Autonomic Nervous System PDF

AUTONOMIC NERVOUS SYSTEM NG SOOK LUAN, PhD Jabatan Diagnostik Kraniofasial & Biosains Fakulti Pergigian UKM 012-9305208 [email protected]  LEARNING OBJECTIVES 1. Explain the function of the sympathetic and parasympathetic system...

AUTONOMIC NERVOUS SYSTEM NG SOOK LUAN, PhD Jabatan Diagnostik Kraniofasial & Biosains Fakulti Pergigian UKM 012-9305208 [email protected]  LEARNING OBJECTIVES 1. Explain the function of the sympathetic and parasympathetic system. 2. Explain the physiological effects of the ANS on body functions. 3. Explain the different neurotransmitters and receptors of the ANS. 4. Explain the tissues innervated exclusively by the sympathetic and parasympathetic systems and those with dual innervations.  AUTONOMIC NERVOUS SYSTEM (ANS) Definition: the system for involuntary subconscious functions, it control the internal environment to maintain homeostasis Involuntary branch of the peripheral efferent division Innervates Heart (cardiac muscle) – increased pumping of blood by the heart when BP ↓ sympathetic parasymp Stomach (smooth muscle) – delayed emptying of the stomach until the intestine is ready to process the food symp. Sweat glands (exocrine glands) – initiation of sweating on exposure to a hot environment parasymp Endocrine pancreas (endocrine gland) – increased secretion of insulin. following a meal  AUTONOMIC NERVOUS SYSTEM Often work in opposition Cooperate to fine-tune homeostasis Regulated by the brain; hypothalamus, pons and medulla Also regulated by spinal reflexes; no higher order input Pathways both consist of a two-neuron system: Preganglionic neuron from CNS → autonomic Relaxes the body and Prepares the body for inhibits or slows intense physical activity ganglion outside CNS → postganglionic many high energy fxn Catabolic (expend neuron → target homeostasis energy)  ANATOMICAL DISTRIBUTION OF ANS Sympathetic Sympathetic neurons originate from the lateral horn of thoracic and lumbar portions of the spinal cord. Parasympathetic Parasympathetic neurons originate in the midbrain, medulla oblongata and sacral spinal cord. -mon S  TWO MOTOR NEURONS First neuron: Preganglionic neuron – cell body is located in the brain or spinal cord Sympathetic: the cell body is located in the lateral grey horns (thoraco-lumbar) Norepinephrine O Parasympathetic: the cell body is located in (adrenal gland) O Epinephrine sproduced various nuclei of brain stem or in the lateral adrenal from medulla) grey horns (sacral) Second neuron: Postganglionic neuron – cell body is in an autonomic ganglion The ganglionic fibre sends impulses to a target organ. The effects at the target organs are due to the type of neurotransmitters and specific release acetylcholine cell surface receptors on the effector cells. IMPORTANT A PREGANGLIONIC VS POSTGANGLIONIC NEURONS flight or fight Characteristics Sympathetic Parasympathetic shorter CNS origin Thoraco-lumbar Cranio-sacral Preganglionic Short Long neuron &Myelinated A transmissions - Myelinated ②Cholinergic release ACH S C Cholinergic r longer Receptor on Nicotinic (ACh) Nicotinic (ACh) / I I postganglionic - Postganglionic Long Short neuron Unmyelinated Unmyelinated by **FE, > sympathetic preganglin Noradrenergic E Cholinergic b *** NE , E AcH paasymp postganglion Divergence High Low Receptor on Adrenergic (α, β) Muscarinic (ACh) target NE Sympathetic innervation of sweat glands: Target tissues Smooth, cardiac Smooth, cardiac cholinergic; Acetylcholine (ACh); postganglionic muscles, endocrine muscles, exocrine neurons and muscarinic receptors glands, fat glands, fat & fx NE: norepinephrine Wa opp..  