Overview
This lecture explains how the brain and heart interact to control heart rate through neural, hormonal, and intrinsic mechanisms during exercise and recovery.
Brain-Heart Connection
- The medulla oblongata, located at the base of the brain, contains the cardiac control center.
- The medulla connects to the heart’s sinoatrial (SA) node (pacemaker) via neural pathways.
- Two nervous pathways influence heart rate: sympathetic (increases rate) and parasympathetic (decreases rate).
- Sympathetic control uses the accelerator nerve to stimulate the SA node and speed up heart rate.
- Parasympathetic control uses the vagus nerve to slow down heart rate.
Neural Control Mechanisms
- Chemoreceptors in the blood and brain detect changes in blood acidity (pH).
- During exercise, a decrease in pH (increase in acidity) triggers sympathetic stimulation to increase heart rate.
- During recovery, an increase in pH (decrease in acidity) triggers parasympathetic stimulation to decrease heart rate.
- Baroreceptors in the brain monitor blood pressure changes.
- Increased blood pressure stimulates the sympathetic system; decreased pressure triggers parasympathetic response.
- Proprioceptors (mechanoreceptors) in muscles and tendons detect movement and tension, signaling the medulla to increase heart rate during exercise.
Hormonal Control
- Adrenaline (epinephrine) is released in anticipation of or during exercise.
- Adrenaline acts directly on the SA node to increase heart rate, independent of the brain.
Intrinsic Control
- The heart senses internal changes such as temperature and contractility (changes in venous return).
- Increased heart temperature or greater venous return causes the heart to contract more frequently.
Key Terms & Definitions
- Medulla Oblongata — brain region that regulates cardiovascular function.
- Sinoatrial (SA) Node — the heart's pacemaker, initiates heartbeat.
- Sympathetic Nervous System — increases heart rate via the accelerator nerve.
- Parasympathetic Nervous System — decreases heart rate via the vagus nerve.
- Chemoreceptors — sensors for blood acidity (pH).
- Baroreceptors — sensors for blood pressure.
- Proprioceptors — sensors in muscles/tendons for movement/tension.
- Adrenaline — hormone that increases heart rate.
- Contractility — heart's ability to contract more forcefully in response to greater filling (venous return).
Action Items / Next Steps
- Learn and differentiate the roles of chemoreceptors, baroreceptors, and proprioceptors.
- Remember which changes (increase/decrease) each receptor type detects during exercise and recovery.
- Review the pathways and effects of sympathetic and parasympathetic stimulation on heart rate.