Organ
Arachnoid mater
Middle meningeal layer over the CSF-filled space
High-yield
Pia closely follows the brain surface, while arachnoid bridges the sulci. Cerebral arteries, including the circle of Willis, course in the intervening subarachnoid space.
Overview
The arachnoid lies beneath dura and above pia. It bridges most cortical grooves instead of following their depth. Fine trabeculae extend across the underlying subarachnoid space, where cerebrospinal fluid surrounds the brain and spinal cord.
Reference facts
- Location
- Between dura and pia around the brain and spinal cord
- Parts
- Barrier-cell layers, underlying connective tissue and trabeculae; arachnoid projections include villi and granulations
- Blood supply
- The arachnoid membrane is generally avascular; vessels in the subarachnoid space are distinct from the membrane itself
- Innervation
- Generally described as lacking its own sensory innervation; surrounding meningeal and vascular tissues have sensory fibers
- Function
- Provides a barrier around the subarachnoid CSF compartment and participates in CSF exchange and outflow
Clinical correlation
A ruptured intracranial aneurysm can release blood into the subarachnoid space. Blood may spread through cisterns and sulci, although focal clots and bleeding into other compartments can also occur.
Frequently asked questions
Where is the arachnoid mater located?
Between dura and pia around the brain and spinal cord.
What does the arachnoid mater do?
Provides a barrier around the subarachnoid CSF compartment and participates in CSF exchange and outflow.
What are the parts of the arachnoid mater?
Barrier-cell layers, underlying connective tissue and trabeculae; arachnoid projections include villi and granulations.
What is the blood supply of the arachnoid mater?
The arachnoid membrane is generally avascular; vessels in the subarachnoid space are distinct from the membrane itself.