{"id":95,"date":"2020-04-29T14:05:46","date_gmt":"2020-04-29T14:05:46","guid":{"rendered":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/?post_type=chapter&#038;p=95"},"modified":"2021-09-03T17:21:46","modified_gmt":"2021-09-03T17:21:46","slug":"parts-of-the-nervous-system","status":"publish","type":"chapter","link":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/chapter\/parts-of-the-nervous-system\/","title":{"raw":"Parts of the Nervous System","rendered":"Parts of the Nervous System"},"content":{"raw":"<div class=\"PageContent-ny9bj0-0 iapMdy\">\r\n<div id=\"main-content\" class=\"MainContent__HideOutline-sc-6yy1if-0 bdVAq\">\r\n<div id=\"2c452232-1bb2-4d26-a412-96ee84ff2a89\">\r\n<div id=\"13402\" class=\"ui-has-child-title\"><section>\r\n<div class=\"textbox textbox--learning-objectives\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><span style=\"color: #ffffff\">Learning Objectives<\/span><\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<div id=\"13402\" class=\"ui-has-child-title\"><section>By the end of this section, you will be able to:\r\n<ul>\r\n \t<li>Describe the difference between the central and peripheral nervous systems<\/li>\r\n \t<li>Explain the difference between the somatic and autonomic nervous systems<\/li>\r\n \t<li>Differentiate between the sympathetic and parasympathetic divisions of the autonomic nervous system<\/li>\r\n<\/ul>\r\n<\/section><\/div>\r\n<\/div>\r\n<\/div>\r\n<span style=\"text-align: initial;font-size: 1em\">The\u00a0<\/span><span id=\"term161\" class=\"no-emphasis\" style=\"text-align: initial;font-size: 1em\">nervous system<\/span><span style=\"text-align: initial;font-size: 1em\">\u00a0can be divided into two major subdivisions: the\u00a0<\/span><strong style=\"text-align: initial;font-size: 1em\"><span id=\"term162\">central nervous system (CNS)<\/span><\/strong><span style=\"text-align: initial;font-size: 1em\">\u00a0and the\u00a0<\/span><strong style=\"text-align: initial;font-size: 1em\"><span id=\"term163\">peripheral nervous system (PNS)<\/span><\/strong><span style=\"text-align: initial;font-size: 1em\">, shown in\u00a0<\/span><a class=\"autogenerated-content\" style=\"text-align: initial;font-size: 1em\" href=\"https:\/\/openstax.org\/books\/psychology-2e\/pages\/3-3-parts-of-the-nervous-system#CNX_Psych_03_03_NervSystem\">Figure BB.7<\/a><span style=\"text-align: initial;font-size: 1em\">. The CNS is comprised of the brain and spinal cord; the PNS connects the CNS to the rest of the body. In this section, we focus on the peripheral nervous system; later, we look at the brain and spinal cord.<\/span>\r\n\r\n<\/section><\/div>\r\n<div id=\"CNX_Psych_03_03_NervSystem\" class=\"os-figure\">\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"975\"]<img id=\"223\" src=\"https:\/\/openstax.org\/resources\/d553fb5fdea5e2ff6e86a0508a3048040d759d33\" alt=\"Image (a) shows an outline of a human body with the brain and spinal cord illustrated. Image (b) shows an outline of a human body with a network of nerves depicted.\" width=\"975\" height=\"712\" \/> Figure BB.7\u00a0The nervous system is divided into two major parts: (a) the Central Nervous System and (b) the Peripheral Nervous System.[\/caption]<\/figure>\r\n<div class=\"os-caption-container\"><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1em;font-weight: bold\">Peripheral Nervous System<\/span><\/div>\r\n<\/div>\r\n<section id=\"fs-id1422228\">\r\n<p id=\"fs-id1547472\">The peripheral nervous system is made up of thick bundles of axons, called nerves, carrying messages back and forth between the CNS and the muscles, organs, and senses in the periphery of the body (i.e., everything outside the CNS). The PNS has two major subdivisions: the somatic nervous system and the autonomic nervous system.<\/p>\r\n<p id=\"fs-id1731967\">The\u00a0<strong><span id=\"term164\">somatic nervous system<\/span><\/strong>\u00a0is associated with activities traditionally thought of as conscious or voluntary. It is involved in the relay of sensory and motor information to and from the CNS; therefore, it consists of motor neurons and sensory neurons. <strong>Motor neurons,<\/strong> carrying instructions from the CNS to the muscles, are efferent fibers (efferent means \u201cmoving away from\u201d). <strong>Sensory neurons<\/strong>, carrying sensory information to the CNS, are afferent fibers (afferent means \u201cmoving toward\u201d). A helpful way to remember this is that\u00a0<strong>e<\/strong>fferent =\u00a0<strong>e<\/strong>xit and\u00a0<strong>a<\/strong>fferent =\u00a0<strong>a<\/strong>rrive. Each nerve is basically a bundle of neurons forming a two-way superhighway, containing thousands of axons, both efferent and afferent. There is another type of neuron, called an\u00a0<strong>interneuron<\/strong>, which is by far the most common type of neuron, which is located primarily within the CNS and is\u00a0responsible for communicating among the neurons. Interneurons allow the brain to combine the multiple sources of available information to create a coherent picture of the sensory information being conveyed.