1. Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 0 0 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Chapter 8 The Nervous System Presented by Dawn Duran, PT, MHS, CSCS Adjunct Professor, Kaplan University

2. Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 1 1 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. The Nervous System  Both the nervous and endocrine systems are the two ways that the body communicates with itself.  The nervous system is faster than the endocrine system.  Nervous tissue is responsible for rapid communication between body structures and control of body functions.

3. Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 2 2 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. The Nervous System The nervous system performs various functions, including:  Communication between body parts  Integration of body parts  Control of body functions  Recognition of sensory stimuli

4. 3 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What are the two principal divisions of the nervous system?

5. 4 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Organs and Divisions of the Nervous System Central nervous system (CNS): Consists of the brain a nd spinal cord (SC) Peripheral nervous system (PNS): Consists of all of the nerves in the body  Autonomic nervous system (ANS) is a subdivision of the PNS.  It regulates the body’s autonomic, or involuntary, functions.

6. 5 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Divisions of the Nervous System

7. 6 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Physiology of the Nervous System

8. 7 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cells of the Nervous System The two types of cells found in the nervous system are neurons (nerve cells) and glia (specialized connective tissue cells).  Neurons conduct impulses  Glia (support) cells  In other words, neurons are the conducting cells and glial cells are the supportive and connective tissue cells.

9. 8 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cells of the Nervous System Neurons  Consist of three main parts Dendrites (one or more branches; these carry information/messages towards the cell body) Cell body (main part of the neuron) Axon (one elongated projection that carries information/messages away from the cell body)  In other words, axons carry nerve impulses (known as action potentials away from the cell body of the neuron

10. 9 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cells of the Nervous System  Classified according to function Sensory neurons transmit information towards the CNS  These are afferent neurons Motor neurons carry impulses away from the CNS to either muscle or glandular tissue  These are efferent neurons (E=exit) Interneurons connect the impulses from sensory to motor neurons

11. 10 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cells of the Nervous System  Axons are surrounded by myelin, which is a white fatty substance  Myelin is formed by Schwann cells and is found on the axons in the peripheral nervous system (PNS).  The outer cell membrane of a Schwann cell is called the neurilemma. This plays a critical role in regeneration of cut and injured axons. Axons in the brain and SC do not have neurilemma, so the potential for regeneration in the CNS is less than in the PNS.  Nodes of Ranvier are indentations between adjacent Schwann cells

12. 11 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. What is the purpose of a myelin sheath?  One of the purposes of myelin is to increase the speed of the action potential (ie nerve impulse).  It provides insulation which allows the nerve impulses to travel more quickly along the length of the nerve. The impulse hops from one node of Ranvier to the next and is able to skip across the insulated fiber in between, therefore significantly decreasing the length of time it takes for an impulse to perpetuate and travel to where it needs to go. This is called saltatory conduction.  In unmyelinated nerve fibers, a nerve impulse is a self- propagating wave of electrical disturbance.

13. 12 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Multiple Sclerosis The most common primary disease of the CNS (Central Nervous System) that affects the myelin is multiple sclerosis (MS).

14. 13 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Be able to label a diagram such as that found in Figure 8-2 on page 188 of your textbook

15. 14 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Glial cells are found in nervous tissue. “Glia means glue, and these cells help with support and “holding things together.” Glia (aka neuroglia) do not specialize in conducting impulses as neurons do.  They are support cells, bringing the cells of nervous tissue together structurally and functionally. Glia holding the functioning neurons together, protect them and regulate neuron function. Cells of the Nervous System

16. 15 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cells of the Nervous System There are three main types of glial cells of the CNS  Astrocytes  These are star-shaped cells that help form the blood- brain barrier (BBB).  The BBB separates the blood from nervous tissue to protect the brain from harmful chemicals that may be in the blood.  Microglia  These are small and usually stationary. They can assist with phagocytosis.  Oligodendrocytes  These function to produce myelin in the CNS. This helps hold nerve fibers in the CNS together. They are analogous to the Schwann cells of the PNS in this regard.

