Both the brain and spinal are inside a bony box formed by the cranial cavity and part of the spinal canal, but by virtue of their delicacy and functional importance, are involved by a special shock absorbers, represented by three membranes, the meninges: dura mater, pia mater and arachnoid.
Functions of Cranial Meninges
Biological-Protection: prevents as a filter, the input of chemicals and microorganisms harmful to our nervous system. It protects us from very serious infections (encephalitis) and brain damage produced by some substances.
-Mechanical protection: are 3, exactly, meningeal coverings surrounding the SN, such as plastic food wrap several times to delay its degradation. Between two covers a clear fluid that circulates absorbs shock, is the cerebrospinal fluid. This important feature allows small blows to the head does not involve a serious threat to life.
dura mater of the brain
The dura is the most superficial, also the most resistant (fibrous tissue) of the three and is conventionally described as consisting of two layers, layer endosteal and meningeal layer, the which are in close apposition except along certain lines, which separate to form venous sinuses.
endosteal layer is nothing more than the periosteum, which covers the inner surface of the skull bones. In the spinal cord was not continuous with the dura mater of the spinal cord.
Around the edges of all holes the skull is continuous with the periosteum on the outside of the skull bones. In the suture is continuous with sutural ligaments.
is more firmly attached to the bones of the skull base.
meningeal layer is the dura itself. Is a strong, dense membrane covering the brain and continues through the foramen magnum to the dura mater of the spinal cord. Provides tubular sheaths cranial nerves as they pass through the holes of the skull. Pods outside the skull fuse with the epineurium of the nerves.
meningeal layer sends inward four partitions, which divide the cavity cranial spaces that freely communicate and stay subdivisions of the brain. The function of these walls is to limit the movement of encéfalo0 movements associated with acceleration and deceleration when moving the head.
outer surface: It meets regularly rounded bony walls and ligaments of the spinal canal, from which is separated by the epidural space. Free at the back, above, is in contact with the posterior longitudinal ligament. Laterally, extending around each spinal nerve, which accompanies increasingly thinning out of the intervertebral foramen.
inner surface: is glossy and smooth and corresponds to the arachnoid.
Top End: Continue unlimited net with the cranial dura mater. On its outer surface, adheres to the foramen magnum and the atlas.
End Lower : constitutes the bottom of the dural sac, which stops at the level of S2-S3. Contains the cauda equina and filum terminal. This latest in the lowest part of the dural sac pierces the dura, which is applied to the sheathing. Descend into the first coccygeal vertebra. The dura mater adheres the anterior sacral canal.
The falx cerebri is a fold of dura mater with a sickle which is located in the midline between the two cerebral hemispheres. Narrow front end is attached to the inside front crest and the crista galli apophysis. His broad back is fused in the midline with the upper surface of the tentorium. The superior sagittal sinus runs in its concave free margin and the straight sinus runs along its insertion in the tentorium.
The tentorium is a fold of dura mater with crescent that forms a roof over the posterior cranial fossa. Covering the upper surface of the cerebellum and supports the occipital lobes of the hemispheres brain. At the edge there is a gap, notch store for the passage of the midbrain, which produces a free inner edge and an outer edge attached or fixed. Bound edge is attached to the posterior clinoid process, the upper edges of the margins and petrous portions of the grooves for the transverse sinuses on the occipital bone. The free edge running forward towards both ends, cross the border attached and fixed to the anterior clinoid process on each side. At the point where the borders are crossed, the third and fourth cranial nerves pass forward to enter the cavernous sinus lateral wall.
Near the apex of the petrous temporal bone, the Shop bottom layer of the cerebellum as a forward pocket below the superior petrosal sinus to create a break to the trigeminal nerve and trigeminal ganglion.
The falx cerebri and falx cerebelli are attached to the upper and lower surfaces of the store, respectively. The straight sinus runs along its insertion into the mouth of the brain, the superior petrosal sinus along its insertion into the petrous and cavernous sinus, alo during their insertion into the occipital bone.
The falx cerebelli, a small fold of dura mater with a sickle attached to the internal occipital crest, projecting forward between the two cerebellar hemispheres. Its rear fixed margin contains the occipital sinus.
