Final answer:
Neurosurgical sponges are used on the structures of the brain during surgical procedures to absorb fluids and control bleeding while protecting the delicate neural tissue.
Step-by-step explanation:
The type of sponge that is used directly on the structures of the brain is a neurosurgical sponge. These specialized sponges are designed to be non-adherent and are used during neurosurgical procedures to protect delicate neural tissue, absorb fluids, and control bleeding without damaging the brain tissue. Neurosurgical sponges are made from a soft, absorbent material that is suitable for contact with neural structures.