<\/p>\r\n<p id=\"fs-id1580778\">The\u00a0<strong><span id=\"term165\">autonomic nervous system<\/span>\u00a0<\/strong>controls our internal organs and glands and is generally considered to be outside the realm of voluntary control. It can be further subdivided into the sympathetic and parasympathetic divisions (<a class=\"autogenerated-content\" href=\"https:\/\/openstax.org\/books\/psychology-2e\/pages\/3-3-parts-of-the-nervous-system#CNX_Psych_03_03_Autonomic\">Figure BB.8<\/a>). The\u00a0<strong><span id=\"term166\">sympathetic nervous system<\/span><\/strong>\u00a0is involved in preparing the body for stress-related activities; the\u00a0<strong><span id=\"term167\">parasympathetic nervous system<\/span><\/strong>\u00a0is associated with returning the body to routine, day-to-day operations. The two systems have complementary functions, operating in tandem to maintain the body\u2019s homeostasis.\u00a0<strong><span id=\"term168\">Homeostasis<\/span><\/strong>\u00a0is a state of equilibrium, or balance, in which biological conditions (such as body temperature) are maintained at optimal levels.<\/p>\r\n&nbsp;\r\n<div id=\"CNX_Psych_03_03_Autonomic\" class=\"os-figure\">\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"650\"]<img id=\"92526\" src=\"https:\/\/openstax.org\/resources\/b561c8c913a538c0b36aec494521aa27287a785b\" alt=\"A diagram of a human body lists the different functions of the sympathetic and parasympathetic nervous system. The parasympathetic system can constrict pupils, stimulate salivation, slow heart rate, constrict bronchi, stimulate digestion, stimulate bile secretion, and cause the bladder to contract. The sympathetic nervous system can dilate pupils, inhibit salivation, increase heart rate, dilate bronchi, inhibit digestion, stimulate the breakdown of glycogen, stimulate secretion of adrenaline and noradrenaline, and inhibit contraction of the bladder.\" width=\"650\" height=\"676\" \/> Figure BB.8\u00a0The sympathetic and parasympathetic divisions of the autonomic nervous system have the opposite effects on various systems.[\/caption]<\/figure>\r\n<p class=\"os-caption-container\"><span style=\"text-align: initial;font-size: 1em\">The sympathetic nervous system is activated when we are faced with stressful or high-arousal situations. The activity of this system was adaptive for our ancestors, increasing their chances of survival. Imagine, for example, that one of our early ancestors, out hunting small game, suddenly disturbs a large bear with cubs. At that moment, the hunter's body undergoes a series of changes\u2014a direct function of sympathetic activation\u2014preparing the hunter to face the threat. The hunter's pupils dilate, their heart rate and blood pressure increase, their bladder relaxes, their liver releases glucose, and adrenaline surges into the hunter's bloodstream. This constellation of physiological changes, known as the\u00a0<\/span><strong style=\"text-align: initial;font-size: 1em\"><span id=\"term169\">fight or flight response<\/span><\/strong><span style=\"text-align: initial;font-size: 1em\">, allows the body access to energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.<\/span><\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-id1490744\" class=\"psychology link-to-learning ui-has-child-title\"><header>\r\n<div class=\"textbox textbox--key-takeaways\"><header class=\"textbox__header\">\r\n<p class=\"textbox__title\"><span style=\"color: #ffffff\">LINK TO LEARNING<\/span><\/p>\r\n\r\n<\/header>\r\n<div class=\"textbox__content\"><span style=\"text-align: initial;font-family: Lora, serif;font-size: 1em;font-weight: normal\">Watch this\u00a0<\/span><a style=\"text-align: initial;font-family: Lora, serif;font-size: 1em;font-weight: normal\" href=\"http:\/\/openstax.org\/l\/response\" target=\"_blank\" rel=\"noopener nofollow\">video about the Fight Flight Freeze response<\/a><span style=\"text-align: initial;font-family: Lora, serif;font-size: 1em;font-weight: normal\">\u00a0to learn more.