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You are watching: The subarachnoid space lies between what two layers of meninges
Three layers referred to as the meninges encase the brain and spinal cord. Native superficial to deep, this layers are the dura mater, arachnoid mater, and pia mater. The dura mater is a dense connective organization layer the is adherent to the inner surface of the skull. Following is the arachnoid mater the is a thin impermeable layer, and also the innermost is the pia mater, which is a vascular great that very closely invests end the mind and spinal cord.<1> These membranes specify three potential clinically significant spaces: the epidural space, which exists in between the skull and also the dura mater; the subdural space, found in between the dura mater and arachnoid mater; and the subarachnoid space, which is between the arachnoid mater and also pia mater. The epidural room in the skull is a potential space, while the is actually current in the spinal cord. The subarachnoid room consists that the cerebrospinal liquid (CSF), major blood vessels, and also cisterns. The cisterns room enlarged pockets of CSF developed due come the separation that the arachnoid mater from the pia mater based on the anatomy of the brain and spinal cord surface. The cisterns are produced due come the close and firm follow of the pia mater come the mind and spinal cord surface while rather loosely come the arachnoid mater.
Structure and Function
Anatomically, the subarachnoid room exists in between the arachnoid mater externally and pia mater internally. A network of fine delicate connective tissue called trabeculae connect these 2 layers and gives this room its characteristic spider net appearance. The subarachnoid trabeculae act together supportive pillars in between the pia mater and arachnoid mater, and also due to the curtain-like structure with holes, it allows the circulation of CSF.<2> Besides trabeculae, over there are significant cerebral blood vessels that penetrate the nervous organization within this space.
The subarachnoid room does not have actually a uniform depth throughout the main nervous system and also forms extensions roughly the neurovascular structures, spaces, and cisterns. It develops sleeve-like extensions around the cranial and spinal nerves and also terminates whereby the pia mater and the arachnoid mater fuses through the perineum of this nerves. Besides, this room surrounds the arteries and veins the the central nervous system up come the suggest where they permeate the nervous tissue and also divide right into arterioles and also venules. When the pia mater carefully adheres to the surface of the mind and adheres to the contours of cortical sulci and also gyri, the arachnoid mater only bridges over the sulci, resulting in the formation of CSF filled triangular spaces. Also, in ~ some places where the mind draws far from the skull due to the fact that of its natural variation in shape, the arachnoid mater and also the pia mater room not in close approximation. This results in naturally enlarged CSF to fill expansions called the subarachnoid cisterns. These expansions transmit intracranial vessels along with cranial nerves and hold far-ranging clinical relevance.<3> Although theses cisterns are typically described as different compartments, they are not important anatomically separate. They space in totally free communication v each other and also with the remainder of the subarachnoid space. Some significant cisterns include<4>:
1) Cistern the the lamina terminalis:
It is located anterior to the 3rd ventricle and also contains the anterior cerebral arteries, the anterior communicating artery, the hypothalamic artery, Heubner"s artery, and also the origin of the fronto-orbital arteries.
2) Sylvian cistern:
Also known as the insular cistern, is discovered in the fissure between the temporal and frontal lobes. It contains the middle cerebral artery and also vein and also the fronto-orbital veins.
3) Suprasellar cistern:
Also recognized as the chiasmatic cistern contains the anterior element of the optic chiasm, optic nerves (cranial nerve II), the hypophyseal stalk, and the origin of the anterior cerebral artery.
4) Interpeduncular cistern
Located between the 2 cerebral peduncles the the midbrain. The communicates inferiorly with the pontine cistern and superiorly v the chiasmatic cistern and contains the bifurcation of the basilar artery, peduncular part of the posterior cerebral artery and superior cerebellar artery, the posterior connecting arteries that affix with the peduncular segment of the posterior cerebral arteries, the basal vein and the oculomotor nerve (cranial nerve III).
5) Superior cistern
Located posterolateral to the midbrain. Its lateral extensions affix it to the interpeduncular cistern. That contains the great cerebral vein, the 3rd part of the posterior cerebral arteries and the superior cerebellar arteries. That infratentorial portion contains the trochlear nerve (cranial nerve IV).
6) Pontine cistern:
It is situated anterior to the pons and receives CSF from the combine foramen that Luschka (lateral aperture) that the 4th ventricle. It includes the basilar artery, the beginning of the anterior inferior cerebellar artery, the origin of the premium cerebellar artery, and also the abducens nerve (cranial nerve VI).
7) Cerebellopontine cistern:
Situated in the lateral angle in between the pons and also the cerebellum. It consists of the facial nerve (cranial nerve VII), the vestibulocochlear nerve (cranial nerve VIII), the trigeminal nerve (cranial nerve V), and the anterior worse cerebellar artery.
8) Cerebellomedullary cistern:
Also recognized as the cisterna magna is the biggest subarachnoid cistern. It is located in between the medulla oblongata and also the cerebellum. That receives CSF native the 4th ventricle v foramen of Magendie (median aperture). It contains the vertebral artery, the beginning of the posterior worse cerebellar artery, the glossopharyngeal nerve (cranial nerve IX), vagus nerve (cranial nerve X), accessory nerve (cranial nerve XI) and also hypoglossal nerve (cranial nerve XII).
9) Lumbar cistern:
It is located at the lower lumbar spinal canal. The extends indigenous the conus medullaris around the level of the an initial and 2nd lumbar vertebrae come the level that the 2nd sacral vertebra. It consists of the filum terminale and the cauda equina. During lumbar puncture, the clinician paint, etc CSF native this cistern.
Functionally, the CSF operation within the subarachnoid an are and the ventricular system. The choroid plexus mainly secretes the cerebrospinal liquid at a rate of 0.3 ml/min, and there are approximately 150 ml the CSF circulating at any given time.<5> While the ventricular system has 25 mL, the remainder is present within the subarachnoid space. A smaller sized amount the CSF is also secreted by the ependymal lining of the ventricles and the dura mater of the nerve roots sleeves in the spinal canal.<3> After production, CSF operation from the lateral ventricles v the left and also right foramen that Monro and also enters the third ventricle. Next, that flows into the 4th ventricle v the cerebral aqueduct. After ~ that, CSF flows into the subarachnoid an are through the foramen the Lushka laterally and foramen the Magendie medially. It flows superiorly and also inferiorly overlying the cerebral cortex and also spinal cord.
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<6> Eventually, it reaches the arachnoid granulations that room projections the the arachnoid mater into the premium sagittal sinus and also act together an avenue because that reabsorption that CSF into the blood with a pressure-dependent gradient.