Heart rate persons with coronary artery disease. The heart rate is rhythmically generated by the sinoatrial node. It is also influenced by central factors through sympathetic and parasympathetic nerves. Nervous influence over the heartrate is centralized within the two paired cardiovascular centres of the medulla oblongata. The cardioaccelerator regions stimulate activity via sympathetic stimulation of the cardioaccelerator nerves, and the cardioinhibitory centers decrease heart activity via parasympathetic stimulation as one component of the vagus nerve. During rest, both centers provide slight stimulation to the heart, contributing to autonomic tone. This is a similar concept to tone in skeletal muscles. Normally, vagal stimulation
The Heart Part 4 fourth installment in Lamar's "The Heart" song series. "The Heart Part 1" was released as a loose track in April 2010, while "Part 2" was featured on Lamar's "Overly Dedicated" mixtape, released later that same year. "Part 3," featuring Ab-Soul and Jay Rock, preceded the release of "good kid, m.A.A.d city" in 2012. He finishes the song with the line, "Y'all got til April the 7th to get y'all shit together", hinting at the release date for his fourth album (the date turned out to be the day pre-orders opened and the release date was announced to be April 14).