Some of the tyrosine is formed from phenylalanine, by Phenylalanine hydroxylase

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#Id: 5441

#Unit 7. System Physiology – Animal

The opening of voltage-gated K+ channels is slower and more prolonged than the opening of the Na + channels, and much of the increase in K + conductance comes after the increase in Na+ conductance

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#Id: 5442

#Unit 7. System Physiology – Animal

voltage-gated K + channels bring the action potential to an end and cause closure of their gates through a negative feedback process

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#Id: 5443

#Unit 7. System Physiology – Animal

The net movement of positive charge out of the cell due to K+ efflux at this time helps complete the process of repolarization

Relative refractory period

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#Id: 5444

#Unit 7. System Physiology – Animal

The slow return of the K + channels to the closed state also explains the after-hyperpolarization, followed by a return to the resting membrane potential

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#Id: 5445

#Unit 7. System Physiology – Animal

Sodium channels can be blocked by a toxin called tetrodotoxin when it is applied to the outside of the cell membrane (activation gates)

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#Id: 5446

#Unit 7. System Physiology – Animal

Tetraethylammonium ion blocks the potassium channels when it is applied to the interior of the nerve fiber.