Final answer:
Alterations to cardiac rate are referred to as positive or negative inotropic effects, which relate to the heart's contraction strength. Sympathetic and parasympathetic stimulations are respectively associated with positive and negative inotropy. Factors like body temperature and electrolyte levels also influence these effects.
Step-by-step explanation:
Alterations to cardiac rate are termed positive or negative inotropic effects. These effects are related to the strength of the heart's contractions. Sympathetic stimulation is considered a positive inotrope, which increases the heart rate (HR) and the force of contraction. This is due to the release of neurotransmitters like norepinephrine (NE) and epinephrine, which bind to alpha and beta receptors on the cardiac muscle cell membrane, enhancing metabolic rate and contractility. Conversely, parasympathetic stimulation is a negative inotrope, reducing HR and the strength of contraction through the release of acetylcholine (ACh) from the vagus nerve, leading to hyperpolarization of the cardiac cell membrane and inhibition of contraction. In addition, factors such as body temperature and the presence of electrolytes like sodium and potassium can influence these inotropic effects on the heart.
The P wave is a component of the electrocardiogram (ECG) that represents the depolarization of the atria, and the pacemaker is a cluster of specialized myocardial cells in the sinoatrial (SA) node that initiates the sinus rhythm. The balance and modulation of these two nervous systems—sympathetic and parasympathetic—as well as other factors like body temperature, nicotine, and electrolyte levels, are essential for maintaining a healthy cardiac function.