Protection of the CNS

Bones, Meninges & Cerebrospinal Fluid (CSF) do a good job under normal everyday conditions.

The Meninges

n 3 layers of connective tissue enclosing brain & spinal cord

n Starting from the outside, the layers are:

• dura mater

• arachnoid mater

• pia mater

Dura Mater (“tough mother”)

n Actually has 2 layers which run close together in most locations

• outer layer is anchored to skull bone in certain places

• inner layer forms folds that partition skull cavity into compartments

– one between R & L hemispheres: falx cerebri

– one between occipital lobe & cerebellum:tentorium cerebelli

n spaces between layers at those folds form “dural venous sinuses” for blood leaving brain

Falx cerebri (picture) divides upper portion of skull into right and left compartments–

can also see the “tentorium cerebelli” between occipital lobe and cerebellum, separating lower compartment of skull from upper area of skull

Arachnoid Mater(“spiderlike”)

n Thinner layer loosely enclosing CNS

n Space beneath arachnoid is filled with cerebrospinal fluid (CSF)

n Spider-like filaments cross this “subarachnoid space” to the inner most layer of meninges, the pia mater

n Blood vessels supplying brain are also travel in the subarachnoid space (SAS)

Pia Mater (“tender matter”)

n Very thin layer that tightly follows brain surface

n Contains lots of small capillaries supplying blood to the CNS

Clinical Applications

n Dural partitions (Falx cerebri & tentorium cerebelli) play a significant role in brain damage related to head injuries as well as brain damage resulting from increased intracranial pressure.

n Meningioma- ~15% of “brain tumors” arise from the meninges

n Meningitis – infection/inflammation of the meninges (we’ll come back to this shortly)