CVS - Autonomic Nervous System Flashcards

1
Q

What areas of the body does the ANS control?

A
  • smooth muscle (vascular and visceral)
  • exocrine secretion
  • rate and force of contraction of the heart
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2
Q

What are the two divisions of the ANS?

A
  • parasympathetic nervous system (cranio-sacral origin)

- sympathetic nervous system (thoraco-lumbar origin)

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3
Q

Which receptors does the sympathetic nervous system use to increase the rate of contraction in the heart?

A

Beta-1

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4
Q

Which receptors does the para-sympathetic nervous system use to decrease the heart rate?

A

Muscarinic (m2)

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5
Q

Which receptors does the sympathetic nervous system use to relax the lungs?

A

Beta-2

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6
Q

What does the ANS control within the cardiovascular system?

A
  • heart rate
  • force of contraction
  • peripheral resistance of blood vessels
  • amount of venoconstriction
  • DOES NOT initiate electrical activity in the heart, if heart is denervated will beat extremely quickly
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7
Q

Where does the parasympathetic input enter the heart?

A

It synapses with postganglionic cells on the epicardial surface or within walls at SA and AV node

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8
Q

Which neurotransmitter and receptor does the parasympathetic nervous system use in the heart?

A

Acetylcholine, which acts on m2 receptors

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9
Q

Describe the sympathetic input to the heart

A
  • postganglionic fibres from sympathetic trunk innervate SA and AV node and myocardium
  • release noradrenaline
  • acts on beta-1 adrenoreceptors
  • increases heart rate and force of contraction
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10
Q

Where are baroreceptors found in the heart?

A

In the arch of the aorta and in the carotid sinus

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11
Q

What effect does the sympathetic nervous system have on the slope of the pacemaker potential?

A

It increases it, meaning there is less time between action potentials so the heart rate speeds up.

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12
Q

What effect does the parasympathetic nervous system have on the pacemaker potential?

A

It decreases the slope, meaning that there is more time between action potentials and the heart rate slows

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13
Q

How does noradrenaline increase the force of contraction in the heart?

A
  • it acts on beta-1 receptors in myocardium which causes an increase in cAMP
  • this activates PKA
  • phosphorylation of Ca2+ channels increases Ca2+ entry during plateau of the action potential
  • increased uptake of Ca2+ in SR
  • increased sensitivity of contractile machinery to Ca2+
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14
Q

True or false - most vessels have sympathetic innervation and alpha-1 adrenoceptors

A

True

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15
Q

Some blood vessels have beta-2 receptors as well as alpha-1 receptors. Which would circulating adrenaline bind to more preferentially?

A

Noradrenaline from the SNS would bind to alpha-1, and circulating adrenaline would bind to beta-2

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16
Q

How does activating beta-2 adrenoceptors cause vasodilation?

A

Increases cAMP, increases PKA, opens potassium channels and inhibits MLCK which leads to relaxation of smooth muscle

17
Q

How does activating alpha-1 adrenoceptors cause vasoconstriction?

A

Stimulates IP3 production, causing an increase in interior [Ca2+] from stores and via influx from outside cell. This leads to contraction of smooth muscle.

18
Q

What is the role of metabolites in vasodilation?

A

Active tissue produces more metabolites, eg. H+ which leads to a vasodilator effect in the local area of the increase. This allows adequate perfusion of muscles

19
Q

Which receptors detect low blood pressure?

A

Atrial receptors - baroreceptors detect high blood pressure

20
Q

What happens if raised arterial pressure activates the baroreceptors in the aorta?

A

Impulse travels via the afferent pathway to the coordinating centre. Impulse travels via efferent pathways to the effectors. Bradycardia and vasodilation counteract the increased mean arterial pressure

21
Q

Give a weakness of baroreceptors

A

They can reset to higher levels with persistent increases in blood pressure

22
Q

Give some samples of cardiovascular uses of sympathomimetics

A
  • administration of adrenaline to restore function in cardiac arrest
  • dobutamine (b1 agonist) can be given in cardiogenic shock
  • adrenaline given for anaphylactic shock
23
Q

Give an example of a use of alpha-adrenoceptor antagonists

A

Can be used as an anti-hypertensive agent

24
Q

Give an example of a beta-adrenoreceptor antagonist

A
  • propranolol can be used to slow heart rate and reduce force of contraction, but also causes bronchoconstriction
25
Q

Give an example of a use of a muscarinic agonist

A

Pilocarpine is used in treatment of glaucoma, activates constrictor pupillae muscle

26
Q

Give an example of a muscarinic antagonist

A

Atropine increases heart rate and bronchial dilation, used to dilate pupils for examination of the eye