ANS and CVS

Question 1

how does the ANS regulate physiological functions like heart rate, temperature etc?

Answer 1

• exerts control over smooth muscle in vessels and bronchi, exocrine secretions, rate and force of contrcation.

Question 2

what are the functions of the autonomic nervous system?

Answer 2

• regulate physiological function.
• sympathetic increases under stress and parasympathetic more dominant in basal conditions.
• both work together to maintain balance.

Question 3

what control does the ANS have on the cardiovascular system?

Answer 3

• control heart rate, force of contraction, peripheral resistance of blood vessels.
• ANS does not initiate electrical activity!!! denervated heart beats faster. at rest vagal influence allows normal heart beat.

Question 4

where does the parasympathetic input to the heart arise from?

Answer 4

• vagus nerve.
• post-ganglionic cells within walls of heart at SA and AV node.
• acts on M2 receptors to decrease heart rate or decrease AV node conduction velocity.

Question 5

explain the sympathetic effect on the heart.

Answer 5

• post-ganglionic from the sympathetic trunk, innervates SA, AVN or myocardium releasing NA.
• acts mainly on B1 adrenoreceptors to increase HR AND force of contraction.

Question 6

describe the activity of the SAN.

Answer 6

• sets rhythm of heart.
• slow depolarisation of pacemaker potential, turning on slow Na+ conductance (funny current).
• opening of Ca2+ channels and turning off K+ conductance.

Question 7

what effects does ANS have on vasculature?

Answer 7

• sympathetic innervation except specialised erectile tissue with parasympathetic.
• most arteries and veins have a1 adrenoreceptors that NA work on.
• coronary and skeletal muscle vasculature also have B2 receptors.

Question 8

what regulates the vasomotor tone of vessels?

Answer 8

SYMPATHETIC output.

- decreases at vasodilation, increases at vasoconstriction.

Question 9

what is the significance of having alpha and beta adrenoreceptors in vessels in skeletal, myocardium, liver?

Answer 9

• physiological concentration of adrenaline prefers B2 whereas high concentrations will also activate a1.
• B2 activation causes vasodilation by inhibiting MLCK.
• a1 activation causes vasoconstriction stimulating vasoconstriction via IP3 production.

Question 10

what governs the overall control of CVS?

Answer 10

• changes are communicated to brain via afferent nerves.
• baroreceptors for high pressure or atrial receptors for low pressure.
• alters efferent (motor) nerves.

Question 11

why is the baroreceptor reflex important?

Answer 11

• for maintaining blood pressure short term, compensating for momentary changes to BP.
• baroreceptors reset to higher levels with persistent high BP to a ‘new normal’ at hypertension.

Question 12

what is the use of sympathomimetics?

Answer 12

• drugs that stimulate SNS.
• adrenaline : restore and support circulation after cardiac arrest, anaphylactic shock to activate alpha 1 receptors.
• dobutamine at cardiogenic shock (pump failure) after MI.
• salbutamol for asthma (vasodilation).

Question 13

what are adrenoreceptors antagonists?

Answer 13

• alpha adrenoreceptor antagonist, antihypertensive agent inhibiting NA action vasodilation.
• B adrenoreceptor antagonists like propanolol which slows HR but also acts on B2 receptors and causes bronchoconstriction, atenolol selective to only B1.

Question 14

what are cholinergics?

Answer 14

• mimics acetylcholine.
• muscarinic agonists : improves drainage in glaucoma.
• muscarinic antagonist : like atropine increasing HR, bronchial dilation used to dilate pupils in eye examinations.