<\/span><\/div>\r\n<\/div>\r\n<\/header><\/div>\r\n<p id=\"fs-id1590023\">While it is clear that such a response would be critical for survival for our ancestors, who lived in a world full of real physical threats, many of the high-arousal situations we face in the modern world are more psychological in nature. For example, think about how you feel when you have to stand up and give a presentation in front of a roomful of people, or right before taking a big test. You are in no real physical danger in those situations, and yet you have evolved to respond to a perceived threat with the\u00a0<span id=\"term170\" class=\"no-emphasis\">fight or flight<\/span>\u00a0response. This kind of response is not nearly as adaptive in the modern world; in fact, we suffer negative health consequences when faced constantly with psychological threats that we can neither fight nor flee. Recent research suggests that an increase in susceptibility to heart disease (Chandola, Brunner, &amp; Marmot, 2006) and impaired function of the immune system (Glaser &amp; Kiecolt-Glaser, 2005) are among the many negative consequences of persistent and repeated exposure to stressful situations. Some of this tendency for stress reactivity can be wired by early experiences of trauma.<\/p>\r\n<p id=\"fs-id1523937\">Once the threat has been resolved, the parasympathetic nervous system takes over and returns bodily functions to a relaxed state. Our hunter\u2019s heart rate and blood pressure return to normal, their pupils constrict, they regains control of their bladder, and the liver begins to store glucose in the form of glycogen for future use. These restorative processes are associated with activation of the parasympathetic nervous system.<\/p>\r\n\r\n<\/section><\/div>\r\n<\/div>\r\n<\/div>","rendered":"<div class=\"PageContent-ny9bj0-0 iapMdy\">\n<div id=\"main-content\" class=\"MainContent__HideOutline-sc-6yy1if-0 bdVAq\">\n<div id=\"2c452232-1bb2-4d26-a412-96ee84ff2a89\">\n<div id=\"13402\" class=\"ui-has-child-title\">\n<section>\n<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><span style=\"color: #ffffff\">Learning Objectives<\/span><\/p>\n<\/header>\n<div class=\"textbox__content\">\n<div class=\"ui-has-child-title\">\n<section>By the end of this section, you will be able to:<\/p>\n<ul>\n<li>Describe the difference between the central and peripheral nervous systems<\/li>\n<li>Explain the difference between the somatic and autonomic nervous systems<\/li>\n<li>Differentiate between the sympathetic and parasympathetic divisions of the autonomic nervous system<\/li>\n<\/ul>\n<\/section>\n<\/div>\n<\/div>\n<\/div>\n<p><span style=\"text-align: initial;font-size: 1em\">The\u00a0<\/span><span id=\"term161\" class=\"no-emphasis\" style=\"text-align: initial;font-size: 1em\">nervous system<\/span><span style=\"text-align: initial;font-size: 1em\">\u00a0can be divided into two major subdivisions: the\u00a0<\/span><strong style=\"text-align: initial;font-size: 1em\"><span id=\"term162\">central nervous system (CNS)<\/span><\/strong><span style=\"text-align: initial;font-size: 1em\">\u00a0and the\u00a0<\/span><strong style=\"text-align: initial;font-size: 1em\"><span id=\"term163\">peripheral nervous system (PNS)<\/span><\/strong><span style=\"text-align: initial;font-size: 1em\">, shown in\u00a0<\/span><a class=\"autogenerated-content\" style=\"text-align: initial;font-size: 1em\" href=\"https:\/\/openstax.org\/books\/psychology-2e\/pages\/3-3-parts-of-the-nervous-system#CNX_Psych_03_03_NervSystem\">Figure BB.7<\/a><span style=\"text-align: initial;font-size: 1em\">. The CNS is comprised of the brain and spinal cord; the PNS connects the CNS to the rest of the body. In this section, we focus on the peripheral nervous system; later, we look at the brain and spinal cord.<\/span><\/p>\n<\/section>\n<\/div>\n<div id=\"CNX_Psych_03_03_NervSystem\" class=\"os-figure\">\n<figure>\n<figure style=\"width: 975px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"223\" src=\"https:\/\/openstax.org\/resources\/d553fb5fdea5e2ff6e86a0508a3048040d759d33\" alt=\"Image (a) shows an outline of a human body with the brain and spinal cord illustrated. Image (b) shows an outline of a human body with a network of nerves depicted.\" width=\"975\" height=\"712\" \/><figcaption class=\"wp-caption-text\">Figure BB.7\u00a0The nervous system is divided into two major parts: (a) the Central Nervous System and (b) the Peripheral Nervous System.