Nervous System Physiology (Neurophysiology) Autonomic Nervous System (ANS) PDF

Nervous System Physiology (neurophysiology) Autonomic Nervous system (ANS) Prof. Dr. Faten Mahmoud A. Diab 4, 2024 physiology ProfessorApril of Medical Egypt www.gmu.ac.ae COLLEGE OF MEDICINE What are the main functions of the autonomic nervous system? The ANS primarily controls involuntary body fun...

Nervous System Physiology (neurophysiology) Autonomic Nervous system (ANS) Prof. Dr. Faten Mahmoud A. Diab 4, 2024 physiology ProfessorApril of Medical Egypt www.gmu.ac.ae COLLEGE OF MEDICINE What are the main functions of the autonomic nervous system? The ANS primarily controls involuntary body functions such as respiration, heart rate, and digestion ……… via regulating contraction of the smooth muscle & and cardiac muscle & and secretion of the glands 6 Comparison between sympathetic & parasympathetic NS Parasympathetic NS D activities: digestion & defecation Constricts pupils Near vision Constrict bronchioles Slows heart Decrease arterial blood pressure Stimulates GI motility GI secretion Urination Defecation  Erection 4/4/2024 15 Comparison between sympathetic & parasympathetic NS Sympathetic NS E activities: Excitation & Exercise & Emergency Dilate pupils Far vision Dilate bronchioles increase heart rate Increase heart force of contraction increase arterial blood pressure Increase blood flow to active muscles & organs Increase renin secretion from the kidney. Inhibit GI motility GI secretion Urination Defecation Fight or flight response. 4/4/2024 16 Comparison between sympathetic & parasympathetic NS Parasympathetic NS Sympathetic NS 17 Organs with dual innervation: The effects of the sympathetic & parasympathetic systems on the same organ may be: antagonistic complementary  Pacemaker of the heart  Digestive tract (GIT)  Pupil of the eye  Salivary gland 4/4/2024 cooperative  Reproductive system 18 What is the sympathetic tone? It is continuous sympathetic impulses even during rest to:  Smooth muscles of arterioles: leading to the partial continuous degree of vasoconstriction (VC).  Adrenal medulla: leading to basal secretion of small amounts of catecholamines. These actions are called sympathetic tone, and they help in the maintenance of blood pressure and blood glucose. 19 Is there a parasympathetic tone? YES or NO Yes, there is a parasympathetic tone or vagal tone to the heart at rest ----> keeps the heart rate at the resting level. 20 What is Horner’s syndrome? An injury to the cervical sympathetic nerve fibers produces a syndrome group of symptoms) on the same (affected) side of the face:  Ptosis (= drooping of the upper eyelid which covers the eye) due to paralysis of the superior tarsal muscle.  Miosis (= pupil-constriction) due to paralysis of the dilator pupillae muscle.  Anhydrosis (= absence of sweat secretion).  VD (due to loss of the symp. VC effect), so it becomes warmer and more red than the healthy side.  Enophthalmos (= sinking of the eyeball backward in the orbit) to paralysis of Muller's muscle (not prominent in man). 21 Receptors & Neurotransmitters in the autonomic ganglia  At all autonomic ganglia, the preganglionic axon synapses on the postganglionic neuron.  Acetylcholine (ACh) is released from the axon terminal of the presynaptic neuron and crosses the synaptic cleft (the space between the neurons).  The ACh then binds to receptors called postsynaptic nicotinic receptors (abbreviated N1 or NN).  Nicotinic receptors are transmembrane ion channels. When ACh binds to the receptor, the channel opens and allows Na+ to diffuse into the postganglionic neuron.  The influx of Na+ depolarizes the cell (makes it less negatively charged) and results in the generation of an action potential within the postganglionic neuron 22 Receptors & Neurotransmitters of the postganglionic parasympathetic fibers: In parasympathetic neurons, which neurotransmitter is released at the postganglionic synapse? 4/4/2024 23 Receptors & Neurotransmitters of the postganglionic sympathetic fibers: Which neurotransmitter is released most commonly by adrenergic neurons to stimulate their target organs?? 