SYMPATHETIC VS PARASYMPATHETIC Similarities Both are efferent (motor) systems “visceromotor” Both involve regulation of internal environment which outside of conscious control “autonomous” Both involve 2 neurons that synapse in a peripheral ganglion and innervate glands, smooth muscle and cardiac muscle - IMPORTANT DIFFERENCES - General a. ↑ light to enter ↓ breathing digestion - -  PARASYMPATHETIC NERVOUS SYSTEM... Preganglionic & postganglionic neurotransmitters: ACh Effect of ACh on postsynaptic tissue is terminated by rapid action of acetylcholinesterase (AChE) that metabolizes ACh to acetate and choline. Neurotransmisssion in the ganglia is achieved by preganglionic fibres releasing ACh into the synaptic cleft, which activates nicotinic (N) receptors on postganglionic nerve dendrites. Depolarization of postganglionic cholinergic nerve results in the release of stored ACh within the innervated tissue, that activates muscarinic (M) receptors to produce biological effects. Choline is taken into the nerve terminal where it is conjugated to acetate by choline acetyltransferase (ChAT) to produce ACh. Synthesized ACh is transported into synaptic vesicles.  PARASYMPATHETIC NERVOUS SYSTEM A Effector Organ Receptor Response to Cholinergic Stimulation Subtype Eye: 3 Sphincter muscle, iris M3 Contract to cause miosis (constriction of pupil) Ciliary muscle M3 Contract for near vision Heart: Sinoatrial node M2 Decrease rate of depolarization 2 Atria M2 Decrease contractility Atrioventricular node M2 Decrease rate of depolarization Arteries, 1 3 Endothelial cells blood vessels (dilate) M1, M3 Vasodilation (predominant) , arterioles: Smooth muscle cells (constrict] M1, M3 Vasoconstriction by direct action on smooth muscle Lungs: Tracheal, bronchial sm M1, M3 Constriction ?? Bronchial glands M2, M3 Increase mucous secretion / - Gastrointestinal tract: ⑬ M2, M3 Increased contractility, motility & secretions E 3 Urinary Detrusor muscle M2, M3 Contraction bladder: Trigone & sphincter muscle M2, M3 Relaxation Salivary glands: M2, M3 Increased watery secretion Erectile tissue: M2, M3 Vasodilation of cavernosa of penis & clitoris, increased blood pooling  * PARASYMPATHETIC – VAGAL STIMULATION Heart GIT - Inhibits all cardiac properties (decrease heart rate, - Contraction of walls of oesophagus, stomach, small contractility & conductivity) intestine and proximal large intestine - Causes vasoconstriction of coronary vessels and - Relaxation of sphincter reduction of O2 consumption by cardiac muscle - These responses promote deglutition, increased - These responses lead to bradycardia. secretion of GIT and evacuation of foods ↳ slow heart rate Lungs Gall bladder - Bronchoconstriction - Contraction of the gall bladder wall - Increased bronchial secretion - Relaxation of its sphincter - Vasodilatation of pulmonary blood vessels - These responses lead to evacuation of the gall - These responses lead to precipitation of asthma. bladder. dilate muscle constrict , vessels.  PARASYMPATHETIC – CHOLINERGIC STIMULATION Preganglionic cell bodies located in cranial nerve nuclei in the brain stem Preganglionic fibres run via: Cranial outflow: Oculomotor nerve (CN III) – leads to miosis, near vision and movement of the eye balls Facial nerve (CN VII) – vasodilatation & secretion of the submandibular & sublingual glands, tongue, soft palate, nasopharynx and lacrimal glands; sensory innervation of face, facial expression, taste, Glossopharyngeal nerve (CN IX) – vasodilatation and secretion of parotid glands, innervation of tongue and pharynx, taste Vagus nerve (CN X): heart, lungs, GIT, gall bladder % Sacral outflow: S2 to S4  PARASYMPATHETIC – SACRAL OUTFLOW (PELVIC NERVE) Urinary bladder Rectum and descending colon - Contraction of the bladder wall - Contraction of its wall - Relaxation of its sphincter ↓ urination - Relaxation of internal anal sphincter - These responses lead to micturition. - These responses lead to defecation. Seminal vesicles and prostate Erectile tissue - Secretion of seminal vesicle fluid and prostatic - Vasodilatation of tissue fluid. - These responses lead to erection.  - & distant cell - L - phenyl - ↑ - -> in advanc medulla D FT  SYMPATHETIC NERVOUS SYSTEM Preganglionic: ACh; Postganglionic: NE s The amino acid tyrosine is converted to by dpy dopamine which is taken into vesicles where it is converted to NE, and stored in the vesicle with ATP and neuropeptide Y. Depolarization of the nerve terminal results in the fusion of the neurotransmitter vesicles with the synaptic membrane resulting in release of the contents into synaptic cleft. NE interacts with specific adrenergic receptors to produce tissue/organ response. α2-adrenergic & muscarinic M1,2 receptors decrease NE release Nicotinic N receptors increase NE release NE is taken back into the nerve terminal. NE can be incorporated into vesicles or metabolized by Lmonamine oxidase (MAO) or catechol-O- methyltransferase (COMT)Sto inactive intermediates and finally to homovanillic acid (HVA) methoxyhydroxy mandelic acid (VMA).  SYMPATHETIC NERVOUS SYSTEM Effector Organ Receptor Subtype Response to Cholinergic Stimulation Eye: Radial muscle, iris α1 Contracts to cause mydriasis (dilation of pupil) Ciliary muscle β2 Relaxes to allow for far vision Heart: Sinoatrial node β1, β2 Increased rate of depolarization Atrioventricular node β1 Increased conduction rate Atria, ventricles β1 Increased contractility Arteries, Smooth muscle cells α1, α2 Contraction arterioles: β2 Relaxation Lungs: Tracheal, bronchial sm β2 Relaxation Bronchial glands α, β Decreased mucous secretion GIT Smooth muscle wall β2 Relaxation, decreased motility Sphincters α1 Contraction, decreased transit time Urinary Detrusor muscle β2 Relaxation, decreases voiding bladder Trigone & sphincter m. α1 Contraction, decreases voiding Metabolic Liver α1, β2 Glycogenolysis fxn Fat cells β3 Increased lipolysis Kidneys β1 Renin release Sexual organs: α1 Ejaculation, orgasm Adrenal medulla: N (nicotini Epinephrine release  SYMPATHETIC – CERVICAL DIVISION (T1-T4) Eye Salivary gland - Pupil dilatation, widening of palpebral fissure, - Trophic secretion exophthalmos - Vasoconstriction of its blood vessels - Vasoconstriction of eye ball vessels - Squeezing of salivary secretion - Relaxation of ciliary muscle Lacrimal gland Hair - Trophic secretion - Erection due to contraction of erector pilae - Vasoconstriction muscles Sweat secretion Cerebral vessels - Copious secretion - Weak vasoconstriction Face skin blood vessel - Vasoconstriction (pale skin)  SYMPATHETIC – CARDIOPULMONARY DIVISION (T1-T6) Heart Coronary vessels (sympathetic supply) - Increase all properties of cardiac muscle - At first, it causes vasoconstriction, and then it (contraction, rhythmicity, excitability, conductivity) causes vasodilatation due to accumulation of metabolites. Bronchi Hair - Bronchodilation, decrease bronchial secretion - Erection due to contraction of erector pilae - Vasoconstriction of pulmonary blood vessels muscles  SYMPATHETIC - SPLANCHNIC DIVSION (T5-L2) GREATER SPLANCHNIC NERVE Stomach & intestine Spleen - Contraction of sphincter - Contraction of the capsule of spleen - Leading to food retention - Leading to evacuation of about 200 ml of blood Liver Adrenal medulla - Glycogenolysis - Secrete epinephrine and norepinephrine - Leading to increase of blood glucose LESSER SPLANCHNIC NERVE Urinary bladder Rectum - Relaxation of the bladder wall - Relaxation of the distal part of large intestine - Contraction of internal urethral sphincter - Relaxation of the rectum wall - These responses lead to urine retention. - Contraction of internal anal sphincter - These responses lead to faeces retention. Genital organs Vas deferens - Vasoconstriction of its blood vessels - Contraction of its wall, and wall of seminal vesicles, - Leading to shrinkage of penis and clitoris ejaculatory ducts and prostate - These responses lead to ejaculation.  SYMPATHETIC – SOMATIC DIVISION (31 SPINAL NERVES TO SOMATIC TISSUES OF NECK, BODY WALL AND LIMBS) Skin Skeletal muscle - Vasoconstriction giving the pale colour of the skin - Its blood vessels show vasodilatation due to - Stimulation of the sweat glands, the eccrine glands cholinergic effect. give copious secretion, while the apocrine glands - Its blood vessels show vasoconstriction due to give thick odoriferous secretion. adrenergic effect. - Muscles: its stimulation causing delayed fatigue and early recovery ADRENAL MEDULLA Secretes great quantities of epinephrine (a little norepinephrine) Stimulated to secrete NE by preganglionic sympathetic fibres