PHARMACOLOGY PRESENTATION INTRODUCTION.pptx

presentation

1. SYMPATHETIC SYSTEM -INTRODUCTION

2. CONTENTS INTRODUCTION SYMPATHETIC SYSTEM NEUROTRANSMITTER ACTIONS OF SYMPATHETIC SYSTEM SYNTESIS OF ACH SYNTHESIS OF ADRENALIN SYMPATHETIC RECEPTORS

3. INTRODUCTION Autonomic Nervous System (ANS) is involuntary in nature and the activities of this system are maintained autonomically. In contrast to somatic nervous system, organs supplied by ANS do not atrophy even after the section of an autonomic nerve (rather, denervation supersensitivity of receptors occur). Neurotransmitter (NT) secreted at somatic nerves (at neuromuscular junction) as well as at all preganglionic autonomic (sympathetic as well as parasympathetic) nerves is acetylcholine ( ACh ).

4. SYMPATHETIC NERVOUS SYSTEM Division of ANS into sympathetic and parasympathetic system is anatomical in origin. Fibers of sympathetic system originates from thoracic and lumbar spinal cord (thoracolumbar outflow) whereas parasympathetic system originates from cranial nerves (III, VII, IX and X) and sacral (S2,3,4 ) spinal cord (craniosacral outflow). In sympathetic system, postganglionic fibres are either equal to or longer than preganglionic fibres

5. NEUROTRANSMITTERS Acetylcholine ( ACh ) is the principal NT at NMJ as well at all preganglionic fibres . In sympathetic system, at most of the postganglionic fibres , NT secreted is nor adrenaline (NA) but it can be : Dopamine (renal and mesenteric vasculature), ACh (sweat glands; sympathetic cholinergic) Adrenaline (adrenal medulla).

6. Sympathetic “Fight or Flight” Impulse is conducted along the axon till it reaches the cell body forming the synapse. Cell body releases the NT that acts on the receptors present on the post-synaptic membrane (post-synaptic receptors) as well as on the pre-synaptic membrane (pre-synaptic receptors). Pre-synaptic receptors increase (nicotinic, β) or decrease (muscarinic, α2 ) the release of neurotransmitter from their own neuron ( autoreceptors ) or from adjoining neurons (heteroreceptors).

7. SYNTHESIS OF ACETYLCHOLINE Choline (from diet or recycled) Uptake into presynaptic neuron (via Na⁺-dependent choline transporter, CHT) Choline + Acetyl-CoA (Choline Acetyltransferase, ChAT ) Acetylcholine ( ACh ) Storage in synaptic vesicles (via Vesicular Acetylcholine Transporter, VAChT ) Released into synaptic cleft upon neuronal stimulation Acts on nicotinic or muscarinic receptors (depending on target tissue) Degraded by Acetylcholinesterase ( AChE ) → Choline + Acetate Choline is reuptaken for resynthesis

8. ADRENERGIC TRANSMISSION Adrenergic (more precisely ‘Noradrenergic’) transmission is restricted to the sympathetic division of the ANS. There are three closely related endogenous catecholamines (CAs). Noradrenaline (NA) It acts as transmitter at postganglionic sympathetic sites (except sweat glands, hair follicles and some vasodilator fibres ) and in certain areas of brain . Adrenaline ( Adr ) It is secreted by adrenal medulla and may have a transmitter role in the brain. Dopamine (DA) It is a major transmitter in basal ganglia, limbic system, CTZ, anterior pituitary, etc. and in a limited manner in the periphery.

9. SYNTHESIS OF ADRENALIN

10. SYMPATHETIC RECEPTORS

11. Heart (β₁ Receptors) ↑ Heart rate (Positive chronotropic effect) ↑ Contractility (Positive inotropic effect) ↑ Conduction velocity (Positive dromotropic effect) 2. Blood Vessels α₁ → Vasoconstriction (Skin, mucosa, splanchnic vessels) β₂ → Vasodilation (Skeletal muscles, coronary arteries) 3. Renal vessels → Mixed effect (α₁ → Vasoconstriction, D₁ → Vasodilation)

12. 4. Gastrointestinal Tract β₂ → Smooth muscle relaxation α₂ → ↓ ACh release (presynaptic inhibition) → Reduced motility 5. Urinary System β₂ → Detrusor muscle relaxation → Urine retention α₁ → Trigone & sphincter contraction → Urine retention 6. Genital System β₂ → Uterine relaxation (Pregnancy) 7. Respiratory System β₂ → Bronchodilation (No direct sympathetic innervation; effect via drugs) α₁ → Mucosal vasoconstriction → Increased airway diameter

13. 8. Eye α₁ → Mydriasis (Pupil dilation via dilator pupillae muscle) β₂ → ↑ Aqueous humor production (Ciliary vasodilation) α → ↓ Aqueous humor secretion Clinical relevance: β-blockers & α-agonists used in glaucoma treatment 9.Glands Salivary glands → Thick secretion Sweating → M₃ receptor activation (Sympathetic cholinergic).

14. Metabolic Effects β₃ → Lipolysis (Breakdown of triglycerides into free fatty acids) β₂ → Hyperglycemia (↑ Glycogenolysis & Gluconeogenesis) α₂ → ↓ Insulin release (Pancreatic β- cells) → Contributes to hyperglycemia β₂ → ↑ Glucagon secretion (Minor role in hyperglycemia ) K⁺ Shifts: Initial Hyperkalemia (K⁺ efflux from liver) Later Hypokalemia (K⁺ uptake by skeletal muscles)

15. References Essentials of medical Pharmacology- K.D Tripathi Review of Pharmacology-Govind Rai Garg and Sparsh Gupta Pharmacology for dentistry- Tara.V.Shanbag