Nerve growth factor (NGF) is a neurotrophin that supports the survival, growth and differentiation of sensory and sympathetic neurons. NGF binds the high affinity receptor tyrosine kinase TrkA (NTRK1) and the p75 neurotrophin receptor (NGFR). TrkA activation triggers the RAS-MAPK, PI3K-AKT and PLC-gamma pathways, promoting neuron survival and neurite outgrowth, while p75 signaling can activate NF-kappaB and JNK and, in some settings, apoptosis. NGF signaling is important in pain, inflammation and neurodegenerative diseases.