The materials below, including the drawing, are taken from the site http://www.rlocman.ru/shem/shem-cache.htmldi/18720, author: Zagnetkin V.I.
Changes have been made to the text.
Motor neurons - these are motor neurons located in the anterior horns of the spinal cord, transmitting excitation to the muscles of the body, which causes the contraction of these muscles.
Action potential (PD) motor neurons that excite muscle fibers has some features.
As a result of the appearance of an excitatory postsynaptic potential (EPSP) on the motor neuron at the moment t1 is happening depolarization membranes. Due to this, electronegativity decreases from the resting potential level (PP) Upp to a critical level of depolarization (KUD) – Ukr in a time of ~ 1.2 ms. After this, with a delay of ~0.3 ms at the moment t2 an avalanche begins exponential potential growth to a level of + 30÷40 mV in a time of ~ 0.1÷0.5 ms (moment t3). What happens next reversion membrane potential and the phase begins repolarization to the level Ukr (again according to exponential) for ~ 0.5÷3.0 ms (moment t4). Full recovery PP occurs after the end of trace potential oscillations. First observed negative trace potential – trace depolarization – up to t6and then positive trace potential - trace hyperpolarization – up to t7. The duration of trace potentials significantly exceeds the duration PD (up to 10 ms).
As a result, we have the following picture:
t1 – t2 – period of primary depolarization ~ 1.2 + 0.3 = 1.5 ms;
t2 – t4 – (PD in person) - period of absolute and relative refractoriness ~ 0.6÷3.5 ms (during this period the membrane first completely, and then partially, loses the ability to respond with excitation to stimulation of any magnitude);
t4–t5 – supernormal period (excitement can occur even under the influence of a stimulus of subthreshold strength);
t5 – t6 – subnormal period (excitation can occur only under the influence of a stimulus of superthreshold strength);
t6–t7 – excitation can occur even under the influence of a stimulus of subthreshold strength;
t7 – restoration of resting potential.