efferent autonomic regulation of the heart Flashcards

1
Q

what is chronotropy?

A

heart rate

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2
Q

what is inotropy?

A

contractile force of heart

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3
Q

what is lusitropy?

A

rate of relaxation of the heart

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4
Q

what is dromotropy?

A

AV node sonduction velocity

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5
Q

where do sympathetic nerves innervate the heart?

A
  • they richly innervate the ventricles and the atria and pacemaker
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6
Q

where do the parasympathetic post ganglionic fibres innervate?

A
  • just the pacemaker cells - SA & AV node
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7
Q

where do the preganglionic sympathetic fibres originate from and compare the length of the pre and post ganglionic fibres..

A
  • preganglionic sympathetic fibres originate from the T1-T6 segments of the spinal chord
  • the pre ganglionic fibres are short
  • the post ganglionic fibres are long
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8
Q

where do the preganglionic **parasympathetic **fibres originate from and compare the length of the pre and post ganglionic fibres..

A
  • they originate from the vagal motor nuclei in the brain stem and the preganglionic fibres travel in the vagus nerve
  • the preganglionic fibres are long
  • the post ganglionic fibres are short
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9
Q

what is the resting heart rate dominated by?

A
  • it is dominated by the parasympathetic system
  • the vagus nerve exerts a tonic inhibitory action on the SA node to slow the intrinsic heart rate
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10
Q

what NT is involved with the sympathetic system and what effects does it have?

A
  • noradrenaline is released by the post-ganglionic fibres and it binds onto the B1 receptors in the heart
  • activation of the B1 receptors causes an increase in heart rate (chronotropic effect),
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11
Q

Describe the cellular mechanism for the activation of the B1 receptor with NA or A

A
  • the B1 receptor is attached to a G stimultaory protein
  • when NA or A binds to the receptor.. it causes the G protein to activate adenylate cyclase which catalyses the conversion of ATP to cAMP
  • cAMP then has 4 main effects
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12
Q

what are the main effects of cAMP** when NA or A binds to the B1 receptor?

A
  1. cAMP interacts directly with the pacemaker channels to increase their open state probability - they increase the rate of delay of the pacemaker potential which causes the SA node to reach threshold more quickly
  2. cAMP activates the enzyme protein kinase A which has 3 main effects
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13
Q

after cAMP activates protein kinase A, what effects does this enzyme have?

A
  • PKA phosphorlyates L type CA2+ channels which increases the contractile force (inotropic effect)
  • PKA phosphorlyates the delayed rectifier K+ channels which increases the outward current of K+ (repolarisation) which shortens the ventricular AP and allows more excitations per minute
  • PKA also phosphorlyates phospholamban which reduces its inhibitory effect on the Ca2+ ATPase pump
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14
Q

what are the **chronotropic and dromotropic effects **of sympathetic stimulation of the heart?

A
  • the** rate of decay of the pacemaker potential is increased** which allows the threshold to be reached sooner and the heart rate increases (caused by increase in depolarising current LCA2+ and deactivation of rectifer K+)
    * conduction through the AV node is increased by activated B1 receptors in the AV node
  • action potential of atrial and ventricular myocytes is shortened
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15
Q

what NT does the parasympathetic system release and what effects does it have?

A
  • Ach is released by the post-ganglionic neurons
  • Ach slows the rate of decay of the pacemaker potential and therefore decreases heart rate
  • it also increases the membrane permeability to K+ through the KACH channels
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16
Q

Describe the cellular mechanism of acetylcholine with the M2 receptors

A
  • The M2 receptor is linked to an **inhibitory G protein **
  • when Ach binds to the M2 receptor, the** G protein reduces activity of adeylate cyclase** and reduces cAMP and protein kinase A which reduces the activation of L type Ca2+ channels etc
  • The M2 receptor is also linked to a class of K+ channel called Kach
  • the activation of the Kach channel increases the outward K+ current and hyperpolarises the membrane
17
Q

what effect does sympathetic stimulation have on** blood vessels**?

A
  • causes vasoconstriction
  • also causes venoconstriction which increases venous return and therefore stroke volume and CO