Spinal Meninges
The spinal cord are separated from the vertebral canal) by three layers of meninges made of connective tissue.
They are continuous with those of the brain.
The meninges are supplied by the general sensory branches of the cranial and spinal sensory nerves.
The cerebrospinal fluid is contained within the subarachnoid space between the pia and arachnoid.
The outermost layer is the dura mater, a tough fibrous sheath closely applied to the inner layer of bone surrounding the spinal canal.
Between the dura and the bone is a potential space, the epidural space, which normally contains a small amount of fat and vertebral veins. The spinal dura mater is continuous with the dura mater lining the skull and continues to the level of the second sacral vertebra.
It covers each of the spinal nerves as they leave the spinal canal and forms a tough sheath about the dorsal root ganglion.
Beneath the dura mater is a thin and delicate membrane called the arachnoid mater, because of its resemblance to a spider's web. Normally the arachnoid mater is closely applied to the underside of the dura mater, but a potential space exists, the subdural space, which can fill with blood or pus under pathologic conditions.
SUBARACHNOID SPACE: The space between the arachnoid and pia maters that contains delicate connective tissue, blood vessels, and cerebrospinal fluid (CSF).
Beneath the arachnoid mater and intimately applied to the spinal cord is the pia mater. Both the arachnoid and pia mater are continuous with the arachnoid and pia surrounding the brain, but unlike the arachnoid, which follows the dura mater, the pia essentially ends, with the caudal end of the spinal cord, at the level of the second lumbar vertebra.
A rope like extension of the pia mater, the filum terminale attaches the end of the spinal cord to the caudal end of the dura mater. In addition, the pia mater contains lateral projections called denticulate ligaments, which connect the spinal cord to the dura mater by projecting between the dorsal and ventral roots. The space between the arachnoid mater and pia mater is the subarachnoid space. It is normally filled with cerebrospinal fluid, which surrounds the entire brain and spinal cord.
Although the spinal coverings are generally similar to those of the brain, there are some differences.
The spinal dura is single layered and lacks the periosteal layer of the cranial dura. The spinal epidural space is an actual space in which venous plexuses are located and is used clinically for the administration of epidural anesthesia to produce a paravertebral nerve block. On the other hand, the cranial epidural space is a potential space that becomes filled with a fluid only in pathological conditions; normally, there is no space between the dura and the cranium. The spinal epidural space is located between the meningeal layer of the dura (there is no periosteal layer) and the periosteum of the vertebra, while the cranial epidural space (when present) is located between the periosteal layer of the dura and the cranium.
Dura Mater
As stated earlier, the spinal dura consists of only meningeal layer and lacks the periosteal layer of the cranial dura. Rostrally, the spinal dura joins the meningeal layer of the cranial dura at the margins of the foramen magnum. The spinal epidural space separates the spinal dura from the periosteum of the vertebra and is filled with fatty connective tissue and plexuses of veins. Caudally, the spinal dura ends at the level of the second sacral vertebra. At this level, the spinal dura becomes a thin extension (the coccygeal ligament or the filum terminale externum) and serves to anchor the spinal dura to the base of the vertebral canal.
Arachnoid
This membrane loosely invests the spinal cord and is connected to the dura via connective tissue trabeculae. Rostrally, it passes through the foramen magnum to join the cranial arachnoid, and caudally it surrounds the cauda equina (a bundle of nerve roots of all the spinal nerves caudal to the second lumbar vertebra) ). The subarachnoid space contains cerebrospinal fluid (CSF).
Pia Mater
The spinal pia is thicker as compared to the cranial pia. It is a vascular membrane and projects into the ventral fissure of the spinal cord. At intervals, toothed ligaments of pial tissue, called dentate ligaments, extend from the lateral surfaces of the spinal cord; these ligaments serve to anchor the spinal cord to the arachnoid and through it to the dura. As mentioned earlier, at caudal levels, spinal pia continues along the filum terminale that then anchors the spinal cord to the dura at the level of the second sacral vertebra. Rostrally, the spinal pia joins the cranial pia.
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A 44-year-old woman is suspected of having meningitis. To confirm the diagnosis, a lumbar puncture is ordered to collect a sample of the cerebrospinal fluid (CSF). Identify the last layer of tissue the needle will traverse in this procedure before reaching CSF.
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The correct answer is A. You answered D.
A lumbar puncture collects cerebrospinal fluid and, therefore, the needle has to enter the subarachnoid space, which is located between the arachnoid and pia mater. Therefore, the last layer of tissue the needle would traverse to enter the subarachnoid space is the arachnoid mater.
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