What occurs in cardiac tissue in response to stimulation of muscarinic receptors?

Stimulation of muscarinic receptors, which are part of the parasympathetic nervous system, leads to a decrease in heart rate and contractility in cardiac tissue. These receptors primarily respond to the neurotransmitter acetylcholine and are predominantly located in the heart, particularly in the atria.

When muscarinic receptors are stimulated, they promote the opening of potassium channels and cause hyperpolarization of cardiac pacemaker cells, resulting in a slower heart rate. This effect is known as negative chronotropy. Additionally, the stimulation reduces the force of contraction within the heart muscle, known as negative inotropy. This overall response translates to a decrease in both heart rate and contractility, which is the body's mechanism for conserving energy and reducing workload under resting conditions or during a relaxed state.

In summary, the correct answer reflects the physiological effects of muscarinic receptor activation in cardiac tissue, which results in decreased heart rate and contractility. This contrasts with the other options, which relate to different physiological systems or responses that do not occur as a direct response to muscarinic receptor stimulation in the heart.