CVS 4.2 - Autonomic Nervous System in the CVS Flashcards
Describe the organisation of the sympathetic nervous system
- Origin = Thoracolumbar (T1-L2/L3)
- Synapse at paravertebral chain (heart, lungs etc) or prevertebral ganglia (to liver, GI tract etc)
Describe the length of the ganglia in the SNS
- Preganglionic = Short
- Postganglionic = Long
What types of ganglia are in the SNS?
- Preganglionic = Cholinergic (have nicotinic receptors)
- Postganglionic = Noradrenergic (except sweat with is Ach - muscarinic receptors)
Name some sympathetic receptors to Adrenaline and Noradrenaline. Which is significant to CVS?
- Gq alpha 1 - Pupil dilation and localised secretion
- Gs beta 1 (SIGNIFICANT TO CVS) - Increase heart rate and force of contraction
- Gs beta 2 - Relaxation of airways
- Gq m1/3 - Generalised secretion
Where do sympathetic post ganglionic fibres synapse on the heart?
- Sinoatrial node
- Atrioventricular node
- Myocardium (force of contraction)
What happens when Noradrenaline activates Beta-1 receptors in the heart?
- Increased heart rate (positive chronotropic effect)
- Increased force of contraction (positive inotropic effect)
How is heart rate increased by the SNS?
- Noradrenaline binds to Beta-1 receptors coupled to Gs proteins on SAN
- Stimulates adenylyl cyclase which increases cAMP (cyclic nucleotide for HCN channels)
- Increased cAMP = Increased open HCN channels
- Faster depolarisation
How is force of contraction increased by the SNS?
- Noradrenaline binds to Beta-1 receptors coupled to Gs proteins in myocardium
- Stimulates adenylyl cyclase which increases cAMP
- Activates PKA so Ca2+ channels are phosphorylated
- Increases Ca2+ entry into myocytes
- Increased CICR and sensitivity of contractile machinery
- Increased uptake of Ca2+ into SR which decreases duration of contraction
Describe the innervation of vasculature
Sympathetic except erectile tissue
Which receptors are present in arteries and veins
Alpha-1 adrenoreptors (noradrenaline)
Which receptors are present in coronary and skeletal muscle?
Beta-1 and beta-2 receptors
Why is having only beta-2 receptors in coronary muscle significant?
- Needs a continuously high blood flow so unable to constrict
How is vasoconstriction caused by SNS?
- Binding of Noradrenaline to alpha-1 receptors stimulates production of IP3
- Increases intracellular Ca2+ from stores and via influx (IP3 gated ion channel)
- Binds to calmodulin which activates MLCK
- Myosin light chain is phosphorylated = CONTRACTION
How is vasodilation caused by SNS?
- Noradrenaline binds to beta-2 receptors which stimulates adenylyl cyclase
- Increased cAMP production stimulates PKA
- Opens K+ channels (hyperpolarisation) and inhibits MLCK = DILATION
Describe the organisation of the parasympathetic nervous system
- Origin = Craniosacral - medulla (cranial nerves - eye, salivary glands etc.) or sacral region (S2-S4 - bladder, genitalia)
- Synapse close to target tissue
Describe the length of ganglia in the PNS
- Preganglionic = long
- Postganglionic = short
What types of ganglia are in the PNS?
- Preganglionic = cholinergic (nicotinic receptors that have integral ion channels)
- Postganglionic = cholinergic (muscarinic that are G protein coupled)
Name some parasympathetic receptors to Acetylchline. Which is significant to CVS?
- Gq m1/3 - Stimulates phospholipase C - Constriction of pupil and contraction of airways
- Gi m2/4 - Inhibits adenylyl cyclase - Decreases heart rate (SIGNIFICANT TO CNS)
Where does the vagus nerve of the PNS synapse on the heart?
- Epicardial surface
- Walls of SAN and AVN
- Some in ventricles
How is heart rate reduced by the PNS?
- Acetylcholine binds to m2 receptors coupled to Gi proteins in the SAN
- Inhibits adenylyl cyclase which decreases cAMP levels so open HCN channels are decreased
- Also increases K+ conductance so RMP is further from threshold
- Reduces pacemaker potential therefore slower depolarisation
What is the function of the ANS?
Regulation of physiological processes
Give two details about the SNS
- Can be independently regulated
- Dominant under stress
What does the SNS control?
- Smooth muscle
- Exocrine secretion
- Heart rate
- Force of contraction of heart
When is the PNS dominant?
Basal states
