Autonomic Nervous System II PDF

Autonomic Nervous System II Lecturer dr. jumana M. Kareem  Objectives 1. Compare the overall functions of the parasympathetic and sympathetic nervous systems 2. Identify the neurotransmitters and receptor types involved in neurotransmission within the autonomic nervous system and its targe...

Autonomic Nervous System II Lecturer dr. jumana M. Kareem  Objectives 1. Compare the overall functions of the parasympathetic and sympathetic nervous systems 2. Identify the neurotransmitters and receptor types involved in neurotransmission within the autonomic nervous system and its target organs. FUNCTIONS OF PNS Dominate roles under normal physiological condition Digest and Rest FUNCTIONS OF SNS prepares organism to handle various environmental stresses Fight and Flight  Horner Syndrome Horner syndrome is a rare disorder resulting from interruption of preganglionic or postganglionic sympathetic innervation to the face. The problem can result from (injury to the nerves, injury to the carotid artery, a stroke or lesion in the brainstem, or a tumor in the lung). In most cases the problem is unilateral, with symptoms occurring only on the side of the damage. The hallmark of Horner syndrome is the triad of a) anhidrosis (reduced sweating), b) ptosis (drooping eyelid), c) and miosis (constricted pupil). *Symptoms also include enophthalmos (sunken eyeball) and vasodilation. Chemical Transmission at Autonomic Junctions 1. Ach  Cholinergic transmission 2. Epinephrine (E or adrenaline) and 3. Norepinephrine (NE or noradrenaline)  Adrenergic transmission.  Cholinergic Autonomic Neurons (Release Acetylcholine): 1.All Preganglionic Neurons 2.All Parasympathetic Postganglionic Neurons 3.Sympathetic Postganglionic Neurons: 1.Innervate sweat glands 2.End on blood vessels in some skeletal muscles (stimulate vasodilation)  Adrenergic Neurons (Release Epinephrine and Norepinephrine): 1) Majority of Sympathetic Postganglionic Neurons. EXCEPT to sweat gland, some blood vessels & piloerector m. 2) adrenal gland  ACh Synthesis & Degredation  acetyle CoA + Choline  acetylcholine  stored in the vesicles of nerve endings  after doing its effect, there will be splitting of ACh into acetate ion + choline by acetylcholine esterase (AChE).  choline transported back into the axon terminals where it reused for synthesis of new ACh.  small amounts of ACh diffuse into the surrounding fluids where "pseudocholine esterase destroys it.  NE Synthesis & Degredation  Tyrosin  DOPA  Dopamine  Norepinephrine  Epinephrine stored in synaptic vesicles  after doing its effect  destructed by monoaminooxidase (MAO) in the nerve endings  destructed by catechol-o-methyle transferase (COMT) in all other tissue. Autonomic Receptors  Cholinergic Receptors i. Muscarinic ii. Nicotinic  Adrenergic Receptors i. Alpha ii. Beta Recepors Charasteristics: A-Cholinoceptors 1-Nicotinic Receptors Respond to ACh Respond to nicotine (another ACh mimic) Do not respond to muscarine Act throught Ligand-gated ion channels  Agonist effects blocked by tubocurarine Receptor activation results in: rapid increases of Na+ and Ca2+ conductance deplorization excitation Direct effect – receptors are part of the ion channel 2 Subtypes of nicotinic receptors:  Nn-neuronal (ANS ganglia) are in sympathetic and parasympathetic ganglia (effects blocked with ganglionic blockers (e.g., trimethaphan, hexamethonium)  Nm-neuromuscular endplate (skeletal muscle) are at the neuromuscular junction (effects blocked with neuromuscular blockers (e.g., curare)  2-Muscarinic Receptors chemical found in the mushroom Amanita muscarina coupled via G-proteins  activated by muscarine, carbachol, and ACh  blocked by atropine At least five receptor subtypes have been described by molecular cloning. (3 receptors are important M1 M2 M3) M1-(excitatory) CNS M2-(inhibitory)heart, some nerve endings M3-(excitatory)effector cells, smooth muscle, exocrine glands, endothelium Indirect effect – through G-protein and 2nd messenger B-Adrenoceptors: 1-Alpha receptors Located in Blood vessels Presynaptic nerve terminals Blood platelets Fat cells (lipocytes) Neurons in the brain 2 subtypes ALPHA1-effector tissues, smooth muscles, glands ALPHA2-nerve endings, some smooth muscles. 2-Beta receptors Located on Most types of smooth muscle Cardiac muscle Some presynaptic nerve terminal Lipocytes Brain Subdivided into β1 β2 β3 , they are similar and use the same G-coupling protein BETA1-heart and kidney BETA2-lungs, uterus, liver, heart BETA3-fat or adipose tissue Receptor Major locations Effect of binding type b1 Heart, kidney, adipose tissue i. Increase heart rate & strength ii. stimulate rennin secretion by kidney b2 Lungs, blood vessels serving the i. Dilates blood vessels and heart, liver & skeletal muscles bronchioles ii. relaxes smooth m. wall of digestive and urinary visceral organs iii. relaxes uterus b3 Adipose tissue i. Stimulate lipolysis by fat cells a1 Blood vessels serving skin, i. Constrict blood vessels and mucosa, abdominal viscera, visceral organ sphincters kidneys, and salivary glands ii. dilates pupils of the eyes a2 Membrane of adrenergic axon i. Inhibits NE release from terminals, pancreas and platelets adrenergic terminals ii. inhibit insulin secretion by pancreas iii. promotes blood clotting Thank you