Respiratory effects [edit]. The PRG antagonizes the apneustic center, cyclically inhibiting inhalation. The PRG limits the burst of action potentials in the phrenic nerve, effectively decreasing the tidal volume and regulating the respiratory rate.espiratory effects [edit]. The PRG antagonizes the apneustic center, cyclically inhibiting inhalation. The PRG limits the burst of action potentials in the phrenic nerve, effectively decreasing the tidal volume and regulating the respiratory rate.
Because the ones at the bottom, the animals would have died first and soil would have covered them building a cliff and the fossils up top would have died later. 3 people found this useful.
The oldest fossil obtained, belongs to a period of 540 million years old.Anatomy The body of a Sponge is typically hollow and full of pores. It retains a shape and structure due to the presence of a jelly like substance made of collagen, known as mesohyl, and also has a thick network of fiber made of collagen.