Dr Farah Nabil Abbas MBChB, MSc, PhD Chair Dept. of Physiology
Autonomic Nervous SystemThe Autonomic Nervous System
The autonomic nervous system is activated mainly by centers located in the spinal cord, brain stem, and hypothalamus. Also, portions of the cerebral cortex, especially of the limbic cortex, can transmit signals to the lower centers and in this way influence autonomic control. The autonomic nervous system also often operates by means of visceral reflexes. That is, subconscious sensory signals from a visceral organ can enter the autonomic ganglia, the brain stem, or the hypothalamus and then return subconscious reflex responses directly back to the visceral organ to control its activities.General Organization of the Autonomic Nervous System
ANS has 2 subdivisions:
Sympathetic: fight or flight. Parasympathetic: vegetative functions.Physiological Anatomy:Sympathetic Nervous SystemCNS – Spinal cord – T1-L2Intermediolateral horn (preganglionic) Anterior horn white ramus (Ganglia) in the sympathetic chain (paravertebral) postganglionic gray ramus spinal nerveFate of Preganglionic Fibers:1.Synapse at the ganglia.2.Goes up or down, then synapse in a ganglia.3.Synapse at an outlying sympathetic ganglia.
Parasympathetic Nervous System1. CNS – Cranial outflowX vagus – 75% of parasympathetic outflow thoracicIII oculomotor: sphincter of pupils ciliary muscleVII facial: lacrimal, nasal, sub maxillary glands.IX glossopharyngeal: parotid gland. 2.Sacral outflow – nervi egents – lower GI - bladderPreganglionic: long, ganglia, outlying in the wall of the organPostganglionic: short, 1mm
Cholinergic fibers secrete acetyl choline. Adrenergic fibers secrete norepinephrine (noradrenalin). Non-adrenergic non-cholinergic (NANC)1.All preganglionic neurons (sympathetic & parasympathetic) cholinergic2.Postganglionic parasympathetic cholinergic3.Postganglionic sympathetic adrenergic except: postganglionic sympathetic to sweat glands and few blood vessels cholinergic Neurotransmitters of the ANS:
Mechanism of secretion of Ach & NE:
Action potential depolarization increased permeability to Ca+2 secretion of neurotransmitterSynthesis of Ach & Its Destruction: Synthesis:Acetyl-CoA + choline Cholineacetyl transferase AchAxoplasm to vesicle Destruction:Ach Acetylcholine esterase Choline + acetatePresent in terminal nerve endingreceptor organ (tissue acetylcholine esterase)serum acetylcholinedestruction in seconds
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