{"id":193,"date":"2023-02-17T22:37:17","date_gmt":"2023-02-17T22:37:17","guid":{"rendered":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/chapter\/parts-of-the-nervous-system\/"},"modified":"2025-11-05T15:40:25","modified_gmt":"2025-11-05T15:40:25","slug":"parts-of-the-nervous-system","status":"publish","type":"chapter","link":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/chapter\/parts-of-the-nervous-system\/","title":{"raw":"The Peripheral Nervous System and the Endocrine System: Learn It 1\u2014The Peripheral Nervous System","rendered":"The Peripheral Nervous System and the Endocrine System: Learn It 1\u2014The Peripheral Nervous System"},"content":{"raw":"<section class=\"textbox learningGoals\">\r\n<ul>\r\n\t<li>Describe the difference between the central and peripheral nervous systems and the somatic and autonomic nervous systems<\/li>\r\n\t<li>Describe the difference between the sympathetic and parasympathetic divisions of the autonomic nervous system<\/li>\r\n\t<li>Describe the endocrine system and how it affects behavior<\/li>\r\n<\/ul>\r\n<\/section>\r\n<section class=\"textbox keyTakeaway\">\r\n<h3>the peripheral nervous system<\/h3>\r\n<p id=\"fs-id1547472\">We learned about the central nervous system (the brain and spinal cord); now we turn our attention to the rest of the body systems, starting with the peripheral nervous system (PNS). The <strong>peripheral nervous system<\/strong> 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. The PNS has two major subdivisions: the somatic nervous system and the autonomic nervous system.<\/p>\r\n\r\n[caption id=\"attachment_2079\" align=\"aligncenter\" width=\"599\"]<img class=\"wp-image-2079 \" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/5837\/2022\/09\/16172138\/original-2.png\" alt=\"The various components of the peripheral nervous system \u2013 the peripheral nervous system consists of two parts \u2013 the somatic and the autonomic nervous system. Somatic nervous system is comprised of cranial nerves and spinal nerves which process sensory information and control the voluntary muscle movements. And the autonomic nervous system is comprised of the sympathetic nervous system and the parasympathetic nervous system which control other muscles and visceral organs. &quot; title=&quot;The various components of the peripheral nervous system \u2013 the peripheral nervous system consists of two parts \u2013 the somatic and the autonomic nervous system. Somatic nervous system is comprised of cranial nerves and spinal nerves which process sensory information and control the voluntary muscle movements. And the autonomic nervous system is comprised of the sympathetic nervous system and the parasympathetic nervous system which control other muscles and visceral organs.\" width=\"599\" height=\"221\" \/> <strong>Figure 1<\/strong>. The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system, with the autonomic system divided into both sympathetic and parasympathetic systems.[\/caption]\r\n<\/section>\r\n<section class=\"textbox keyTakeaway\">\r\n<h3>the somatic nervous system<\/h3>\r\n<p>The <strong><span data-type=\"term\">somatic nervous system<\/span><\/strong> is 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.<\/p>\r\n<ul>\r\n\t<li><strong>Motor neurons<\/strong>, carrying instructions from the CNS to the muscles, are <strong>efferent<\/strong> fibers (efferent means \u201cmoving away from\u201d\u2014away from the brain, in this instance).<\/li>\r\n\t<li><strong>Sensory neurons<\/strong>, carrying sensory information to the CNS, are <strong>afferent<\/strong> fibers (afferent means \u201cmoving toward\u201d).\r\n\r\n<ul>\r\n\t<li>A helpful way to remember this is that efferent = exit and afferent = arrive.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n<p>Each nerve is basically a bundle of neurons forming a two-way superhighway, containing thousands of axons, both efferent and afferent.<\/p>\r\n<\/section>\r\n<section class=\"textbox keyTakeaway\">\r\n<h3>the autonomic nervous system<\/h3>\r\n<p>The <strong><span data-type=\"term\">autonomic nervous system<\/span><\/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 divisions.\u00a0<\/p>\r\n<p>&nbsp;<\/p>\r\n<p>The two systems, the sympathetic and parasympathetic nervous systems, have complementary functions, operating in tandem to maintain the body\u2019s homeostasis. <br \/>\r\n<br \/>\r\n<strong><span data-type=\"term\">Homeostasis<\/span><\/strong> is a state of equilibrium, or balance, in which biological conditions (such as body temperature) are maintained at optimal levels.