Nervous System Chapter 10 PDF

Nervous System Chapter 10 Copyright © 2017, Elsevier Inc. All Rights Reserved. 1  Learning Objectives Lesson 10.1: Structure and Function of Nerves 1. List the organs and divisions of the nervous system and describe the generalized functions of th...

Nervous System Chapter 10 Copyright © 2017, Elsevier Inc. All Rights Reserved. 1  Learning Objectives Lesson 10.1: Structure and Function of Nerves 1. List the organs and divisions of the nervous system and describe the generalized functions of the nervous system as a whole. 2. Do the following related to the cells of the nervous system: Identify the major types of cells in the nervous system and discuss the function of each. Describe the function, size, and shape of glia. Discuss various disorders of nervous tissue. Copyright © 2017, Elsevier Inc. All Rights Reserved. 2  Learning Objectives Lesson 10.1: Structure and Function of Nerves (Cont.) 3. Identify the structure of a nerve. 4. Identify the anatomical components of a reflex arc and explain its function. 5. Explain the mechanisms of transmission of a nerve impulse along a nerve fiber and across a synapse. Copyright © 2017, Elsevier Inc. All Rights Reserved. 3  Organs and Divisions of the Nervous System  Central nervous system (CNS)  Brain and spinal cord  Peripheral nervous system (PNS)  All nerves Copyright © 2017, Elsevier Inc. All Rights Reserved. 4 Divisions of the Nervous System Copyright © 2017, Elsevier Inc. All Rights Reserved. 5 Copyright © 2017, Elsevier Inc. All Rights Reserved. 6  Cells of the Nervous System  The two types of cells found in the nervous system are Neurons, or nerve cells, and glia, specialized connective tissue cells.  Neurons are most important in the transmission of information  Neurons  Sensory neurons: Conduct impulses to the spinal cord and brain; also called afferent neurons  Motor neurons: Conduct impulses away from brain and spinal cord to muscles and glands; also called efferent neurons  Interneurons: conduct impulses from sensory neurons to motor neurons. They are also called central or connecting neurons, Interneurons are located entirely within the gray matter of the brain or spinal cord Copyright © 2017, Elsevier Inc. All Rights Reserved. 7  Structure of a eurons Neuron Consist of three parts Cell body of neuron Main part contains nucleus Dendrites Branching projections that conduct impulses to cell body of neuron Axon Elongated projection that conducts impulses away from cell body of neuron Myelin is a white, fatty substance Copyright © 2017, Elsevier Inc. All Rights Reserved. 8  Dendrites are tree-like structures that receive signals from other neurons and then transmit signals toward the cell body. Neurons can carry various numbers of dendrites.  The cell body contains the nucleus and is essential for the life of the cell. Usually receives thousand of signals from the dendrites and “decides” on the signal that it wants to send to the axon.  The axon is a long extension that transmits signals away from the cell body. The end of the axon undergoes extensive branching to form many axon terminals. Chemical neurotransmitters are stored with in the axon Copyright © 2011, 2007 by Saunders, terminals. an imprint of Elsevier Inc. All rights 9 Copyright © 2017, Elsevier Inc. All Rights Reserved. reserved.  Myelin Sheath  White fatty material that protects and insulates the axon  Nerve fibers covered by myelin are said to be myelinated; Some are not encased in myelin and are called unmyelinated neurons  Myelination begins during the 4th month of fetal life until teenage years  Myelin sheath differs in peripheral and CNS. Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights 10 Copyright © 2017, Elsevier Inc. All Rights Reserved. reserved.  Glia (Neuroglia)  Support cells, bringing the cells of nervous tissue together structurally and functionally  Three main types of connective tissue cells of the CNS  Astrocytes: Star-shaped cells that anchor small blood vessels to neurons  Microglia: Small cells that move in inflamed brain tissue carrying on phagocytosis  Oligodendrocytes: Form myelin sheaths on axons in the CNS (Schwann cells form myelin sheaths in PNS only) Copyright © 2017, Elsevier Inc. All Rights Reserved. 