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For many years, it was believed that the axon hillock was the usual site of initiation of action potentials—the trigger zone. It is now thought that the earliest site of action potential initiation is at the axonal initial segment: just between the peak of the axon hillock and the initial (unmyelinated) segment of the axon. [3]
Some fraction of an excitatory voltage may reach the axon hillock and may (in rare cases) depolarize the membrane enough to provoke a new action potential. More typically, the excitatory potentials from several synapses must work together at nearly the same time to provoke a new action potential.
These electrical signals may be excitatory or inhibitory, and, if the total of excitatory influences exceeds that of the inhibitory influences, the neuron will generate a new action potential at its axon hillock, thus transmitting the information to yet another cell. [1] This phenomenon is known as an excitatory postsynaptic potential (EPSP).
The axon leaves the soma at a swelling called the axon hillock and travels for as far as 1 meter in humans or more in other species. It branches but usually maintains a constant diameter. At the farthest tip of the axon's branches are axon terminals, where the neuron can transmit a signal across the synapse to another cell. Neurons may lack ...
Summation of excitatory postsynaptic potentials increases the probability that the potential will reach the threshold potential and generate an action potential, whereas summation of inhibitory postsynaptic potentials can prevent the cell from achieving an action potential. The closer the dendritic input is to the axon hillock, the more the ...
In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential. This temporary depolarization of postsynaptic membrane potential , caused by the flow of positively charged ions into the postsynaptic cell, is a result of opening ligand-gated ion ...
Summation is the adding together of these impulses at the axon hillock. If the neuron only gets excitatory impulses, it will generate an action potential. If instead the neuron gets as many inhibitory as excitatory impulses, the inhibition cancels out the excitation and the nerve impulse will stop there. [10]
Fig. 1. Neuron and myelinated axon, with signal flow from inputs at dendrites to outputs at axon terminals. The signal is a short electrical pulse called action potential or 'spike'. Fig 2. Time course of neuronal action potential ("spike"). Note that the amplitude and the exact shape of the action potential can vary according to the exact ...