Regulation of the HUMAN BODY: The Brain’s Contribution
Control of the human body and its ability to adapt to exercise training is regulated by the central nervous system. Within the brain is a center known as the central command, which is responsible for recruiting muscles for physical activity, coordinating the heart’s response and determining the body’s response to an increase in physical demands. The central command regulates these functions through the sympathetic and parasympathetic components of the autonomic nervous system. They are responsible for promoting or inhibiting the desired actions of the heart and skeletal muscles. At rest, the parasympathetic system predominately influences the control of tissues and organs to remain in a ‘normal’ state and conserve energy. it is considered to be the anabolic, or builder, of the body’s systems. Conversely, the sympathetic system predominates with the onset of exercise. This causes the parasympathetic system to withdraw and allows for the heart to accelerate, lungs to relax and increase airflow, energy from stored fat and carbohydrate to break down and muscles to contract. The sympathetic system is considered to be catabolic in nature as it prepares the body to take on any stimuli, exercise or other element that is presented to the body.
Central command responds to extrinsic and intrinsic signals that provide feedback on the function of the body’s systems. Within the brain, it is believed that a ‘governor’ exists that protects the body from too great of an exercise (or other) stimulus. Extrinsic regulators during exercise include hormones, the ph (acidity or alkalosis) of the blood, body temperature and other peripheral mechanical and chemical ‘messengers’ that circulate in the blood. Intrinsic regulators include alterations in brain chemistry and feedback from motor neurons of the muscle that indicate how well a tissue is handling the bout of exercise. The brain’s ability to integrate all of the inputs received from the body determines an individual’s exercise capacity. Together, these inputs determine the amount of work the skeletal muscles can perform and therefore control the response of the cardiopulmonary system.