The axon hillock is the point of impulse (AP) generation in this motor neuron, through both spatial and temporal summation of post-synaptic potentials — excitatory (EPSP) and inhibitory (IPSP).
Through the flow of current, the membrane potential of the axon hillock (resting: -70mV) is gradually driven up to threshold level of depolarisation (-40 mV), then rapidly discharged by firing an AP and returning to baseline; then it is driven up toward threshold again, and so on.
Overview of Impulse Transmission of a Motor Unit
EPSPs > IPSPs –> threshold firing of AP (at hillock) –> rapid impulse propagation by salutatory conduction –> activate voltage-gated Ca2+ channels at nerve terminal button which stimulates vesicles to release their stored ACh into the neuromuscular junction synapse –> activate ligand-gated Na+ channels on the motor end-plate –> activate sarcoplasmic reticulum (not shown) to released stored calcium –> muscle contraction
