Peripheral Nervous System<\/h1>\r\nThe 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.\r\n\r\nThe [pb_glossary id=\"2826\"]somatic nervous system[\/pb_glossary] is associated with activities 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. Motor neurons, carrying instructions from the CNS to the muscles, are efferent fibres (efferent means \u201cmoving away from\u201d). Sensory neurons, carrying sensory information to the CNS, are afferent fibres (afferent means \u201cmoving toward\u201d). A helpful way to remember this is that efferent = exit and afferent = arrive. Each nerve is basically a bundle of neurons forming a two-way superhighway, containing thousands of axons, both efferent and afferent.\r\n\r\nThere is another type of neuron, called an interneuron, which is by far the most common type of neuron, located primarily within the CNS responsible 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.\r\n\r\nThe\u00a0[pb_glossary id=\"2827\"]autonomic nervous system[\/pb_glossary] controls our internal organs and glands and is generally considered to be outside of our voluntary control. It can be further subdivided into the sympathetic and parasympathetic divisions (Figure [below]).\r\nThe Divisions of the Autonomic Nervous System<\/h2>\r\nThe [pb_glossary id=\"2828\"]sympathetic nervous system[\/pb_glossary] is involved in preparing the body for stress-related activities; the\u00a0[pb_glossary id=\"2829\"]parasympathetic nervous system[\/pb_glossary] is 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 and respond to the body's needs. [pb_glossary id=\"2830\"]Homeostasis[\/pb_glossary] is a state of equilibrium, or balance, in which biological conditions (such as body temperature) are maintained at optimal levels.\r\n\r\n[caption id=\"attachment_753\" align=\"aligncenter\" width=\"650\" class=\"horiz-picture-small-adjustment\"]![\"A](\"http:\/\/opentextbooks.concordia.ca\/psyc200\/wp-content\/uploads\/sites\/64\/2025\/03\/Figure-BB.-8-SympatheticParasympathetic-Divisions-Diagram.jpeg\" "\\"A")
Figure BB.8. Sympathetic and parasympathetic nervous system.<\/strong> The sympathetic and parasympathetic divisions of the autonomic nervous system have the opposite effects on various systems. Alt. text:<\/strong> Diagram of the human body listing parasympathetic functions\u2014such as constricting pupils, slowing heart rate, and stimulating digestion\u2014and sympathetic functions\u2014such as dilating pupils, increasing heart rate, and inhibiting digestion. Source:<\/strong> Figure 3.14 as found in Psychology 2e by OpenStax<\/a> is licensed under a CC BY 4.0 Licence<\/a>.[\/caption]\r\n\r\nThe 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 suddenly disturbs a large bear with cubs. At that moment, our ancestor\u2019s body undergoes a series of changes \u2014 a direct function of sympathetic activation \u2014 preparing the hunter to face the threat. The hunter\u2019s pupils dilate (expand), their heart rate and blood pressure increase, their bladder relaxes (to reduce the chance of needing a bathroom break!), their liver releases glucose (a sugar readily used by the body for energy), and adrenaline surges into the hunter\u2019s bloodstream. This constellation of physiological changes, known as the\u00a0[pb_glossary id=\"2831\"]fight or flight response[\/pb_glossary], allows the body access to energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.\r\n\r\nWhile 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 fight or flight response.\r\n\r\nThis 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, & Marmot, 2006) and impaired function of the immune system (Glaser & 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.\r\n\r\nAfter the threat has been resolved, the parasympathetic nervous system takes charge and restores bodily functions to a relaxed state. Our ancestor\u2019s heart rate and blood pressure return to normal, their pupils constrict (become small), they regain control of their bladder, and the liver starts storing glucose as glycogen (a modified form of glucose that is easier to store) for future use. These restorative processes happen due to the activation of the parasympathetic nervous system.\r\n\r\nThe autonomic nervous system does not act alone in regulating the body\u2019s internal environment. It works closely with the endocrine system<\/span>, a network of glands that release hormones into the bloodstream. Whereas the nervous system communicates quickly through electrical and chemical signals in neurons, the endocrine system communicates more slowly through hormones, but its effects are longer-lasting. The interaction between these two systems is especially important in the stress response: when the sympathetic nervous system is activated, it triggers the adrenal glands to release hormones such as adrenaline and cortisol, which help the body cope with challenge and threat. In this way, the nervous and endocrine systems <\/span>operate<\/span> together to <\/span>maintain<\/span> homeostasis and adapt to changing demands<\/span><\/span>\u00a0<\/span>","rendered":"The nervous system can be divided into two major subdivisions: the central nervous system (CNS)<\/a> and the\u00a0peripheral nervous system (PNS)<\/a>, shown in Figure BB.7. The CNS comprises 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.<\/p>\n![\"Image](\"http:\/\/opentextbooks.concordia.ca\/psyc200\/wp-content\/uploads\/sites\/64\/2024\/02\/Figure-BB.7-Central-Nervous-System-Diagram-2.jpeg\")
Figure BB.7. The nervous system.<\/strong> The nervous system is divided into two major parts: (a) the Central Nervous System and (b) the Peripheral Nervous System. Alt. text:<\/strong> 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. Source:<\/strong> Figure 3.13 as found in Psychology 2e by OpenStax<\/a> is licensed under a CC BY 4.0 Licence<\/a>.<\/figcaption><\/figure>\nPeripheral Nervous System<\/h1>\n
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
