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Download nervous system part 5 autonomic system
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Section 5 Regulation of the Visceral Function by the Nervous System I Autonomic Nervous System 1. Basic of the Anatomy ANS We subdivide the ANS into the parasympathetic, sympathetic, and enteric divisions. The enteric system is essentially an independent nervous system responsible for regulation of digestive functions. The ANS coordinates cardiovascular, respiratory, digestive, excretory and reproductive systems. Somatic and Autonomic Nervous System Somatic and Autonomic Nervous System Somatic Skeletal muscle Conscious and unconscious movement Skeletal muscle contracts One synapse Acetylcholine Autonomic Smooth and cardiac muscle and glands Unconscious regulation Target tissues stimulated or inhibited Two synapses Acetycholine by preganglionic neurons and ACh or norepinephrine by postganglionic neurons Sympathetic Division Preganglionic cell bodies in lateral horns of spinal cord T1-L2 Parasympathetic Division Preganglionic axons organ innervated Preganglionic cell bodies in nuclei of brainstem or lateral parts of spinal cord gray matter from S2-S4 – Preganglionic axons from brain pass to ganglia through cranial nerves – Preganglionic axons from sacral region pass through pelvic nerves to ganglia pass to terminal ganglia within wall of or near Parasympathetic and sympathetic nerve distribution 2. Neurotransmitters and Neuroreceptors Acetylcholine and Norepinephrine All preganglionic neurons are cholinergic Parasympathetic post ganglionic neurons are cholinergic Sympathetic post ganglionic neurons are adrenergic except Sympathetics innervating sweat glands, blood vessels in skeletal muscle, and piloerection muscles are cholinergic Neurotransmitters SOMATIC NERVOUS SYSTEM AUTONOMIC NERVOUS SYSTEM Sympathetic ACh ACh ACh Parasympathetic Ad. M. ACh ACh Striated muscle NE Heart Sm. mus. Glands ACh Sweat glands ACh Heart Sm. mus. Glands E, NE Acetylcholine Nicotinic receptors – Nm (muscular-type or N2): skeletal muscle – Nn (neuron-type, or N1): autonomic ganglia, CNS Muscarinic receptors – Postganglionic parasympathetic and a few sympathetic sites, CNS (also autonomic gang.) – Receptor subtypes: M1-5 Catecholamines Norepinephrine – Postganglionic sympathetic, CNS, adrenal medulla – Receptors: a1, a2, b1 Epinephrine – Adrenal medulla, CNS – Receptors: a1, a2, b1 , b2 Dopamine – Autonomic ganglia, CNS – Receptors: D(1-5), a1, b1 Location of ANS Receptors 3 Function of the Sympathetic and Parasympathetic Nerve SNS Sympathetic nervous system prototypically “fight” or “flight”. Associated with increased energy expenditure, cardiopulmonary adjustments for intense activity, blood flow adjustments for maximum energy expenditure. SNS - Fight & Flight Reaction You’re walking alone at night and all the sudden you hear an unfamiliar noise near by… In a matter of seconds, your heart rate increases dramatically, blood vessels in your skeletal muscles dilate, blood vessels in the visceral muscles constrict, digestion is ceased, your liver ramps up glucose release, your pupils dilate, salivary production decreases, sweat increases. Parasympathetic Nervous System If that noise turns out to be the result of wind, then the body is returned to “pre-noise” state. This is the job of the parasympathetic nervous system. Autonomic Nervous System • Parasympathicus • Sympathicus • Wind down, relaxation, digestion • Dominated by Acetylcholine • Fight & Flight Reaction • Dominated by Noradrenaline (Adrenaline) • Fear, exercise, rage Interactions of the ANS Most visceral organs are innervated by both types of nerves. Most blood vessels are innervated only by sympathetic nerves. PS activity dominates the heart and GI tract. Activation of the sympathetic division causes wide spread, long-lasting mobilization of the fight-orflight response. PS effects are highly localized and short lived. II. Central Regulation of Visceral Function 1. Spinal cord bladder and rectum reflex (micturition and defecation) the baroreceptor reflex, sweating of the skin 2. Medulla oblongata Vital (respiratory and cardiovascular) center: Other autonomic reflexes: Swallow, cough, sneeze, gag, and vomit. 3. Hypothalamus Tu :19.17 Hypothalamic Functions 1). Body temperature: heat loss center in anterior HT (preoptic area) stimulates sweating and peripheral vasodilation, lesions cause hyperthermia; heat gain center in posterior HT stimulates cutaneous vasoconstriction, piloerection, shivering; lesions cause poikilothermy (the difference between poikilothermal or cold-blooded animal and homoiothermal or warm-blooded animal) Hypothalamic Functions 2). Food intake: ventromedial and paraventricular nuclei are satiety centers, lesion causes obesity; lateral HT (feeding center) stimulates food and water intake Hypothalamus Functions 3) Water balance ADH (vasopressin) Osmotic pressure in hypothalamus – Thirst - Drink 4) Sleep/wake cycle: suprachiasmatic nuc is biological clock; preoptic nuc can initiate sleep; lat HT can change cortical arousal; post HT lesion can cause coma or impaired arousal Hypothalamus Functions 5). Emotions and behavior: ventromedial lesions can cause viciousness/rage Posterior HT stimulates sympathetic functions Anterior HT stimulates parasympathetic functions Mamillary nuclei: recent memory Hypothalamus Functions 6). Circadian: Almost all land animals coordinate their behavior according to circadian rhythms, the daily cycles of lightness and darkness that result from the spin of the earth. Most if not all living organisms have rhythmic fluctuation in bodily function that are about 24 hs in length. (sleep-wake, and body temperature cycles). Suprachiasmatic muclei (SCN) Circadian rhythms of physiologic al functions. Hypothalamus Functions 7) Regulation of the Endocrine Function 4 Influence of Brain on Autonomic Functions III Function of Sympathetic and Parasympathetic nerve on the target organs Physiology (Table 5-1) Eye Effector Radial muscle Sphinctor Ciliary muscle Cornea Iris Lens Ciliary muscle Sympathetic Parasympathetic Contraction — (mydriasis, a1) — Contraction (miosis) Slight relaxa- Contraction (near tion (b2) vision) Heart Atria SA node AV node Ventricles Effector SA node Atria AV node Ventricles Sympathetic Tachycardia (b1,b2) contractility and conduction (b1,b2) conduction and automaticity (b1,b2) contractility, conduction, and automaticity (b1,b2,a1) Parasympathetic Bradycardia contractility, conduction (usually) conduction — Blood vessels Effector Skin and mucosa Skeletal muscle Salivary glands Erectile tissue Sympathetic Constriction (a1,a2) Constriction (a), dilation (b2) Constriction (a1,a2) Constriction (a) Parasympathetic Dilation (?) — Dilation Dilation Lungs and salivary glands Effector Bronchial sm. musc. Bronchial glands Salivary glands Sympathetic Parasympathetic Relaxation (b2) Constriction (a1),(b2), secretion Viscous, amylase secretion (a1,b1,b2) secretion Profuse watery secretion Gastrointestinal tract and liver Effector Smooth muscle Sympathetic Parasympathetic motility and motility and tone tone (a1,a2,b1,b2) Sphincters Contraction Relaxation (a1) Secretions secretion (a2) secretion Liver Glycogenolysis, Glycogen gluconeogene- synthesis sis (a1,b2)
