When the nerve is damaged,the action potential remains between the electrodes and doesn't reach the second electrode (i.e potential difference remains positive and doesn't go into negative phase) , the biphasic action potential changes into monophasic action potential.
Action potentials in neurons are also known as  nerve impulses  or spikes, and the temporal sequence of action potentials generated by a neuron is called its  spike train . A neuron that emits an action potential is often said to fire. In animal cells, there are two primary types of action potentials. One type is generated by voltage-gated sodium channels, the other by voltage-gated calcium channels. Sodium-based action potentials usually last for under one millisecond, whereas calcium-based action potentials may last for 100 milliseconds or longer. When the action potential conducts into the region under the first (negative) recording electrode, the extracellular surface of the membrane becomes negative with respect to the extracellular surface under the second (positive) recording electrode and the voltmeter records a positive potential difference (V+ - V-).  The Compound muscle action potential (CMAP) or Compound motor action potential is an electromyography investigation (electrical study of muscle function). The CMAP idealizes the summation of a group of almost simultaneous action potentials from several muscle fibers in the same area.  An action potential is initiated at the one end of the nerve. The sodium influx associated with the rapid depolarization phase of the action potential in the region where the nerve is depolarized makes the extracellular surface negative with respect to the surrounding regions. RE: biphasic action potential change into the monophasic action? Why does the biphasic action potential change into the monophasic action potential after nerve injury between the two recording electrodes? As the action potential conducts along the nerve, the difference in potential will be zero when the action potential is between the two electrodes, negative when the action potential is under the second recording electrode, and zero again when the action potential has conducted past the second recording electrode. RE: biphasic action potential change into the monophasic action? Why does the biphasic action potential change into the monophasic action potential after nerve injury between the two recording electrodes? In this laboratory, you will be recording an extracellular, biphasic, compound action potential. Clarifying those three terms in the context of the experiment will help you to understand and interpret your results. The nerve is made of thousands of axons whose size, myelination and position with respect to the stimulating and recording electrodes all affect the size of their contribution to the compound action potential. Both the classic intracellular action potential and the compound action potential are biphasic. In other words, they have both positive and negative deflections, but for different reasons. The negative phase of the intracellular action potential is attributed to the mechanism of after-hyperpolarization The action potential is an electrical event occurring when a stimulus of sufficient intensity is applied to a neuron or muscle cell, allowing sodium to move into the cell and reverse the polarity. An action potential can also be called a nerve impulse which is known to be stimulated by an external stimuli or upon internal excitation. This action potential travels thro … ugh a neuron and involves charged ions (the key ones are sodium ions and potassium ions) that cross the membrane barrier of the neuron. Stimulator Settings Stimulus Duration: 0.2 ms Stimulus Voltage: 0.05 V Delay: 1 ms Rate: 1 Hz Mode: Repeat A sample display might look something like what you see to the right below. The Compound Action Potential is the second biphasic waveform, the Stimulus Artifact (explained below) appears first. It is important not to confuse the two! Note the Input Channels A and B ranges. By setting the A to D range, you change the A to D(hardware) gain, in order to more accurately view the CAP signal. When the nerve is damaged,the action potential remains between the electrodes and doesn't reach the second electrode (i.e potential difference remains positive and doesn't go into negative phase) , the biphasic action potential changes into monophasic action potential i.e with single phase. Source(s): RE: biphasic action potential change into the monophasic action? Why does the biphasic action potential change into the monophasic action potential after nerve injury between the two recording electrodes?
https://en.wikipedia.org/wiki/Action_potentials http://www.humanphysiology.tuars.com/program/section1/1ch6/s1ch6_22.htm https://en.wikipedia.org/wiki/Compound_muscle_action_potential https://answers.yahoo.com/question/index?qid=20070330081646AAPyxJe https://answers.yahoo.com/question/index?qid=20070330081646AAPyxJe http://www.medicine.mcgill.ca/physio/vlab/cap/recording.htm http://wiki.answers.com/Q/What_causes_the_action_potential_be_biphasic_or_triphasic http://www.medicine.mcgill.ca/physio/vlab/CAP/character.htm https://answers.yahoo.com/question/index?qid=20070330081646AAPyxJe
what is biphasic action potential