The autonomic nervous system plays a vital role in the regulation of blood pressure throughout the body. Specialized receptors sensitive to changes in arterial diameter are located at various strategic locations within the upper thoracic cavity and neck. These specialized nerve clusters are commonly known as arterial baroreceptors. Substantial groupings of such baroreceptors can be found at the arch of the aorta and in the internal carotid arteries (just distal to where the common carotid bifurcates). This focal density of carotid baroreceptors is also termed the carotid sinus. The majority of such receptors are located in areas within these arteries where the walls decrease in thickness, enabling pressure changes to be somewhat magnified at these locations (Fig. 3).
Under even minimal pressure increases, these large arteries will elicit detectable wall dilations. In contrast, under decreased pressure, the internal diameter will decline, also resulting in a change of firing frequency of these receptors. The axons of these afferent neurons travel from baroreceptors along para-sympathetic corridors to the medullary cardiovascular center in the brain stem. Under increases in the mean pressure detected by these arterial baroreceptors, efferent sympathetic stimulation will decrease, which is accompanied by an increase in parasympathetic outflow to the heart. This neural activity is intended to return the mean pressure to a normal state. The opposite autonomic response would commence if the mean arterial pressure at the baroreceptor locations decreased. The
synergistic functioning briefly noted here between both divisions of the autonomic nervous system is discussed in much greater detail in Sections 6 through 10.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.