Final answer:
Spatial summation is the combination of graded potentials across the neuronal cell membrane caused by signals from separate presynaptic elements that add up to initiate an action potential.
Step-by-step explanation:
Spatial summation refers to the combination of graded potentials across the neuronal cell membrane caused by signals from separate presynaptic elements that add up to initiate an action potential. It involves the integration of multiple inputs onto a neuron to determine whether an action potential will be initiated.
For example, if multiple presynaptic neurons release neurotransmitters onto a postsynaptic neuron, each producing a small graded potential, the summation of these potentials will determine whether the postsynaptic neuron reaches its threshold for firing an action potential.
This process allows for the integration of information from multiple sources, enhancing the ability of the nervous system to process and respond to stimuli.