Page 65 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)
Excitatory Postsynaptic Potentials Inhibitory Postsynaptic Potentials

• synaptic inputs ➔ depolarize the postsynaptic  synaptic inputs ➔ hyperpolarize the postsynaptic

cell, bringing the membrane potential closer cell, taking the membrane potential away from
to threshold and closer to firing an action threshold and farther from firing an action

potential. potential.

• EPSPs are produced by opening Na+ and K+  IPSPs are produced by opening Cl− channels.
channels,

• The membrane potential is driven to a value  The membrane potential is driven toward the Cl−

approximately halfway between the equilibrium potential (approximately −90 mV),
equilibrium potentials for Na+ and K+, or 0 which is a hyperpolarized state.

mV, which is a depolarized state.

• Excitatory neurotransmitters:  Inhibitory neurotransmitters are γ-aminobutyric
ACh, norepinephrine, epinephrine, dopamine, acid (GABA) and glycine.

glutamate, and serotonin

Membrane Potential & Action Potential

Membrane Potential

 Intracellular fluid (ICF) & extracellular fluid (ECF) are electrically neutral solutions  containing an

equal number of positively and negatively charged ions.

 In a non-stimulated (resting) cell:
a slight accumulation of -ve charges on the internal surface of the plasma membrane is

attracted to an equal number of +ve charges on the external surface  polarized.
This separation of charge across the plasma membrane is called the membrane potential 

measured in mV (millivolt)
 The membrane potential value takes –ve or +ve signs according to the predominant charge on the

internal surface of the cell membrane.

 Nerve cells and muscles are the main cells that depend on the membrane potential in their function.

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