During routine operation, the heart operates in a cycle that aims to pump blood throughout the body. As Hall et al. (2018) describe it, two phases take place as the liquid moves through the heart’s four chambers: systole, where the ventricles contract and eject blood into the aorta and pulmonary artery, and diastole, where they relax and are filled with blood. The process takes place in a steady fashion and adjusts its speed depending on the activities in which the person is currently engaged. For most non-demanding tasks, the heart rate stays close to its resting value, with the heart exerting itself as little as possible.
However, being surprised by the neighbor provokes a response of fear and surprise in the person. Per Psychogios and Dimitriadis (2016), the two share initial signals and are characterized, in particular, by high amounts of serotonin and dopamine being secreted, with surprise also linked to noradrenaline production. In regard to the heart, Herlihy (2017) claims that the sympathetic nervous system activates in times of stress and increases the rate and strength of the heart’s contractions. The fight-or-flight response activates temporarily until the person can recognize that there is no danger at present.
With that said, the heart is characterized by dual innervation, and once this recognition has taken place, the parasympathetic system takes effect. Herlihy (2017) states that the heart demonstrates a classic example of an antagonistic relationship between the two nervous system types, with the parasympathetic response causing the heart to contract slower (but not affecting strength directly). As such, the heart returns to its normal operation eventually, maintaining homeostasis in this manner. Both of the systems linked are part of the autonomic nervous system (ANS), which cannot be consciously controlled. Its consciously controlled counterpart is the somatic nervous system, which receives sensory inputs and innervates skeletal muscles (Derrickson & Tortora, 2018). It does not innervate the heart and, therefore, does not control its operations directly, though exertion can affect its operation indirectly.
References
Derrickson, B. H., & Tortora, G. J. (2018). Principles of anatomy and physiology (15th ed.). Wiley.
Hall, A., Perry, A. G., Potter, P. A., & Stockert, P. (2018). Essentials for nursing practice (9th ed.). Elsevier Health Sciences.
Herlihy, B. (2017). The human body in health and illness (6th ed.). Elsevier Health Sciences.
Psychogios, A., & Dimitriadis, N. (2016). Neuroscience for leaders: A brain adaptive leadership approach. Kogan Page.