Conduction System Flashcards
Define a heart beat
It is when cardiac fibres undergo rhythmic contraction without external stimulus
What is the origin of the heart beat?
It is muscular (myogenic) rather than neural (neurogenic)
What is the innervation of the myocardium necessary?
It is necessary for efficient and appropriate response to changing situations
What is the sinoatrial node?
Where is the SA node?
The sinoatrial (SA) node has the highest rate and therefore is the pacemaker of the heart.
It is situated in the right atrial myocardium near the junction with the cranial vena cava.
How are the SA nodes regulated?
They are regulated by the sympathetic Adrian nerve fibres and right vagal. The Adrian fibres increase rate of discharge and right vagal which are parasympathetic nerve fibres, decrease rate of discharge.
How do electrical impulses move from the SA node?
The wave of electrical impulses spread over the atria by electrical coupling between cardiac muscles cells which cause them to contract during atrial systole
What is the atrioventiclar node?
Where is the AV node?
This has the second highest frequency of discharge.
It is situated in the right ventral region of the intertribal septum which is above the entry of the coronary sinus
How is the AV node different to the SA node?
The AV node has small fibres which delays the spread of depolarisation until the atrial systole is complete. The AV node receives innervation predominately from the left vagal nerve.
How do electrical impulses move from the AV node?
paid conduction of electrical impulses spread from the AV node via the AV bundle, which divides into left and right branches, spreads throughout the ventricular myocardium from the apex as Purkinje fibres.
How does trabecular septomarginalis affect electrical impulses?
They also carry Purkinje fibres to aid in the coordination and rapid spread of the electrical impulses to the ventricles.
How does the fibrous skeleton affect electrical impulses?
The fibrous skeleton of the heart prevents the passage of electrical stimuli directly from the atria to the ventricles except where it is penetrated by specialised fibres of the atrioventricular bundle
How is the ventricular contraction distributed from the AV bundle?
It spreads in the following order:
- interventricular septum and papillary muscles
- apex of ventricle
- base of ventricle
Overall the contraction is a wringing pattern, from the apex forward which is forcing the blood up and out of the ventricle
What efferent nerves affect the heart?
Adrenergic sympathetic cardiac nerves = increase heart rate and force contractions
Parasympathetic supply via cardiac branches of vagal and recurrent laryngeal nerves = decrease heart rate
Sympathetic and parasympathetic branches of the cardiac nerves join to form a cardiac plexus ventral to the bifurcation of the trachea, caudal and lateral to the arch of the aorta and around branches of the pulmonary trunk at the bifurcation
what afferent nerves affect the heart?
The afferent fibres are carried from the heart in the same nerves which carry efferent supply = the cardiac branches of the vagus and cardiac nerves
