Periaqueductal gray neurons send descending axons into various regions of the medulla releasing serotonin.
a. true
b. false

True

Explanation:

Periaqueductal gray matter is found in the middle portion of brain.  When this grey matter is stimulated it activates neurons that releases enkephalin. Enkephalin further direct the stimulation to the raphe nuclei  with in the brain stem that releases serotonin. In this process, the ascending and descending axons are released  from  

a)subcortical nuclei

b)spinal trigeminal nuclei  

c)the spinal cord

Hence, the given statement is true

the transfer of energy between two molecules spaced just nanometers apart plays a key role in many technologies, including photovoltaics, quantum information systems, lighting, and sensors, as well as in biophysics to measure nanometer distances and in photosynthesis. but an open question in this area is what effect, if any, the surrounding photonic environment has on this nanoscale energy transfer. by designing and performing a carefully controlled experiment to answer this question, scientists have settled the debate and found clues to improving the efficiency of many of the technologies that rely on this process.

explanation:

substitution is the answer in this case