Physio

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...