Hey everyone! This is Nicole from Kenhub, and in this tutorial, we will be looking at one of the meningeal layers that cover the spinal cord and the brain – the dura mater.
The dura mater is the outermost layer of the three meningeal layers that cover the brain and the spinal cord. These membranous connective tissue layers all together known as the meninges are named the dura mater, the arachnoid mater, and the pia mater which you can see here on this beautiful diagram. The green layer here is the dura mater, that light purplish layer is the arachnoid mater, and the pia mater is that translucent layer that's just covering the sulci of the brain just here.
The meninges protect the brain and the spinal cord and their accompanying blood vessels. They also enable the channeling of cerebrospinal fluid around the brain and the spinal cord. You might be interested to know that the name dura mater comes from the Latin meaning "hard mother" due to the fact that it is the thickest and toughest of the three membranes that cover the brain and the spinal cord.
The dura mater is derived from the mesoderm during embryonic development. It is comprised of two layers – the periosteal layer, the outer layer of the cranial dura mater which forms the inner aspect of the skull; the meningeal layer, the inner layer of the dura mater which forms the supporting capsule of the brain and is responsible for the formation of the dural infoldings which we'll talk about later. Now, you can't distinguish these two layers on the slide but trust me, they're there.
The dura mater also contributes to the subdural and epidural spaces. The meningeal layer of the dura mater tends to firmly attach to the underlying arachnoid mater. The potential space between them is called the subdural space. Similarly, the space between the skull and the dura mater has the potential to form an epidural space. Clinically, this important to note as subdural and epidural hematomas are brain injuries resulting from the entrapment and subsequent buildup of blood within these spaces.
So, now, we're coming to our sort of cross-sagittal/transverse section of the skull so we can have a little chat about dural infoldings. The two layers of the dura mater separate from each other in certain places creating partitions within the cranial cavity which help to hold the brain in place. There are four areas of dural infolding where the meningeal layer reflects inwards, away from the periosteal layer. The four dural infoldings are the falx cerebri, a sickle-shaped projection of the dura mater which you can see illustrated by this lovely green arrow which extends downward into the longitudinal fissure separating the two cerebral hemispheres; the tentorium cerebelli, a tent-like structure that spreads between the petrous part of the temporal bone and the transverse sinus separating the cerebellum from the occipital lobe; the falx cerebelli, another sickle-shaped dural projection situated in the posterior part of the posterior cranial fossa between the right and left hemispheres of the cerebellum; and the diaphragma sellae, a small sheath of dura covering the pituitary gland.
The separation of the two dural layers at the dural infoldings also creates cranial venous channels spaces known as dural venous sinuses. You may remember these from our tutorial from our sigmoid sinus. These sinuses allow venous blood to drain into the internal jugular vein which you can see here in green towards the heart. Arachnoid granulations – outgrowths of the underlying arachnoid mater through the dura mater – can be found within the dural venous sinuses. Obviously, you can't see these in the slide but, again, they're there. These granulations allow cerebrospinal fluid to move from the space between the pia mater and the arachnoid mater called the subarachnoid space into the bloodstream.
The dura mater is also the outermost meningeal covering of the spinal cord. The periosteal layer of the cranial dura mater does not extend beyond the foramen magnum, meaning that the spinal dura mater is only composed of the dural meningeal layer – the true dura mater. As you can see on this diagram, we have the pia mater here which is below the blood vessels and directly on the spinal cord, the arachnoid mater here, and the dura mater just here highlighted in green.
The dura mater forms a dural sac that envelops the cauda equina of the spinal cord and extends downwards together with the filum terminale to the periosteum of the coccyx. Now, just quickly, the filum terminale is actually the point at which the spinal cord ends and you could call it, I suppose, a thread of connective tissue. The elongation of the spinal dura mater past the termination of the spinal cord allows for the retrieval of cerebrospinal fluid from this area. Such a procedure is called a lumbar puncture, which you may remember, we often use to clinically diagnose diseases of the central nervous system.
The dura mater is innervated by branches of the fifth cranial nerve – the trigeminal nerve – as well as the tenth cranial nerve – the vagus nerve – and the first three cervical nerves – C1, C2, and C3. One last thing that might be interesting to know is that the innervation of the dura mater causes it to be very sensitive so stretching of the dura mater can result in headaches.
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