What effect do signals from the medulla to the heart through sympathetic nerves have?

Signals from the medulla to the heart via sympathetic nerves are primarily responsible for increasing both heart rate and the strength of contractions. This response is part of the body’s "fight or flight" mechanism, where adrenaline (epinephrine) is released, stimulating the sympathetic nervous system. The sympathetic nerves increase the release of catecholamines, which bind to beta-adrenergic receptors in the heart.

This interaction results in several physiological changes, such as an increase in the heart rate (positive chronotropic effect) and enhanced force of contraction (positive inotropic effect). This is essential during situations that require increased blood flow and oxygen delivery to vital organs and muscles, such as physical exertion or stress. Thus, the increase in both heart rate and contraction strength effectively prepares the body for immediate action.