Changes In Heart Rate Flashcards
What are the three mechanisms which control the rate at which impulses are fired in the heart by the SAN (sinoatrial node)
• Sympathetic nervous system
• Parasympathetic nervous system
• Medulla oblongata
What is the sympathetic nervous system?
A part of the autonomic nervous system that speeds up heart rate.
What is the parasympathetic system?
A part of the autonomic nervous system that decreases heart rate.
What is the medulla oblongata?
The most important part of the brain as it regulates processes that keep us alive such as breathing and heart rate.
How does the sympathetic nervous system increase cardiac output?
• Increases HR by adrenaline
• Adrenaline increases the strength of ventricular contraction, thus increases stroke volume
• Noradrenaline helps the spread of electrical impulses throughout the heart, increasing HR
• Increased metabolic activity causes increased concentration of CO2 and lactic acid, decreasing pH of blood
• These changes are picked up by chemoreceptors and inform the sympathetic centre to increase HR to flush out the waste products
How does the parasympathetic nervous system slow down cardiac output?
• Releases acetylcholine, slowing the spread of impulses throughout the heart resulting in a lower HR
• This leads to less blood being pumped = lower cardiac output
How do you remember that the parasympathetic nervous system slows down the heart?
Think of a parachute slowing down a skydiver.
What do parasympathetic nerves do?
• Constrict pupils
• Stimulate saliva
• Slow heartbeat
• Constrict airways
• Stimulate activity of stomach
• Inhibit release of glucose; stimulate gallbladder
• Contract bladder
What do sympathetic nerves do?
• Dilate pupils
• Inhibit salivation
• Increase heartbeat
• Relax airways
• Inhibit activity of stomach
• Stimulate release of glucose; inhibit gallbladder
• Inhibit activity of intestines
• Secrete epinephrine and norepinephrine
• Relax bladder
What are the three receptors you need to know?
• Chemoreceptors -> increase in CO2 -> increase in heart rate
• Baroreceptors -> increase in blood pressure -> decrease in heart rate
• Proprioceptors -> increase in muscle movement -> increase in heart rate
What are the chemoreceptors and where are they found?
• Found in carotid arteries and aortic arch
• Sense chemical changes
• Exercise -> increased concentration of CO2 -> sympathetic nervous system -> increased HR
What are baroreceptors?
• Detect pressure changes due to stretching in the arterial walls (from their nerve endings)
• Set baselines for pressure
• Fluctuations about the baseline sends signals to the medulla oblongata
• Increase stretch -> decreased heart rate
• Decreased stretch -> increased heart rate
• Increased set point during exercise so heart rate doesn’t decrease
What are proprioceptors and where are they found?
• Sensory nerve endings that provide information about movement and body position
• Found in muscles, tendons and joints
• Exercise -> impulse to medulla -> sympathetic nervous system -> SAN -> increased heart rate
What is cardiovascular drift?
The gradual increase in heart rate during steady state exercise.
What causes cardiovascular drift?
• Warm environments
• Sweating leads to fluid loss in plasma
• Loss of plasma volume reduces venous return and stroke volume
• Heart rate increases to compensate and maintain a higher cardiac output to cool the body down
