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Chapter 16: The Autonomic System and Higher-Order Functions Learning Outcomes Upon completing this chapter, you will be able to 16-1 Compare the functions of the autonomic nervous system with that of the somatic nervous system. 16-6 Discuss the functional significance of dual innervation and autonomic tone. Discuss examples of organs that are controlled by dual innervation vs. single division of ANS and the result on autonomic tone. 16-7 Describe or recognize an example of a visceral reflex. Compare and contrast the sympathetic and parasympathetic divisions of the ANS Describe the structure and function of the RAS and describe its importance in the sleep-wake cycle. Chapter 16: The Autonomic System and Higher-Order Functions I. Introduction to Autonomic Nervous System A. Makes routine homeostatic adjustments (adjusts internal water, electrolyte, nutrient and dissolved gas concentrations in body fluids) B. Adjustments occur without instructions from conscious mind/occur at subconscious level II. 16-1 Somatic vs. Autonomic Nervous System A. Somatic Nervous system (SNS) 1. Operates under conscious control 2. Seldom affects long-term survival 3. controls skeletal muscles B. Autonomic Nervous System (ANS) 1. Operates without conscious instruction 2. controls visceral effectors (smooth muscles, glands, cardiac muscle) 3. Coordinates system functions III. The Organization of the Autonomic Nervous Systems A. Efferent division that carry motor commands B. Integrative centers for autonomic activity found in hypothalamus C. Preganglionic neurons: visceral motor neurons in brains stem/spinal cord (CNS) 1. part of visceral reflex arcs 2. activities represent direct reflex responses 3. contain preganglionic fibers which leave CNS and synapse at visceral motor neurons (autonomic ganglia) innervating smooth muscle, glands, cardiac muscle D. Autonomic ganglia (PNS) 1. innervate smooth muscle, glands, cardiac muscle 2. axons called postganglionic fibers E. visceral/sensory info triggers visceral reflexes F. ANS distributes motor commands of those reflexes 1. Example: cold weather = ANS stimulate contraction of arrector pili muscles = goosebumps 2. Example: loud noise = increase heart rate by ANS IV. Divisions of the ANS A. Sympathetic vs. Parasympathetic Division 1. Usually have opposing effects (sympathetic = excitation and parasympathetic = inhibition) 2. May work independently or together Chapter 16: The Autonomic System and Higher-Order Functions B. Functional comparison of the divisions of the ANS Sympathetic Division (“Fight or Flight”) Parasympathetic Division (Rest and Digest”) Kicks in during exertion, stress or emergency situations Kicks in under resting conditions Increases: Alertness/awareness Metabolic rate Respiration Cardiovascular Activates sweat glands Increases: Digestion Salivary gland secretions Elimination Reduces: Digestion/urinary Decreases: Reduces metabolic rate Cardiovascular C. Structural comparison of the divisions of the ANS Sympathetic Division Location of CNS (preganglionic) Thoracocolumbar (Thoracic and neurons Lumbar Regions) Locations of PNS ganglia Paravertebral (both sides of vertebral column) collateral (anterior to vertebral column) suprarenal (center of adrenal gland) Length of preganglionic fibers to Short to long postganglionic fibers Neurotransmitters released by ACh preganglionic fibers Parasympathetic Division Craniosacral (Cranial and Sacral Regions) Terminal (located near target organ) Intramural (embedded in tissue of target organ) Long to short ACh Neurotransmitters released by preganglionic fibers Most release Norepinephrine (NE) ACh Degree of Divergence Great divergence (single preganglionic fiber may innervate 24 or more ganglionic neurons in different ganglia) Little divergence (single pregalnglionic fiber synapses w/ 6-8 ganglionic neurons) Chapter 16: The Autonomic System and Higher-Order Functions V. 16-6 Dual Innervation A. Most vital organs innervated by both sympathetic and parasympathetic divisions B. Postganglionic fibers of each division “mingle” to form autonomic plexuses (Example cardiac plexus) C. Autonomic Tone 1. Autonomic motor neurons maintain resting level of spontaneous activity 2. Background level = autonomic tone 3. If nerve is inactive under normal conditions, can only increase activity 4. If nerve maintains background level of activity, can increase or decrease activity D. Dual Innervation and Autonomic Tone 1. Dual innervation = two divisions commonly have opposing effects a. Example: i. Heart receives dual innervation ii. Parasympathetic releases ACh = decrease HR iii. Sympathetic division release NE = increase HR iv. Balance between two = autonomic tone 2. No dual innervation = only one ANS innervation controls response a. Example: i. Blood vessels controlled by sympathetic division ii. Sympathetic division release NE = increase partial contraction of BVs = autonomic tone iii. Decrease in NE = dilation of BVs VI. 16-7 Visceral Reflexes A. Provide automatic motor responses that can be modified, facilitated or inhibited by higher centers, such as hypothalamus B. All are polysynaptic, can be long or short 1. Long reflexes coordinate activities of entire organs, involves CNS 2. Short reflexes bypass CNS and control activity in one small part of organ C. Examples of Visceral Reflexes Table 16-4 VII. 16-8 Consciousness and Reticular Activating System (RAS) A. RAS: network found in brain stem B. Interacts with cerebral cortex via nuclei in thalamus C. Stimulus = RAS active = cortex active = arousal from sleep + maintaining consciousness D. Neural fatigue/decrease in response to stimuli = RAS inactive = cortex inactive = decrease in alertness + lethargy