Question

Which group of pacemaker cells is responsible for setting the heart rate in a healthy patient? Write a flow diagram (eg: structure A --> structure B --> structure C, etc.) to describe the path that an action potential would take as it makes its way through the electrical conduction system of the heart, being sure to name all structures. What structure enables action potentials to directly spread between neighbouring cardiomyocytes? Be specific.

Answer 1

1. The SA node is the natural pacemaker of the heart. The SA node gives off electrical impulses to generate a heart beat in the range of 60 to 100 times per minute.

2. Conduction system of the heart

Structure 1 -   SINOATRIAL NODE      - situated in the upper wall of the right atrium ( transmits message to right atrium and left arium)

Structure 2 - INTERNODAL ATRIAL PATHWAY - message from the SA node passes to the AV node via this

Structure 3 - ATRIOVENTRICULAR NODE - situated in the interatrial septum near the coronary sinus ( transmits messages from the atria to the ventricles)

Structure 4 - A V BUNDLE - situated in the anterior inferior end of the interatrial septum ( transmits messages to the ventricles)

Srtucture 5 - BUNDLE BRANCHES - Right and left . Located along the interventricular septum

Structure 6 - PURKINJE SYSTEM - located in the inner ventricular walls of the heart, just beneath the endocardium.

Structure 7 - VENTRICULAR SYNCTIUM - located at the point between the atria and the ventricles.

Intercalated disc are structures that connects the cardiomyocytes. There are three types of cell junction in intercalated disc. They are

• Fascia adherens
• Desmosomes
• Gap junctions - they allow the action potential to spread between the cardiac cells by permitting passage of ions between cells causing depolarization of the heart muscles.