<\/p>\r\n<\/section>\r\n<section class=\"textbox tryIt\">[ohm2_question height=\"200\"]3950[\/ohm2_question]<\/section>\r\n<h2>Fight-or-Flight<\/h2>\r\n<section class=\"textbox keyTakeaway\">\r\n<h3>the sympathetic nervous system<\/h3>\r\n<p>The <strong><span data-type=\"term\">sympathetic nervous system<\/span><\/strong> is involved in preparing the body for stress-related activities. It\u00a0is activated when we are faced with stressful or high-arousal situations.<\/p>\r\n<ul>\r\n\t<li>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 her cubs. At that moment, the body would undergo a series of changes\u2014a direct function of sympathetic activation\u2014preparing a person to face the threat. Their pupils dilate, their heart rate and blood pressure increase, their bladder relaxes, their endocrine system kicks in\u2014their liver releases glucose, and adrenaline surges into their bloodstream.<\/li>\r\n<\/ul>\r\n<\/section>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"563\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224553\/CNX_Psych_03_03_Autonomic.jpg\" 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, and cause the bladder to contract. The sympathetic nervous system can dilate pupils, inhibit salivation, increase heart rate, dilate bronchi, inhibit digestion, and inhibit contraction of the bladder. \" width=\"563\" height=\"586\" data-media-type=\"image\/jpg\" \/> <strong>Figure 1<\/strong>. The sympathetic and parasympathetic divisions of the autonomic nervous system have the opposite effects on various systems.[\/caption]\r\n\r\n<section class=\"textbox keyTakeaway\">\r\n<h3>the parasympathetic nervous system<\/h3>\r\n<p>The <strong><span data-type=\"term\">parasympathetic nervous system<\/span><\/strong> is associated with returning the body to routine, day-to-day operations and a relaxed state.<\/p>\r\n<ul>\r\n\t<li>Our hunter\u2019s heart rate and blood pressure return to normal, their pupils constrict, they regain 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.<\/li>\r\n<\/ul>\r\n<\/section>\r\n<p>The \"fight or flight\" response is a physiological response that prepares the body to either confront a perceived threat or escape from it. For example, if a person sees a snake, whether the individual decides to\u00a0<em>fight<\/em>\u00a0the snake or\u00a0<em>run<\/em> away from it, either action requires energy; in short, the sympathetic nervous system says \u201cgo, go, go.\u201d If the person decides that it's not a real threat, the parasympathetic nervous system curtails undue energy mobilization into muscles and glands and modulates the response by saying \u201cstop, stop, stop.\u201d This push\u2013pull tandem system regulates fight-or-flight responses in all of us.<\/p>\r\n<p id=\"fs-id1590023\">While it is clear that a fight-or-flight 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 any perceived threat with the <span class=\"no-emphasis\" data-type=\"term\">fight or flight<\/span> response. 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.<\/p>\r\n<section class=\"textbox tryIt\">[ohm2_question height=\"1150\"]3951[\/ohm2_question]<\/section>","rendered":"<section class=\"textbox learningGoals\">\n<ul>\n<li>Describe the difference between the central and peripheral nervous systems and the somatic and autonomic nervous systems<\/li>\n<li>Describe the difference between the sympathetic and parasympathetic divisions of the autonomic nervous system<\/li>\n<li>Describe the endocrine system and how it affects behavior<\/li>\n<\/ul>\n<\/section>\n<section class=\"textbox keyTakeaway\">\n<h3>the peripheral nervous system<\/h3>\n<p id=\"fs-id1547472\">We learned about the central nervous system (the brain and spinal cord); now we turn our attention to the rest of the body systems, starting with the peripheral nervous system (PNS). The <strong>peripheral nervous system<\/strong> 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. The PNS has two major subdivisions: the somatic nervous system and the autonomic nervous system.