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Autonomic Nervous System (ANS)

CHAPTER 9. Autonomic Nervous System (ANS). Divisions of ANS Sympathetic Parasympatheitc Functions of ANS Control of ANS. Dr. Hameed Al-Sarraf Dept. Physiology hameed@hsc.edu.kw. Autonomic Nervous System. Nervous system that controls many involuntary functions of the body.

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Autonomic Nervous System (ANS)

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  1. CHAPTER 9 Autonomic Nervous System (ANS) • Divisions of ANS • Sympathetic • Parasympatheitc • Functions of ANS • Control of ANS Dr. Hameed Al-Sarraf Dept. Physiology hameed@hsc.edu.kw

  2. Autonomic Nervous System • Nervous system that controls many involuntary functions of the body. • ANS effects (controls) organs which are under involuntary control. • Effectors of ANS usually are: • Cardiac Muscle • Smooth Muscle • Glands HEART Many internal Organs

  3. Divisions of ANS • 1- Sympathetic (Thoracolumbar) Division • 2- Parasympathetic (Craniosacral) Division.

  4. Sympathetic hain Sympathetic Thoracolumbar

  5. Sympathetic Chain

  6. Sympathetic Chain

  7. Parasympathetic Vagus Craniosacral

  8. Parasympathetic

  9. Innervation of Body Organs • In the body there are organs which are innervated by both sympathetic and • parasympathetic systems: • - Heart • - Digestive tract • - Pupil of the eye • - Salivary glands, etc • There are organs with only sympathetic innervation: • - Adrenal medulla • - Sweat glands • - Most blood vessels

  10. Functions of ANS • 1- Sympathetic system: • Mass discharge of sympatheic system prepares the body for • activity (Fight/Flight). • Excitation of sympathetic centers will cause: • - Increase in heart rate. • - increase in blood pressure, • - blood glucose is elevated • - increase in the rate of metabolism • - mental activity is also raised, • - blood is diverted to skeletal muscle. • 2- parasympathetic system: usually has opposite effects to those of sympathetic • system. Excitation of parasympathetic causes: • - decrease in heart rate, • - increase blood flow to the digestive system, • - increase activity of the digestive system.

  11. Sympathetic Tone • Fast rate of action potentials • Slow rate of action potentials Vasoconstriction Vessel diameter at rest

  12. Sympathetic Tone • Slow rate of action potentials • Stop sending action potentials Vasodilatation Vessel diameter at rest

  13. Fast rate of action potentials Vasoconstriction slow rate of action potentials vessel diameter at rest Sympathetic tone Stop sending action potentials Vasodialatation Sympathetic and Prasympathetic Tone - Normally both symathetic and parasympathetic systems continuously transmit action potentials (signals) at low rate throughout their nerve fibers. - By doing this the ANS can have both positive and negative effects on its effector organs: e.g control of blood vessel diameter by sympathetics,

  14. Examples of Sympathetic System in Action Mass discharge (activation) of sympathetic system prepares the body for activity Example 1: Blood flow to muscle in exercise: Sympathetic nervous system causes blood shift to muscle during exercise by vasoconstriction of blood vessels of all other organs except heart and brain. Example 2: Liver: Stimulation of glycogenolysis to produce glucose which will be release into blood to provide muscle with fuel.

  15. Examples of Parasympathetic System in Action Activation of parasympathetics usually has opposite effects to the sympathetics. Example 1: on gastrointestinal tract: Parasympathetic system causes increased blood flow, motility and secretion of gastrointestinal tract (e.g. stomach, small intestine) Example 2: Heart and lungs: Reduced heart rate and constriction of air tubes (bronchioles) in the lung.

  16. Neurotransmitters of the ANS 1- Acetylcholine (ACh)- the transmission is said to be cholinergic. - ACh is the transmitter released by: - all preganglionic fibers - most parasympathetic postganglionic fibers - some sympathetic postganglionic fibers (in both sympathetic and parasympathetic) 2- Norepinephrine (noradrenaline)- the transmission is said to be adernergic. - Norepinephrine is the transmitter released by: - most postganglionic sympathetic fibers, 3- Non-adernergic non-cholinergic (NANC)- - the transmitter is neither ACh nor NE - proposed candidates are: ATP, VIP, and NO.

  17. Preganglionic Postganglionic *Some sympathetics that innervate blood vessels and all sympathetics that supply sweat glands release acetylcholine (ACh) as their neurotransmitter.

  18. Receptors - NE causes excitation to some tissues while it inhibits others. This is due to the presence of different receptors on the target cells. - There are two types of adernergic receptors: - a-adernergic receptors - b-adernergic receptors - ACh also has two types of receptors: - Nicotinic - Muscarinic

  19. Second messenger Adernergic Stimulation 1- Binding of epinephrine or norepinephrine (NE) to a-receptor causes increase in cytoplasmic Ca++ levels: NE Membrane a-receptor Phospholipase C Increase cytoplasmic Ca ++ Inositol triphosphate (IP3) receptor Endoplasmic Reticulum Opening Ca++ channels Closed Ca++ channels

  20. Second messenger Adernergic Stimulation 2- Binding of epinephrine or norepinephrine to b-receptor stimulates the production of cyclic adonesine monophosphate (cAMP). NE Membrane b-receptor Adenylate cyclase (inactive) Adenylate cyclase (active) ATP cAMP Cytoplasm Catalyse many Reactions in the cell Protein kinase (inactive) Protein kinase (active)

  21. Always excitatory Mainly excitatory but with exceptions Cholinergic Stimulation Nicotinic receptors = n Muscarinic receptors = m n Brain m Parasympathetic ACh ACh n somatic ACh n Adernal Medulla ACh Sympathetic n NE ACh m n ACh ACh Parasympathetic

  22. Contain centers which control: cardiovascular, pulmonary, urinary, reproductive and digestive system. Control of the ANS by Higher Brain Centers Higher Brain Centers Hypothalamus Medulla Oblongata Preganglionic Sensory Inputs Postganglionic Effector Organs

  23. Medulla Oblongata Control of ANS by Centers in Brain • Brain stem – mainly controls vascular system and respiration. • Hypothalamus- • Cardiovascular system; stimulation of: • - posterior hypothalamus causes increase in blood pressure and heart rate, • - anterior hypothalamus causes decrease in blood pressure and heart rate. • Body temperature: • changes in blood temperature in anterior hypothalamus causes several • mechanisms to operate for temperature regulation. • - Body water- secretion of ADH and signals to initiate thirst • Feeding – hunger and satiety centers • Excitement and rage- perifornical nucleus in hypothalamus • Endocrine function – neurosecretory substances secretion to anterior pituatory.

  24. These receptors are different than cell receptors ! These are sensory receptors Reflex Effects of Sensory Inputsto Brain Centers Organ Type of Receptor Reflex Effect Lung Stretch receptor inhalation is inhibited and heart rate increase Aorta Chemoreceptor increase breathing and heart rate Baroreceptor decrease in heart rate Heart Stretch receptor increase volume of urine excreted and decrease in heart rate G.I. Tract Stretch receptor feeling of satiety

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