Autonomic Nervous System PDF

ANS Nervous System Central nervous system (CNS) Peripheral nervous system (PNS) Brain Spinal cord Cranial Nerves Spinal nerves (Except CN...

ANS Nervous System Central nervous system (CNS) Peripheral nervous system (PNS) Brain Spinal cord Cranial Nerves Spinal nerves (Except CN II) Functional divisions of peripheral nervous system Somatic nervous system Autonomic nervous system Controls skeletal muscles Controls smooth muscles, cardiac muscle & glands. (Voluntary action) (Involuntary action) Sensory Motor (afferent) (efferent) Sympathetic Parasympathetic 1 ANS Autonomic nervous system: Definition: It is the system for involuntary subconscious functions, it controls the internal environment to maintain homeostasis. Controls visceral involuntary actions i.e. cardiac & smooth muscles & endocrinal & exocrine glands. Relation between sympathetic and parasympathetic systems: 1- Reciprocal: once sympathetic is stimulated, parasympathetic is inhibited and vice versa. 2- Complemental: e.g micturition and defecation reflex. sympathetic for FILLING and parasympathetic for EVACUATION 2 ANS Organization of sympathetic nervous system. T1 – L3 (Thoracolumbar) Organization of parasympathetic nervous system. Cranial nerves III, VII, IX, and X (oculomotor, Facial, Glossopharyngeal, and Vagus nerves); S2-4 (Cranio-sacral) 3 ANS Autonomic ganglia: Definition: It is the site of physiological contact between pre and postganglionic neuron. Types: a) Lateral (sympathetic) b) Collateral (sympathetic) c) Terminal (parasympathetic) Function of Autonomic Ganglion: 1. Distributing center: Sympathetic 1:32 Parasympathetic 1:9 2. Relay station: between pre and postganglionic fiber Sympathetic Ganglia: 1. Sympathetic chain (paravertebral ganglion): sympathetic preganglionic neurons are located in the lateral column of the first thoracic to the third lumbar segments (thoracolumbar). 2. Prevertebral (collateral ganglia): some preganglionic neurons pass through the paravertebral ganglion chain and end on postganglionic neurons located in prevertebral ganglia close to the viscera, including: celiac, superior mesenteric, inferior mesenteric ganglia. Pathway of pre-ganglionic sympathetic fibers: 1- May synapse in first sympathetic chain ganglion, it enters. 2- Synapsing in other sympathetic chain ganglia up or down. 3- Synapse in collateral ganglia. 4- Synapse in substance of adrenal medulla itself. 4 ANS Parasympathetic Ganglion: Preganglionic neurons are located in several cranial nerve nuclei (III, VII, IX, X) and in the lateral column of the sacral spinal cord. 1. Terminal ganglion (parasympathetic) 2. Cranial nerves ganglia. Cranial nerve Parasympathetic nucleus Supplies Oculomotor nerve Edinger-Westphal nucleus Intrinsic muscles of the eye: the (CN III) axons project to ciliary constrictor muscle of iris, and ciliary ganglia. muscles. Facial nerve Superior salivatory nucleus (CN VII) axons project to: sphenopalatine ganglia lacrimal gland, submandibular ganglia Submaxillary and sublingual salivary glands. Glossopharyngeal Inferior salivatory nucleus Parotid salivatory gland. (CN IX) axons project to otic ganglion. Vagus nerve Nucleus ambiguous Sinoatrial (SA) and atrioventricular (CN X) * (AV) nodes in the heart. Dorsal motor vagal nucleus Esophagus, trachea, lungs and gastrointestinal tract. *Note: 75% of parasympathetic fibers of the body are from the vagus nerve. 5 ANS Anatomical Preganglionic Postganglionic Transmitter Transmitter Location Fibers Fibers (Ganglia) (Organs) Thoracic/ Sympathetic Short Long ACh NE Lumbar Cranial/ Parasympathetic Long Short ACh ACh Sacral 6 ANS Sympathetic Parasympathetic Metabolism Catabolic (energy consuming) Anabolic (energy preserving) Origin Thoraco-Lumber (Tl - 12 , LI,2,3) Cranio-sacral Function Stress (muscular exercise, fear, fight, Digestion and sleep flight) Emptying (micturition, defecation) Distribution widespread Localized Eye: Contraction of radial Contraction of circular 1. Pupil muscles of the iris muscles of the iris causes pupil dilation causes pupil (mydriasis) constriction (miosis). 