Autonomic Control of the Heart Flashcards
What is the autonomic nervous system?
The neural network that control subconcious functions
What are the divisions of the autonomic nervous system?
Sympathetic nervous system: Control functions under times of acute stress
Parasympatic nervous system: Control the body function during rest
What are the cardiovascular centers?
Collection of neurons in the reticular formation of the medulla oblongata
What are the components of the cardiovascular centers?
Vasomotor Center (divided into Cardiac Acceleration Center and Vasodilator C)
Cardiac Inhibitory Center
Function of the cardiac acceleration center (CAC) or vasoconstrictor center
Vasomotor center component
Stimulation fo the CAC increases sympathetic discharge to:
1) Adrenal medulla causing Catecholamine (adrenaline and noradrenaline) release
2) Blood Vessels causing vasoconstriction
Function of the vasodilator center (VDC)
Vasomotor center component
Stimulation of VDC causes generalized vasodilation through inhibition of vasoconstriction center
Function of the Cardiac Inhibitory Center (CIC)
Contains dorsal motor neurons of the vagus which send inhibitory signals to the heart via the vagus nerve
What is vagal tone?
Vagal stimulation of the SA node decreases the heart rate to 60-100 bpm from the typical SA node rhythm of 90-110 bpm
Under resting conditions, vagal tone predominates
What is ventricular vagal escape?
A reduction in blood pressure due to muscarinic stimulation which is then compensated for stimulation from the sympathetic system to increase heart rate and thus blood pressure
What is idioventricular rhythm?
A cardiac rhythm characterized by a rate of <50 beats per minute, absence of P waves and widening of the QRS complex
Where are the sympathetic nerves derived from?
T1-T5
What parts of the heart does the sympathetic nervous system system supply?
Sympathetic nervous system supply all part of the heart (atria, ventricles, conduction system and the coronary vessels)
What are the effects of the sympathetic stimulation?
Increases all cardiac properties (Excitability, Rhythmicity , Conductivity and Contractility)
1) Increase the heart rate in young adult humans from 70 beats/min up to 180 to 200 beats/min and, rarely, even 250 beats/min
2) Increase the force of heart contraction, increasing the volume of blood pumped and the ejection pressure
3) Increase the cardiac output as much as twofold to threefold
4) Increase cardiac output, heart work and O2 consumption
5) Vasodilation of the coronary blood vessels
Where is the parasympathetic nervous system of the heart derived from?
Derived from the vagus nerve
What parts of the heart does the parasympathetic nervous system supply?
Parasympathetic nervous system supply part of the heart (SA Node, AV Node, atria, conduction system and the coronary vessels)
Right vagus supply SA Node, While left vagus supply AV Node
What are the effects of parasympathetic stimulation?
Depression of all cardiac properties (Excitability, Rhythmicity , Conductivity and Contractility)
1) It causes –ve chronotropic effect, decrease atrial contraction (-ve inotropic), decrease atrial excitability, and decrease conductivity
2) Decrease cardiac output, heart work and O2 consumption
3) Vasoconstriction of the coronary blood vessels
Describe how sympathetic stimulation affects heart rate
Post-ganglionic sympathetic fibres release norepinephrine (NE) → activate β1 adrenergic receptors located in the SA node → opens sodium (Na+) channels, “funny” current (If) → increase pacemaker potential
Describe how parasympathetic stimulation affects heart rate
Post-ganglionic parasympathetic fibres release Acetylcholine (ACh) → activate Muscarinic receptors M3 located in the SA node → closes sodium (Na+) channels → decrease “funny” current (If) → decrease pacemaker potential
Describe how sympathetic stimulation affects conductivity
Post-ganglionic sympathetic fibres release norepinephrine (NE) → activate β1 adrenergic receptors located in the AV node → opens (Ca++) channels → faster conduction through the AV node
Describe how parasympathetic stimulation affects conductivity
Post-ganglionic parasympathetic fibres released Acetylcholine (ACh) → activate Muscarinic receptors M3 located in the AV Node → closes (Ca++) channels → Slow conduction through the AV node
Describe how sympathetic stimulation affects contractility
Post-ganglionic sympathetic fibres release norepinephrine (NE) → activate β1 adrenergic receptors located in the myocyte → Open more Ca++ channels which increases the activity of the Ca++ pump and Ca++ storage in the sarcoplasmic reticulum → elevation of the plateau → increase ventricular contraction
Describe how parasympathetic stimulation affects contractility
Parasympathetic nervous system does not innervate ventricular myocytes → NO direct effect on ventricular contractility
How does the autonomic nervous system affect vascular tone?
The main ANS factor altering vascular tone is the sympathetic nervous system
Post-ganglionic sympathetic fibres to the blood vessels releases norepinephrine (NE) → binds strongly to α1 and α2 receptors or weakly to β2 receptors
α1 and α2 receptors → vasoconstriction of the blood vessel → increase arterial blood pressure
β2 adrenergic receptors → vasodilation of the blood vessel
Overall, the predominate effect of norepinephrine on the vasculature is vasoconstrictive → increasing vascular tone
