Lecture 10- Autonomic Control Of CVS Flashcards
What does the ANS control when it comes to the cardiovascular system?
Heart rate
Force of heart contraction
Peripheral resistance of blood vessels
Parasympathetic Inuit to heart?
Preganglionic fibres synapse with post ganglionic cells on epicardial surface or within walls of heart at SA and AV node.
Post ganglionic cells release ACh
Activates M2 muscarinic receptors leading to slowed heart rate and decreased conduction through AV node
Sympathetic activity impact on heart?
Post ganglionic fibres from sympathetic trunk. Innervate SA, AV and myocardium. Noradrenaline acts on B1 receptors and cause increased heart rate and force of contraction
How does the SA node work?
Cells slowly depolarise (pacemaker potential) through sodium channels (funny current) and calcium channels to threshold
How do action potentials in SA node occur?
At -60mV pacemaker potential occurs and funny current causes slow depolarisation until threshold reached where calcium channels open and rapid depolarisation occurs. Calcium channels then close and potassium channels open which brings the membrane potential back down and the process repeats
Sympathetic and parasympathetic affect on pacemaker potentials?
Sympathetic affects will activate B1 receptors in which pacemaker potential will be speeded up and threshold reached more rapidly. Parasympathetic affects do the opposite through M2 receptors increasing K+ conductance and reducing cAMP
How does noradrenaline increase force of contraction?
Activates B1 receptors. This increases cAMP which activates PKA which then phosphorylase Ca+ channels increasing Ca+ entry during plateau of AP.
How does the autonomic nervous system affect vasculature?
Most vessels have alpha 1 adrenoreceptors but coronary and skeletal muscle vasculature have B1 also.
Increased sympathetic output leads to vasoconstriction.
However vessels with B2 receptors will vasodilate at physiological adrenaline levels while at higher than physiological levels of adrenaline alpha 1 receptors will also be activated
Role of local metabolites on tissue perfusion?
Active tissues produce CO2, K+, H+ etc which cause a stronger vasodilatory effect than B2 activation and aids tissue perfusion
What receptors are important for overall control of blood pressure?
Baroreceptors (high pressure side of system) and atrial receptors (low pressure side of system)
Where are baroreceptors found?
Carotid sinus and aortic arch
What is to be noted about the baroreceptors reflex?
Only used for short term control as if blood pressure increases persistently their set point can be re set to a higher level.
What are sympathomimetics?
Adrenoreceptors agonists (mimic sympathetic neurotransmitters)
When can adrenaline be used in an emergency?
Anaphylactic shock and to restore function in cardiac arrest
Actions of adrenaline?
High dose acts mainly on alpha 1 causing vasoconstriction but also on beta2
