Innervation of the Heart

Question 1

What are the two types of innervation?

Answer 1

Extrinsic (nerves coming from outside the heart)

Intrinsic (nerves coming from inside the heart)

Question 2

What are the extrinsic innervation of the heart?

Answer 2

Autonomic motor fibres - parasympathetic and sympathetic

Sensory and pain fibres

Question 3

What nerve is used in parasympathetic control of the heart?

Answer 3

Vagus nerve
Function: reducing the heart rate, reducing the force of contraction of the heart, vasoconstriction of the coronary arteries

Question 4

What autonomic nerve fibres is used in sympathetic control of the heart?

Answer 4

Spinal cord segments T1-T4

Function: increasing heart rate, increasing the force of contraction of the myocardium

Question 5

Where are autonomic motor fibres routed?

Answer 5

To the heart and coronary arteries via the cardiopulmonary plexus situated at the bifurcation of the trachea

Question 6

Where do sensory and pain fibres travel?

Answer 6

From the heart wall, to the spinal cord levels T1-T4 in the sympathetic nerves

Question 7

Somatic sensory fibres and dermatomes

Answer 7

Somatic sensory fibres from the heart wall travel to the spinal cord levels T1-T4 supplying the dermatomes on the inner aspect of the upper arm so pain coming from the heart in these segments is interpreted as pain in the upper arm

Question 8

Intrinsic innervation from the heart

Answer 8

Sympathetic motor fibres innervate the SA and AV nodes which consist of modified cardiac muscle cells that generate electrical impulses.

Modified cells are known as Prukinje cells and their axons/fibres are Purkinje fibres

Impulses then spread down the atrioventricular bundle branches to the myocardium of the ventricles.