17. 16 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cells of the Nervous System Astrocytes Microglia Oligodendrocytes Types of Glial cells:

18. 17 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerves  Nerve consists of a bundle of axons in the Peripheral Nervous System (PNS)  Tract consists of a bundles of axons in the Central Nervous System (CNS)  White matter of the brain: Formed by myelinated tracts. Myelin gives this tissue a white color.  Gray matter: Tissue composed primarily of cell bodies and unmyelinated axons and dendrites. Since white myelin is not present it appears gray.

19. 18 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerves  Nerve coverings are composed of fibrous connective tissue  Endoneurium: Surrounds individual fibers within a nerve  Groups of wrapped axons are called fascicles  Perineurium: Surrounds a group (or fascicle) of nerve fibers  Epineurium: Surrounds the entire nerve

20. 19 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerves A group of nerve cell bodies located in the PNS is called a ganglion. It is located near the spinal cord.

21. 20 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What is a reflex arc? What purpose does it serve?

22. 21 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Reflex Arcs Nerve impulses are conducted from receptors to effectors over neuron pathways or reflex arcs An effector is an organ that puts nerve signals “into effect.” A neuron pathway is the route traveled by a nerve impulse. The reflex arc is a specialized path of the neuron pathway, allowing impulse conduction in only one direction. Conduction by a reflex arc results in a reflex, either contraction by a muscle or secretion by a gland Somatic reflexes are contractions of skeletal muscle

23. 22 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Reflex Arcs The simplest type of reflex arcs are two-neuron arcs; they consist of sensory neurons synapsing in the spinal cord with motor neurons Example: Knee Jerk Reflex Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that then synapse with motor neurons

24. 23 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Reflex Arcs The purpose of a reflex arc is to provide even faster rate of transmission by cutting out the middle man in order to provide a protective reflex.

25. 24 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What is a nerve impulse?

26. 25 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerve Impulses Special signals called nerve impulses are used by the nervous system. They are also referred to as action potentials. Self-propagating waves of electrical disturbances that travel along the surface of a neuron membrane Impulses usually originate in receptors, which are specialized dendrites of sensory neurons A stimulus is normally a pressure, temperature or chemical change

27. 26 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerve Impulse The membrane of each resting neuron has a slight positive charge on the outside and a negative charge on the inside This is a result of the excess of sodium ions that exist on the outside of the membrane

28. 27 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerve Impulses Mechanism  A stimulus triggers the opening of Na + channels in the plasma membrane of the neuron  ie it increases permeability to Na+  Inward movement of positive sodium ions leaves a slight excess of negative ions outside at a stimulated point  This marks the beginning of a nerve impulse

29. 28 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Saltatory Conduction If the traveling impulse encounters a section of membrane insulated with myelin it can jump over the myelin to the next exposed section of the neuron This type of impulse conduction is much faster than is possible in nonmyelinated neurons

30. 29 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Conduction of Nerve Impulses

31. 30 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. The Synapse  A synapse is a place where impulses are transmitted from one neuron (the presynaptic neuron) to another neuron (the postsynaptic neuron)  Synapses are composed of three structures, in addition to a very narrow synaptic cleft  Synaptic knob  Synaptic cleft  Postsynaptic neuron plasma membrane

32. 31 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. The Synapse  The synaptic knob is a bulge at the end of a presynaptic neuron’s axon which is composed of small sacs that contain neurotransmitters  When a nerve impulse arrives at the synaptic nob, neurotransmitters are released into the synaptic cleft, which is the space between the synaptic knob and the plasma membrane of the postsynaptic neuron  The postsynaptic neuron plasma membrane contains receptors specific to the neurotransmitter released

33. 32 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Components of a Synapse

34. 33 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. The Synapse A synapse is a microscopic space that separates the axon ending of one neuron from the dendrites of another neuron. Neurotransmitters are stored in the presynaptic neuron and cross the synaptic cleft to the postsynaptic neuron Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron  They then open ion channels and stimulate impulse conduction by the membrane

35. 34 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Question What are examples of neurotransmitters?

