Module 11: The Autonomic Nervous System PDF

Module 11: The Autonomic Nervous System Site: TRU Moodle Printed by: Saboura Ahmadzadeh Seddeighi Course: BIOL 1593_SW7 - Anatomy and Physiology I (Winter 2021 Rittenhouse) Date: Thursday, 17 August 2023, 10:52 AM Book: Module 11: The Autonomic Nervous System Table of contents Overview Ob...

Module 11: The Autonomic Nervous System Site: TRU Moodle Printed by: Saboura Ahmadzadeh Seddeighi Course: BIOL 1593_SW7 - Anatomy and Physiology I (Winter 2021 Rittenhouse) Date: Thursday, 17 August 2023, 10:52 AM Book: Module 11: The Autonomic Nervous System Table of contents Overview Objective 1: Discuss the structure of the autonomic nervous system (ANS). Objective 2: Describe the function of the sympathetic and parasympathetic divisions of the ANS. Objective 3: Discuss sympathetic and parasympathetic responses. Objective 4: Compare the structural and functional differences of the somatic and autonomic portions of the nervous system. Self-Test Overview Introduction The autonomic nervous system (ANS) is the part of the peripheral nervous system that controls homeostasis and regulates involuntary vital functions, including the activity of smooth muscle, cardiac muscle, and the glands. Functionally, the ANS usually operates without conscious control; however, because certain actions, such as breathing, can be consciously controlled (in part), this system is not truly autonomous. The ANS is anatomically and functionally linked to the rest of the nervous system and is regulated mainly by the hypothalamus and medulla oblongata in the brain. The output (motor) portion of the ANS has two divisions: parasympathetic and sympathetic. This module examines the structure and function of the ANS, describes its sympathetic and parasympathetic divisions, and discusses the differences between the somatic and autonomic divisions of the peripheral nervous system (PNS). Objectives Overview 1. Discuss the structure of the autonomic nervous system (ANS). 2. Describe the function of the sympathetic and parasympathetic divisions of the ANS. 3. Discuss sympathetic and parasympathetic responses. 4. Compare the structural and functional differences of the somatic and autonomic portions of the nervous system. Note To accomplish these objectives, carefully read through Chapter 15: “The Autonomic Nervous System” in your textbook, OpenStax A&P. Relevant passages are referenced under each objective in this module. The most important figures and tables have been copied herein for your convenience, and edited for content in some cases. Complete the self-test at the end of the module to identify any topics requiring further study. Contact your Open Learning Faculty Member if you need assistance. Licenses and Attributions: All figures and tables are taken or modified from OpenStax A&P under a Creative Commons 4.0 License, unless indicated otherwise. All micrographs are provided by the Regents of University of Michigan Medical School @ 2012. For each module in BIOL 1593, a list of Online Educational Resources (OERs), i.e., animations, videos and/or quizzes, has been compiled to support the teaching and learning of your course materials. These OERs are optional to view, but you may find them helpful as they are presented in a lecture format by experts in anatomy and physiology. The Objectives in your modules and the pages referenced in your text remain the basis for the questions on your exams. Objective 1: Discuss the structure of the autonomic nervous system (ANS). See OpenStax A&P pages 655–658, 660–661, 665–668; Fig. 15.6. In Module 10, Objective 7, the concept of a generalized reflex arc was discussed—where a stimulated receptor sends a signal through an afferent (sensory) pathway to an integrating neuron, then to a subsequent efferent (motor) pathway that terminates at an effector. Both the autonomic and somatic divisions of the peripheral nervous system have reflex arcs, but their motor (efferent) pathways differ in multiple respects: the presence or absence of ganglia and myelin along their pathways, and whether the signal being sent is excitatory or inhibitory in effect. The efferent pathway in all ANS circuits consists of the following three components: 1. Preganglionic neuron (myelinated). 2. Autonomic ganglion (a collection of nerve cell bodies). 