Myogenic stimulation of the heart and transmission of a subsequent wave of…

The idea

Cardiac muscle is myogenic: it contracts rhythmically without nerve impulses. The intrinsic rhythm originates in the sinoatrial node (SAN) in the right atrium, which depolarises spontaneously to set the basic heart rate. A wave of depolarisation spreads across both atria, causing atrial systole. Cardiac muscle cells are electrically coupled via gap junctions, allowing ions to pass directly. A band of non-conducting connective tissue between the atria and ventricles prevents the wave passing straight down. Consequently, ventricular contraction only begins after the wave is routed through the atrioventricular node (AVN).

What earns the marks

• Cardiac muscle is myogenic, contracting without stimulation by nerve impulses.
• The sinoatrial node acts as the pacemaker, originating the wave of electrical activity.
• A wave of depolarisation spreads across both atria, stimulating them to contract.
• Non-conducting tissue between atria and ventricles prevents the wave passing directly downwards.
• The autonomic nervous system alters the rate of the heartbeat rather than initiating it.

Common mistakes and how to put them right

• Using vague terms like 'message' or 'signal' instead of 'wave of depolarisation' or 'impulses'.

• Saying the brain initiates each heartbeat, rather than modifying the baseline myogenic rate.

• Describing the wave as travelling along nerves inside the heart rather than passing between muscle cells.

Exam tips

• Define myogenic clearly as contracting without nerve stimulation to secure foundational marks.
• Use precise terminology such as 'wave of depolarisation' and avoid vague terms like 'signal'.