When the impulses reach the body of the neuron, they travel towards the axon hillock, where if the sum of the strengths of the impulses reaches the threshold of the neuron, it fires. The junction between a synaptic terminal and a dendrite is known as a synapse. Synapses vary in strength, allowing some inputs to a neuron to be weighted more heavily than others in building towards that neuron s threshold. Also, synapses can be excitatory or inhibitory, meaning that incoming impulses can make the neuron either more likely or less likely, respectively, to fire. Input signals undergo both spatial and temporal summation before reaching the axon hillock, where the sum may then fire the neuron.
Spatial summation involves the conversion of several weak signals into a large one.
Temporal summation refers to a rapid succession of weak pulses being converted into a single large signal. Also, each time a neuron fires, the output strength is the same, no matter how far the sum of input signals is over the neuron s threshold. The above gives an overview of the structure of both the neural network of the brain, and the neurons themselves. Eric H. Chudler. Whats and Whos of Neuroscience.