ANS control of the heart Flashcards
HR, BP, temp etc
Response to exercise
Response to stress
are all controlled by what?
Autonomic nervous system - involunatry
What are the effectors of the ANS?
Smooth muscle
Exocrine glands
Heart- rate and force
What is the enteric nervous system?
Network of neurones found in GI tract controlled by sympathetic and parasympathetic fibres.
Which branch of the ANS predominates in Basal conditions?
Parasympathetic
Do the parasympathetic and sympathetic nervous systems work together?
Yes the oppose one another to achieve a balance.
In the eye which receptors are found in the iris muscle and what neurotransmitter innervates them to do what action?
alpha 1- adrenaline- dilation
M3- Acetyl choline - contraction
What do M3 receptors in the lungs do?
Broncho-constrict
What neurotransmitter is at NMJ of parasympathetic nerves?
Acetyl choline
What receptor type is at the NMJ of most parasympathetic nerves?
mAChR
What is Qiss Qiq
A memory aid to help remember what receptor is where.
alpha1 Q vasoconstriction
alpha2 I inhibits nerotransmitter release
beta 1 S heart (inc, HR and inotropy)
beta 2 S lungs bronchodilation
M1 Q glands
M2 I heart (decrease HR and force)
M3 Q lungs (bronchoconstriction)
What does parasympathetic innervation do to sweat glands?
No effect
What causes sweat gland activity?
Sympathetic effect
Is the sympathetic effect systemic or localised?
More often than not it is localised but in fight or flights its systemic.
Which nerve slows the heart?
Vagus nerve pre-ganglionic fibres innervate post-ganglionic cells on the epicardial surface or with n the walls at the SAN or AVN.
Which nerve speeds up heart rate?
Sympathetic trunk feeds into cardiac accelerator nerve
Does the ANS initiate the heart beat?
NO
SAN is automated. The vagal nerve slows the intrinsic heart rate down in normal circumstances but does not initiate it.
Venoconstriction is controlled by?
ANS
How do M2 slow heart rate?
Slow AVN conduction velocity.
What neurotransmitter is released at M2 receptors?
Acetyl choline
B1 stimulation has positive inotropic and chronotropic effects where are the receptors in the heart and what stimulates it?
Noradrenaline
SAN, AVN and myocardium
B1 is the predominant sympathetic receptor affecting the heart but what other types are there?
B2 and B3
Outline the baroreceptor reflex if pressure is high.
Baroreceptors detects pressure changes and respond to stretch. They feedback to the cardiovascular centre by the glossopharyngeal nerve. The vagus nerve will relay a signal to slow the heart to post ganglionic cells at the SAN and AVN.
Where do you find baroreceptors?
Arch of the Aorta
Carotid Sinus
If pressure is low what happens ?
Atrial receptors detect low pressure and communicate with the cardiovascular centre. An intermediate neurone carries it from the medulla oblongata to the spinal cord. The sympathetic trunk receives input and sends a sympathetic signal via the cardiac accelerator nerve. This nerve innervates SAN, AVN and ventricular myocardium.
Where in the brain do you find the cardiac centre?
Medulla Oblongata
Outline SAN potential.
Funny current - slow conductance Na+ channel slowly depolarises cell to threshold.
Ca2+ channel open, fast upstroke to +10mV
Ca2+ channels shut and K+ channels open to repolarise
How long is an SAN AP?
0.8 s
The SAN node carries HCN, why is this important when considering the action of sympathetic innervation at the SAN speeding up HR?
B1 receptors are Gs. Adenylyl cyclase activated so ATP converted to cAMP. HCN are cyclic dependent- i.e. activated by cAMP. More HCN activation means a faster pacemaker potential- faster heart rate
How does parasympathetic innervation slow heart rate?
M2 are Gi receptos so reduce cAMP . The beta gamma subunit also increases K+ conductance making the cell more hyper-polarised.
Outline the steps of NA increasing contractility of the heart?
cAMP activates PKA.
PKA phosphorylates calcium channels. Increased Ca2+ entry in plateau
Calcium induced calcium release is increased
Increased calcium sensitivity of the contractile machinery
More forceful contratin
Which vessels carry parasympathetic receptor?
Erectile
Point and Shoot
Erection - Para-sympathtic
Ejaculation - Sympathetic
Which vessels contain B2 receptors as well as alpha 1?
Coronary vessels and skeletal muscle vessels
How does the sympathetic system generate vasodilation?
decrease from basal sympathetic tone.
Noradrenaline stimulates which sympathetic receipt preferentially in vascular smooth muscle?
Alpha 1
What stimulates beta 2 receptors in vascular smooth muscle?
Circulating adrenaline
Circulating adrenaline can stimulate alpha 1 as well as beta 1 in vascular smooth muscle, under what circumstance is this the case?
High concentrations of circulating adrenaline
How do Beta 2 receptors in smooth muscle cause vasodilation?
Increase cAMP- PKA activated
K+ channels open and MLCK inhibited
smooth muscle relaxes.
What do local metabolites do in smooth muscle of vasculature?
Vasodilate
Name some vasodilating local metabolites
K+ H+ CO2
Which has the greater vasodilating affect in coronary vessels and skeletal muscle vessels local mediators or Beta 2 receptors?
Local mediators.
How do we increase mean arterial pressure?
Barorecetor detects drop in pressure afferent pathway to brain Brain coordinate an output Efferent pathway Heart beats slower and less hard while vessels dilate
In hypertension why don’t the bar receptor reflexes lower it?
Reset to a higher level of pressure to induce an effect.
List drug types that act on the ANS in CVS
alpha- adreno-receptor agonist
beta adreno-recpetor agonists
adrenoreceptor antagonists
Muscarinc agonists and antagonists.
Which sympathomimetic is given in cardiac arrest?
adrenaline
What would you give in cariogenic shock?
dobutamine B1 agonist- increase hearts rate and force
Why would you give adrenaline in anaphylaxis?
vaso-constriction
Why would you want to antagonise alpha 1 receptors?
Resistant hypertensives
Name a nonselective beta blocker and why you would give it.
Propranolol used to slow HR and reduce BP
Risk bronchoconstriction
Selective beta 1 blockers are known as cardio-selective, what do they do and give an example?
Atenolol
Inhibit Beta 1 receptor in heart only so decrease inotropy and chronotropy
The iris muscarinic receptor is in the sphincter and when stimulated causes contraction. What pharmaceutical agent is used to agonise this?
Pilocarpine
Tropicamide is a…. and is used to …. the pupil by antagonising on the …. receptors on the …. muscle
antimuscarinic
dilate
M3
sphincter
