Nervous System 4-Autonomic NS4.pdf

Learning objectives Autonomic Nervous System Compare the somatic and autonomic nervous systems relative to effectors, efferent pathways, and neurotransmitters released. Compare and contrast the functions of the parasympathetic and sympathetic divisions. Application of homeostatic mechanisms Ex...

Learning objectives Autonomic Nervous System Compare the somatic and autonomic nervous systems relative to effectors, efferent pathways, and neurotransmitters released. Compare and contrast the functions of the parasympathetic and sympathetic divisions. Application of homeostatic mechanisms Explain the role of the nervous system in the maintenance of homeostasis and give examples of how the nervous system interacts with other body systems to accomplish this. Predictions related to disruption of homeostasis Given a factor or situation (e.g., a demyelinating disease), predict the changes that could occur in the nervous system and the consequences of those changes (i.e., given a cause, state a possible effect). ANS vs Somatic nervous system Somatic nervous system (SNS) Voluntary control of skeletal muscles Automatic nervous system (ANS) consists of motor neurons that: Innervate smooth muscles, cardiac muscle, and glands Make adjustments to ensure optimal support for body activities Shunts blood to areas that need it and adjusts heart rate, blood pressure, digestive processes, etc. Operate via subconscious control-also called involuntary nervous system or general visceral motor system Differ in Effectors Efferent pathways and ganglia Target organ responses to neurotransmitters © 2016 Pearson Education, Ltd. ANS vs Somatic nervous system Somatic Autonomic Effectors Skeletal muscles Cardiac muscle, smooth muscle, and glands Efferent Heavily myelinated Axons of the ANS are a two-neuron chain Pathways axons of the somatic 1) The preganglionic (first) neuron has a motor neurons extend lightly myelinated axon from the CNS to the 2) The ganglionic (second) neuron extends to effector an effector organ Neurotran All somatic motor Preganglionic fibers release Ach smitter neurons release Effects Acetylcholine (ACh) Postganglionic fibers release excitatory effect norepinephrine (NE) or ACh and the effect is either stimulatory or inhibitory. ANS effect on the target organ is dependent upon the neurotransmitter released and the receptor type of the effector  Figure 14.2 Comparison of motor neurons in the somatic and autonomic nervous systems. Cell bodies in central Neurotransmitter Effector nervous system Peripheral nervous system at effector organs Effect Single neuron from CNS to effector organs SOMATIC NERVOUS + ACh SYSTEM Stimulatory Heavily myelinated axon Skeletal muscle Two-neuron chain from CNS to effector organs ACh NE SYMPATHETIC AUTONOMIC NERVOUS SYSTEM Nonmyelinated postganglionic axon Lightly myelinated Ganglion +– preganglionic axons Epinephrine and ACh norepinephrine Stimulatory or inhibitory, depending on neuro- Adrenal medulla Blood vessel transmitter PARASYMPATHETIC and receptors on effector ACh ACh organs Smooth muscle (e.g., in gut), glands, cardiac muscle Lightly myelinated Nonmyelinated preganglionic axon postganglionic Ganglion axon Acetylcholine (ACh) Norepinephrine (NE) © 2013 Pearson Education, Inc. 14.2 Divisions of Autonomic Nervous System Two arms of ANS: Parasympathetic division: promotes maintenance functions, conserves energy Sympathetic division: mobilizes body during activity Dual innervation: all visceral organs are served by both divisions, but these divisions cause opposite effects Dynamic antagonism between two divisions maintains homeostasis Sympathetic division increases heart and respiratory rates, and inhibits digestion and elimination Parasympathetic division decreases heart and respiratory rates, and allows for digestion and discarding of wastes © 2016 Pearson Education, Ltd. Role of the Parasympathetic Division Keeps body energy use as low as possible, even while carrying out maintenance activities Directs digestion, diuresis, defecation Referred to as “rest-and-digest” system Example: person relaxing and reading after a meal Blood pressure, heart rate, and respiratory rates are low Gastrointestinal tract activity is high Pupils constricted, lenses accommodated for close vision © 2016 Pearson Education, Ltd. Role of the Sympathetic Division Mobilizes body during activity Referred to as “fight-or-flight” system Exercise, excitement, emergency, embarrassment activates sympathetic system Increased heart rate; dry mouth; cold, sweaty skin; dilated pupils During vigorous physical activity: Shunts blood to skeletal muscles and heart Dilates bronchioles Causes liver to release glucose © 2016 Pearson Education, Ltd. Sympathetic and Parasympathetic Tone Almost all blood vessel smooth muscle is entirely innervated by sympathetic fibers only, so this division controls blood pressure, even at rest Sympathetic tone (vasomotor tone): continual state of partial constriction of blood