The cardiac muscle cells of the heart (called the myocardium) are tightly bound together in layers and encircle the blood filled chambers of the heart. When the heart contracts the myocardium encloses on the blood filled chambers and blood is propelled around the body. With greater filling of blood (i.e. increased end diastolic volume; EDV) the force of contraction of the heart is subsequently greater. Experiments in the late 19th century, using frog hearts, demonstrated this ability of the heart, known as the Frank-Starling Law of the heart, named after Otto Frank and Ernest Starling.
The heart requires a number of important resources to carry out its role. Calcium, oxygen and adrenaline are all required for normal functioning and any changes in their levels can affect the force of contraction.
This simulation examines factors that control the Contraction of Cardiac Muscle. The "data" you will collect is "real" data, taken from recordings made of the test conditions you will see in this simulation, done in previous years. This practical uses isolated strips of toad ventricular muscle that are electrically stimulated to contract. The force of cardiac muscle contraction is recorded (with grams of tension of the Y axis and time in seconds on the X axis of the recording).
Watch the video below before commencing with the simulation:
Effects of adrenaline and nifedipine on the force of contraction
Adrenaline is a hormone and neurotransmitter produced by the adrenal medulla. It plays an important role in the normal activity of the heart, modulating the rate and force of cardiac contractions. It does this by activating beta-adrenoceptors in the cardiac muscle cell membrane.
Nifedipine modulates the force of cardiac muscle contraction by blocking voltage-dependent calcium channels in the cell membrane.
- Press the Start button and observe your recording.
- After a few seconds select the Adrenaline solution from the dropdown box. Click the Add drug button and record your observations. What happens to the force of contraction (tension)?
- Repeat this process using the drug nifedipine. What effect is this drug having on the force of contraction?
Adrenaline & nifedipine simulation
Mobile Support Warning
This simulation was designed with a desktop interface in mind, and may not function correctly on smaller screens or mobile devices.
Full instructions can be found on the previous tab. In short:
- Press the Start button to start recording.
- After 100 seconds select the Adrenaline solution from the dropdown box and click the Add drug button.
- Once the recording has stabilised, repeat the process with the drug Nifedipine.