Final answer:
The heart is under control of the autonomic nervous system, with the medulla oblongata's cardiovascular center modulating heart activity via sympathetic and parasympathetic stimulations. The sympathetic system can increase heart rate through cardioaccelerator nerves, and the parasympathetic system can decrease heart rate via the vagus nerve, maintaining cardiovascular homeostasis.
Step-by-step explanation:
The heart is under the control of the autonomic nervous system (ANS). The ANS has two main divisions: the sympathetic and parasympathetic nervous systems. The heart's rhythmic activity is primarily modulated by these systems via the medulla oblongata in the brain. During rest, both the sympathetic and parasympathetic systems supply slight stimulation known as autonomic tone, which is similar to the tone in skeletal muscles. Usually, the parasympathetic stimulation, which is a component of the vagus nerve (cranial nerve X), predominates, reducing the heart rate from its intrinsic rate established by the sinoatrial (SA) node. The cardiovascular center within the medulla contains nuclei that exert control over the heart by sending signals through the autonomic connections. The sympathetic component, which includes the cardioaccelerator nerves, can increase heart rate and force of contraction, while the parasympathetic fibers, part of the vagus nerve, can decrease heart rate. All these processes are important in maintaining the homeostasis of the cardiovascular system, and they adjust according to the body's needs, such as during stress, rest, or physical activity.
Moreover, the sympathetic nervous system has a significant effect on blood pressure regulation by controlling the contraction of smooth muscle in the walls of blood vessels, primarily through adrenergic receptors which respond to norepinephrine and epinephrine. These hormones, released from the adrenal medulla, contribute to the control of vascular tone by causing constriction of the blood vessels, hence increasing blood pressure. The sympathetic nervous system also controls the tone of systemic blood vessels as the parasympathetic system has no significant input in this regulation.