Pia mater

Hey everyone! This is Nicole from Kenhub, and in this tutorial, we will be looking at the innermost layer of the meninges – the pia mater. The brain and spinal cord collectively called the central nervous system or CNS are covered by three connective tissue membranes together known as the meninges. The meninges provide protection to the CNS and its vessels and allow for the channeling of cerebrospinal fluid (CSF) around the surfaces of the brain and spinal cord. These three layers of the meninges that cover the CNS are the dura mater highlighted in green, the arachnoid mater now highlighted, and the pia mater which you can see here in green.

So now we're coming to our superior view of the brain. The pia mater is the innermost layer of the meninges. The name pia mater comes from Latin meaning "tender mother" which refers to the delicacy and thinness of this layer. The pia mater is highly vascular containing numerous small blood vessels from both the brain and spinal cord and, in this slide, you can see here how the vessels sit between the brain and the pia mater. The pia mater is also impermeable to fluid which enables it to contain and circulate cerebrospinal fluid.

Cranial pia mater is adhered closely to the brain by astrocytes which are a type of glial cell. Glial cells are non-neuronal cells that support and insulate neurons. Superiorly, the cranial arachnoid mater connects to the cranial pia mater by arachnoid trabeculae, thin connective tissue filaments, which cross the CSF-filled subarachnoid space. So, you can't see the arachnoid trabeculae here but remember that arachnoid means spider-like while trabeculae comes from the Latin word for "small bean". So, I just imagine little spidery beans connecting the cranial pia mater to the arachnoid mater.

Cranial pia mater closely follows the surface of the brain but unlike the dura mater and arachnoid mater, the pia mater follows all the curvatures of the brain including the fissures and sulci. The pia mater forms the mesodermal side of the pia-glial barrier, also called the glia limitans and is invaginated into the substance of the brain by entering the cerebral arteries which it surrounds. Now, what does that mean? That means essentially that the pia mater becomes confluent with the brain through the connection to the cerebral arteries.

The spinal pia mater represented by the green line encircling the spinal cord in the image adheres directly to the spinal cord and also lines the anterior median sulcus of the spinal cord indicated by the green arrow here. It also covers the cranial nerves and the spinal nerve roots. The spinal pia mater extends from the cervical spinal cord to the filum terminale. There at the level of the S2 vertebra, the spinal pia mater projects laterally on either side of the midline to form the denticulate ligaments which attach to the spinal dura mater providing stability for the spinal cord. So, if we're looking at our image here, we have the pia mater in green here, this thin capsule of arachnoid mater here, and the dura mater on the outside just here. The denticulate ligaments are not illustrated but if they were they would be here on either side stretching from these points in the midline to connect to the dura mater.

Meningitis is the inflammation of the cranial pia and arachnoid mater caused by a typically bacterial or viral infection within the CSF-filled subarachnoid space. Brain tissue swelling is a result of the inflammation and subsequently blood and oxygen flow to the brain tissues are limited. Symptoms include neck pain and rigidity, severe headaches and photosensitivity. If left untreated, bacterial meningitis can be fatal while viral meningitis is often able to resolve itself. Meningitis can also occur in the spinal cord called spinal meningitis though it is more rare.

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