Control of heart rate Flashcards
Define myogenic
Contraction and relaxation of heart able to happen without signals from nerves
State the name and location of the 2 nodes involved in heart contraction
SAN node~ within the walls of right atrium
AVN~ near lower end of right atrium
What is the role of the Sinoatrial Node (SAN) in controlling heart rate?
The Sinoatrial Node (SAN) is the pacemaker of the heart, located in the right atrium.
It generates electrical impulses that initiate the contraction of the heart.
The impulse spreads across the atria, causing them to contract and move blood into the ventricles.
How does the Autonomic Nervous System (ANS) influence heart rate?
The ANS has two branches that influence heart rate:
Sympathetic Nervous System: Increases heart rate by releasing noradrenaline to stimulate the SAN.
Parasympathetic Nervous System: Decreases heart rate by releasing acetylcholine to slow down the SAN’s activity.
The balance between these two systems regulates the heart rate to meet the body’s needs.
How do baroreceptors help control heart rate?
Baroreceptors are pressure-sensitive receptors found in the walls of blood vessels (e.g., aorta, carotid arteries).
They detect changes in blood pressure. If blood pressure is too high, baroreceptors send signals to the medulla, which activates the parasympathetic nervous system to lower heart rate.
If blood pressure is too low, the sympathetic nervous system is activated to increase heart rate.
How do chemoreceptors regulate heart rate?
Chemoreceptors detect changes in the concentration of carbon dioxide (CO₂), oxygen (O₂), and pH in the blood.
High CO₂ levels or low pH (acidic conditions) trigger chemoreceptors to signal the medulla, which increases heart rate to pump more blood to the lungs for gas exchange.
Low O₂ levels also stimulate chemoreceptors, leading to an increased heart rate.
Exam Question:
Explain how the nervous system controls heart rate in response to changes in blood pressure
The baroreceptors in the carotid arteries and aorta detect changes in blood pressure. If blood pressure is too high, they send signals to the medulla, which activates the parasympathetic nervous system, decreasing heart rate. If blood pressure is too low, the sympathetic nervous system is activated to increase heart rate.
The heart rate of an organism is controlled by both intrinsic and extrinsic factors. Using your knowledge of the nervous and hormonal control of heart rate, describe how the heart rate is regulated and explain the roles of different receptors and effectors involved.
[6 marks]
The Sinoatrial Node (SAN), located in the right atrium, acts as the natural pacemaker of the heart. It generates electrical impulses that initiate the contraction of the heart muscle. These impulses spread through the atria, causing atrial contraction and setting the basic rhythm of the heart.
Extrinsic Control - Autonomic Nervous System (2 marks):
The autonomic nervous system (ANS) regulates heart rate through the sympathetic and parasympathetic nervous systems.
Sympathetic Nervous System (1 mark): Stimulates the heart rate by releasing noradrenaline, which increases the rate of impulse generation in the SAN and enhances the force of contraction.
Parasympathetic Nervous System (1 mark): Slows the heart rate by releasing acetylcholine, which reduces the rate of SAN firing and decreases the force of contraction.
Role of Receptors - Baroreceptors and Chemoreceptors (2 marks):
Baroreceptors (1 mark): Found in the aorta and carotid arteries, these receptors detect changes in blood pressure. If blood pressure is too high, they send signals to the medulla, triggering a parasympathetic response (lowering heart rate) to reduce blood pressure. If blood pressure is too low, the sympathetic nervous system is activated, increasing heart rate to raise blood pressure.
Chemoreceptors (1 mark): Located in the aorta and carotid arteries, chemoreceptors detect changes in CO2 levels, pH, and oxygen concentration. High CO2 or low pH (acidity) signals the need for an increased heart rate to deliver more oxygen and remove CO2. If oxygen levels are low, chemoreceptors also stimulate an increased heart rate.
Effectors - Heart Muscle (1 mark):
The effectors are the cardiac muscle cells in the heart. The signals from the autonomic nervous system affect the pacemaker cells in the SAN, which adjust the rate of impulse generation, controlling the heart rate accordingly.
