the central nervous system is lacking in animals that have
î î î. Although an exact count is not available, it is likely that the human brain has as many as A) 10,000 neurons. B) 500,000 neurons. C) 1 million neurons. D) 10 million neurons. E) 100 billion neurons. The central nervous system is lacking in animals that have A) a complete gut. B) bilateral symmetry. C) radial symmetry. D) a closed ... E) ...he stretch receptors of the sensory neurons in the human knee-jerk reflex are located in the A) gastrocnemius muscle, in the calf.