Autonomic Input to the heart

Question 1

Which parts of the spine does the parasympathetic nerves leave?

Answer 1

Cranial and Sacral parts of the spine

Question 2

Which parts of the spine does the sympathetic nerves leave?

Answer 2

the lumber, thoracic region of the spine

Question 3

Describe the pre-ganglionic axons and post ganglionic axons of the sympathetic and parasympathetic nervous system

Answer 3

Sympathetic: Short pre, Long post

Parasympathetic: Long pre, short post

Question 4

What nerve provides the parasympathetic input to the heart

Answer 4

Vagus Nerve

Question 5

What nerve supplies the sympathetic input to the heart

Answer 5

Cardiac accelerator nerve

Question 6

What would happen to the heart beat if all nervous supply was to be cut off

Answer 6

Carry beating, faster

Question 7

From what vertbrae does the vagus nerve arise

Answer 7

10th cranial vertebra

Question 8

On what receptors does the vagus nerve act on and what effect does it have

Answer 8

M2-receptors
decreases heart rate, inotropy and conduction velocity (Increased delay between contraction of atria and ventricles–> decreased heart rate)

Question 9

What receptors does the cardiac accelorator nerve act on and to what effect

Answer 9

Beta-1 adrenoceptors

Increases heart rate and inotropy

Question 10

What is the pacemaker potential

Answer 10

Slope where the funny current enter the SAnode cells

Question 11

What effect does parasympathetic innervation from the vagus nerve have on the pacemaker potential and how does it have this effect

Answer 11

Decreases the slope to decrease the heart rate
ACh binds to M2 receptors to cleave G alpha i
Inhibits adenylate cyclase so decreases cAMP production
Less HCN activated
Less Na+ influx
Shallower slope

Question 12

What effect does sympathetic innervation from the vagus nerve have on the pacemaker potential and how does it have this effect

Answer 12

Increases slope to increase heart rate
Noradrenaline activates Beta 1 receptors
Cleaves G protein into G alpha s
Stimulates adenylate cyclase so increases cAMP production
Activates more HCN so increases Na+ influx

Question 13

How is the force of contractility increased

Answer 13

Noradrenaline acts on Beta 1 receptors–>Increased cAMP production (Remember G alpha s stimulates Adenylate Cyclase)
cAMP activates Protein Kinase A
Protein Kinase A phosphorylates the Ca2+ channels which increases the Ca2+ entry
Increased contractility

Question 14

What effect does noradrenaline have on alpha 1 receptors and where are alpha 1 receptors found

Answer 14

Vasoconstriction

Found in blood vessels present in the skin, sphincters in the blood vessels going to the GI system, kidney and brain

Question 15

At physiological conditions, which receptor does adrenaline act most strongly on
What effect does it have
Where are β 2 receptoes found

Answer 15

β 2
Acts to vasodilate
Β 2 found in blood vessels going to skeletal muscle, in the bladder wall, GI tract wall, and bronchi

Question 16

What will happen in terms of alpha 1 and β 1 when given a shot of adrenaline

Answer 16

Overwhelming effect is on alpha 1 receptors to cause mass vasoconstriction

Question 17

How does the activation of β 2 receptors lead to its effect

Answer 17

Vasodilation
Activation causes g protein cleavage into G alpha s–> stimulation of adenylate cyclase–>increased cAMP production, so increases activated Protein Kinase A, that inhibits Myosin light chain kinase by phosphorylating it
Reduces contractility so relaxes smooth muscle cells

Question 18

How does alpha 1 receptors have their desired effect

Answer 18

Vasoconstriction
Causes stimulatation of IP3 production, that binds to IP3R and allows calcium to flood out of the SER and into the cytoplasm, so smooth muscle contracts

Question 19

Name three local metabolites that have a strong vasodilatory effect

Answer 19

K+, H+ and adenosine
Note these have a more important role in ensuring adequate perfusion of skeletal and coronary muscle than activation of Β 2 receptors

Question 20

Name three types of drugs that act on the Autonomic nervous system

Answer 20

Sympathomimetics, adrenoceptor antagonist and choliergics

Question 21

Give three examples of sympathomimetics

Answer 21

Adrenaline- Restore function in cardiac arrest and anaphylactic shock
Dobutamine in cardiogenic shock (B1 agonist)
Salbutamol on asthma (B2 agonist)

Question 22

2 examples of adrenoceptor antagonist

Answer 22

Propranolol- B1 and B2 antagonist- Slows heart rate and reduces force of contraction but also acts on smooth muscle of broncus to cause bronchoconstriction
Atenolol- B1 antagonist- Does the above, but less risk of bronchoconstriction