11  Glia Copyright © 2017, Elsevier Inc. All Rights Reserved. 12  Disorders of Nervous Tissue  Multiple sclerosis: Characterized by myelin loss in central nerve fibers and resulting conduction impairments; resulting nerve damage disrupts communication between the brain and the body.  Multiple sclerosis causes many different symptoms, including vision loss, pain, fatigue, and impaired coordination. The symptoms, severity, and duration can vary from person to person. Some people may be symptom free most of their lives, while others can have severe chronic symptoms that never go away.  Physical therapy and medications that Copyright © 2017, Elsevier Inc. All Rights Reserved. 13 Effects of Multiple Sclerosis (MS) Copyright © 2017, Elsevier Inc. All Rights Reserved. 14  Tumors  General name for nervous system tumor is neuroma. A neuroma is a benign tumor of nerve tissue that is often associated with pain or specific types of various other symptoms. Copyright © 2017, Elsevier Inc. All Rights Reserved. 15  Neurofibromatosis  A group of genetic disorders that cause tumors to form on nerve tissue. A condition that causes tumors to form in the brain, spinal cord, and nerves.  Neurofibromatosis is usually noncancerous. There are three types of this condition. Type 1 usually appears in childhood, while Types 2 Copyright © 2017, Elsevier Inc. All Rights Reserved. 16  Glioma Gliomas can occur in the brain and in various locations in the nervous system, including the brain stem and spinal column. Different types of gliomas cause different symptoms. Some include headaches, seizures, irritability, vomiting, visual difficulties, and weakness or numbness of the extremities. Treatments include surgery, radiation therapy, chemotherapy, and targeted molecular therapy. From Feldman M, Friedman L, Brandt L: Sleisenger & Fordtran's gastrointestinal and liver disease, ed 8, Philadelphia, 2006, Saunders. Copyright © 2017, Elsevier Inc. All Rights Reserved. 17  Nerves  Nerve: Bundle of peripheral axons  Tract: Bundle of central axons  White matter: Brain or cord tissue composed primarily of myelinated axons (tracts)  Gray matter: Brain or cord tissue composed primarily of cell bodies and unmyelinated fibers  Nerve coverings: Fibrous connective tissue  Endoneurium Surrounds individual fibers within a nerve  Perineurium Surrounds a group (fascicle) of nerve fibers  Epineurium Surrounds the entire nerve Copyright © 2017, Elsevier Inc. All Rights Reserved. 18 Copyright © 2017, Elsevier Inc. All Rights Reserved. 19 Patellar Reflex Copyright © 2017, Elsevier Inc. All Rights Reserved. 21  Simple, Two-Neuron Reflex Arc  Stimulus generates a nerve impulse  Impulse travels down the sensory neuron’s dendrite to its cell body in the dorsal root ganglion and into the axon  Impulse travels across the microscopic space (synapse) from the axon of the sensory neuron and into the dendrite of a neuron in the gray matter of the spinal cord  In synapse, chemical signals are sent across gap, and the impulse continues along the motor neuron  Motor neuron then forms a synapse with an effector, an organ that puts nerve signals “into Copyright © 2017, Elsevier Inc. All Rights Reserved. 22  Nerve Impulses  Definition: Self-propagating wave of electrical disturbance that travels along the surface of a neuron membrane; often called action potentials Copyright © 2017, Elsevier Inc. All Rights Reserved. 24  Saltatory Conduction  When traveling impulses encounter a section of membrane covered with insulating myelin, they “jump” around the myelin from one gap to the next Copyright © 2017, Elsevier Inc. All Rights Reserved. 29  Synapses  Definition: The place where impulses are transmitted from one neuron to another  Synapse made of three structures  Synaptic knob  Synaptic cleft  Plasma membrane A nerve impulse travels from one neuron to another through a synapse via a neurotransmitter Copyright © 2017, Elsevier Inc. All Rights Reserved. 