<\/p>\n<figure id=\"attachment_2079\" aria-describedby=\"caption-attachment-2079\" style=\"width: 599px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-2079\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/5837\/2022\/09\/16172138\/original-2.png\" alt=\"The various components of the peripheral nervous system \u2013 the peripheral nervous system consists of two parts \u2013 the somatic and the autonomic nervous system. Somatic nervous system is comprised of cranial nerves and spinal nerves which process sensory information and control the voluntary muscle movements. And the autonomic nervous system is comprised of the sympathetic nervous system and the parasympathetic nervous system which control other muscles and visceral organs. &quot; title=&quot;The various components of the peripheral nervous system \u2013 the peripheral nervous system consists of two parts \u2013 the somatic and the autonomic nervous system. Somatic nervous system is comprised of cranial nerves and spinal nerves which process sensory information and control the voluntary muscle movements. And the autonomic nervous system is comprised of the sympathetic nervous system and the parasympathetic nervous system which control other muscles and visceral organs.\" width=\"599\" height=\"221\" \/><figcaption id=\"caption-attachment-2079\" class=\"wp-caption-text\"><strong>Figure 1<\/strong>. The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system, with the autonomic system divided into both sympathetic and parasympathetic systems.<\/figcaption><\/figure>\n<\/section>\n<section class=\"textbox keyTakeaway\">\n<h3>the somatic nervous system<\/h3>\n<p>The <strong><span data-type=\"term\">somatic nervous system<\/span><\/strong> is 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.<\/p>\n<ul>\n<li><strong>Motor neurons<\/strong>, carrying instructions from the CNS to the muscles, are <strong>efferent<\/strong> fibers (efferent means \u201cmoving away from\u201d\u2014away from the brain, in this instance).<\/li>\n<li><strong>Sensory neurons<\/strong>, carrying sensory information to the CNS, are <strong>afferent<\/strong> fibers (afferent means \u201cmoving toward\u201d).\n<ul>\n<li>A helpful way to remember this is that efferent = exit and afferent = arrive.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>Each nerve is basically a bundle of neurons forming a two-way superhighway, containing thousands of axons, both efferent and afferent.<\/p>\n<\/section>\n<section class=\"textbox keyTakeaway\">\n<h3>the autonomic nervous system<\/h3>\n<p>The <strong><span data-type=\"term\">autonomic nervous system<\/span><\/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 divisions.\u00a0<\/p>\n<p>&nbsp;<\/p>\n<p>The two systems, the sympathetic and parasympathetic nervous systems, have complementary functions, operating in tandem to maintain the body\u2019s homeostasis. <\/p>\n<p><strong><span data-type=\"term\">Homeostasis<\/span><\/strong> is a state of equilibrium, or balance, in which biological conditions (such as body temperature) are maintained at optimal levels.<\/p>\n<\/section>\n<section class=\"textbox tryIt\"><iframe loading=\"lazy\" id=\"ohm3950\" class=\"resizable\" src=\"https:\/\/ohm.one.lumenlearning.com\/multiembedq.php?id=3950&theme=lumen&iframe_resize_id=ohm3950&source=tnh&show_question_numbers\" width=\"100%\" height=\"200\"><\/iframe><\/section>\n<h2>Fight-or-Flight<\/h2>\n<section class=\"textbox keyTakeaway\">\n<h3>the sympathetic nervous system<\/h3>\n<p>The <strong><span data-type=\"term\">sympathetic nervous system<\/span><\/strong> is involved in preparing the body for stress-related activities. It\u00a0is activated when we are faced with stressful or high-arousal situations.<\/p>\n<ul>\n<li>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 her cubs. At that moment, the body would undergo a series of changes\u2014a direct function of sympathetic activation\u2014preparing a person to face the threat. Their pupils dilate, their heart rate and blood pressure increase, their bladder relaxes, their endocrine system kicks in\u2014their liver releases glucose, and adrenaline surges into their bloodstream.<\/li>\n<\/ul>\n<\/section>\n<figure style=\"width: 563px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224553\/CNX_Psych_03_03_Autonomic.jpg\" 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, and cause the bladder to contract. The sympathetic nervous system can dilate pupils, inhibit salivation, increase heart rate, dilate bronchi, inhibit digestion, and inhibit contraction of the bladder.