Autonomic nervous system ANS is to a large extent responsible for automatically and subconsciously regulating the cardiovascular, renal, gastrointestinal, therm oregulatory, and other systems. The ANS affects heart rate, digestion, respiratory rate, salivation, perspiration, pupillary dilation , micturition and sexual arousal
Autonomic nervous system The ANS is located in the medulla oblongata. The ANS helps in homeostasis. The autonomic nervous system along with endocrine system coordinates the regulation
Autonomic nervous system The autonomic nervous system (ANS) is to a large extent responsible for automatically and subconsciously regulating the cardiovascular, renal, gastrointestinal, thermoregulatory, and other systems The hypothalamus is the main integration center of ANS activity.
SubdivisionsThe nervous system is divided into two major types:• CNS• PNS
Cholinergic Receptors The two types of receptors that bind ACh are nicotinic and muscarinic . These are named after drugs that bind to them and mimic ACh effects
Nicotinic Receptors Nicotinic receptors are found on: Motor end plates (somatic targets) All ganglionic neurons of both sympathetic and parasympathetic divisions The hormone-producing cells of the adrenal medulla The effect of ACh binding to nicotinic receptors is always stimulatory
Muscarinic Receptors Muscarinic receptors occur on all effector cells stimulated by postganglionic cholinergic fibers The effect of ACh binding: Can be either inhibitory or excitatory Depends on the receptor type of the target organ
Adrenergic Receptors The two types of adrenergic receptors are alpha and beta Each type has two or three subclasses ( 1, 2, 1, 2 , 3) Effects of NE binding to: receptors is generally stimulatory receptors is generally inhibitory A notable exception – NE binding to receptors of the heart is stimulatory
Subdivisions ANS:• Sympathetic nervous system• Parasympathetic nervous system
SubdivisionsSympathetic nervous system:Sympathetic “Fight or flight” “E” division Exercise, excitement, emergency, and embarrassment .
SubdivisionsParasympathetic nervous system:Parasympathetic “Rest and digest” “D” division Digestion, defecation, and diuresis
Innervations: Autonomic nerve fibers innervate cardiac muscle, smooth muscle, and glands. A muscle or gland innervated by autonomic fibers is called an effector organ.
Innervations: AUTONOMIC INNERVATION Heart: The heart is well supplied by SNS and PNS. These nerves affect cardiac pumping is 3 ways - By changing the rate By changing the strength of contraction . Modulating coronary blood flow. The PNS cardiac vagal fibres approaches the stellate ganglion and then join the efferent cardiac SNS fibres.
Innervations: Lungs : Lungs are innervated by both SNS and PNS. Postganglionic SNS fibres from upper thoracic ganglia (stellate) pass to the lungs to innervate the smooth muscles of the bronchi and pulmonary blood vessels. PNS innervation of these structures is from the vagus nerve
Dual Innervation: Most of viscera receive nerve fibers from both parasympathetic and sympathetic divisions Both divisions do not normally innervate an organ equally
Dual Innervation: Antagonistic effects oppose each other exerted through dual innervation of same effector heart rate decreases (parasympathetic) heart rate increases (sympathetic) exerted because each division innervates different cells pupillary dilator muscle (sympathetic) dilates pupil constrictor pupillae (parasympathetic) constricts pupil
Dual Innervation: Cooperative effects seen when 2 divisions act on different effectors to produce a unified effect parasympathetics increase salivary serous cell secretion sympathetics increase salivary mucous cell secretionANS cooperation is best seen in control of the external genitalia Parasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitoris Sympathetic fibers cause ejaculation of semen in males and reflex peristalsis in females
Without Dual Innervation: Some effectors receive only sympathetic adrenal medulla, arrector pili muscles, sweat glands and many blood vessels Sympathetic tone a baseline firing frequency vasomotor tone provides partial constriction increase in firing frequency = vasoconstriction decrease in firing frequency = vasodilation can shift blood flow from one organ to another as needed sympathetic stimulation increases blood to skeletal and cardiac muscles -- reduced blood to skin
Sympathetic and VasomotorTone: Sympathetic divisionprioritizes blood vesselsto skeletal muscles andheart in times ofemergency.
Sympathetic and VasomotorTone: Blood vessels to skin vasoconstrict to minimize bleeding if injury occurs during stress or exercise.
references Page 37 in: Costanzo, Linda S. (2007). Physiology. Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 0-7817- 7311-3. Loppincott’s illustrated reviews (pharmacology) http://www.neurophysiology.ws/autonomicns.htm http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/PN S.html ^ Rang, H. P. (2003). Pharmacology. Edinburgh: Churchill Livingstone. ISBN 0-443-07145-4. Page 270. http://www.ld99.com/reference/old/text/2878909-413.html http://www.pc.maricopa.edu/Biology/pfinkenstadt/BIO201/20 1LessonBuilder/UnitFour/ANS/index.html
references Essentials of medical physiology by jaypee , 5th edition.