30 Components of a Synapse Copyright © 2017, Elsevier Inc. All Rights Reserved. 31  Video demo  https://youtu.be/ VitFvNvRIIY? si=7KhvdnqKv3dJ3 nml Copyright © 2017, Elsevier Inc. All Rights Reserved. 32  Synapses (Cont.)  Names of neurotransmitters: Acetylcholine, catecholamines (norepinephrine, dopamine, and serotonin), endorphins, enkephalins, nitric oxide (NO), and other compounds  Neurotransmitters are chemicals by which neurons communicate. At least 30 different compounds have been identified as neurotransmitters. Copyright © 2017, Elsevier Inc. All Rights Reserved. 33 Parkinson disease (PD): Parkinsonism Characterized by abnormally low levels of dopamine in motor control areas of the brain; patients usually exhibit involuntary trembling and muscle rigidity. Parkinson's often starts with a tremor in one hand. Other symptoms are slow movement, stiffness, and loss of balance. Medications can help control the symptoms of Parkinson’s. It cannot be cured, Copyright © 2017, Elsevier Inc. All Rights Reserved. 34  Video Demonstration  https://youtu.be/7SyTpEdhBLw? si=Tt4vbh2PlUCjSwUe Copyright © 2017, Elsevier Inc. All Rights Reserved. 35  Learning Objectives Lesson 10.2: Central Nervous System 6. Identify and discuss the major anatomical components of the brain and spinal cord, their functions, and brain disorders. 7. Identify and discuss the coverings and fluid spaces of the brain and spinal cord. Copyright © 2017, Elsevier Inc. All Rights Reserved. 36  Central Nervous System  Brain  Cerebrum Frontal Parietal Temporal Occipital  Cerebellum  Diencephalon  Brainstem Midbrain Pons Medulla oblongata  Spinal cord Copyright © 2017, Elsevier Inc. All Rights Reserved. 37 Copyright © 2017, Elsevier Inc. All Rights Reserved. 38  Cerebrum: Four Lobes  Largest part of the brain and is divided into the right and left cerebral hemispheres.  The corpus callosum, bands of white matter that form a large fiber tract, joins the two hemispheres and allows them to communicate with each other.  Each cerebral hemisphere has four major lobes that are named for the overlying cranial bones.  Frontal lobe  Parietal lobe  Temporal lobe  Occipital lobe Copyright © 2017, Elsevier Inc. All Rights Reserved. 39 Copyright © 2017, Elsevier Inc. All Rights Reserved. 40 Copyright © 2017, Elsevier Inc. All Rights Reserved. 41 Copyright © 2017, Elsevier Inc. All Rights Reserved. 42  Cerebellum  Second largest part of the human brain  Helps control muscle contractions to produce coordinated movements so that we can maintain balance, move smoothly, and sustain normal postures  Recent evidence shows that the coordinating effects of the cerebellum may be more extensive, also assisting the cerebrum and other regions of the brain Copyright © 2017, Elsevier Inc. All Rights Reserved. 43  Diencephalon The diencephalon is involved in many crucial bodily functions including coordinating with the endocrine system to release hormones, relaying sensory and motor signals to the cerebral cortex, and regulating Copyright © 2017, Elsevier Inc. All Rights Reserved. 44  Diencephalon There are two parts of the diencephalon, the thalamus and the hypothalamus. The thalamus acts as a sensory pathway for information coming from the lower brain and the spinal cord to the sensory areas of the cerebrum. It is especially important with regard to pain sensation. The hypothalamus sits above the pituitary gland and controls endocrine function. It is also the body’s thermostat and helps regulate autonomic functions. Copyright © 2017, Elsevier Inc. All Rights Reserved. 45  Hypothalamus  Structure and function of the hypothalamus  Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter  Acts as the major center for controlling the ANS; helps control the functioning of most internal organs  Controls hormone secretion by anterior and posterior pituitary glands; it indirectly helps control hormone secretion by most other endocrine glands  Contains centers for controlling Copyright © 2017, Elsevier Inc. All Rights Reserved. 