How are sensory neurons formed?
Sensory Neurons are formed by neural stem cells which differentiate in embryos following proliferation and determination and form subpopulations of sensory neurons. Neurons can't reproduce on their own through cell division, but the sensory neurons that are formed during fetal development and during childhood are not the only neurons that a person will have for their entire life. This regenerative process is called neurogenesis. Once thought to stops after full maturity, it has since been proven that neurogenesis continues throughout life. During neurogenesis, the neural stem cell divides and differentiates the neuron as a specialized cell, becoming the parent cell, which continues to reproduce, and the daughter neuron, which cannot reproduce. While most stem cells have the potential to become any sort of specialized cell, a property called pluripotancy, neural sensory cells are multipotant and can only become sensory neurons. For example, stem cells located in the eyes become sensory neurons coded for sight.
Sensory neurons receive and transmit the direct stimulus of the outside world, such as sight and touch. These neurons are activated by physical sensory stimulus, rather than information transmitted by other neurons (Wikipedia). Sensory neurons are nerve cells and so are produced by the body's stem cells during gestation. Neuron reproduction is more difficult than normal cell reproduction because of the specific complexity of the neuron; each neuron responds to a different type of stimulus, and so a light-sensing neuron cannot replicate a taste-sensing neuron. Neurons tend to be locked in place after the body matures, so sensory neurons may not reproduce after a certain age. This is why nerve loss can be so devastating; the nerve cells in the affected area cannot reproduce to fix the injury, so the affected portion of the body cannot receive or send signals. However, there is evidence that both cerebral neurons and sensory neurons can be stimulated to reproduce with medical treatment.