level: Valium is a drug that triggers the opening of chloride ion channels. Will treatment with Valium depolarize or hyperpolarize a cell? Explain. Answer: Valium will hyperpolarize. Chloride ions are negatively charged and as the number of negative ions inside the cell increases, the cells resting membrane potential moves further from zero. Level: Predict the effect of a drug that reduces the permeability of the plasma membranes to sodium ions. Would such a drug have any medical applications? Explain. Answer: This drug would cause the rate of sodium movement into cells to decrease. Therefore a greater stimulus would be required to develop depolarization. This drug could have a use in treatment of conditions where there is a need to reduce euphoria, hyperactivity, and other manic symptoms. Level: The sciatic nerve of a pithed frog was carefully removed and placed in a nerve chamber with recording electrodes. When both recording electrodes were placed on the surface of the nerve (both were extracellular), a resting membrane potential was not recorded. However, when

25 one electrode was extracellular and the other electrode was intracellular, a resting membrane potential was recorded. Explain these two sets of results. Answer: When both electrodes are placed on the surface of the nerve, no RMP is recorded, as there is no difference in electrical charge between the two electrodes. However, when one electrode is placed inside the cell and the other is left outside the cell, then there will be an RMP recorded, because there is an unequal concentration of ions separated by the cell membrane. Level: A virus causes damage to the sodium channels of the postsynaptic neuron such that they open very slowly in response to a neurotransmitter. How would this modify the generation of an action potential in the postsynaptic neuron? Answer: The action potential would be more difficult to generate (or would take longer) because the sodium influx necessary for depolarization will occur more slowly. Level: 3