46 Brainstem Copyright © 2017, Elsevier Inc. All Rights Reserved. 47  The midbrain contains nuclei that serve as reflex centers for vision and hearing.  The pons plays an important role in regulating breathing rate and rhythm.  The medulla oblongata descends through the foramen magnum as the spinal cord. It is called the vital center because it controls heart rate, blood pressure, and respiration. Its emetic center stimulates vomiting, either as a result of direct stimulation (e.g., fear, spinning, or distressing odors) or from indirect stimulation from the chemoreceptor trigger zone as in cancer chemotherapy. Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights 48 Copyright © 2017, Elsevier Inc. All Rights Reserved. reserved. Brainstem  Functions  All three parts of brainstem are two-way conduction paths Sensory tracts in the brainstem conduct impulses to the higher parts of the brain Motor tracts conduct from the higher parts of the brain to the spinal cord  Gray matter areas in the brainstem function as important reflex centers Copyright © 2017, Elsevier Inc. All Rights Reserved. 49  Brain Disorders  Damage to brain tissue  Cerebrovascular accident (CVA): Hemorrhage from or cessation of blood flow through cerebral blood vessels; a “stroke”  Cerebral palsy (CP): Condition in which damage to motor control areas of the brain before, during, or shortly after birth causes paralysis (usually spastic) of one or more limbs Copyright © 2017, Elsevier Inc. All Rights Reserved. 52 Hemiplegia—spastic paralysis of one side of the body Paraplegia—paralysis of both legs Triplegia—paralysis of both legs and one arm Quadriplegia—paralysis of all four extremities Paralysis—inability to initiate voluntary contractions, may be accompanied by involuntary contractions of affected muscles From Zitelli BJ, Davis HW: Atlas of pediatric physical diagnosis, ed 5, Philadelphia, 2007, Mosby. Copyright © 2017, Elsevier Inc. All Rights Reserved. 53  Degenerative Disease  Dementia: Syndrome that includes progressive loss of memory, shortened attention span, personality changes, reduced intellectual capacity, motor control deficit  Alzheimer disease (AD): Brain disorder of the middle and late adult years characterized by dementia; the exact cause is unknown  Huntington disease (HD): Inherited disorder characterized by chorea (purposeless movement) progressing to severe dementia  HIV (also causes AIDS): Can infect neurons and thus cause dementia Copyright © 2017, Elsevier Inc. All Rights Reserved. 54  Alzheimer Disease The computed tomography (CT) scan on the left shows a horizontal section of a normal brain. In the CT scan on the right, however, you can see the dark patches in the cerebral cortex that show damage to brain tissue typical of AD. Copyright © 2017, Elsevier Inc. All Rights Reserved. 55  Seizure Disorders  Seizure: Sudden burst of abnormal neuron activity that results in temporary changes in brain function  Epilepsy: Many forms, all characterized by recurring seizures Most epilepsy is idiopathic, or of unknown cause, though it can be caused by tumors, trauma, or chemical imbalances.  Electroencephalogram (EEG): Graphic representation of voltage changes in the brain used to evaluate brain activity Copyright © 2017, Elsevier Inc. All Rights Reserved. 56  Electroencephalography From Chipps EM, Clanin NJ, Campbell VG: Neurologic disorders, St Louis, 1992, Mosby. Copyright © 2017, Elsevier Inc. All Rights Reserved. 57  Video Demonstration  https://youtu.be/tZcKT4l_JZk?si=fL8coZb SG0p5PuDg  https://youtu.be/p38nzOGJZtI? si=a4ZjQaAVPeiA-n6U Copyright © 2017, Elsevier Inc. All Rights Reserved. 58  Spinal Cord  Columns of white matter, composed of bundles of myelinated nerve fibers, form the outer portion of the H-shaped core of the spinal cord; bundles of axons called tracts  Typically, the spinal cord is about 17 to 18 inches long  Interior composed of gray matter made up mainly of neuron dendrites and cell bodies  Spinal cord tracts provide two-way conduction paths—ascending and descending  Spinal cord functions as the primary center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain Copyright © 2017, Elsevier Inc. All Rights Reserved. 