Short answers, pulled from the story.
Molecular evidence suggests that the ability to generate electric signals first appeared in evolution some 700 to 800 million years ago during the Tonian period. Predecessors of neurons were peptidergic secretory cells that eventually gained new gene modules enabling them to create post-synaptic scaffolds and ion channels.
The German anatomist Heinrich Wilhelm Waldeyer introduced the term neuron in 1891 based on the ancient Greek word for sinew or cord. The place of the neuron as the primary functional unit of the nervous system was first recognized in the late 19th century through the work of Santiago Ramón y Cajal.
Axons travel for as far as 1 meter in humans or more in other species with the longest human motor neuron axon reaching over a meter from the base of the spine to the toes. Sensory neurons can have axons running from the toes to the posterior column of the spinal cord over 1.5 meters in adults while giraffes possess single axons several meters in length along their necks.
The soma or cell body is a compact structure containing the nucleus mitochondria and Golgi bodies. Dendrites typically branch profusely and extend a few hundred micrometers from the soma while the axon leaves at a swelling called the axon hillock.
Alzheimer's disease is characterized by progressive cognitive deterioration together with declining activities of daily living and neuropsychiatric symptoms including loss of short-term memory. Parkinson's disease impairs motor skills and speech through muscle rigidity tremor and slowing of physical movement while multiple sclerosis results from demyelination of axons in the central nervous system.