<\/figcaption><\/figure>\n<\/figure>\n<div class=\"os-caption-container\"><span style=\"font-family: 'Cormorant Garamond', serif;font-size: 1em;font-weight: bold\">Peripheral Nervous System<\/span><\/div>\n<\/div>\n<section id=\"fs-id1422228\">\n<p id=\"fs-id1547472\">The peripheral nervous system is made up of thick bundles of axons, called nerves, carrying messages back and forth between the CNS and the muscles, organs, and senses in the periphery of the body (i.e., everything outside the CNS). The PNS has two major subdivisions: the somatic nervous system and the autonomic nervous system.<\/p>\n<p id=\"fs-id1731967\">The\u00a0<strong><span id=\"term164\">somatic nervous system<\/span><\/strong>\u00a0is associated with activities traditionally thought of as conscious or voluntary. It is involved in the relay of sensory and motor information to and from the CNS; therefore, it consists of motor neurons and sensory neurons. <strong>Motor neurons,<\/strong> carrying instructions from the CNS to the muscles, are efferent fibers (efferent means \u201cmoving away from\u201d). <strong>Sensory neurons<\/strong>, carrying sensory information to the CNS, are afferent fibers (afferent means \u201cmoving toward\u201d). A helpful way to remember this is that\u00a0<strong>e<\/strong>fferent =\u00a0<strong>e<\/strong>xit and\u00a0<strong>a<\/strong>fferent =\u00a0<strong>a<\/strong>rrive. Each nerve is basically a bundle of neurons forming a two-way superhighway, containing thousands of axons, both efferent and afferent. There is another type of neuron, called an\u00a0<strong>interneuron<\/strong>, which is by far the most common type of neuron, which is located primarily within the CNS and is\u00a0responsible for communicating among the neurons. Interneurons allow the brain to combine the multiple sources of available information to create a coherent picture of the sensory information being conveyed.<\/p>\n<p id=\"fs-id1580778\">The\u00a0<strong><span id=\"term165\">autonomic nervous system<\/span>\u00a0<\/strong>controls our internal organs and glands and is generally considered to be outside the realm of voluntary control. It can be further subdivided into the sympathetic and parasympathetic divisions (<a class=\"autogenerated-content\" href=\"https:\/\/openstax.org\/books\/psychology-2e\/pages\/3-3-parts-of-the-nervous-system#CNX_Psych_03_03_Autonomic\">Figure BB.8<\/a>). The\u00a0<strong><span id=\"term166\">sympathetic nervous system<\/span><\/strong>\u00a0is involved in preparing the body for stress-related activities; the\u00a0<strong><span id=\"term167\">parasympathetic nervous system<\/span><\/strong>\u00a0is associated with returning the body to routine, day-to-day operations. The two systems have complementary functions, operating in tandem to maintain the body\u2019s homeostasis.\u00a0<strong><span id=\"term168\">Homeostasis<\/span><\/strong>\u00a0is a state of equilibrium, or balance, in which biological conditions (such as body temperature) are maintained at optimal levels.<\/p>\n<p>&nbsp;<\/p>\n<div id=\"CNX_Psych_03_03_Autonomic\" class=\"os-figure\">\n<figure>\n<figure style=\"width: 650px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" id=\"92526\" src=\"https:\/\/openstax.org\/resources\/b561c8c913a538c0b36aec494521aa27287a785b\" alt=\"A diagram of a human body lists the different functions of the sympathetic and parasympathetic nervous system. The parasympathetic system can constrict pupils, stimulate salivation, slow heart rate, constrict bronchi, stimulate digestion, stimulate bile secretion, and cause the bladder to contract. The sympathetic nervous system can dilate pupils, inhibit salivation, increase heart rate, dilate bronchi, inhibit digestion, stimulate the breakdown of glycogen, stimulate secretion of adrenaline and noradrenaline, and inhibit contraction of the bladder.\" width=\"650\" height=\"676\" \/><figcaption class=\"wp-caption-text\">Figure BB.8\u00a0The sympathetic and parasympathetic divisions of the autonomic nervous system have the opposite effects on various systems.