Dendrites are one of the three primary parts of a neuron. They extend in a branching, tree-like fashion (hence their name) from the cell body or soma, and are used primarily for receiving input from other cells. Information is carried out of a cell along its axon which terminates near the tips of dendrites from other neurons. Between the ends of the axon and neighboring dendrite is a small space called a synaptic cleft. Small chemical messengers called neurotransmitters are released from the terminating axon and enter the synaptic cleft. These neurotransmitters may be either excitatory or inhibitory, and different ones are released by different types of neurons. Here the neurotransmitters may bind to receptors; small proteins held in place in the cellular membrane along the dendrite edge. If enough excitatory neurotransmitters bind to the matching receptors, the dendrite will activate and propagate an electrical impulse to the soma. If sufficient inhibitory neurotransmitters bind, the dendrite will effectively inactivate or at least reduce the frequency of its impulses. The soma then integrates the inputs from its many (typically thousands) of dendrites, and its output along the axon, or lack thereof, is determined by the summed dendritic signals.
Martin, JH (2003). Neuroanatomy text and atlas 3rd ed., New York: McGraw-Hill.