The Autonomic Nervous System Introduction 1 Define autonomic nervous system and explain its relationship to the peripheral nervous system The autonomic nervous system is part of the peripheral nervous system and primarily serves a regulatory function by helping the body adapt to internal and environmental demands thereby maintaining homeostasis 2 Compare the somatic and autonomic nervous systems relative to effectors efferent pathways and neurotransmitters released 1 The somatic nervous system stimulates skeletal muscles while the ANS innervates cardiac and smooth muscle and glands 2 In the somatic nervous system the cell bodies of the neurons are in the spinal cord and their axons extend to the skeletal muscles they innervate The ANS consists of a two neuron chain 3 The neurotransmitter released by the somatic motor neurons is acetylcholine which always has an excitatory effect the neurotransmitters released by the ANS are epinephrine and acetylcholine and both may have either an excitatory or an inhibitory effect 4 There is overlap between the somatic and autonomic nervous systems and most body responses to changing internal and external stimuli involve both skeletal muscle activity and visceral organ responses 3 Compare and contrast the roles of the parasympathetic and sympathetic divisions 1 The parasympathetic division keeps body energy use as low as possible while directing digestion and elimination activities 2 The sympathetic division prepares the body to respond to an emergency or threatening situation or vigorous exercise ANS Physiology 4 Define cholinergic and adrenergic fibers and list the different types of their receptors Cholinergic receptors such as nicotinc and muscarnic receptors bind ACh Adrenergic receptors alpha and beta bind to epinephrine 5 Explain the clinical importance of drugs that mimic or inhibit adrenergic or cholinergic effects Knowing the locations of the cholinergic and adrenergic receptor substypes allows specific drugs to be prescribed to obtain desired inhibitory or stimulatory effecrs on target organs 6 Underscore the effects of the parasympathetic and sympathetic divisions on the following organs heart blood vessels gastrointestinal tract lungs adrenal medulla and external genitalia 1 Most visceral organs receive dual innervation by both ANS divisions allowing for a dynamic antagonism to exist between the divisions and precise control of visceral activity 2 The sympathetic division increases heart rate dilates airways and inhibits digestion and elimination while the body is under stress 3 After the stress has passed the parasympathetic division returns heart rate and airway diameter to normal and allows digestion and elimination to resume 4 Sympathetic tone throughout the vascular system allows the firing rate of sympathetic neurons to control the diameter of blood vessels regulating stemic blood pressure 5 Parasympathetic tone is usually dominant in the heart digestive system and urinary tracts maintaining normal homeostatic levels of function unless overridden by the sympathetic system during stress 6 The divisions of the autonomic nervous system may work together rather than antagonistically as in sexual arousal 7 The sympathetic system has a unique role in control of the adrenal medulla sweat glands arrector pili muscles of the skin the kidneys and most blood vessels 8 The parasympathetic division exerts short lived localized control over its effectors whereas effects of the sympathetic division are persistent and widespread 7 Identify the autonomic nervous system controls of the spinal cord brain stem hypothalamus and cerebral cortex 1 The brain stem appears to exert the most direct influence over autonomic functions 2 The hypothalamus is the main integration center for the autonomic nervous system 3 Cortical or voluntary control of the autonomic nervous system does appear to be possible IV Homeostatic Imbalances of the ANS A Hypertension or high blood pressure may result from an overactive sympathetic vasoconstrictor response due to continuous high levels of stress B Raynaud s disease is characterized by intermittent attacks causing the skin of the fingers and the toes to become pale then cyanotic and painful C Autonomic dysreflexia is a life threatening condition involving uncontrolled activation of both somatic and autonomic motor neurons
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