\" width=\"563\" height=\"586\" data-media-type=\"image\/jpg\" \/><figcaption class=\"wp-caption-text\"><strong>Figure 1<\/strong>. The sympathetic and parasympathetic divisions of the autonomic nervous system have the opposite effects on various systems.<\/figcaption><\/figure>\n<section class=\"textbox keyTakeaway\">\n<h3>the parasympathetic nervous system<\/h3>\n<p>The <strong><span data-type=\"term\">parasympathetic nervous system<\/span><\/strong> is associated with returning the body to routine, day-to-day operations and a relaxed state.<\/p>\n<ul>\n<li>Our hunter\u2019s heart rate and blood pressure return to normal, their pupils constrict, they regain 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.<\/li>\n<\/ul>\n<\/section>\n<p>The &#8220;fight or flight&#8221; response is a physiological response that prepares the body to either confront a perceived threat or escape from it. For example, if a person sees a snake, whether the individual decides to\u00a0<em>fight<\/em>\u00a0the snake or\u00a0<em>run<\/em> away from it, either action requires energy; in short, the sympathetic nervous system says \u201cgo, go, go.\u201d If the person decides that it&#8217;s not a real threat, the parasympathetic nervous system curtails undue energy mobilization into muscles and glands and modulates the response by saying \u201cstop, stop, stop.\u201d This push\u2013pull tandem system regulates fight-or-flight responses in all of us.<\/p>\n<p id=\"fs-id1590023\">While it is clear that a fight-or-flight 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 any perceived threat with the <span class=\"no-emphasis\" data-type=\"term\">fight or flight<\/span> response. 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.<\/p>\n<section class=\"textbox tryIt\"><iframe loading=\"lazy\" id=\"ohm3951\" class=\"resizable\" src=\"https:\/\/ohm.one.lumenlearning.com\/multiembedq.php?id=3951&theme=lumen&iframe_resize_id=ohm3951&source=tnh&show_question_numbers\" width=\"100%\" height=\"1150\"><\/iframe><\/section>\n","protected":false},"author":20,"menu_order":21,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Parts of the Nervous System\",\"author\":\"OpenStax College\",\"organization\":\"\",\"url\":\"https:\/\/openstax.org\/books\/psychology-2e\/pages\/3-3-parts-of-the-nervous-system\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at https:\/\/openstax.org\/books\/psychology-2e\/pages\/1-introduction.\"},{\"type\":\"cc\",\"description\":\"The Nervous System\",\"author\":\"Aneeq Ahmad \",\"organization\":\"Henderson State University\",\"url\":\"https:\/\/nobaproject.com\/modules\/the-nervous-system\",\"project\":\"The Noba Project\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"}]","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"part":210,"module-header":"learn_it","content_attributions":[{"type":"cc","description":"Parts of the Nervous System","author":"OpenStax College","organization":"","url":"https:\/\/openstax.org\/books\/psychology-2e\/pages\/3-3-parts-of-the-nervous-system","project":"","license":"cc-by","license_terms":"Download for free at https:\/\/openstax.org\/books\/psychology-2e\/pages\/1-introduction."},{"type":"cc","description":"The Nervous System","author":"Aneeq Ahmad ","organization":"Henderson State University","url":"https:\/\/nobaproject.com\/modules\/the-nervous-system","project":"The Noba Project","license":"cc-by-nc-sa","license_terms":""}],"internal_book_links":[],"video_content":null,"cc_video_embed_content":{"cc_scripts":"","media_targets":[]},"try_it_collection":null,"_links":{"self":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters\/193"}],"collection":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/users\/20"}],"version-history":[{"count":13,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters\/193\/revisions"}],"predecessor-version":[{"id":7092,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters\/193\/revisions\/7092"}],"part":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/parts\/210"}],"metadata":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapters\/193\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/media?parent=193"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/pressbooks\/v2\/chapter-type?post=193"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/contributor?post=193"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/wp-json\/wp\/v2\/license?post=193"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}