Final answer:
During a craniotomy, the flat bone of the cranium is entered, which includes two layers of compact bone with spongy bone in between. The compact bone provides structural support and protection, while the spongy bone offers resilience.
Step-by-step explanation:
During a craniotomy, the type of bone entered is typically the flat bone of the cranium. This type of bone consists of two layers of compact bone with an inner layer of spongy bone, known as diploë, in between. The compact bone in a flat bone is dense and provides protection and support, while the spongy bone, comprising tiny plates called trabeculae, gives the bone additional strength and resilience.
The skull's flat bones protect the brain by having an outer and inner layer of compact bone, ensuring that if the outer layer is fractured, the inner layer continues to safeguard the brain. Compact bone is organized into units called osteons, which contain a network of blood vessels and nerves. Spongy bone, located centrally within the bone, helps to absorb shock and distribute pressure.