Signal transduction pathways are processes that involve an extra cellular signal, such as a hormone or a neurotransmitter, binding to a receptor on a cell to initiate a change at the level of the second messenger. This change alters the function of the cell.
Three examples of signal transduction include the signaling by nerve growth factor, long-term depression and phosphorylation of tyrosine hydroxylase. Nerve growth factor is responsible for many functional aspects of the sensory neuron, including differentiation and survival. Long-term depression plays a role in signaling between parallel fibers and Purkinje cells in the cerebellum. Tyrosine hydroxylase is involved with nervous system regulation.