Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project. Electrical stimulation is transmitted onto dendrites by upstream neurons via synapses which are located at various points throughout the dendritic arbor. Dendrites play a critical role in integrating these synaptic inputs and in determining the extent to which action potentials are produced by the neuron. Recent research has also found that dendrites can support action potentials and release neurotransmitters, a property that was originally believed to be specific to axons. The long outgrowths on immune system dendritic cells are also called dendrites. These dendrites do not process electrical signals. Certain classes of dendrites (i.e. Purkinje cells of cerebellum, cerebral cortex) contain small projections referred to as "appendages" or "spines". Appendages increase receptive properties of dendrites to isolate signal specificity. Increased neural activity at spines increases their size and conduction which is thought to play a role in learning and memory formation. There are approximately 200,000 spines per cell, each of which serve as a postsynaptic process for individual pre synaptic axons.