4/4/2024 24 Receptors for acetyl choline: Cholinergic receptors Nicotinic receptor N-AChR:  At all autonomic ganglia (sympathetic & parasympathetic NS): lateral, collateral & terminal ganglia.  At the skeletal muscles: in the neuromuscular junction of the somatic nervous system). Muscarinic receptor M-AChR: (M1-M5)  All postganglionic parasympathetic terminals to organs, cardiac muscle, smooth muscles and exocrine glands.  Some postganglionic sympathetic terminals supplying sweat glands & blood vessels of skeletal muscle. Ion channels 4/4/2024 G protein–coupled receptors 25 Receptors for catecholamines: Adrenergic receptors α1 α2 β1 β2 β3  Plasma membrane receptor.  Adrenergic receptors are G protein–coupled receptors.  The response in the effector organ depends on the neurotransmitter present and the receptor stimulated.  Norepinephrine excites more α receptors than β receptors.  Epinephrine has a greater effect in stimulating the β receptors,  Interaction of catecholamines with α1 and β1 ----> excitatory response. While with α2 and β2 ----> inhibitory response. Adrenal medulla Epinephrine VS norepinephrine: Epinephrine causes almost the same effects as those caused norepinephrine, but the effects differ in the following respects:  Epinephrine, has a greater effect on cardiac stimulation than does norepinephrine. (because epinephrine has greater effect in stimulating the β receptors).  Epinephrine has only weak constriction of the blood vessels in the muscles, in comparison with much stronger constriction caused by norepinephrine (because norepinephrine action is more on α receptors).  Epinephrine has 5 to 10 times greater metabolic effect than norepinephrine. Adrenal medulla Stimuli for secretion: Stress threats body homeostasis Stresses:          physical trauma, prolonged exposure to cold, prolonged heavy exercise, infection, shock, pain, sleep deprivation, decreased oxygen supply, emotional stresses Homeostasis Stress ……………….. 4/4/2024 28 Adrenal medulla Body responses to stress: What are the other hormones involved? Stress Cortisol Epinephrine & norepinephrine 4/4/2024 29 Adrenal medulla & sympathetic NS “STRESS” OR “ALARM” RESPONSE OF THE SYMPATHETIC NERVOUS SYSTEM  All portions of the sympathetic nervous system discharge simultaneously as a complete unit, a phenomenon called mass discharge.  The result is a widespread reaction throughout the body called the alarm or stress response.  It is also called the fight-or-flight reaction.  The purpose is to provide extra activation of the body in states of stress.  This reaction increases the ability of the body to perform vigorous muscle activity in many ways: Stress Adrenal medulla & sympathetic NS “ALARM” OR “STRESS” RESPONSE OF THE SYMPATHETIC NERVOUS SYSTEM             arterial pressure. heart rate heart contractility blood flow to active muscles rates of cellular metabolism throughout the body. blood glucose concentration, as a source of energy glycolysis in the liver and in muscle. lipolysis increase free fatty acids as a source of energy muscle strength rate of blood coagulation mental activity Stress How Does the Central Nervous System Control the ANS? At the level of the hypothalamus At the level of the brain stem At the level of the spinal cord 4/4/2024 32 How Does the Central Nervous System Control the ANS? At the level of the hypothalamus 4/4/2024 33 How Does the Central Nervous System Control the ANS? At the level of the brain stem 4/4/2024 How Does the Central Nervous System Control the ANS? At the level of the spinal cord Reflexes such as micturition, defecation and erection are integrated at the spinal cord level (sacral segment of the spinal cord). 4/4/2024 4/4/2024 36 Thank you 4/4/2024 37 4/4/2024 38 4/4/2024 39 4/4/2024 40 4/4/2024 41 Parasympathetic NS 4/4/2024 42 Sympathetic NS 4/4/2024 43 Learning Resources  https://exchange.scholarrx.com/brick/autonomic-nervous-system  Textbook: Hall, J. and Hall, M. Guyton and Hall textbook of medical physiology, Fourteenth Edition, Elsevier 2021. ISBN: 978-0-323-59712-8. International Edition ISBN: 978-0-323-67280-1. Chapters 61, Page no. 763775.  PowerPoint presentation in the Moodle.  https://youtu.be/D96mSg2_h0c April 4, 2024 www.gmu.ac.ae COLLEGE OF MEDICINE