Dr Farah Nabil Abbas MBChB, MSc, PhD Chair Dept. of Physiology Autonomic Nervous System Dr Farah Nabil Abbas MBChB, MSc, PhD Chair Dept. of Physiology

The Autonomic Nervous System   The Autonomic Nervous System (ANS) is that portion of the nervous system that controls the visceral functions of the body e.g. arterial pressure, GI motility, secretion, urinary bladder emptying, sweating, & body temperature. One of the most striking characteristics of the autonomic nervous system is the rapidity and intensity with which it can change visceral functions. For instance, within 3 to 5 seconds it can increase the heart rate to twice normal, and within 10 to 15 seconds the arterial pressure can be doubled; or, at the other extreme, the arterial pressure can be decreased low enough within 10 to 15 seconds to cause fainting. Sweating can begin within seconds, and the urinary bladder may empty involuntarily, also within seconds

General Organization of the 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 System CNS – Spinal cord – T1-L2 Intermediolateral horn  (preganglionic)  Anterior horn  white ramus  (Ganglia) in the sympathetic chain (paravertebral)  postganglionic  gray ramus  spinal nerve Fate 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 System 1. CNS – Cranial outflow X vagus – 75% of parasympathetic outflow  thoracic III oculomotor: sphincter of pupils ciliary muscle VII facial: lacrimal, nasal, sub maxillary glands. IX glossopharyngeal: parotid gland.   2.Sacral outflow – nervi egents – lower GI - bladder Preganglionic: long, ganglia, outlying in the wall of the organ Postganglionic: short, 1mm

Neurotransmitters of the ANS: Cholinergic fibers secrete acetyl choline. Adrenergic fibers secrete norepinephrine (noradrenalin). Non-adrenergic non-cholinergic (NANC) 1. All preganglionic neurons (sympathetic & parasympathetic)  cholinergic 2. Postganglionic parasympathetic  cholinergic 3. Postganglionic sympathetic  adrenergic except: postganglionic sympathetic to sweat glands and few blood vessels  cholinergic

Mechanism of secretion of Ach & NE: Action potential  depolarization  increased permeability to Ca+2  secretion of neurotransmitter Synthesis of Ach & Its Destruction:   Synthesis: Acetyl-CoA + choline Cholineacetyl transferase Ach Axoplasm to vesicle Destruction: Ach Acetylcholine esterase Choline + acetate Present in terminal nerve ending receptor organ (tissue acetylcholine esterase) serum acetylcholine destruction in seconds

Autonomic Effects on Various Organs of the Body

Functions of the adrenal Sympathetic stimulation – large quantities of epinephrine (80%) & norepinephrine (20%) 1. Epinephrine & norepinephrine have similar effects, but with the following differences: 2. Epinephrine has greater effects on the heart 3. Epinephrine has a weak constriction on blood vessels of muscles NE increase total peripheral resistance Increase blood pressure 4. Epinephrine causes a greater increase in BMR (basal metabolic rate) The effects of adrenal medulla stimulation are more prolonged and widely distributed in the body.