Nerves of the heart. Innervation of the heart.
The nerves that provide innervation of the cardiac muscles, which have a special structure and function, are complex and form numerous plexuses. The entire nervous system is composed of:
1) suitable trunks,
2) extracardiac plexuses,
3) plexuses in the heart, and
4) nodal fields associated with the plexus.
Functionally, the nerves of the heart are divided into 4 types (I. P. Pavlov): slowing and accelerating, weakening and strengthening. Morphologically, these nerves are part of n. vagus and truncus sympathicus branches. The sympathetic nerves (mainly postganglionic fibers) extend from the three upper cervical and five upper thoracic sympathetic ganglions: n. cardiacus cervicalis superior – from ganglion cervicale superius, n. cardiacus cervicalis medius, from ganglion cervicale medium, n. cardiacus cervicalis inferior – from ganglion cervicale inferius or ganglion cervicothoracicum and nn. cardiaci thoracici from the chest nodes of the sympathetic trunk.
The cardiac branches of the vagus nerve begin from its cervical (rami cardiaci cervicales superiores), thoracic (rami cardiaci thoracici) and from n. laryngeus recurrens vagi (rami cardiaci cervicales inferiores). Nerves suitable to the heart are composed of two groups – superficial and deep. In the upper part, the superficial group is adjacent to the carotid and subclavian arteries, and in the lower part, to the aorta and pulmonary trunk. The deep group, composed mainly of the branches of the vagus nerve, lies on the anterior surface of the lower third of the trachea. These branches are in contact with the lymph nodes located in the trachea, and with an increase in nodes, such as pulmonary tuberculosis, they can be compressed by them, which leads to a change in heart rhythm. From these sources, two nerve plexuses are formed:
1) superficial, plexus cardiacus superficialis, between the aortic arch (under it) and the pulmonary bifurcation;
2) deep, plexus cardiacus profundus, between the aortic arch (behind it) and the trachea bifurcation.
These plexuses continue in the plexus coronarius dexter et sinister, surrounding the somatic vessels, as well as in the plexus located between the epicardium and myocardium. Intraorganic branching of the nerves depart from the last plexus. The plexus contains numerous groups of ganglion cells, nerve nodes.
Afferent fibers begin from receptors and go along with efferent ones in the composition of the vagus and sympathetic nerves.