Control of Heart Rate Control of Heart Rate

Control of Heart Rate Our internal systems are continuously monitored by sensors within our bodies. The autonomic nervous system controls the involuntary activity of our heart rate. The sympathetic and parasympathetic nervous systems normally oppose each other. They are antagonistic. One stimulates the effector, the other inhibits it.

Control of Heart Rate Resting heart rate = approx 70 beats per minute. This rate needs to be altered to meet varying demands of oxygen. During exercise, the heart rate can double.

Control of Heart Rate Changes to the heart rate are controlled by a region of the brain called the medulla oblongata.

Medulla Oblongata There are two centres: A centre that increases heart rate (linked to Sino atrial node by the sympathetic nervous system). CARDIOACCELERATORY CENTRE A centre that decreases heart rate (linked to the Sino atrial node by the parasympathetic nervous system). CARDIOINHIBITORY CENTRE

Control of Heart Rate Which of these centres is stimulated depends upon the information they receive from two types of receptor. The two receptors detect changes in: Chemical changes in blood (chemoreceptors) Pressure changes in blood (pressure receptors)

Control by Chemoreceptors Found in wall of carotid arteries. Sensitive to changes in pH of blood. Changes in pH are due to changes in CO2 conc. Respiring cells will release CO2 which when dissolved in blood, forms carbonic acid and lowers pH.

Control by Chemoreceptors If CO2 conc is higher than normal (due to increased muscular/metabolic activity) pH is lowered. Chemoreceptors detect this and increase the frequency of nervous impulses to medulla oblongata. This increases heart rate by sending more impulses to SAN (via sympathetic, but less via parasympathetic). Increased heart rate, increases blood flow which removes CO2 build up. CO2 conc drops to normal levels.

Control by Pressure Receptors Occur within walls of carotid arteries and aorta. Detect changes in blood pressure. If pressure is higher than normal, impulses sent to MO, then centre of MO sends more impulses via parasympathetic nerve (but less via sympathetic system) to SAN. This decreases heart rate.

Control by Pressure Receptors If blood pressure is lower than normal, receptors send impulses to centre of MO. This then sends more impulses to SAN via sympathetic nervous (but less via parasympathetic system). This increases heart rate.

http://msjensen. cehd. umn http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0031-swf_chemoreceptor_.swf

Summary Questions What is the function of the autonomic nervous system? Distinguish between the functions of the sympathetic and parasympathetic nervous systems. Suppose the parasympathetic nerve connections from the medulla oblongata to the SAN were cut. Suggest what might happen if a person’s blood pressure increased above normal. The nerve connecting the carotid artery to the medulla oblongata of a person is cut. This person then undertakes some strenuous exercise. Suggest what might happen to the person’s: Heart rate Blood carbon dioxide concentration Explain your answers