36. 35 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Neurotransmitters Neutrotransmitters are chemicals by which neurons communicate. There are at least 30 different neurotransmitters in our bodies. Types of neurotransmitters include…  Acetylcholine (ACh) – works in SC and at neuromuscular junction

37. 36 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Neurotransmitters  Endorphins and enkephalins – morphine-like substances that inhibit pain impulses (ie are natural pain killers)  Athletes and people who exercise heavily may release endorphins regularly during activity

38. 37 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Neurotransmitters  Catecholamines (norepinephrine, epinephrin, dopamine, and serotonin) – play a role in sleep, motor function, mood and pleasure recognition A deficiency of dopamine may result in Parkinson Disease

39. Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 38 38 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Structure of the Nervous System

40. Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 39 39 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System Consists of: Brain (located in the dorsal and cranial cavities) Spinal Cord

41. Copyright © 2005, Elsevier, Inc. All rights reserved. Slide 40 40 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Divisions of the Brain Brainstem Cerebrum Cerebellum

42. 41 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System Divisions of the brain  Brainstem – this structure is responsible for basic vital life functions such as breathing, heartbeat and blood pressure. The brainstem is composed of:  Pons  Midbrain  Medulla oblongata  Contains the vital centers (cardiac, respiratory and vasomotor centers )

43. 42 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System  Diencephalon – located above the midbrain and below the cerebrum  Hypothalamus – this pea-sized structure makes some hormones and is responsible for regulation of body temperature  The posterior pituitary gland is an extension of the hypothalamus  Thalamus – helps produce sensations, associates sensations with emotions and plays a part in the alerting mechanism

44. 43 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Thalamus The thalamus is involved with the association of senses with emotions. For example, a certain aroma may bring back pleasant childhood memories of grandma baking cookies.

45. 44 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System  Cerebellum  Second largest part of the human brain  Lies under the occipital lobe  Functions in balance and coordination of body movements  Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain posture  An individual with a tumor in his cerebellum may have problems with coordination and keeping his balance.

46. 45 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System  Cerebrum (Figure 8-10)  Largest part of the human brain  The part of the brain that has to do with thinking, or “cognition”  Divided into lobes called frontal, parietal, temporal and occipital  Divided into two halves which are connected by the corpus callosum. This structure connects and allows communication between the left and right cerebral hemispheres.  Shallow grooves of the cerebrum are called sulci while the ridges or convolutions are called gyri

47. 46 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Lobes of the Brain Motor movements are associated with the frontal lobe Hearing is associated with the temporal lobe Vision is associated with the occipital lobe

48. 47 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System  Outer layer of gray matter is the cerebral cortex, composed mainly of dendrites and cell bodies of neurons  Interior of the cerebrum composed mainly of white matter (nerve fibers arranged in bundles called tracts)  Islands of gray matter found within the hemisphere of the cerebrum are known as cerebral nuclei of basal ganglia

49. 48 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System When a blood vessel in the brain is blocked with a blood clot or the blood vessel ruptures, the individual may suffer a stroke. Another name for stroke is CVA (CerebroVSascular Accident).

50. 49 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. The Cerebrum Central Nervous System

51. 50 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System Spinal cord (lies within the spinal column)  Outer part composed of white matter made up of many bundles of axons called tracts  Interior is composed of gray matter made up mainly of neuron dendrites and cell bodies  Functions as the center for all spinal cord reflexes  Sensory tracts conduct impulses to the brain  Motor tracts conduct impulses from the brain

52. 51 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Nerve tissue needs to be protected, so the brain and spinal cord are covered by tough, fluid- containing membrane called the meninges, which are then covered by bone. Central Nervous System

53. 52 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Meninges & CSF  Cerebral and spinal meninges—dura mater (tough outer layer) ; arachnoid mater (found between dura and pia mater); and pia mater (innermost layer)  These layers extend from the SC into the brain  The fluid spaces found between the menginges are called epidural, subdural and subarachnoid  Cerebrospinal fluid (CSF) fills the subarachnoid spaces as well as ventricles of the brain  Hydrocephalus refers to too much CSF, or “water on the brain”

54. 53 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Central Nervous System  Be able to identify structures of the CNS as illustrated in Figure 8-9, p 198

55. 54 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Peripheral Nervous System Cranial nerves  Structure— 12 pairs are attached to the undersurface of the brain  Function—conducts impulses between the brain and structures in the head and neck and in the thoracic and abdominal cavities