The somatic nervous system<\/a> is associated with activities 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. Motor neurons, carrying instructions from the CNS to the muscles, are efferent fibres (efferent means \u201cmoving away from\u201d). Sensory neurons, carrying sensory information to the CNS, are afferent fibres (afferent means \u201cmoving toward\u201d). A helpful way to remember this is that efferent = exit and afferent = arrive. Each nerve is basically a bundle of neurons forming a two-way superhighway, containing thousands of axons, both efferent and afferent.<\/p>\nThere is another type of neuron, called an interneuron, which is by far the most common type of neuron, located primarily within the CNS responsible 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
The\u00a0autonomic nervous system<\/a> controls our internal organs and glands and is generally considered to be outside of our voluntary control. It can be further subdivided into the sympathetic and parasympathetic divisions (Figure [below]).<\/p>\nThe Divisions of the Autonomic Nervous System<\/h2>\n
The sympathetic nervous system<\/a> is involved in preparing the body for stress-related activities; the\u00a0parasympathetic nervous system<\/a> is 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 and respond to the body’s needs. Homeostasis<\/a> is a state of equilibrium, or balance, in which biological conditions (such as body temperature) are maintained at optimal levels.<\/p>\nFigure BB.8. Sympathetic and parasympathetic nervous system.<\/strong> The sympathetic and parasympathetic divisions of the autonomic nervous system have the opposite effects on various systems. Alt. text:<\/strong> Diagram of the human body listing parasympathetic functions\u2014such as constricting pupils, slowing heart rate, and stimulating digestion\u2014and sympathetic functions\u2014such as dilating pupils, increasing heart rate, and inhibiting digestion. Source:<\/strong> Figure 3.14 as found in Psychology 2e by OpenStax<\/a> is licensed under a CC BY 4.0 Licence<\/a>.<\/figcaption><\/figure>\nThe 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 suddenly disturbs a large bear with cubs. At that moment, our ancestor\u2019s body undergoes a series of changes \u2014 a direct function of sympathetic activation \u2014 preparing the hunter to face the threat. The hunter\u2019s pupils dilate (expand), their heart rate and blood pressure increase, their bladder relaxes (to reduce the chance of needing a bathroom break!), their liver releases glucose (a sugar readily used by the body for energy), and adrenaline surges into the hunter\u2019s bloodstream. This constellation of physiological changes, known as the\u00a0fight or flight response<\/a>, allows the body access to energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.<\/p>\nWhile 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 fight or flight response.<\/p>\n
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, & Marmot, 2006) and impaired function of the immune system (Glaser & 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
After the threat has been resolved, the parasympathetic nervous system takes charge and restores bodily functions to a relaxed state. Our ancestor\u2019s heart rate and blood pressure return to normal, their pupils constrict (become small), they regain control of their bladder, and the liver starts storing glucose as glycogen (a modified form of glucose that is easier to store) for future use. These restorative processes happen due to the activation of the parasympathetic nervous system.<\/p>\n
The autonomic nervous system does not act alone in regulating the body\u2019s internal environment. It works closely with the endocrine system<\/span>, a network of glands that release hormones into the bloodstream. Whereas the nervous system communicates quickly through electrical and chemical signals in neurons, the endocrine system communicates more slowly through hormones, but its effects are longer-lasting. The interaction between these two systems is especially important in the stress response: when the sympathetic nervous system is activated, it triggers the adrenal glands to release hormones such as adrenaline and cortisol, which help the body cope with challenge and threat. In this way, the nervous and endocrine systems <\/span>operate<\/span> together to <\/span>maintain<\/span> homeostasis and adapt to changing demands<\/span><\/span>\u00a0<\/span><\/p>\ndefinition<\/span>Central Nervous System (CNS):<\/strong><\/p>\nThe collection of neurons that make up the brain and the spinal cord. Is the major controller of the body\u2019s functions, charged with interpreting sensory information and responding to it with its own directives.<\/p>\n<\/div>
Figure BB.8. Sympathetic and parasympathetic nervous system.<\/strong> The sympathetic and parasympathetic divisions of the autonomic nervous system have the opposite effects on various systems. Alt. text:<\/strong> Diagram of the human body listing parasympathetic functions\u2014such as constricting pupils, slowing heart rate, and stimulating digestion\u2014and sympathetic functions\u2014such as dilating pupils, increasing heart rate, and inhibiting digestion. Source:<\/strong> Figure 3.14 as found in Psychology 2e by OpenStax<\/a> is licensed under a CC BY 4.0 Licence<\/a>.[\/caption]\r\n\r\nThe 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 suddenly disturbs a large bear with cubs. At that moment, our ancestor\u2019s body undergoes a series of changes \u2014 a direct function of sympathetic activation \u2014 preparing the hunter to face the threat. The hunter\u2019s pupils dilate (expand), their heart rate and blood pressure increase, their bladder relaxes (to reduce the chance of needing a bathroom break!), their liver releases glucose (a sugar readily used by the body for energy), and adrenaline surges into the hunter\u2019s bloodstream. This constellation of physiological changes, known as the\u00a0[pb_glossary id=\"2831\"]fight or flight response[\/pb_glossary], allows the body access to energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.\r\n\r\nWhile 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 fight or flight response.