2. Ciliary Relaxation Contraction muscle (far vision) (near vision) 3. Tarsal elevation of eye lid = widening of eye muscle Exophthalmos = Protrusion of eye ball 4. Muller's m. Skin: Sweat glands Secretion (sweating) Cutaneous BV VC (pallor) Erector pilae m Erection of hair Salivary glands Trophic, small amount secretion Profuse watery (concentrated, viscid). secretion Thorax: 1) Heart: Increase all cardiac properties (β1 & Decrease all cardiac properties β2) * Coronaries Vasodilation (β2) 2) Lungs Bronchodilation (β2) Bronchoconstriction Pulmonary Mildly V.C. (α1) V.D. BVs Abdomen: 1) Upper GIT: Walls: Inhibition (relaxation); decrease Stimulation (contraction); motility (β2)= retention increase motility Sphincters: Contraction (α1) Relaxation BVs: V.C. (α1) -------- 7 ANS 2)Liver: Increase glycogenolysis (α1, β2) Slight glycogen synthesis (glycogen converted to glucose) and glucose release. 3)Gallbladder: Relaxation of gall bladder and Contraction (evacuation) contraction of its sphincter. Inhibit the intestinal juice secretion GIT glands, liver & pancreas; increase secretions spleen → contraction & release of RBCs in case of haemorrhage adipose tissues → lipolysis --- Pelvis: 1) Lower GIT Walls: Relaxation. Contraction Sphincters: Contraction of internal anal sphincter Relaxation (defecation) (retention of faeces)** 2) Urinary sys kidneys Decrease urine output None bladder Wall: Relaxation Contraction Sphincter: Contraction of internal urethral Relaxation (micturition) sphincter; retention of urine 3) Genital tract: Male: a) Inhibition of erection (V.C. of Erection of penis (vasodilatation erectile tissue) of blood vessels of penis) b) Ejaculation (contraction of vas deferens, prostate and ejaculatory duct) Female: Variable effects on uterus. Skeletal ms. Vasodilatation of skeletal muscles blood vessels (delays fatigue). Increase glycogenolysis Increase strength Adrenal Stimulation of secretion of medulla catecholamine (release of 80% epinephrine, 20% nor epinephrine) Organs purely 1- Ventricles (vagal escape). 1- Constrictor pupillary muscle. supplied by this 2- Skin structures. 2- Oesophagus. system 3- Skeletal B.V. 3- Gastric glands. 4- Dilator pupillary muscles. 4- Erectile tissue. 5- Adrenal medulla. **Increase all cardiac properties Positive inotropic effect = ↑ contractility Positive chronotropic effect = ↑ Heart rate. ↑ Conductivity- ↑ Excitability. ** External urethral or anal sphincters are not under autonomic control but under somatic control via pudendal nerve. N.B Sympathetic → causes V.C of all blood vessels, except: 1-Coronaries.2- Skeletal blood vessels. 8 ANS 9 ANS Sympathetic N.S. HORNER'S SYNDROME Cause Lesion in one side of the cervical sympathetic chain. Eye: Contraction of radial 1. Pupil muscles of the iris 1. Miosis: pupillary causes pupil dilation constriction (mydriasis) 2. Ciliary muscle Relaxation (far vision) 3. Tarsal muscle elevation of eye lid = widening of 2. Ptosis: drop of upper eye eyelid 4. Muller's m. Exophthalmos = Protrusion of eye 3. Enophthalmos: intrusion ball of the eyeball. Skin: 1. Anhydosis: dryness of skin Sweat glands (no sweating) Cutaneous BV 2. V.D: Flushing of the face (red Secretion (sweating) Erector pilae m and warm). VC (pallor) ALL THESE EFFECTS ARE AT Erection of hair SAME SIDE OF LESION. 10  ANS Mass “stress” response: When large portions of the sympathetic nervous system discharges at the same time >> that is mass effect / mass discharge. This occurs when the hypothalamus is activated by fright or fear or sever pain. Leads to: 1. Increased arterial pressure. 2. Increased blood flow to the active muscles concurrent with decreased blood flow to organs such as gastro intestinal tract and kidneys that are not needed for the rapid motor activity. 3. Increased rates of cellular metabolism throughout the body. 4. Increased blood glucose concentration. 5. Increased glycolysis in the liver and the muscle. 6. Increased muscle strength. 7. Increased mental activity. The sum of these effects permits a person to perform far more physical activity than would otherwise be possible. 