The Heart Electricity

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❤️ The Biophysics of the Beating Heart

Our heart beats because it is triggered by electrical impulses generated by the sinoatrial (SA) node in the right atrium, creating a rhythm for the heartbeat.

Heart signals arise from a resting potential (nearly -70mV) and create what we know as an action potential (-55mV or -65mV depending on cell type). This is the electrical potential difference across the cell membrane, much like in a neuron or muscle cell. This rise is caused by the movement of ions — mainly sodium (Na⁺), calcium (Ca²⁺), and potassium (K⁺) — across cell membranes.

Once an action potential is formed, it propagates through the heart. After the impulse is generated in the SA node, it spreads through the atria, pauses at the atrioventricular (AV) node, then travels via the bundle of His and Purkinje fibers to contract the ventricles.

We can detect this electrical activity through an electrocardiogram (ECG), which records voltage changes across the skin. This is a crucial medical tool for diagnosing heart rhythm disorders — an application of biophysics in medicine.

🧪 Fun Experiment: Measuring Your Heart Rate

Materials:

  • A timer (stopwatch, phone, or clock with seconds)
  • A notebook and pen
  • Yourself!

Steps:

  1. Find Your Pulse: Sit quietly and place two fingers (not your thumb) on your wrist or neck. Feel the steady pulse — each beat is triggered by an electrical signal from your SA node.
  2. Count Your Resting Heart Rate: Count beats for 15 seconds, then multiply by 4 to get beats per minute (BPM). Record it.
  3. Do Light Exercise: 30 seconds of jumping jacks or 1 minute jogging in place.
  4. Measure Again: Immediately check your pulse again using the same 15-second method and record your new BPM.

Optional Extension:

  • Keep measuring your pulse every minute after exercise until it returns to resting rate.
  • Plot a recovery graph to visualize how quickly your heart recovers.

📊 Final Analysis

Your increased heart rate after exercise is due to faster electrical firing from the SA node. Biophysically, your body is meeting higher oxygen and energy demands by speeding up ion exchange and action potentials in heart muscle cells.

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