\r\n\r\nThis 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, & Marmot, 2006) and impaired function of the immune system (Glaser & 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.\r\n\r\nAfter the threat has been resolved, the parasympathetic nervous system takes charge and restores bodily functions to a relaxed state. Our ancestor\u2019s heart rate and blood pressure return to normal, their pupils constrict (become small), they regain control of their bladder, and the liver starts storing glucose as glycogen (a modified form of glucose that is easier to store) for future use. These restorative processes happen due to the activation of the parasympathetic nervous system.\r\n\r\nThe autonomic nervous system does not act alone in regulating the body\u2019s internal environment. It works closely with the endocrine system<\/span>, a network of glands that release hormones into the bloodstream. Whereas the nervous system communicates quickly through electrical and chemical signals in neurons, the endocrine system communicates more slowly through hormones, but its effects are longer-lasting. The interaction between these two systems is especially important in the stress response: when the sympathetic nervous system is activated, it triggers the adrenal glands to release hormones such as adrenaline and cortisol, which help the body cope with challenge and threat. In this way, the nervous and endocrine systems <\/span>operate<\/span> together to <\/span>maintain<\/span> homeostasis and adapt to changing demands<\/span><\/span>\u00a0<\/span>","rendered":"The nervous system can be divided into two major subdivisions: the central nervous system (CNS)<\/a> and the\u00a0peripheral nervous system (PNS)<\/a>, shown in Figure BB.7. The CNS comprises 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.<\/p>\n 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 The somatic nervous system<\/a> is associated with activities 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. Motor neurons, carrying instructions from the CNS to the muscles, are efferent fibres (efferent means \u201cmoving away from\u201d). Sensory neurons, carrying sensory information to the CNS, are afferent fibres (afferent means \u201cmoving toward\u201d). A helpful way to remember this is that efferent = exit and afferent = arrive. Each nerve is basically a bundle of neurons forming a two-way superhighway, containing thousands of axons, both efferent and afferent.<\/p>\n There is another type of neuron, called an interneuron, which is by far the most common type of neuron, located primarily within the CNS responsible 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 The\u00a0autonomic nervous system<\/a> controls our internal organs and glands and is generally considered to be outside of our voluntary control. It can be further subdivided into the sympathetic and parasympathetic divisions (Figure [below]).<\/p>\n The sympathetic nervous system<\/a> is involved in preparing the body for stress-related activities; the\u00a0parasympathetic nervous system<\/a> is 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 and respond to the body’s needs. Homeostasis<\/a> is a state of equilibrium, or balance, in which biological conditions (such as body temperature) are maintained at optimal levels.<\/p>\n 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 suddenly disturbs a large bear with cubs. At that moment, our ancestor\u2019s body undergoes a series of changes \u2014 a direct function of sympathetic activation \u2014 preparing the hunter to face the threat. The hunter\u2019s pupils dilate (expand), their heart rate and blood pressure increase, their bladder relaxes (to reduce the chance of needing a bathroom break!), their liver releases glucose (a sugar readily used by the body for energy), and adrenaline surges into the hunter\u2019s bloodstream. This constellation of physiological changes, known as the\u00a0fight or flight response<\/a>, allows the body access to energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.<\/p>\n 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 fight or flight response.<\/p>\n 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, & Marmot, 2006) and impaired function of the immune system (Glaser & 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 After the threat has been resolved, the parasympathetic nervous system takes charge and restores bodily functions to a relaxed state. Our ancestor\u2019s heart rate and blood pressure return to normal, their pupils constrict (become small), they regain control of their bladder, and the liver starts storing glucose as glycogen (a modified form of glucose that is easier to store) for future use. These restorative processes happen due to the activation of the parasympathetic nervous system.<\/p>\n The autonomic nervous system does not act alone in regulating the body\u2019s internal environment. It works closely with the endocrine system<\/span>, a network of glands that release hormones into the bloodstream. Whereas the nervous system communicates quickly through electrical and chemical signals in neurons, the endocrine system communicates more slowly through hormones, but its effects are longer-lasting. The interaction between these two systems is especially important in the stress response: when the sympathetic nervous system is activated, it triggers the adrenal glands to release hormones such as adrenaline and cortisol, which help the body cope with challenge and threat. In this way, the nervous and endocrine systems <\/span>operate<\/span> together to <\/span>maintain<\/span> homeostasis and adapt to changing demands<\/span><\/span>\u00a0<\/span><\/p>\n Central Nervous System (CNS):<\/strong><\/p>\n The collection of neurons that make up the brain and the spinal cord. Is the major controller of the body\u2019s functions, charged with interpreting sensory information and responding to it with its own directives.<\/p>\n<\/div>Peripheral Nervous System<\/h1>\n
The Divisions of the Autonomic Nervous System<\/h2>\n