Page 69 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025
Level 2 Pharm D Physiology and Pathophysiology (MD303)
The Action Potential
 At the resting membrane potential (–70 mV)  most ion channels are in their
resting state (closed but capable of opening)
+
 When the neuron is stimulated  the activation gates of the voltage-gated Na
channels open  permitting the influx of Na ions  further depolarization toward
+
threshold
+
 At the threshold potential  all voltage-gated Na channels are open  the
“spike” of the action potential
 Approximately 1m sec after the activation gates open  the inactivation gates
+
+
of the Na channels close; in addition, the activation gates of the K channels open,
resulting in the repolarization of the neuron.
 The increase in K ion permeability results in the after-hyperpolarization [the
+
cell is in its relative refractory period (RRP)]
The absolute refractory period (ARP) begins when the voltage-gated Na+ channels
become activated & continues through the inactivation phase.
During this time  no further Na+ ion influx & no new action potentials can be
generated.
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