L.14 ANS control of the heart

Question 1

What nerves are the parasympathetic and sympathetic conduit to the heart

Answer 1

Parasympathetic: Vagus CNX with ganglia close to target organ

Sympathetic: T1-L3 outflow with ganglia close to the spinal cord and post ganglionic fibres exiting from the spinal cord level then go back up

Question 2

What does the parasympathetic nerve and sympathetic nerve innervate on the heart therefore what do they affect

Answer 2

PS; pacemaker cells: slow down HR not really SV. Acts fast
S: pacemaker cells and ventricles: speed up transmission throughout the heart= increase HR. Increase strength of contraction= increase SV. slow to affect.

Question 3

What are the receptors and neurotransmitters for the parasympathetic pathway

Answer 3

At the ganglion: preganglionic fibre releases Acetylcholine to a Nicotinic ACh receptor

At the target organ; post ganglionic fibre releases acetylcholine to a muscarinic ACh receptor.

Question 4

What are the receptors and neurotransmitters for the sympathetic pathway

Answer 4

At the ganglion: preganglionic fibre releases Acetylcholine to a Nicotinic ACh receptor

At the target organ; post ganglionic fibre releases noradrenaline to adrenergic receptor. (B1)

Question 5

What is the effect of sympathetic stimulation by the release of norepinephrine by the adrenal medulla into the blood on blood vessels.

Answer 5

It targets adrenergic receptor a1 which causes vasoconstriction of most blood vessels which increase TPR

Question 6

How does both ANS stimulation change HR

Answer 6

Vagal nerves release ACH which decrease the rate of spontaneous depolarisation and hyperpolarises the resting membrane by increasing the efflux of K+ and close funny Na+ influx

Sympathetic nerves release noradrenaline which increases the rate of spontaneous depolarisation by increasing funny channels and transient calcium channel influx

Question 7

How does sympathetic activation increase SV

Answer 7

-increases Ca2+ influx during AP
-increases the release of Ca2+ by SR due to faster/greater SR uptake via phospholambin.
So more contractility and faster to relaxation

• Increase HR so less time for Ca2+ to pump out of cell
  Both of these increase inotropy: the strength of contraction at any preload.

Question 8

Describe the arterial baroreflex regulation of arterial pressure - managing sympathetic/ parasympathetic tone

Answer 8

Stretch receptors in the carotid sinus and aortic arch increase afferent activity when there is increased blood pressure - conveyed in glossopharyngeal and vagus nerves

Central processing in the medullary cardiovascular control centre leads to
-increased parasympathetic activity,
-decreased sympathetic activity
–>
Reduced HR, stroke volume and some vasodilation (reduced TPR)

Question 9

Describe the mammalian dive reflex (oxygen conserving response)

Answer 9

In response to breath holding, afferent fibres of Vth cranial nerve (cold and pressure), sustained by chemoreceptors.
Triggers
-increased sympathetic activity: peripheral vasoconstriction and rise of blood pressure
- increase parasympathetic activity: bradycardia