Page 71 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)

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Na – K pump
▪ For each molecule of ATP expended by the pump  3 Na+ ions are pumped out of the cell

& 2 K+ ions are pumped into the cell.

▪ Role of the pump

 It maintains the concentration differences for Na+ & K+ by accumulating Na+ ions
outside and K+ ions inside the cell  indirect role in the resting membrane potential

generation.

Depolarization:

A decrease in the potential difference between the inside & outside of the cell.

Hyperpolarization:

An increase in the potential difference between the inside and outside of the cell.

Repolarization:

Returning to the resting membrane potential from either direction.

Conduction of the action potential along neuronal axon

Factors Influencing Conduction Speed of action potential:

Large diameter axons provide a low resistance to current flow within the
1- Axon diameter:
axon  speeds up conduction.

 Wraps around vertebrate axons  prevents current leak out of

the cells (Acts like an insulator).
2- Myelin sheath  However, portions of the axons lack the myelin sheath, and these

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are called Nodes of Ranvier.  Contain high concentration of Na
channels (Action potential generated here).

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