Sympathetic Nervous System
At rest, the resting membrane potential of sinus node is -60 mV and the threshold for generation of impulse is -40 mV. The resting heart rate is approximately 70-75 bpm.
Upon sympathetic stimulation, the activation of β1 receptors in sinus node by neurotransmitter noradrenaline increases the resting membrane potential from -60 mV to -50 mV. This allows the threshold of the ion channels (-40 mV) to be reached more quickly (more rapid depolarisation), thus increasing the depolarisation frequencies. In other words, the heart rate increases (E.g.: 120 bpm)
In addition, sympathetic stimulation elsewhere in the myocardium promotes increased Ca2+ transport into the contractile muscle cells. The heart is then able to contract both faster and more powerfully, and consequently squeeze out more blood per heartbeat.
Transcript
Sympathetic Nervous System.
At rest, the resting membrane potential of sinus node is -60 mV and the threshold for generation of impulse is -40 mV. The resting heart rate is approximately 70-75 bpm.
Upon sympathetic stimulation, the activation of β1 receptors in sinus node by neurotransmitter noradrenaline increases the resting membrane potential from -60 mV to -50 mV. This allows the threshold of the ion channels (-40 mV) to be reached more quickly (more rapid depolarisation), thus increasing the depolarisation frequencies. In other words, the heart rate increases (E.g.: 120 bpm)
In addition, sympathetic stimulation elsewhere in the myocardium promotes increased Ca2+ transport into the contractile muscle cells. The heart is then able to contract both faster and more powerfully, and consequently squeeze out more blood per heartbeat.