Heart Rate Flashcards
What effects do nicotine have on the heart
Stimulates the SNS and epinephrine and norepinephrine release
Increases vasoconstriction
Increases platelet aggregation
What effects to caffeine have on the heart
Increases calcium influx increasing contractility
Increases epinephrine release stimulating heart rate
Describe the parasympathetic input
Opposes the SNS
Why the heart is said to possess Vagal tone at rest
Produces acetylcholine which hyperpolarises the membrane preventing depolarisation by opening potassium channels
Discuss the factors increasing heart rate
Sympathetic input
The sympathetic nervous system sends excitatory stimuli from higher brain areas, hypothalamus and limbic system.
Proprioceptors from Muscles and joints send excitatory information from muscles and joints.
Chemoreceptors send information about blood pH from aortic bodies.
Baroceptors send information about degree of stretch on vessel walls.
Via sympathetic fibres to the heart, epinephrine and norepinephrine are released and alter membrane potential for the SA node, causing the threshold for contraction to be met more frequently, increasing heart rate.
They also increase contractility increasing SV therefore heart rate does not need to increase as much to achieve the same cardiac output.
Hormonal input
Chemicals normally present in the blood directly affect heart rate, adrenaline and noradrenaline produced by the adrenal gland particularly if they are excessive or reduced.
Thyroxine produced by the thyroid produces a more sustained contraction of cardiac muscle with a slower heart rate. Also it enhances the efficiency of the adrenal hormones.
Ion/ chemical input
Plasma electrolyte balances rapidly affect the heart rate
Hypocalceima depresses the heart
Hypercalceimac produces rapid spastic contractions
Hypokaleima lowers resting potential making it harder to achieve depolarisation
Hyperkalemia causes the heart to beat arrhythmically