11 ANS Autonomic reflexes: 1. Cardiovascular autonomic reflex: This reflex helps to control the arterial blood pressure and heart rate. Stretch receptors called baroreceptors are located in the walls of several major arteries (especially the internal carotid arteries and the arch of aorta). When these become stretched by high pressure, signals are transmitted to the brain stem, where they inhibit the sympathetic impulses to the heart and blood vessels and excite the parasympathetic; this allows the arterial pressure to fall back to normal. 2. Gastrointestinal autonomic reflex: The uppermost part of the GIT and the rectum are controlled principally by autonomic reflexes e.g. the smell of appetizing food or the presence of food in the mouth initiates signals from the nose and mouth to the vagal, glossopharyngeal and salivatory nuclei of the brain stem. These in turn transmit signals through the parasympathetic nerves to the secretory glands of the mouth and stomach, causing secretion of digestive juices sometimes even before food enters the mouth. 3. Other autonomic reflex: Emptying the urinary bladder is controlled in the same way as emptying the rectum. Stretching of the bladder sends impulses to the sacral cord, and this in turn causes reflex contraction of the bladder and relaxation of the urinary sphincters, thereby promoting micturition. Sexual reflexes: Erection (parasympathetic function) followed by ejaculation (sympathetic function). Control of A.N.S by Higher centers: 1. Some autonomic reflexes as micturition, defecation and erection are under inhibitory control of centers in C.N.S. 2. Cardiovascular, respiratory and digestive activity are under control of medulla within the brain stem. 3. Stimulation of anterior nucleus of hypothalamus is accompanied by parasympathetic effects, while stimulation of posterior nucleus is accompanied by sympathetic effects. 12 ANS Somatic reflex Autonomic reflex Function Voluntary Involuntary Controls skeletal Controls smooth muscles, cardiac muscle & muscles glands (visceral function). Afferent Relay at dorsal horn Relay at lateral horn cells cells Efferent Anterior (ventral) horn Lateral horn cells LHC + some motor cranial Origin: cells AHC + all motor nuclei cranial nuclei No. of neurons: 1 neuron between CNS 2 neurons (preganglionic and postganglionic and effector organ. neurons). pathway: Pass directly to skeletal The preganglionic axon diverges to an average muscles. of 8 to 9 postganglionic neurons (diffuse). Type of fiber: A fibers Preganglionic axons are small-diameter, myelinated, relatively slowly conducting B fibers. Postganglionic axons are mostly umyelinated, smaller, slower conducting C fibers. neurotransmitter acetylcholine Acetylcholine & noradrenaline (norepinephrine) Figure: general arrangement of the somatic part of the nervous system (on the left) compared with the autonomic part of the nervous system (on the right). 13 ANS Neurotransmitters: Definition: it is the substance which transmits the nerve impulse from pre - synaptic to post - synaptic membrane. 1. acetylcholine: All preganglionic neurons in both sympathetic and parasympathetic NS. All parasympathetic postganglionic neurons Sympathetic postganglionic neurons that innervate sweat glands, pilorector muscles of the hairs, blood vessels of skeletal muscles and few blood vessels (vasodilation), see Figure. M.E.P = motor end plate (i.e. neuro - muscular junction). Adrenal medulla (pre ganglionic). 2. noradrenaline (norepinephrine) Most of sympathetic postganglionic neurons are adrenergic (release norepinephrine). The adrenal medulla is a sympathetic ganglion in which the postganglionic cells secrete norepinephrine and epinephrine directly to the blood stream. Figure: Types of neurotransmitters and receptors in ANS. 14 ANS Receptors: Acetylcholine receptors: Nicotinic receptors Muscarinic receptors Site Autonomic ganglia at the All organs that are stimulated by the synapses between pre and postganglionic cholinergic neurons postganglionic neurons of both of either the sympathetic or sympathetic and parasympathetic NS. parasympathetic NS. Neuromuscular junction (M.E.P: motor end plate) in