Autonomic cardiac control

Question 1

Where do the preganglionic fibres of the parasympathetic nervous system arise

Answer 1

Either in the brainstem of the sacral region of the spinal cord.
From brainstem they exit as carinal nerves III, VII, IX, X. From the sacral region they leave through the 3rd or fourth sacral spinal nerve roots.

Question 2

Where do the preganglionic fibres of the sympathetic nervous system arise

Answer 2

In the spinal cord between the first thoracic segment (T1) and the second or third lumbar segment (L2-L3).

Question 3

What is the neurotransmitter for preganglionic fibres for both the parasympathetic and sympathetic nervous systems

Answer 3

Acetylcholine

Question 4

What does preganglionic NT ACh bind with on postganglionic fibres

Answer 4

Nicotinic Ach receptors

Question 5

Where do the ganglia of the parasympathetic nervous system lie

Answer 5

Close to the organ which they innervate

Question 6

Where do the ganglia for the sympathetic nervous system lie

Answer 6

Close to the spinal cord either para or prevertebrally

Question 7

What do the postganglionic fibres of the parasympathetic nervous system release and where does it bind

Answer 7

Acetylcholine

Muscarinic ACh receptors on the target organs

Question 8

What do the postganglionic sympathetic fibres release and where do they bind

Answer 8

Mostly noradrenaline

Acts on adrenergic receptors on target organs

Question 9

How is acetylcholine synthesised

Answer 9

In the cytoplasm from acetyl-CoA and choline by the actions of choline acetyltransferase

Question 10

What is the enzyme that inactivates acetylcholine and what does it do

Answer 10

Acetylcholinesterase

Splits Ach into acetate and choline

Question 11

Two classes of cholinergic receptors

Answer 11

Nicotinic and muscarinic

Question 12

Two classes of nicotinic receptors

Answer 12

Nn (found in autonomic ganglia)

Nm (found in endplates of skeletal muscle)

Question 13

What do ‘ganglion blockers’ do

Answer 13

They are antagonists for Nn receptors. So they inhibit parasympathetic activity adverse effects include postural hypotension, flushing, impotence.

Question 14

Where are muscarinic receptors located

Answer 14

On cell membranes of organs innervated by postganglionic parasympathetic fibres

Question 15

What is the result of ACh acting on muscarinic fibres in the cardiovascular system

Answer 15

Heart rate is slowed by direct action on the SA node and by slowing conduction to the AV node.
Contractility of the heart is reduced
Dilates blood vessels (through infusion of ACh into the bloodstream as there are few cholinergic nerves on blood vessels)

Question 16

What is the action of atropine and what is its effects

Answer 16

It is a muscarinic antagonist so blocks the physiological effect of parasympathetic activity thus increases heart rate. Also reduces salivation.

Question 17

What is the main neurotransmitter released by the sympathetic post-ganglionic nerve

Answer 17

Noadrenaline.
Two exceptions- post ganglionic nerves that innervate sweat glands (these release ACh)
The adrenal medulla releases primarily adrenaline

Question 18

What are the receptors for catecholamines

Answer 18

Adrenergic receptors. Include alpha 1 and 2, beta 1, 2, & 3

Question 19

What are the main effects of receptor activation of alpha 1 receptors

Answer 19

Vasoconstriction, relaxation of GI smooth muscle, salivary secretion, and hepatic gycogenolysis

Question 20

What are the main effects of receptor activation of alpha 2 receptors

Answer 20

Inhibition of transmitter release (located on presynaptic cell), platelet aggregation, contraction of vascular smooth muscle, inhibition of insulin release.

Question 21

What are the main effects of activation of beta 1 receptors

Answer 21

Increased cardiac rate and force

Question 22

What are the main effects of activation of beta 2 receptors

Answer 22

Bronchodilation, vasodilation, relaxation of visceral smooth muscle, hepatic glycogenolyis, and muscle tremor

Question 23

What are the main effects of activation of beta 3 receptors

Answer 23

Lipolysis

Question 24

Example of alpha 1 agonist

Answer 24

phenylephrine (vasoconstrictors useful in treating nasal congestion)

Question 25

Example of alpha 2 agonist

Answer 25

Clonidine (cause fall in BP due to reduction of sympathetic activity with decreased noradrenaline release)

Question 26

Example of beta 1 agonist

Answer 26

Dobutamine (increased cardiac contractility)

Question 27

Example of beta 2 agonist

Answer 27

Salbutamol (bronchial dilator- asthma)

Question 28

Define antagonist

Answer 28

A drug that binds to a receptor and blocks the effects of physiological agonist

Question 29

What would an alpha 1 antagonist do and give an example?

Answer 29

Vasodilation.

Prazosin

Question 30

What would an beta 1 antagonist do and example

Answer 30

Decrease HR and contractility

Propanolol, atenolol

Question 31

Describe the mechanism behind slowing of the HR with parasympathethic stimuation

Answer 31

ACh release at pre-ganglionic fibres binds to muscarinic receptors at the SA node.
Activation of these receptors opens K+channels through a stimulatory G protein, and closes funny channels and T-type Ca2+ channel . This results in a hyper polarised membrane and slower rate of spontaneous depolarisation

Question 32

Describe the mechanism of increasing the HR through sympathetic stimulation

Answer 32

NA binds to B1 receptors activating the cAMP second messenger system, this augments the opening of funny channels and T-type calcium channels increasing rate of spontaneous depolarisation

Question 33

Mechanism behind control of SV through sympathetic activation

Answer 33

NA binds to B1 adrenergic receptors, this activates adenylate cyclase that catalyses synthesis of cAMP which ultimately results in increased intracellular Ca2+

Question 34

What system is vascular tone predominantly controlled by

Answer 34

Sympathetic. The autonomic system is tonically active, an increase in sympathetic activity will result in vasoconstriction and a decrease will result in vasodilation.

Question 35

Describe the baroreceptor reflex

Answer 35

Afferent input from the (peripheral) carotid and aortic body baroreceptors, an increase in arterial pressure results in an increase in baroreceptor firing, increase NTS activity, increase vagal stimulation and inhibition of sympathetic nerve activity (BP drops)

Question 36

Describe the chemoreceptor reflex

Answer 36

Hypoxia, hypercapnia, low pH is detected by peripheral chemoreceptors in the aortic and carotid bodies. Causes increase in ventilation and sympathetic vasoconstrictor activity.

Question 37

describe the human dive reflex

Answer 37

Sensory receptors on the face detect temperature, wetness and water pressure- afferent fibres stimulated (trigeminal nerve) does to cardio and respiratory control centres in medulla and then vagal efferent stimulation to heart and lungs. Breath hold, bradycardia and peripheral vasoconstriction increasing central perfusion.