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The heart rate is the number of time the heart beats per minute. Normal heart rate varies from person to person. The resting heart rate is the heart pumping the lowest amount of blood needed, it is said that the normal resting heart rate for adult’s ranges from 60 to 100 beats per minute. However, this can easily increase during exercise. The heart rate is controlled by nervous system, when at rest or during physical activity. This is due to the autonomic nervous system in the peripheral nervous system.
In the sympathetic division, the hormone norepinephrine causes arteries to contract, forcing the blood to flow through at a faster rate. Thus, increasing the heart rate and the strength of each pump. However, in the parasympathetic division, the hormone acetylcholine slows the heart rate by performing the opposite.
During extended periods of exercise, sympathetic nerves, transmit nerve impulses from the medulla oblongata in the brain to the heart. The heart responds by increasing the frequency and force of contractions. When exercising strenuously, muscle cells use up tremendous amounts of oxygen and CO2 is produced. The build-up concentration of CO2 in the muscles is detected by the receptors in the aorta and carotid arteries of the heart, and is then passed on to the medulla oblongata in the brain via nerve impulses along neurons. Furthermore, the more the muscle contracts during exercise, the more blood is sent to the right atrium of the heart. As the atrium receives all this blood, it must stretch to adapt to the blood pressure. In this case, the stretch receptors in the heart muscle pass on this information via nerve impulses to the medulla oblongata in the brain. This information being transmitted across the neurons in form of nerve impulses, causes the activation of the pathway that will increase the heart rate, as a result relieving the full atrium and removing excess CO2 via lungs.

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