59 Spinal Cord and Spinal Nerves Note that the spinal cord ends at about the level of vertebra T12 or L1 Copyright © 2017, Elsevier Inc. All Rights Reserved. 60 Spinal Cord Cross Section Copyright © 2017, Elsevier Inc. All Rights Reserved. 61  Spinal Cord Injuries  Impulses are carried to and from the brain through the spinal cord tracts.  If an injury cuts the cord across, impulses can no longer pass to and from the brain  Anesthesia: Loss of sensation  Paralysis: Loss of ability to make voluntary movements Copyright © 2017, Elsevier Inc. All Rights Reserved. 62  Coverings and Fluid Spaces of the Brain and Spinal Cord  Cranial bones and vertebrae  Cerebral and spinal meninges (tough, fluid-cushioned membrane): Dura mater (tough outer membrane), arachnoid mater (cobweb-like middle layer), and pia mater (delicate inner layer; adheres to CNS tissue)  The meninges are surrounded by bone. The spinal meninges form a tubelike covering around the spinal cord and line the bony vertebral foramen of the vertebrae that surrounds cord.  Fluid spaces  Subarachnoid spaces of meninges  Central canal inside cord  Ventricles in brain  Fluid is called cerebrospinal fluid (CSF) Copyright © 2017, Elsevier Inc. All Rights Reserved. 63 Copyright © 2017, Elsevier Inc. All Rights Reserved. 64 Copyright © 2017, Elsevier Inc. All Rights Reserved. 65 Cerebrospinal fluid (CSF) is formed within the ventricles of the brain by the choroid plexus (the ependymal cells). CSF is a clear fluid and is similar in consistency to plasma. Some of the CSF flows through the central canal, which is a hole in the center of the spinal cord. It eventually drains into the subarachnoid space at the base of the spinal cord. A second drainage path is through foramina near the brain. rights reserved. Elsevier Inc. All an imprint of Copyright © 2017, Elsevier Inc. All Rights Reserved. 66 Spinal Cord and Its Coverings Copyright © 2017, Elsevier Inc. All Rights Reserved. 67  Flow of Cerebrospinal Fluid The fluid produced by filtration of blood by the choroid plexus of each ventricle flows inferiorly through the lateral ventricles, interventricular foramen, third ventricle, cerebral aqueduct, fourth ventricle, and subarachnoid space and then to blood. Copyright © 2017, Elsevier Inc. All Rights Reserved. 68 Hydrocephalus A, Hydrocephalus is caused by narrowing or blockage of the pathways for CSF, causing the retention of CSF in the ventricles. B, This condition can be treated by surgical placement of a or tube to drain the excess fluid. Note in the cross sections of the brain how the ventricles and surrounding tissue return to their normal shapes and size after shunt placement. Copyright © 2017, Elsevier Inc. All Rights Reserved. 69  Video Demonstration: Clinical example  https://youtu.be/4RNfZbPdjxY? si=Tn33sZgc1_eH03yk Copyright © 2017, Elsevier Inc. All Rights Reserved. 70 Copyright © 2017, Elsevier Inc. All Rights Reserved. 71  Learning Objectives Lesson 10.3: Peripheral Nervous System 8. Compare and contrast cranial nerves and spinal nerves, and identify peripheral nerve disorders. 9. Discuss the structure and function of the two divisions of the autonomic nervous system, and identify disorders of these two divisions. Copyright © 2017, Elsevier Inc. All Rights Reserved. 72  Peripheral Nervous System  Cranial nerves  12 pairs: Attached to undersurface of the brain  Connect brain with the neck and structures in the thorax and abdomen  Spinal nerves  31 pairs: Contain dendrites of sensory neurons and axons of motor neurons  Conduct impulses necessary for sensations and voluntary movements  Dermatome: Skin surface area supplied by a single cranial or spinal nerve Copyright © 2017, Elsevier Inc. All Rights Reserved. 73 Cranial Nerves Copyright © 2017, Elsevier Inc. All Rights Reserved. 