BIOL355 Lecture Notes - Lecture 30: Sympathetic Nervous System, Vagus Nerve, Sinoatrial Node
21 Apr 2017
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Document Summary
Major contributing factor is a decrease in hr. Decrease in maximum heart rate (exercise) by about 25% - this decrease is not affected by physical conditioning. Sa node initiates beat at 100 beats/min but parasympathetic slows down to 70. Done through hypothalamus to vagus nerve to control sa to slow down hr. Baroreceptors in aorta and carotid arteries monitor blood pressure. Primary control of resting hr (little on co) Heart rate is controlled by both parasympathetic and sympathetic pathways. Sympathetic nerves of spine stimulate adrenal glands to release epinephrine and norepinephrine (adrenaline and noradrenaline) These hormones cause an increase in hr and heart contractility. Have major effect on co (little effect on resting hr) If blood pressure increases will feedback to inhibit the sympathetic nerves and stimulate parasympathetic will slow down hr and drops blood pressure. May be due to a decrease in sensitivity of aging myocardium to sympathetic stimulation.