3. Postganglionic neuron (unmyelinated). The postganglionic neurons of all ANS pathways are either: 1. Sympathetic (excitatory), or 2. Parasympathetic (inhibitory), in function. Therefore, the three linked components can be sympathetic or parasympathetic. Figure 15.6: The Efferent Pathway of an Autonomic (Visceral) Reflex. Efferent pathways of visceral reflexes consist of a presynaptic (preganglionic) neuron projecting to a ganglion, followed by a postsynaptic (postganglionic) fibre to the target effector. (Caption modified and figure truncated from OpenStax College, Anatomy & Physiology. Used under a CC BY 4.0 license. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.) Objective 2: Describe the function of the sympathetic and parasympathetic divisions of the ANS. See OpenStax A&P pages 656–657, 660–661, 663–664, 670; Table 15.1. Autonomic neurons are classified on the basis of the neurotransmitter they release: Cholinergic Adrenergic Cholinergic neurons release acetylcholine. Their effects are short-lived and localized. Adrenergic neurons release norepinephrine, and their effects are long-lasting and widespread. Table 15.1. (From OpenStax College, Anatomy & Physiology. Used under a CC BY 4.0 license. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.) Objective 3: Discuss sympathetic and parasympathetic responses. See OpenStax A&P pages 655–656; pages 760-762. The sympathetic response is the “fight or flight” response. Because the adrenal medulla produces epinephrine and norepinephrine, which stimulate the "fight or flight" response, the adrenal glands are included here as part of the body's sympathetic response mechanism. The parasympathetic response is the “rest and digest” response. Objective 4: Compare the structural and functional differences of the somatic and autonomic portions of the nervous system. See OpenStax A&P pages 656–658; 665–668; Fig. 15.6. The somatic nervous system contains both sensory and motor neurons. The somatic sensory neurons receive input from the receptors of the special and somatic senses, and these sensations are consciously perceived. Somatic motor neurons innervate skeletal muscle to produce conscious, voluntary movements. The effect of a motor neuron is always excitation. The autonomic nervous system contains both autonomic sensory and motor neurons. Autonomic sensory neurons are associated with sensory receptors, but autonomic sensory input is not consciously perceived. The ANS also receives sensory input from the somatic senses and special sensory neurons. The autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) the ongoing activities of cardiac muscle, smooth muscle, and the glands. Most autonomic responses cannot be consciously altered or suppressed. All autonomic motor pathways consist of two motor neurons in a series. The axon of the first motor neuron of the ANS extends from the central nervous system (CNS) and synapses with the second motor neuron in a ganglion. The second neuron synapses with an effector. Preganglionic fibres release acetylcholine, and postganglionic fibres release acetylcholine or norepinephrine. The output (efferent) component of the ANS is divided into two principal parts: the sympathetic and the parasympathetic divisions. Organs that receive impulses from both sympathetic and parasympathetic fibres are said to have dual innervation. Figure 15.6: Comparison of Somatic and Visceral Reflexes. The afferent inputs to somatic and visceral reflexes are essentially the same, whereas the efferent branches are different. Somatic reflexes, for instance, involve a direct connection from the ventral horn of the spinal cord to the skeletal muscle. Visceral reflexes involve a projection from the central neuron to a ganglion, followed by a second projection to the target effector. (From OpenStax College, Anatomy & Physiology. Used under a CC BY 4.0 license. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.) Self-Test Module 11: Self-Test The following self-test is designed to help you assess your understanding of the concepts presented in Chapter 15 of your textbook and how well you have met the module objectives. Complete both the short answer and the multiple-choice sections of the self-test, and then check your answers by using the Answer Key that follows it. If you correctly answer all the questions, go on to the next module and Chapter 14 in your textbook. If you have difficulty with any of the self-test questions, review the chapter material until you feel ready to continue. The Key Terms, Chapter Review, Interactive Link Questions, and Review Questions at the end of Chapter 15 in your textbook are also excellent summaries and study aids. Keep in mind, however, that not all topics or questions may be relevant to the material covered in this module, which should be your focus in preparing for your exams. Module 11 Self-Test