56. 55 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cranial Nerves – Know the names and functions of these nerves! Table 8-2, p 210

57. 56 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Cranial Nerves and their Functions I (olfactory) = smell II (optic) = vision X (vagus) = slow heart rate down XII (hypoglossal) = tongue movements

58. 57 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Spinal nerves  Structure—contains dendrites of sensory neurons and axons of motor neurons  Functions—conducts impulses necessary for sensations and voluntary movements  Sensory neurons carry impulses from the periphery of the body to the brain and spinal cord  Motor neurons carry impulses from the brain and spinal cord to the periphery of the body

59. 58 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Spinal nerves by region 8 cervical 12 thoracic 5 lumbar

60. 59 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic Nervous System (ANS) Motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue Regulates the body’s autonomic or involuntary functions

61. 60 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic neurons  Preganglionic autonomic neurons conduct from spinal cord or brainstem to autonomic ganglia  Postganglionic neurons conduct from autonomic ganglia to cardiac muscle, smooth muscle, and glandular epithelial tissue Autonomic Nervous System

62. 61 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic or visceral effectors  Tissues to which autonomic neurons conduct impulses (ie cardiac and smooth muscle and glandular epithelial tissue) Autonomic conduction paths to visceral effects  Consist of two-neuron relays. Impulses travel over preganglionic neurons from the spinal cord or brainstem to autonomic ganglia. There they are relayed across synapses to postganglionic neurons, which then conduct the impulses from the ganglia to visceral effectors.  In contrast, somatic motor neurons conduct all the way from the spinal cord or brainstem to somatic effectors with no intervening synapses. Autonomic Nervous System

63. 62 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic Nervous System ANS consists of two divisions  Sympathetic  Parasympathetic

64. 63 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Sympathetic nervous system  Structure  Sympathetic preganglionic neurons have dendrites and cell bodies in gray matter of thoracic and upper lumbar segments of the spinal cord  Sympathetic postganglionic neurons have dendrites and cell bodies in sympathetic ganglia Autonomic Nervous System

65. 64 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.  Functions  Serves as the emergency or stress system  Group of changes induced by sympathetic control is called the fight-or-flight response  The physiologic changes associated with the fight- or-flight include enlarged pupils, increased heart rate, dilated skeletal blood vessels  The sympathetic nervous system controls visceral effectors during strenuous exercise and strong emotions, such as anger, fear, hate, or anxiety. Autonomic Nervous System

66. 65 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Parasympathetic nervous system:  Structure  Parasympathetic preganglionic neurons have dendrites and cell bodies in the gray matter of brainstem and sacral segments of the spinal cord  This is why it is sometimes called the craniosacral system  Parasympathetic preganglionic neurons terminate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors Autonomic Nervous System

67. 66 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Parasympathetic nervous system  Function  Dominates control of many visceral effectors under normal, everyday conditions  The parasympathetic system slows heart rate and increases peristalsis and the secretion of digestive juices. It dominates in normal, everyday activities.  The sympathetic system has the opposite effect and dominates in emergency situations. Autonomic Nervous System

68. 67 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Autonomic Nervous System Autonomic nervous system as a whole  Regulates the body’s autonomic functions in ways that maintain or quickly restore homeostasis  Emotions can affect the ANS.  Anger and fear can lead to increased sympathetic activity, while meditation deceases sympathetic activity.  Many organs are doubly innervated by the ANS; in other words, they receive fibers from both the parasympathetic and sympathetic divisions. Parasympathetic and sympathetic impulses continually bombard the organs and influence their function in opposite or antagonistic ways but achieve a balance (ie homeostasis).

69. 68 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. For your quiz… Be able to label the autonomic conduction paths shown in Figure 8-19 on page 213

70. 69 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. How does the muscular system interact with other body systems? In other words, what are the functional relationships between the body systems? A system with which the nervous system interacts on a regular basis is the Muscular System How do they interact? Can you think of any more?

71. 70 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. How does the Nervous System contribute to homeostasis? Along the same lines as the previous question: what systems does this system interact with to accomplish this? How does this interaction occur?

72. 71 Copyright (c) 2008, 2005 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. ??????????????????????? Questions???????????