Outer Layers
The central nervous system (CNS) is surrounded by several layers of tissue, with several outer layers not directly related to the CNS and three membranes that directly envelope the CNS. The outer layers are the skin and then a bone layer with associated periosteum. This layer includes the skull and the vertebrae. Below the periosteum is the Epidural Space which lies between periosteum and dura in the vertebral canal. The epidural space contains loose connective tissue, veins and lymphatics. It cushions the cord as it flexes. The epidural space is regularly used for nerve blocks. In cranium, the dura layer is fused with the periosteum and therefore is in effect single layer without an epidural space.
- Dura mater
- dense connective tissue
- fused with the periosteum of cranium
- contains the venous sinuses.
- Folds of dura mater
- Falx cerebri- midline fold between cerebral hemispheres
- Tentorium cerebelli- oblique fold between the cerebrum and cerebellum
- Diaphragma sellae- forms a collar around the neck of the pituitary, forms the roof of the hypophyseal fossa
- Subdural space
- Lies between dura and arachnoid (not fused). Potential space containing only lymph-like fluid. Site of subdural hematoma.
- Arachnoid mater
- Delicate, non-vascular connective tissue
- Adhered to the skull in the calvaria.
- Subarachnoid space
- between arachnoid and pia connected by tiny filaments (spider-like)
- contains CSF from ventricular system
- largest parts are the cisterns
- Cerebellomedullary cistern around the foramen magnum. Used for the collection of CSF
- Lumbar cistern used for lumbar puncture in man
- Pia mater
- highly vascular connective tissue, very closely applied to brain tissue
- Dura mater