vessels If blood pressure drops, sympathetic fibers fire faster than normal to increase constriction of blood vessels and cause blood pressure to rise If blood pressure rises, sympathetic fibers fire less than normal, causing less constriction (dilation) of vessels, which leads to decrease in blood pressure Allows sympathetic system to shunt blood where needed © 2016 Pearson Education, Ltd. Sympathetic and Parasympathetic Tone (cont.) Parasympathetic division normally dominates heart and smooth muscle of digestive and urinary tract organs, and it activates most glands except for adrenal and sweat glands Slows the heart and dictates normal activity levels of digestive and urinary tracts These organs also exhibit parasympathetic tone where they are always slightly activated © 2016 Pearson Education, Ltd. 10  Autonomic Nervous System  Responses to increased sympathetic activity 1. Heightened mental alertness 2. Increased metabolic rate 3. Reduced digestive and urinary functions 4. Activation of energy reserves 5. Increased respiratory rate and dilation of respiratory passageways 6. Increased heart rate and blood pressure 7. Activation of sweat glands 11 © 2018 Pearson Education, Ltd.  Autonomic Nervous System  Responses to increased parasympathetic activity 1. Decreased metabolic rate 2. Decreased heart rate and blood pressure 3. Increased secretion by salivary and digestive glands 4. Increased motility and blood flow in digestive tract 5. Stimulation of urination and defecation 12 © 2018 Pearson Education, Ltd. Figure 14.3 Key anatomical differences between ANS Sympathetic divisions. Parasympathetic Eye Eye Brain stem Salivary Skin∗ glands Cranial Sympathetic Salivary ganglia glands Heart 1 Fibers originate 1 Fibers originate in the brain stem in the thoracic and Lungs (cranial fibers) or lumbar spinal cord. Lungs T1 sacral spinal cord. Heart 2a Preganglionic 2a Preganglionic fibers are long. fibers are short. Stomach Stomach 2b Postganglionic 2b Postganglionic Pancreas fibers are short. fibers are long. Liver Pancreas and gall- 3 Ganglia are 3 Ganglia are L1 bladder within or near close to spinal visceral effector cord. Adrenal Liver and gall- organs. gland bladder Bladder Sacral Bladder Genitals Genitals © 2016 Pearson Education, Inc. 14.6 Neurotransmitters Major neurotransmitters of ANS are acetylcholine (ACh) and norepinephrine (NE) Ach (same as ACh used by somatic motor neuron) is released by cholinergic fibers at: All ANS preganglionic axons and All parasympathetic postganglionic axons NE is released by adrenergic fibers at: Almost all sympathetic postganglionic axons, except those at sweat glands (release ACh) Effects of neurotransmitter depends on whether it binds to cholinergic receptor or adrenergic receptor © 2016 Pearson Education, Ltd. Table 14.3 Cholinergic and Adrenergic Receptors © 2016 Pearson Education, Ltd. Table 14.4 Selected Drug Classes That Influence the Autonomic Nervous System © 2016 Pearson Education, Ltd.  Divisions of the ANS Parasympathetic Sympathetic All preganglionic and All preganglionic axons Neurotransmitters postganglionic axons release release Acetylcholine; Acetylcholine most postganglionic axons release norepinephrine. Functional role Performs maintenance Mobilizes the body during activities and conserves body activity and extreme energy situations Figure 14.8 Levels of ANS control. Communication at subconscious level Cerebral cortex (frontal lobe) Limbic system (emotional input) Hypothalamus The “boss”: Overall integration of ANS Hypothalamus—main integrative Brain stem center of ANS activity (reticular formation, etc.) Regulates pupil size, heart, Subconscious cerebral input via blood pressure, airflow, salivation, etc. limbic system structures on hypothalamic centers Spinal cord Other controls come from cerebral Reflexes for urination, defecation, erection, cortex, reticular formation, and and ejaculation spinal cord © 2013 Pearson Education, Inc.  Higher-Order Functions  Brain chemistry – Changes in levels of neurotransmitters can strongly affect brain function and behavior  Example: Huntington’s disease – Destruction of ACh-secreting and GABA-secreting neurons in basal nuclei – Symptoms appear as basal nuclei and frontal lobes degenerate – Difficulty controlling movements – Intellectual abilities gradually decline 19 © 2018 Pearson Education, Ltd.  Higher-Order Functions  Serotonin – Affects sensory interpretation and emotional states – Compounds that enhance effects also produce hallucinations Example: lysergic acid diethylamide (LSD) – Compounds that inhibit production or block action cause severe depression and anxiety – Fluoxetine (Prozac) slows removal of serotonin at synapses One type of selective serotonin reuptake inhibitor  Dopamine Inadequate levels cause motor problems of Parkinson’s disease Excessive production may be associated with schizophrenia Amphetamines (“speed”) stimulate secretion Important in nuclei that control intentional movements 20 © 2018 Pearson Education, Ltd.