In Drosophila, during the ninth division cycle-Pole cells determination

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#Unit 7. System Physiology – Animal

SA node has Prepotential or pacemaker potential which is the gradual potential rise from the resting membrane potential to threshold  ( -40 mV) & this occur spontaneously.

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#Unit 7. System Physiology – Animal

Membrane ion channels that play important roles in generation of the action potential:

T (transient) channels 

L (long-lasting) channels

Voltage gated potassium ion channel

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#Unit 7. System Physiology – Animal

Between heartbeats, influx of positively charged sodium ions causes a slow rise in the resting membrane potential in the positive direction. 

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#Unit 7. System Physiology – Animal

When the potential reaches a threshold voltage of about −40 millivolts, the L-type calcium channels become “activated,” causing the action potential.

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#Unit 7. System Physiology – Animal

L-type calcium channels become inactivated (i.e., they close) within about 100 to 150 milliseconds after opening

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#Unit 7. System Physiology – Animal

When the L-type calcium channels become inactivated at about the same time, greatly increased numbers of potassium channels open.