Workshop Exploring ANS Structures and Functions (Heart) in PDF

Autonomic Nervous System and the Heart Prof Russ Chess-Williams  COPYRIGHT WARNING This material has been reproduced and communicated to you by or on behalf of Bond University in accordance with section 113P of the Copyright Act 1968 (Act)....

Autonomic Nervous System and the Heart Prof Russ Chess-Williams  COPYRIGHT WARNING This material has been reproduced and communicated to you by or on behalf of Bond University in accordance with section 113P of the Copyright Act 1968 (Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice Autonomic innervation of the heart Sympathetic Nervous System (NA acting at β1-receptors) Innervates the whole heart and vascular system: SA node AV node Myocardium Arteries and veins Parasympathetic Nervous System (Ach acting at M-receptors) Innervates the nodes (SA & AV)  Resting heart rate Pressure transducer on finger records pulse Variations in heart rate: Questions Normal Heart Rate  Approximately what is the normal heart rate at rest in a human?  At what rate does a human isolated heart beat when at normal body temperature? (NB. An isolated heart has no functional nerves running to it).  At rest, is there activity in the sympathetic nerves running to the heart, or activity in the parasympathetic nerves? Autonomic innervation of the heart Sympathetic Nervous System (NA acting at β1-receptors) Innervates the whole heart and vascular system: SA node AV node Myocardium Arteries and veins Parasympathetic Nervous System (Ach acting at M-receptors) Innervates the nodes (SA & AV) Normal heart rate – ANS activity??? Isolated heart = 100 b/m Plus sympathetic activity = 120 b/m Plus parasympathetic activity = 70 b/m At rest, the heart receives both sympathetic and a parasympathetic activity, but parasympathetic dominates  Respiratory effects on resting heart rate Inspiration Expiration Inspiration Expiration 100 HR HR b/m 0 0 5 10 15 20 Time (seconds) Pressure transducer on finger records pulse From trace above…… Heart rate on inspiration = 88 beats/min Heart rate on expiration = 75 beats/min  Respiratory sinus arrhythmia Respiratory Sinus Arrythmia  During respiratory sinus arrythmia, is heart rate increased or decreased during inspiration?  Consequences of RSA for gaseous exchange in the lungs?  What is the mechanism involved in these changes in heart rate? Mechanisms Inspiration (i) Bainbridge reflex venous return stretch atria/IVC (aka “atrial reflex”) vagal afferents medulla Symp & Parasymp Increased heart rate Function of the reflex: Prevents blood pooling on venous side Respiratory Sinus Arrythmia  If these variations in sinus heart rate are absent in a patient (ie, no respiratory variations in heart rate), what might this indicate?  Cardiac Dive Response Pressure transducer on finger records pulse during “dive” Method (you have previously performed this experiment in the laboratory) Heart rate is recorded using a pressure transducer placed on a finger. The subject takes a deep breath and then submerses their face into ice-cold water. The subject maintains this position as long as possible (usually about 20 seconds) before ending the “dive”. Heart rate is recorded throughout the “dive”. Cardiac Dive Response Variations in heart rate: Questions Diving Response  During the dive, is the sympathetic or parasympathetic nervous system activated?  What neurotransmitters and cardiac receptors are involved in the slower large decrease in heart rate that occurs during the dive response?  What possible advantage could this parasympathetic reflex offer to a diving animal? Innervation to heart and vessels? Artery Sympathetic Parasympathetic HEART SA node AV node Myocardium VASCULAR Mesenteric artery Femoral vein Cystic artery Pulmonary artery Carotid artery Summary Heart receives sympathetic and parasympathetic innervation Sympathetic increase rate, force of contraction and AP conduction Parasympathetic reduce heart rate and conduction through AV node At rest, both systems active, parasympathetic dominate Respiration affects heart rate Denervated heart (transplant?) - any ANS control???? (i) Denervated heart sensitive to adrenaline ( rate) (ii) Denervation increases number of β-receptors Increased sensitivity to adrenaline