Brain

The meninges consist of 3 layers of fibrous tissue surrounding and protecting the brain.

The cerebrospinal fluid is contained between the pia mater and the arachnoid mater i.e. in the subarachnoid space.

Bleeding may occur between any of the layers, for example:

• Extradural – between bone and dura mater
• Subdural – between dura mater and arachnoid mater
• Subarachnoid between arachnoid mater and pia mater

From C3 downwards, the vertebrae (although they vary) have a recognizable anterior body, posterolateral pedicles (Latin for ‘little feet’), transverse processes and posterior laminae (‘thin layers’), which fuse to form the spinous processes. The spinal canal enclosed within these structures is also known as the epidural space, apart from the central portion occupied by the dural sac and its contents. The dura mater contains the arachnoid mater. Between the arachnoid and the pia mater, which is applied to the spinal cord, is cerebrospinal fluid. As the vertebral column grows, it leaves behind the spinal cord so that by adulthood the cord ends at the lower border of L1 (although this can vary by one vertebra). The dural sac generally ends at the lower border of S2 below which it continues as the filum terminale, a structure clearly and frequently seen with spinal endoscopy. The dural sac contains the anterior and posterior spinal nerve roots, collectively know as the cauda equina.