As a child, alex was short for his age. but during his teenage years, his height increased and he surpassed most of his friends. what must have occurred to create this growth spurt?

This teenager had a growth spurt due to several factors (external and internal factors).

The growth spurt is influenced by the genes that he inherited from his parents. Their geographical origins are also an indicator.

Living conditions also affect growth.

The decline in infectious diseases and a diet richer in protein explain why the pace of growth has changed significantly for more than a century.

after receiving a stimus, the sensory receptors send(s) signals to the appropriate area of the body.  

the must be sensory neurons.  

hope its .