Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the innervation of the heart. And, on this tutorial, we’re going to be using this image here of the open thorax where you see the heart and a lot of these yellow structures which are representing the main nerves of the heart and also other surrounding structures. On this tutorial, we’re going to be talking about afferent and efferent fibers, also parasympathetic and sympathetic fibers. It is important when we look at the anatomy of your heart to also known in detail the nerves that innervates this really important structure because these nerves are responsible for maintaining and regulating the heart rate as well as the force of each contraction.
The first thing we need to know about the innervation of the heart is that both afferent and efferent fibers of the autonomic nervous system contribute to the heart’s overall innervation and, as a reminder, afferent fibers will be carrying nerve impulses or sensory information from the receptors in the sensory organs to then the central nervous system, while efferent fibers will carry impulses from the central nervous system to then the effector organ. A very good way I use to remember the difference between afferent and efferent nerve fibers is to use this simple mnemonic. So, afferent – A – they arrive, and efferent – E – for exit. This simple mnemonic can help you remember that afferent nerve fibers are carrying impulses towards the CNS or the central nervous system while the efferent nerve fibers carry impulses away from the CNS to then the effector organs.
Let’s carry on and talk about the autonomic fibers. The innervation of your heart is derived mostly from the cardiac plexus – as you can see this structure here highlighted in green – and the cardiac plexus is formed by cardiac nerves which then carry both sympathetic and parasympathetic fibers. As you can also see here on this image that the cardiac plexus is located just in front of the bifurcation of the trachea – as you see here this is the trachea – and it bifurcates right here where then you find the cardiac plexus.
Now, as for the function, the nerve fibers from the cardiac plexus function to innervate the electrical conducting system of the heart, also the atrial and ventricular myocardium as well as the coronary vasculature. As I mentioned earlier, the cardiac plexus is made up of both sympathetic and parasympathetic fibers.
Now, let’s have a look at the origin and function of the parasympathetic fibers. The parasympathetic fibers come from the 10th cranial nerve – the vagus nerve – which you can see here on both of these images, the left vagus nerve and the right vagus nerve, highlighted in green. Now, these fibers are preganglionic fibers that form synapses in ganglia located either in the cardiac plexus or within the heart wall itself. Now, as for the function associated to these fibers, the stimulation of these parasympathetic fibers causes a decrease in heart rate and decrease in the force of cardiac contraction.
Now, we’re going to move on and talk about the sympathetic fibers and the sympathetic fibers come from the intermediolateral cell column of the thoracic spinal cord T1 to T5 after which they merge into these structures that you see here highlighted in green which are the then sympathetic trunks – the right one which you see here and the left one. The preganglionic fibers synapse in the sympathetic ganglia of the cervical and thoracic regions which in turn pass on the postganglionic fibers to the cardiac plexus. And as for the functions, the sympathetic innervation of the heart directly opposes the parasympathetic system. To be more specific, it will be increasing the heart rate as well as increasing the force of contraction of the myocardium.
Now that you just completed this video tutorial, then it’s time for you to continue your learning experience by testing and also applying your knowledge. There are three ways you can do so here at Kenhub. The first one is by clicking on our “start training” button, the second one is by browsing through our related articles library, and the third one is by checking out our atlas.
Now, good luck everyone, and I will see you next time.