skeletal muscles. Adrenal medulla. Stimulant NSD muscarine Blocker large dose of nicotine (autonomic) atropine by competitive inhibition. curare (in MEP). Adrenergic receptors: Alpha receptors Beta receptors α1, α2 β1, β2, β3 Mostly excitatory Mostly inhibitory 1. Vasoconstriction 1. Vasodilatation (β2) 2. Contraction of smooth muscles: 2. Relaxation of smooth muscles: Dilator pupillae muscles (iris Bronchioles (bronchodilator; β2). dilatation) GIT (intestinal relaxation; β2) Sphincters as intestinal or bladder Urinary bladder (β2) sphincter contraction. Except: Except: 3. Stimulation of all cardiac properties: 3. Inhibition of smooth muscles of Cardioacceleration (β1) intestine (intestinal relaxation). Increase myocardial strength (β1) 4. Others: Lipolysis (β1) Glycogenolysis (β2) Thermogenesis (β3) stimulated by : stimulated by: N.E , epinephrine and phenylephrine Isoproterenol, adrenaline and nor adrenalin Blocked by: Ergot alkaloids Blocked by: Propranolol. 15 ANS Acetylcholine synthesis and release: 1. Synthesis of acetyl choline: Choline + acetyl CoA → Ach + CoA. 2. Storage of acetyl choline in the synaptic vesicles. 3. Release of Acetyl choline: Ca++ channels in the presynaptic membrane opens → Ac.ch. Release by exocytosis. Ach 4. Binding to receptors. choline 5. Degradation of Ac.ch: Ac.ch. choline + acetate Esterase 6. Recycling of choline into the neurons for re-synthesis of Ac.ch. 16 ANS Norepinephrine synthesis: Hydroxylase In liver Phenylalanine tyrosine Hydroxylase Tyrosine DOPA In adrenergic fibres Decarboxylase DOPA Dopamine Dopamine B-hydroxylase Noradrenaline In vesicles in adrenal noradrenaline N-methyltransferase adrenaline medulla only Release of NA: by exocytosis Removal of NA: 1. Re-uptake: 80% of NA into the adrenergic neuron by active transport. 2. Diffusion away. 3. Destruction by enzymes: M.A.O. (Monoamine Oxidase): deamination C.O.M.T (Catechol- O- methyl- transferase): Methylation 17 ANS PARASYMPATHOMIMETIC DRUGS Act on the effector organs supplied by cholinergic fibers. Muscarinic drugs: Muscarine Stimulate muscarinic receptors Metacholine Anticholinesterases: a) Reversible: - short acting e.g.Eserine: generalized i.e. ↑ both muscarinic and nicotinic actions. Prostigmine: Nicotinic i.e. ↑ skeletal muscles MEP activity = used in treatment of myasthenia gravis. b) Irreversible: - long acting drugs i.e. toxic, called nerve gases, or insecticides as DFP which causes paralysis of motor functions → difficulty in breathing → death. PARASYMPATHOLYTIC DRUGS Types: A) Ganglion blockers: Nicotine in large doses – Hexamethonium. B) Postganglionic blockers: Atropine (block muscarinic receptors). C) MEP blockers: Curare, Botulinum, Succinyl cholin. Curare:- acts by competitive inhibition to Ac.ch. It can be used together with succinyl choline as muscle relaxants. ATROPINE (anti-muscarinic drug): ACTION: a) EYES: - Mydriasis and cycloplegia (loss of ability for near vision). b) SALIVARY GLANDS: - Dryness of mouth. c) G.I.T:- Decrease motility = antispasmodic. d) RESPIRATION: - Block secretions in respiratory tract. e) C.V.S:- Tachycardia = ↑ heart rate. f) URINARY TRACT: - ↓ motility of urinary bladder. CLINICAL USES OF ATROPINE 1. Fundus examination → Mydriasis. 2. Bronchial asthma → Broncho dilatation. 3. Treatment of colic →↓ motility of G.I.T. 4. Pre anesthetic drugs to prevent cardiac arrest. 5. Before surgery → to block respiratory secretions. 18 ANS Sympathomimetic drugs (Adrenergic Agonists) Mechanism of Action: act on the postganglionic fibers on adrenergic receptors: 1. Stimulate release of catecholamine's e.g. Ephedrine, Amphetamine, Tyramine 2. Inhibit reuptake e.g. Cocaine. 3. α stimulants: phenylephrine, adrenaline, NA 4. β stimulants: adrenaline, isoprenaline. Note: NA excites mainly alpha receptors but excites the beta receptors to a lesser extent as well. Conversely, adrenaline excites both types of receptors approximately equally. SYMPATHOLYTIC DRUGS 1- Inhibit synthesis and storage e.g. reserpine 2- Inhibit release of catecholamine's e.g. guanethidine. 3- α blockers: phentolamine. 4- β blockers: propranolol, Atenolol. 19