Autonomic Input to the heart Flashcards
Which parts of the spine does the parasympathetic nerves leave?
Cranial and Sacral parts of the spine
Which parts of the spine does the sympathetic nerves leave?
the lumber, thoracic region of the spine
Describe the pre-ganglionic axons and post ganglionic axons of the sympathetic and parasympathetic nervous system
Sympathetic: Short pre, Long post
Parasympathetic: Long pre, short post
What nerve provides the parasympathetic input to the heart
Vagus Nerve
What nerve supplies the sympathetic input to the heart
Cardiac accelerator nerve
What would happen to the heart beat if all nervous supply was to be cut off
Carry beating, faster
From what vertbrae does the vagus nerve arise
10th cranial vertebra
On what receptors does the vagus nerve act on and what effect does it have
M2-receptors
decreases heart rate, inotropy and conduction velocity (Increased delay between contraction of atria and ventricles–> decreased heart rate)
What receptors does the cardiac accelorator nerve act on and to what effect
Beta-1 adrenoceptors
Increases heart rate and inotropy
What is the pacemaker potential
Slope where the funny current enter the SAnode cells
What effect does parasympathetic innervation from the vagus nerve have on the pacemaker potential and how does it have this effect
Decreases the slope to decrease the heart rate
ACh binds to M2 receptors to cleave G alpha i
Inhibits adenylate cyclase so decreases cAMP production
Less HCN activated
Less Na+ influx
Shallower slope
What effect does sympathetic innervation from the vagus nerve have on the pacemaker potential and how does it have this effect
Increases slope to increase heart rate
Noradrenaline activates Beta 1 receptors
Cleaves G protein into G alpha s
Stimulates adenylate cyclase so increases cAMP production
Activates more HCN so increases Na+ influx
How is the force of contractility increased
Noradrenaline acts on Beta 1 receptors–>Increased cAMP production (Remember G alpha s stimulates Adenylate Cyclase)
cAMP activates Protein Kinase A
Protein Kinase A phosphorylates the Ca2+ channels which increases the Ca2+ entry
Increased contractility
What effect does noradrenaline have on alpha 1 receptors and where are alpha 1 receptors found
Vasoconstriction
Found in blood vessels present in the skin, sphincters in the blood vessels going to the GI system, kidney and brain
At physiological conditions, which receptor does adrenaline act most strongly on
What effect does it have
Where are β 2 receptoes found
β 2
Acts to vasodilate
Β 2 found in blood vessels going to skeletal muscle, in the bladder wall, GI tract wall, and bronchi
What will happen in terms of alpha 1 and β 1 when given a shot of adrenaline
Overwhelming effect is on alpha 1 receptors to cause mass vasoconstriction
How does the activation of β 2 receptors lead to its effect
Vasodilation
Activation causes g protein cleavage into G alpha s–> stimulation of adenylate cyclase–>increased cAMP production, so increases activated Protein Kinase A, that inhibits Myosin light chain kinase by phosphorylating it
Reduces contractility so relaxes smooth muscle cells
How does alpha 1 receptors have their desired effect
Vasoconstriction
Causes stimulatation of IP3 production, that binds to IP3R and allows calcium to flood out of the SER and into the cytoplasm, so smooth muscle contracts
Name three local metabolites that have a strong vasodilatory effect
K+, H+ and adenosine
Note these have a more important role in ensuring adequate perfusion of skeletal and coronary muscle than activation of Β 2 receptors
Name three types of drugs that act on the Autonomic nervous system
Sympathomimetics, adrenoceptor antagonist and choliergics
Give three examples of sympathomimetics
Adrenaline- Restore function in cardiac arrest and anaphylactic shock
Dobutamine in cardiogenic shock (B1 agonist)
Salbutamol on asthma (B2 agonist)
2 examples of adrenoceptor antagonist
Propranolol- B1 and B2 antagonist- Slows heart rate and reduces force of contraction but also acts on smooth muscle of broncus to cause bronchoconstriction
Atenolol- B1 antagonist- Does the above, but less risk of bronchoconstriction