<\/figcaption><\/figure>\n<\/figure>\n<p class=\"os-caption-container\"><span style=\"text-align: initial;font-size: 1em\">The sympathetic nervous system is activated when we are faced with stressful or high-arousal situations. The activity of this system was adaptive for our ancestors, increasing their chances of survival. Imagine, for example, that one of our early ancestors, out hunting small game, suddenly disturbs a large bear with cubs. At that moment, the hunter&#8217;s body undergoes a series of changes\u2014a direct function of sympathetic activation\u2014preparing the hunter to face the threat. The hunter&#8217;s pupils dilate, their heart rate and blood pressure increase, their bladder relaxes, their liver releases glucose, and adrenaline surges into the hunter&#8217;s bloodstream. This constellation of physiological changes, known as the\u00a0<\/span><strong style=\"text-align: initial;font-size: 1em\"><span id=\"term169\">fight or flight response<\/span><\/strong><span style=\"text-align: initial;font-size: 1em\">, allows the body access to energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.<\/span><\/p>\n<\/div>\n<div id=\"fs-id1490744\" class=\"psychology link-to-learning ui-has-child-title\">\n<header>\n<div class=\"textbox textbox--key-takeaways\"><\/div>\n<\/header>\n<header class=\"textbox__header\">\n<p class=\"textbox__title\"><span style=\"color: #ffffff\">LINK TO LEARNING<\/span><\/p>\n<\/header>\n<div class=\"textbox__content\"><span style=\"text-align: initial;font-family: Lora, serif;font-size: 1em;font-weight: normal\">Watch this\u00a0<\/span><a style=\"text-align: initial;font-family: Lora, serif;font-size: 1em;font-weight: normal\" href=\"http:\/\/openstax.org\/l\/response\" target=\"_blank\" rel=\"noopener nofollow\">video about the Fight Flight Freeze response<\/a><span style=\"text-align: initial;font-family: Lora, serif;font-size: 1em;font-weight: normal\">\u00a0to learn more.<\/span><\/div>\n<\/div>\n<\/section>\n<\/div>\n<p id=\"fs-id1590023\">While it is clear that such a response would be critical for survival for our ancestors, who lived in a world full of real physical threats, many of the high-arousal situations we face in the modern world are more psychological in nature. For example, think about how you feel when you have to stand up and give a presentation in front of a roomful of people, or right before taking a big test. You are in no real physical danger in those situations, and yet you have evolved to respond to a perceived threat with the\u00a0<span id=\"term170\" class=\"no-emphasis\">fight or flight<\/span>\u00a0response. This kind of response is not nearly as adaptive in the modern world; in fact, we suffer negative health consequences when faced constantly with psychological threats that we can neither fight nor flee. Recent research suggests that an increase in susceptibility to heart disease (Chandola, Brunner, &amp; Marmot, 2006) and impaired function of the immune system (Glaser &amp; Kiecolt-Glaser, 2005) are among the many negative consequences of persistent and repeated exposure to stressful situations. Some of this tendency for stress reactivity can be wired by early experiences of trauma.<\/p>\n<p id=\"fs-id1523937\">Once the threat has been resolved, the parasympathetic nervous system takes over and returns bodily functions to a relaxed state. Our hunter\u2019s heart rate and blood pressure return to normal, their pupils constrict, they regains control of their bladder, and the liver begins to store glucose in the form of glycogen for future use. These restorative processes are associated with activation of the parasympathetic nervous system.<\/p>\n<\/div>\n<\/div>\n","protected":false},"author":13,"menu_order":3,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"part":23,"_links":{"self":[{"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/pressbooks\/v2\/chapters\/95"}],"collection":[{"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/wp\/v2\/users\/13"}],"version-history":[{"count":13,"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/pressbooks\/v2\/chapters\/95\/revisions"}],"predecessor-version":[{"id":2060,"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/pressbooks\/v2\/chapters\/95\/revisions\/2060"}],"part":[{"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/pressbooks\/v2\/parts\/23"}],"metadata":[{"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/pressbooks\/v2\/chapters\/95\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/wp\/v2\/media?parent=95"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/pressbooks\/v2\/chapter-type?post=95"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/wp\/v2\/contributor?post=95"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/digitaleditions.library.dal.ca\/intropsychneuro\/wp-json\/wp\/v2\/license?post=95"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}