74  Video Demo: Memorize Tricks  https://youtu.be/fELPJIjC7E4?si=npYL- WfAZVaPysMg Copyright © 2017, Elsevier Inc. All Rights Reserved. 75  Lumbar Puncture  “Spinal tap” is the withdrawal of some CSF from the subarachnoid space in the lumbar region of the spinal cord  CSF is used to reduce pressure from swelling after injury or disease or is analyzed for diagnosis  A normal sample of CSF from a lumbar puncture is slightly yellowish and clear, but red color in an abnormal sample indicates bleeding. Copyright © 2017, Elsevier Inc. All Rights Reserved. 76 Cranial Nerves (Cont.) Copyright © 2017, Elsevier Inc. All Rights Reserved. 77 Copyright © 2017, Elsevier Inc. All Rights Reserved. 78 Copyright © 2017, Elsevier Inc. All Rights Reserved. 79  The sensory tracts carry information from the periphery, up the spinal cord, and toward the brain—hence the name, ascending tracts.  The motor tracts, or descending tracts, carry information from the brain, down the spinal cord, and toward the periphery.  Ascending tracts carry information such a temperature, pressure, pain, and touch. The motor tracts carry information to the muscles for movement. Copyright © 2017, Elsevier Inc. All Rights Reserved. 80  Decussate  Decussation is the crossing over of the tracts from one side to the other. Most motor tracts decussate at the level of the medulla oblongata and descend contralaterally, whereas most sensory tracts decussate in the spinal cord and travel up the opposite side of the cord to the brain. Copyright © 2011, 2007 by Saunders,  Ipsilateral – motor fibers an imprint of Elsevier Inc. All rights Copyright © 2017, Elsevier Inc. All Rights Reserved. 81 reserved.  31 pairs of spinal nerves emerge from spinal cord  8 pairs attach to cervical segments  12 pairs attach to thoracic segments  5 pairs attach to lumbar segments  4 pairs attach to sacrospinal segments  1 pair attaches to coccygeal segment  After exiting the spinal cord, some nerve fibers from several spinal nerves “braid” together into a single peripheral nerve called a plexus  Unlike cranial nerves, spinal nerves do not have special names. Instead, they have a letter and a number. For example, C1 is the first pair attached to the cervical segment. Spinal Nerves Copyright © 2017, Elsevier Inc. All Rights Reserved. 82 Copyright © 2017, Elsevier Inc. All Rights Reserved. 83 Spinal Nerves (Cont.)  Functions  Conduct impulses between the spinal cord and parts of the body not supplied by cranial nerves  Contain sensory and motor fibers  Skin surface areas that are supplied by a single spinal nerve are dermatomes Copyright © 2017, Elsevier Inc. All Rights Reserved. 84  Peripheral Nerve Disorders  Trigeminal neuralgia: Recurring episodes of stabbing pain along one or more branches of the trigeminal (fifth cranial) nerve in the head  Bell palsy: Paralysis of facial features resulting from damage to the facial (seventh cranial) nerve. Bell palsy is usually temporary, but sometimes irreversible, causing permanent disfigurement.  Neuritis: General term referring to nerve inflammation  Sciatica is inflammation of the sciatic nerve that innervates the legs  Neuralgia, or muscle pain, often accompanies neuritis and may lead to atrophy of the leg muscles Copyright © 2017, Elsevier Inc. All Rights Reserved. 85  Peripheral Nerve Disorders (Cont.)  Herpes zoster or shingles  Viral infection caused by chickenpox virus that has invaded the dorsal root ganglion and remained dormant until an episode of shingles  Usually affects a single dermatome, producing characteristic painful plaques or vesicles Copyright © 2017, Elsevier Inc. All Rights Reserved. 86 88  Autonomic Nervous System (ANS)  Allows the organs to respond to changing body needs  Carries out automatic and unconscious visceral responses  Regulates organ function (visceral reflexes)  Examples of visceral reflexes include regulation of heart rate, blood pressure, body temperature, air flow through respiratory passages, pupillary response to light, and secretions and motility of the digestive tract. Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights 89 Copyright © 2017, Elsevier Inc. All Rights Reserved. reserved.  Functions of the Sympathetic Nervous System  Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are triggered  Group of changes induced by sympathetic control is called the fight-or-flight response It functions as an emergency system. It takes control of many internal organs when we exercise strenuously and when strong emotions are elicited. In other words, it functions during stress. Some of the physiological changes associated with the fight-or- flight response are heart beats faster; blood vessels constrict, causing blood pressure to increase; blood vessels in muscle dilate, delivering more blood to the muscles; sweat glands and adrenal glands secrete more abundantly; salivary and other digestive glands secrete more sparingly; peristalsis becomes sluggish; and we are ready for “fight or flight.” Copyright © 2017, Elsevier Inc. All Rights Reserved. 95 Parasympathetic Nervous System (Cont.)  Function: Dominates control of many visceral effectors under normal, everyday conditions; counterbalances sympathetic function  Impulses tend to slow heartbeat, increase peristalsis, and increase secretion of digestive and insulin. Copyright © 2017, Elsevier Inc. All Rights Reserved. 97  Autonomic Nervous System as a Whole  Neurotransmitters are chemicals that continue a nervous impulse through a synapse; stored in the axon terminals  Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis  Many visceral effectors are doubly innervated (i.e., they receive fibers from parasympathetic and sympathetic divisions and are influenced in opposite ways by the two divisions)  It sounds like it is independent from other parts of the nervous system when, in fact, it is deeply interconnected with the central nervous system. Copyright © 2017, Elsevier Inc. All Rights Reserved. 100  Disorders of the Autonomic Nervous System  Stress-induced disease Prolonged or excessive response to stress can disrupt normal functioning throughout the body  Examples of stress-induced conditions include heart disease, digestive problems, and reduced resistance to disease  Neuroblastoma: a type of cancer that forms in nerve cells called neuroblasts. Highly malignant tumor of the sympathetic nervous system, primarily affecting young children Copyright © 2017, Elsevier Inc. All Rights Reserved. 101 Questions? Copyright © 2017, Elsevier Inc. All Rights Reserved. 102  Pop Quiz! Copyright © 2017, Elsevier Inc. All Rights Reserved. 103  Question 1  The organs of the nervous system include all of the following except  A. nerves  B. spinal cord  C. brain  D. vertebrae Copyright © 2017, Elsevier Inc. All Rights Reserved. 104  Question 2  The nervous system is divided into which two principal divisions?  A. autonomic and central  B. peripheral and central  C. autonomic and peripheral  D. Central and afferent Copyright © 2017, Elsevier Inc. All Rights Reserved. 105  Question 3  The part of a neuron that transmits impulses away from the cell body is the  A. axon  B. dendrite  C. neurilemma  D. neurofibril Copyright © 2017, Elsevier Inc. All Rights Reserved. 106  Question 4  The white, fatty substance that sounds an axon is called  A. myelin  B. glia  C. Schwann cells  D. neurilemma Copyright © 2017, Elsevier Inc. All Rights Reserved. 107  Question 5  These chemicals allow neurons to communicate with each other.  A. Sensory transmitters  B. Glial transmitters  C. Neurofibrils  D. Neurotransmitters Copyright © 2017, Elsevier Inc. All Rights Reserved. 108  Question 6  Axon terminals of autonomic neurons release either of two neurotransmitter  A. Norepinephrine and aldosterone  B. Norepinephrine and acetylcholine  C. Acetylcholine and aldosterone  D. Norepinephrine and dopamine Copyright © 2017, Elsevier Inc. All Rights Reserved. 