By Krishnan Prabhakaran Show
Motivation Abnormal functioning of the autonomic nervous system can be life threatening and there is a specific term for it: dysautonomia. Dysregulation of the autonomic nervous system can produce the apparent malfunction of the organs it regulates. For this reason, dysautonomia patients often present with numerous, seemingly unrelated maladies. Symptoms are wide ranging and can include problems with the regulation of heart rate, blood pressure, body temperature and perspiration. Other symptoms include fatigue, lightheadedness, feeling faint or passing out (syncope), weakness and cognitive impairment. Autonomic dysfunction can occur as a secondary condition of another disease process, like diabetes, or as a primary disorder where the autonomic nervous system is the only system impacted. These conditions are often misdiagnosed. Over one million Americans are impacted with a primary autonomic system disorder. The more common forms of these conditions include Postural Orthostatic Syndrome POTS / Orthostatic Intolerance OI (Figure 15.1) , Neurocardiogenic Syncope NCS, Pure Autonomic Failure PAF and Multiple Systems Atrophy MSA. Figure 15.1 Hand of a person with Postural Orthostatic Tachycardia Syndrome (POTS) and dysautonomia exhibiting blood pooling after standing for too long in cold weather. Photo by Yitzilitt on Wikimedia Commons, license CC-BY-SA.Upon completion of the work in this chapter students should be able to:
Background.The Autonomic Nervous SystemThe autonomic nervous system is tied into emotional responses and the fight-or-flight response sounds like a panic attack. In the modern world, these sorts of reactions are associated with anxiety as much as with response to a threat. It is engrained in the nervous system to respond like this. In fact, the adaptations of the autonomic nervous system probably predate the human species and are likely to be common to all mammals, and perhaps shared by many animals. However, the autonomic nervous system is not just about responding to threats. Besides the fight-or-flight response, there are the responses referred to as “rest and digest”. The digestive system has a big job to do. Much of the function of the autonomic system is based on the connections within an autonomic, or visceral, reflex.” The Autonomic Nervous System at WorkJayla is sitting, having an outdoor lunch with friends when a large spider lands on her plate. She immediately freezes, the food in her mouth begins to feel like a wad of dry hay, and she nearly gags as she tries to swallow it. She feels her heart race and pounding in her chest. After swallowing her food, it seems stuck in her throat and chest. In this scenario, Jayla had been sitting, relaxed and enjoying a meal. In this relaxed state, the body would have a heart rate that is at rest, active peristalisis (activity in muscles of the digestive system), ample activity in salivary glands and in digestive gland secretions, and bronchi that are not dilated. In this relaxed state, food can be easily processed due to ample amounts of saliva and digestive enzymes in the saliva released by the salivary glands into the mouth.. Salivation also facilitates swallowing by providing lubrication to the back of the throat and the esophagus. In this relaxed state, digestive fluids and enzymes in the intestines are actively produced and secreted so that food can be further processed and broken down (catabolized) for absorption of nutrients and glucose. While relaxed, Jayla’s heart beats imperceptibly and her breathing is deep. With the sudden appearance of the spider, the rate of Jayla’s heart beat becomes more rapid, and it contracts more powerfully. In this vigilant state, Jayla senses her rapid heart rate as well as the increased force of the contraction of her heart. She also senses a shift to rapid, shallow breathing that she tries to control. Her food seems lodged near the back of her throat as she struggles to swallow her food safely. Within seconds of seeing the spider, Jayla’s body systems shifted from reflecting calm to a state of panic and hyper-vigilance. These responses to the external threat prepare Jayla to either fight or flee the situation. In the hyper-vigilant state, Jayla’s pupils widen, she sweats and more blood is pumped through her blood vessels which permits more blood, chemicals, and hormones to flow to her skeletal muscles and respiratory system. As you can see, the effects on organ systems when in either of the states, relaxed or hyper-vigilant, are nearly opposite. These two states are controlled by two subsets of neural pathways that are part of the peripheral nervous system. The autonomic nervous system is divided into the sympathetic nervous system and the parasympathetic nervous system. It is the complementarity of these two latter branches of the autonomic nervous system that drove the physiological changes in the “Spider Sat Down Beside Her” scenario above. As evident from the impact of the sight of the spider on Jayla’s ability to eat her meal, activity in the parasympathetic system is associated with a relaxing meal; on the other hand, activity in the sympathetic system is associated with alertness and vigilance. In keeping with the complementary functionality of the two systems, they have been given nick names. The parasympathetic branch works for “rest and repose” (also commonly known as “rest and digest”); the sympathetic branch is known for the “fight or flight” response (variously also known as “fight, flight or freeze;” “hyperarousal;” “acute stress”). Comparison of Somatic Motor and Autonomic Nervous Systems
General Information on the Autonomic Nervous System
Divisions of the Autonomic Nervous SystemA. Sympathetic (=thoracolumbar) Division General information
General functions
Anatomy
B. Parasympathetic Division (=craniosacral)–think “vagus” General information
General functions
Anatomy
Physiology of the Autonomic Nervous SystemNeurotransmitters
Receptors
Pre-Laboratory Questions
Exercise 1: Identification of the autonomic divisionsPlace an “X” to show which division is involved for each of the following:
MATCH the following to sympathetic (S) division, parasympathetic (P) division, (B) both, or (N) neither:
Exercise 2: Problem solving: Acetylcholine’s autonomic effectsWe have a problem solving activity using a patient’s case and this is presented in multiple-choice format. Consider each choice individually and write an argument for accepting or rejecting it. Since the problem has one best answer, you will write one argument for acceptance and four for rejection. For each response, first state whether you are accepting or rejecting that statement. Then, write a detailed explanation of why you accept or reject each of the choices. PROBLEM: Mr. A. Prentice has been suffering from functional urinary retention and a hypoactive urinary bladder. Bethanechol, a drug that mimics acetylcholine’s autonomic effects, is prescribed to manage his problem. Which of the following adverse effects might Mr. Coral experience while taking this drug? A. Dry eyes due to deficient tear formation. B. Deficient salivation. C. Constipation. D. Decreased sexual arousal. E. Diarrhea Post-laboratory Questions
4. Why do we feel cold when facing a “fight or flight” situation? 5. Describe major parasympathetic and sympathetic physiological effects on target organs. What are the division of the ANS?It contains three anatomically distinct divisions: sympathetic, parasympathetic, and enteric.
Which division of the ANS is referred to as rest and digest division?The parasympathetic nervous system, also known as “rest and digest,” can be thought of as functioning in opposition to the sympathetic nervous system. Its functions include: A decrease in heart rate and contractility of cardiac muscle. Constriction of the ciliary muscle and the pupil for near vision.
What division of the nervous system is the ANS?Anatomy of the autonomic nervous system
The autonomic nervous system Autonomic nervous system is the part of the nervous system that supplies the internal organs, including the blood vessels, stomach, intestine, liver, kidneys, bladder, genitals, lungs, pupils, heart, and sweat, salivary, and digestive glands.
Which division of the ANS has a more widespread effect on the body?Describe two reasons why the sympathetic division of the ANS has a more widespread effect on visceral effectors of the body than the parasympathetic division does.
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