Autonomic Control Of CVS Flashcards
Where does the majority of the parasympathetic nervous system stem from?
The cranial and sacral regions
Where does the majority of the sympathetic nervous system stem from?
Thoracic and lumbar regions
What does the ANS control in the CV system?
- heart rate
- force of contraction (inotropy)
- peripheral resistance of blood vessels
- controls amount of venoconstriction
*does not initiate heart beat, only speed and force of beat. (Denervated hearts still beat but at a faster rate~100bpm)
How is the parasympathetic NS connected with the heart?
Preganglionic fibres-The vagus nerve (10th cranial nerve)
Post ganglionic cells- epicardial surface/within walls of heart at SA and AV node
What neurotransmitter is released by the post ganglionic cells in the parasympathetic NS innervation the heart? What does this act upon?
ACh
Acts on M2-receptors
What effects can the parasympathetic NS have on the heart?
Decreased heart rate (-ive chronotropic effect)
Decrease AV node conduction velocity
How is the sympathetic NS connected with the heart?
Post ganglionic fibres from the sympathetic trunk
Innervates the SA node, AV node and myocardium.
What neurotransmitter is released by the post ganglionic cells in the sympathetic NS innervation the heart? What does this act upon?
Noradrenline
Acts on beta1 adrenoreceptors
**beta 2 and 3 adrenoreceptors are also present in the heart but the main effect is mediated by beta 1 receptors
What effects can the sympathetic NS have on the heart?
Increases heart rate (+ive chronotropic effect)
Increases force of contraction (+ive inotropic effect)
What part of the brain controls the cv system?
Medulla oblongata
How does the body know how to adapt the messages it sends to heart?
It receives information from the baroreceptors in the carotid sinus and the arch of aorta (these measure blood pressure)
And atrial receptors on the low pressure side of system
Along what nerve does the information collected by the baroreceptors travel?
Glossopharyngeal nerve (cranial nerve IX)
Sensory nerve
What are the two motor (efferent) neurones that innervate the heart?
Vagus (parasympathetic)
Cardiac accelerator nerve (sympathetic)
What are the effects of ANS on pacemaker action potentials in the heart?
Sympathetic activity increased the slope (depolarisation occurs quicker) and in the AV node conduction is speed up
Parasympathetic activity decreases slope (depolarisation occurs slower) and in the AV node conduction is slowed
By what mechanism does the sympathetic NS increase the speed of pacemaker cells?
Sympathetic effect mediated by beta 1 adrenoreceptors
G-alpha-s (gpcr) increase cAMP which has effect f speeding up pacemaker potentials
*the cAMP can have a direct effect on the enhancement of currents
By what mechanism does the parasympathetic NS decrease the activity of the pacemaker cells?
Parasympathetic effect mediated by M2 receptors. G-alpha-i (GPCR) increase k+ conductance and decrease cAMP. Beta-gamma subunit act on k+ channels, meaning the m.p is further from the threshold and it therefore takes longer to fire an AP
How does noradrenaline increase force of contraction?
- It acts on B1 receptors in myocardium which causes an increase in cAMP which in turn activates PKA.
- Phosphorylation of Ca2+ channels increases Ca2+ entry during plateau of the AP
- Increased uptake of Ca2+ in SR
- Increased sensitivity of contractile machinery to Ca2+
All leads to increased force of contraction
What type of receptors do most veins and arteries have and what type of innervation do they receive?
A1 adrenoreceptors
Sympathetic
**coronary and skeletal muscle vasculature may also have B2 receptors
How is vasodilation controlled?
By turning sympathetic control up and down (there is no parasympathetic innervation)
For vasodilation- stop stimulation
For vasomotor tone- normal stimulation
For vasoconstriction- increase stimulation
All about activation of the A1 adrenoreceptors
Some vessels have B2 adrenoreceptors as well as A1 adrenoreceptors. What neurotransmitters are they most sensitive to?
A1- noradrenaline from SNS
B2- more sensitive to circulating adrenaline (as circulating adrenaline has a higher affinity for beta 2 adrenoreceptors)
*at higher concentrations circulating adrenaline will also bind to a1 receptors
For those vessels that have both b2 and a1 adrenoreceptors how is vasomotor tone controlled?
For vasodilation- activate b2 adrenoreceptors
For vasoconstriction- activate a1 adrenoreceptors
How does activating b2 adrenoreceptors in the vascular smooth muscles cause vasodilation?
Increases cAMP= PKA= opens k+ channels (hyperpolarisation occurs)+ inhibits MLCK (stops phosphorylation of myosin light chain) = relaxation of smooth muscle
How does activating a1 adrenoreceptors in the vascular smooth muscles cause vasoconstriction?
Stimulates IP3 production=increase in cystolic [ca2+] = contraction of smooth muscle
What effect do local metabolites have on vasulature?
Cause vasodilation - ensure adequate perfusion of skeletal and coronary muscle .
*H+, k+, adenosine- metabolites all need to be removed before too much vasodilation occurs
