14.5 - Control Of Heart Rate Flashcards
What is the role of the autonomic nervous system in controlling involuntary actions?
- The autonomic nervous system controls involuntary (subconscious) activities of internal muscles and glands.
- Divided into two components:
1) Sympathetic nervous system: Stimulates effectors, speeds up activity, prepares for fight or flight.
2) Parasympathetic nervous system: Inhibits effectors, slows activity, conserves energy, and restores the body during rest. - These systems are antagonistic, working to balance each other.
How does the heart generate its own rhythm?
- The heart is myogenic: it initiates contraction from within its muscle (cardiac muscle), not relying on external nervous signals.
- Key structure: Sinoatrial Node (SAN), located in the right atrium.
- Acts as the pacemaker by generating a wave of electrical excitation.
- This wave determines the heart’s rhythm.
Outline the sequence of events controlling heart contractions.
1) Wave of depolarisation originates in the SAN, spreading across both atria, causing them to contract.
2) A non-conductive layer (atrioventricular septum) prevents the wave from passing to ventricles.
3) The wave reaches the Atrioventricular Node (AVN), which delays the signal briefly.
4) The AVN passes the signal down the Bundle of His into the atrioventricular septum.
5) The Bundle of His branches into Purkyne tissue, spreading the excitation to the ventricles.
6) Ventricles contract from the base upward, ensuring efficient blood pumping
How does the medulla oblongata regulate heart rate?
- The medulla oblongata acts as the coordinator and contains two centers:
1) Center increasing heart rate: Connected to SAN via the sympathetic nervous system.
2) Center decreasing heart rate: Connected to SAN via the parasympathetic nervous system. - Stimuli from chemoreceptors and pressure receptors determine which center is activated.
Explain how chemoreceptors regulate heart rate in response to CO₂ levels.
1) High CO₂ concentration lowers blood pH.
2) Chemoreceptors in carotid arteries/aorta detect low pH, sending impulses to the medulla’s center that increases heart rate.
3) Medulla increases sympathetic impulses to the SAN, raising heart rate.
4) Faster heart rate increases blood flow to lungs, removing CO₂.
5) pH returns to normal, chemoreceptors reduce impulse frequency, and heart rate decreases
—> if this isn’t sorted, could denature enzymes
What is the role of pressure receptors in heart rate control?
1) High blood pressure: Pressure receptors in carotid arteries/aorta send impulses to the medulla’s center that decreases heart rate. Parasympathetic impulses slow down SAN activity.
2) Low blood pressure: Pressure receptors signal the medulla’s center to increase heart rate. Sympathetic impulses stimulate SAN to raise heart rate.
—> if this isn’t sorted it could cause damage to walls of artery
What are the functions of the sympathetic and parasympathetic nervous systems in regulating heart rate?
1) Sympathetic Nervous System:
- Stimulates SAN to increase heart rate during exercise or stress.
- Prepares body for action (fight or flight).
2) Parasympathetic Nervous System:
- Reduces SAN activity, slowing heart rate.
- Active during resting states to conserve energy.
Why is the SAN referred to as the heart’s pacemaker?
- The SAN sets the rhythm of the heart by generating regular electrical impulses.
- These impulses trigger atrial contraction and coordinate the cardiac cycle.
Explain how heart rate is increased during exercise.
During exercise:
- Increased muscular activity raises carbon dioxide levels in the blood.
- Higher CO₂ forms carbonic acid, lowering blood pH.
- Chemoreceptors in the carotid arteries and aorta detect the drop in pH and send impulses to the medulla oblongata (cardiac center).
- The medulla stimulates the sympathetic nervous system, which sends impulses to the sinoatrial node (SAN).
- The SAN increases the frequency of electrical impulses, raising heart rate.
- Increased blood flow delivers more oxygen to muscles and removes CO₂ faster, restoring pH to normal
Describe how chemoreceptors and pressure receptors work together to control heart rate.
1) Chemoreceptors:
- Located in the carotid arteries and aorta.
- Detect changes in blood pH caused by CO₂ levels.
- High CO₂ (low pH): Stimulate the medulla to increase heart rate via the sympathetic nervous system.
- Low CO₂ (high pH): Stimulate the medulla to decrease heart rate via the parasympathetic nervous system.
2) Pressure receptors:
- Also located in the carotid arteries and aorta.
- Detect changes in blood pressure.
- High blood pressure: Stimulate the medulla to decrease heart rate (parasympathetic response).
- Low blood pressure: Stimulate the medulla to increase heart rate (sympathetic response).
——> Together, these receptors maintain homeostasis, balancing oxygen delivery and blood pressure.
What is the role of the sympathetic nervous system in heart rate regulation?
The sympathetic nervous system:
- Stimulates the sinoatrial node (SAN).
- Increases the frequency of electrical impulses generated by the SAN.
- Causes the heart to contract more rapidly and with greater force.
- Prepares the body for fight or flight by increasing oxygen and nutrient delivery to tissues.
Why is cardiac muscle described as myogenic?
- Cardiac muscle is described as myogenic because its contraction is initiated from within the muscle itself.
- The sinoatrial node (SAN) generates electrical impulses spontaneously without requiring nervous system stimulation.
- This property allows the heart to beat independently of external signals, although the nervous system can modify its rate
Outline the sequence of events that controls the basic rhythm of the heartbeat.
- Sinoatrial node (SAN) in the right atrium generates a wave of electrical excitation.
- This spreads across the atria, causing them to contract.
- A layer of non-conductive tissue prevents the wave from passing to the ventricles.
- The wave reaches the atrioventricular node (AVN), which delays it slightly.
- The AVN sends the wave down the bundle of His, located in the ventricular septum.
- The bundle of His branches into Purkyne fibers, which carry the wave to the base of the ventricles.
- The excitation spreads from the base upwards, causing the ventricles to contract simultaneously.
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Yes
