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Far Eastern University – Nicanor Reyes Medical Foundation
Physiology A – Electro Physiology
Felipe Barbon M.D. (with notes from Berne & Levy)
ACTION POTENTIAL
It is a rapid, all-or-none charge in the membrane potential
followed by a return to the resting membrane potential.
- Ineffective stimulation resulting to Subthreshold Potential.
- Causes minimal electrical changes but not enough to cause an
action potential.
In certain tissues local potentials are referred to as:
- Muscles: End Plate Potential
- Neurons: Postsynaptic Potential (Excitatory & Inhibitory)
- Sensory Receptors: Generator or Receptor Potential
During effective stimulation
There is application of a Threshold Potential which is enough to
generate an action potential.
Also known as Critical Firing Level.
The membrane potential reached a value higher than threshold,
or the lowest effective electrical activity to generate an action
potential.
RESTING MEMBRANE POTENTIAL (RMP)
Also known as:
- Steady Potential – cell activity is constant
- Resting Electrical Activity – cell activity is inactive
- Transmembrane Voltage Potential
The record of the negative electrical activity inside the cell.
Approximately, in small nerve fibers, the RMP is -70 mV, while in
bigger nerve fibers it is around -90 mV.
Voluntary Tissues: Application of external stimulus causes
changes in the membrane potential.
Involuntary Tissues: RMP usually fluctuates.
Changes in the RMP can result to the generation of an ACTION
POTENTIAL that is if the cells are “effectively stimulated”.
During ineffective stimulation
It can still cause an electrical change but it will not lead to an
action potential, but will only change or disturb the resting
membrane potential.
The stimulus has changed the membrane potential sufficient
+
enough to open significant numbers of voltage-sensitive Na
channels.
+
Opening of these Na channels changes the membrane’s
+
resistance to Na ions allowing them to enter driven by its...