109  Critical thinking Question #1  Some individuals who are depressed have an abnormally small amount of the neurotransmitter serotonin at certain synapses in the brain. One category of antidepressant drugs is called selective serotonin reuptake inhibitors (SSRIs). Can you deduce what action this drug has at a synapse to increase the amount of serotonin present in the synaptic cleft? (Hint: The name of the drug is a clue, as is the discussion in the section “The Synapse,” Figure 10-10, p. 258 in the text.) Copyright © 2017, Elsevier Inc. All Rights Reserved. 110  Answer  The name of the drug category tells you that it decreases the amount of serotonin that is taken back into the presynaptic knob after a nerve impulse has caused its release into the synaptic cleft. Because the amount of serotonin being taken from the synaptic cleft decreases, the amount remaining in the synaptic cleft increases. Ideally this will reset the chemical imbalance associated with depression and relieve the symptoms. Copyright © 2017, Elsevier Inc. All Rights Reserved. 111  Question #2  Another type of antidepressant inhibits the enzymes that naturally break down serotonin at the synaptic cleft. Can you explain how this might reduce the symptoms of depression? Copyright © 2017, Elsevier Inc. All Rights Reserved. 112  Answer  As explained in the text, some neurotransmitter molecules are taken back into the presynaptic knob, and others are broken down by specific enzymes. This particular category of antidepressants inhibits the breakdown of serotonin after it is released. Such inhibition of serotonin destruction increases the amount of serotonin present in the synaptic cleft, restoring the original balance, and removing the chemical basis for depression. Copyright © 2017, Elsevier Inc. All Rights Reserved. 113  Question #3  Why is it important for doctors to test reflexes, like the patellar (knee-jerk) reflex, in patients? Copyright © 2017, Elsevier Inc. All Rights Reserved. 114  Answer  Doctors can test many reflexes using basic tools and observation. The procedures are simple, and the results may provide important information about disease or damage to the spinal nerves or cord. A doctor can evaluate sensory and motor pathways throughout the brain and spinal cord by testing certain cranial and spinal reflexes. If there are significant differences between reflex responses in the right and left sides of the body, that may suggest specific damage to a part of the reflex arc. Copyright © 2017, Elsevier Inc. All Rights Reserved. 115  Question #4  Explain what a seizure is and how brain activity is measured. Of what benefit is the use of the electroencephalograph (EEG)? Copyright © 2017, Elsevier Inc. All Rights Reserved. 116  Answer  A seizure is a sudden burst of abnormal neuron activity that results in temporary changes in the brain. An EEG is a graphic recording of brain activity obtained from four sets of electrodes attached to the skull. These tracings identify activity as normal or irregular. During a seizure, the tracings are extremely irregular and explosive. Copyright © 2017, Elsevier Inc. All Rights Reserved. 117  Question #5  Mr. Stevens comes to your office complaining that he frequently loses his balance. He says that he feels like a drunken man when he walks and cannot even draw a straight line. Mr. Stevens will have to undergo testing before the physician determines a diagnosis, but what part of his brain do you think might be involved on the basis of the symptoms he reports? Copyright © 2017, Elsevier Inc. All Rights Reserved. 118  Answer  The cerebellum is the part of the brain that controls normal movement. A physician might consider it possible that a tumor on his cerebellum is causing his lack of coordination. Patients who have such tumors often complain of loss of balance and frequent falling, clumsiness, and poor muscle coordination. On the basis of scientific observation of patients with cerebellum diseases and animals with their cerebellum removed, the cerebellum’s key general function is to create smooth, coordinated movements, sustain physical equilibrium, and maintain normal posture Copyright © 2017, Elsevier Inc. All Rights Reserved. 119