Anatomy of the conduction system of the heart Flashcards
Describe the conducting system of the heart
- The heart pumps blood throughout the body, which is achieved by the contraction and relaxation of the (cardiac muscle tissue) in the (myocardium layer)
- The intercalated discs of the heart allow the impulses to travel rapidly between adjacent cells so that they function as one
- The heart is controlled by the sympathetic, parasympathetic, & the conduction system (controls the HR by creating the electrical impulses and sending them through the heart)
What is the pacemaker of the heart?
The sinoatrial node
- It contains a rich supply of autonomic nerve fibers
WHICH MYOCARDIAL STRUCTURE ALLOWA THE EART TO CONTRACT AS A UNIT?
The intercalated discs
What is the pathway of the cardiac conduction system?
1) Sinoatrial Node (SA, Initiate the impulse)
2) Atrioventricular Node (AV, connects the atria to the ventricles, delaying the impulse)
3) Bundle of Hiss (Atrioventricular bundle, Ensures that the ventricle contracts together)
4) Bundle of hiss (right and left branches, Atrioventricular bundle, Ensures that the ventricle contracts together)
5) Purkinje fibers (Atrioventricular bundle, Ensures that the ventricle contracts together)
What is the function of the SA node?
- It initiates impulses 70-80 times per minute (normally it initiates 100-110bpm), but due to the domination of the parasympathetic nerve fibers at rest it reduces it to 70-80
- It establishes the basic rhythm of the heartbeat
- The impulses move through the two atria allowing them to contract and at the same time they reach to the ventricles
Where is the Atrioventricular Node located?
- Between the atria and ventricle
- At the bottom of the right atrium near the septum just above the coronary sinus (the coronary sinus is between the IVC of the RA and the tricuspid orifice)
Describe the course of the purkijee fubers
From the
What is the function of the AV bundle and what are their branches?
They slowly conduct impulses from the AV node to the right and left sides of the septum and the bottom of the heart
Where is the SA node located?
- Back of the right atrium
- Superior ridge of cristae terminalis
- In front of the superior vena cava opening
What is the function of the Atrioventricular node?
- The delay in the sinuatrial impulse allows the atria to finish contracting before the ventricular contraction begins
What is the funtion of the purkinjee fibers?
- They innervate the papillary muscles
- They spread within the muscle wall of the ventricles, transmitting the impulses into the myocardium
- Them and the bundle of his and their branches conduct impulses quickly causing both ventricles to contract at the same time
What will happen if the conducting system of the heart is damaged?
Cardiac Arrhythmias
What is meant by a complete heart block?
When the impulse does not travel at all from the SA node and the AV node
What is the commonest cause of defective conduction of the AV bundle?
Atherosclerosis of the coronary arteries
What is the blood supply of the conduction system?
Right and left coronary artery
What is the first sign of atherosclerosis?
Arrhythmias
What is the cardiac plexus?
- It is the network of nerves supplying the heart
- It receives contributions from the right and left vagus nerves as well as the sympathetic trunk
Where is the cardiac plexus located?
- Below the arch of the aorta
Where is the location of the main control of the heart?
- Medulla oblongata (Caudal part of the brain stem), which contains the cardio-regulatory center.
- The cardio regulatory center is made up of the cardio acceleratory center and the cardioinhibitory center (in the lower part of the Medulla)
What is the function of the sympathetic nervous system?
It acts on the sinoatrial node speeding up the depolarization rate and therefore increasing the heart rate
What is the function of the parasympathetic nervous system on the heart?
- Innervated by the vagus nerve
- The speed up the repolarization of the heart rate, slowing the HR down
Does the heart need a nervous supply?
No, the sinoatrial node acts as a natural pacemaker, if all of the heart’s nervous supply it will continue to beat but faster
Describe the sympathetic nerve supply of the heart
- Sympathetic nerve exits the medulla travelling through a short myelinated preganglionic fiber till the sympathetic ganglia
- The preganglionic sympathetic fibers that innervate the heart arise from the T1-T5 segment of the spinal cord
- The postganglionic fibers terminate at the SA & AV nodes on the cardiac muscle fibers and the coronary artery
- Activation of these nerves results in a flight or fight response, increasing the HR and for of cardiac muscle contraction
- T1 can transfer the pain to the upper limb
- T2-T5 can transfer the pain to the chest wall
Describe the parasympathetic innervation (vagus nerve) of the heart
- Exits the medulla as long preganglionic efferent fibers that synapse with the short postganglionic fibers within the heart or vascular tissue
- They terminate on the SA & AV node and the coronary arteries
- The activation of the parasympathetic nerves results in the reduction of the rate and force of heart contraction and constricts the coronary arteries
