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Control of heart rate WAL: An overview of how the heart rate is controlled What role do chemical and Some pressure receptors play in the process? How does the autonomic nervous Most system control heart rate? All What is the autonomic nervous system? Starter – If the hormonal system and nervous system had a fight who would win and why? Today we are covering from the specification: Pages 147-149 of your textbook The Nervous System Divided into two systems: 1. The CNS – brain and spinal cord 2. The Peripheral Nervous System (PNS) – pairs of nerves Nervous system Nervous system Peripheral Nervous system Central Nervous system Brain Sensory system Spinal cord Motor system Voluntary system Sympathetic Autonomic system Parasympathetic Control of Heart Rate Autonomic Sympathetic Positive stimulation (speed up activity) Parasympathetic Inhibitory (slows down activity) Control of heart rate Heart rate is controlled by the part of the brain called the medulla oblongata Has two centres: 1.Increases heart rate linked to the sinoatrial node by the sympathetic nervous system 2.Decreases heart rate linked to the sinoatrial node by the parasympathetic nervous system The centre that is stimulated depends on: •Chemical changes in the blood •Pressure changes in the blood Control by chemoreceptors Found in the walls of the carotid artery Sensitive to changes in the pH of the blood that result from changes in carbon dioxide concentration. (In solution CO2 forms an acid) Control by chemoreceptors 1) When the blood has a higher than normal concentration of CO2, pH decreases. 2) Chemoreceptors in the wall of the carotid arteries and the aorta detect this and increase the frequency of nervous impulses to the centre in the medulla oblongata that increases heart rate. 3) This centre increases the frequency of impulses via the sympathetic nervous system to the sinoatrial node, increasing heart rate. Control by chemoreceptors 4) The increased blood flow that this causes leads to more CO2 being removed in the lungs and so the CO2 levels return to normal 5) As a consequence the pH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and aorta reduce the frequency of nerve impulses to the medulla oblongata. 6) The medulla oblongata reduces the frequency of impulses to the sinoatrial node, which therefore decreases the heart rate to normal. Control by pressure receptors Pressure receptors occur within the walls of the carotid arteries and the aorta. They operate as follows: When a blood pressure is higher than normal: 1) They transmit a nervous impulse to the centre of the medulla oblongata that decreases heart rate. 2) This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, decreasing heart rate. Control by pressure receptors Pressure receptors occur within the walls of the carotid arteries and the aorta. They operate as follows: http://www.youtube.com/watch?v=G2nLL_O_U7w When a blood pressure is lower than normal: 1) They transmit a nervous impulse to the centre of the medulla oblongata that increases heart rate. 2) This centre sends impulses via the sympathetic nervous system to the sinoatrial node of the heart, increasing heart rate. Modifying heartbeat Carotid artery Chemo receptors Pressure receptors hypothalamus Sinoatrial node medulla Atrioventricular node Cardioinhibitory centre Cardioacceleratory centre Human circulation Control of heart rate WAL: An overview of how the heart rate is controlled What role do chemical and Some pressure receptors play in the process? How does the autonomic nervous Most system control heart rate? All What is the autonomic nervous system? Plenary– Answer the questions on page 149