Diaphragm (tent of the pituitary) of the sella is a small circular fold of dura mater that forms the roof of the sella. A small hole in the center allows the passage of the pituitary stalk.
spinal dura
completely encloses the spinal cord. Above, are continuous through the foramen magnum with the meningeal layer of dura covering the brain. And below, ending in the filum terminale at the bottom of the second sacral vertebra. The dural sheath was placed in loosely into the spinal canal and is separated from the canal walls by the extradural space. It contains loose areolar tissue and the internal vertebral venous plexus. The dura mater extends along each nerve root and continues into the connective tissue around each spinal nerve (epineurium). The inner surface of the dura mater is in contact with the arachnoid.
Innervation of the dura mater
branches of the trigeminal, vagus and spinal nerves and first three branches of the sympathetic trunk pass into the dura.
The dura has many sensitive nerve endings to stretching, which produces the sensation of headache. The stimulation of sensory trigeminal nerve endings above the level of tentorium produce referred pain in an area of \u200b\u200bskin on the same side of the head. Stimulation of dural nerve endings below the level of the tentorium produce referred pain to the back of the neck and scalp, along the greater occipital nerve distribution.
Irrigation Dura
Many arteries supplying the dura from internal carotid artery, maxillary, ascending pharyngeal, occipital and vertebral. From a clinical standpoint, the most important is the middle meningeal artery, which is commonly injured in head injuries.
middle meningeal artery arises from the maxillary artery in the infratemporal fossa. Enters the cranial cavity through the foramen spinosum and is located between the meningeal and endosteal layers of dura mater. Artery then runs forward and laterally in a groove located on the upper surface of the squamous part of temporal bone. The anterior branch crosses deep anteroinferior angle of the parietal bone and tour matches as rude to the line of the precentral gyrus underlying brain. The posterior branch curves backward and supplies the back of the dura.
meningeal veins are located in the endosteal layer of dura mater. The middle meningeal vein follows the branches of the middle meningeal artery and drains into the pterygoid venous plexus or within sphenoparietal. The veins are located outside of the arteries.
dural venous sinuses
The venous sinuses of cranial cavity located between the layers of the dura. Its main function is to receive blood from the brain through brain or spinal fluid from the subarachnoid space through arachnoid villi. The blood of the dural sinuses eventually drain into the internal jugular veins in the neck. The dural sinuses are lined by endothelium and lack muscle walls. They do not contain valves. Emissary veins, which also have valves, connect the dural venous sinuses with veins diploic skull and scalp veins.
The superior sagittal sinus occupies the upper fixed edge of the falx cerebri. Begins earlier in the knockout, which is sometimes called a vein from the nasal cavity. Run back plying the vault of the skull and the internal occipital protuberance it deviates to one side or the other (usually the right) and continues with the corresponding transverse sinus.
The breast is communicated through small holes, with two or three irregular venous lakes on either side. Numerous villi and meningeal arachnoid granulations project into the gaps, which are also diploic and meningeal veins.
The superior sagittal sinus in its course receives the superior cerebral veins. In the internal occipital protuberance swells to form the confluence of the sinuses. Here usually the superior sagittal sinus is continuous with the right transverse sinus, is connected to the opposite transverse sinus receives the occipital sinus.
The inferior sagittal sinus occupies the bottom free of the falx cerebri. Runs back and joins the more cerebral vein in the free margin of the tentorium, to form the straight sinus. Brain receives some veins from the surface medial cerebral hemispheres.
The straight sinus occupies the line of junction of the falx cerebri with the tentorium. It is formed by the junction of inferior sagittal sinus with the more cerebral vein. Ends turn left (sometimes right) to form the transverse sinus.
The transverse sinuses are paired structures and start at the internal occipital protuberance. Usually, the right breast is continuous with the superior sagittal sinus and the left continues the straight sinus. Each occupies within the margin of the store joined the cerebellum, plying the occipital bone and the posteroinferior angle of the parietal bone. Receive superior petrosal sinus and the cerebral veins and inferior cerebellar veins and diploic. They end up turning down as the sigmoid sinus.
sigmoid sinuses are a direct continuation of the transverse sinuses. Each breast down and turns medially and crosses the mastoid portion of temporal bone. This post is located within the mastoid antrum. Then comes back and then down through the back of the jugular foramen to continue with the superior bulb of internal jugular vein.
The occipital sinus is a sinus occupies small room attached to the falx cerebelli. Begins near the foramen magnum, where it communicates with the vertebral veins and drains into the confluence of the sinuses.
The cavernous sinuses are located in the cranial fossa half on each side of the body of the sphenoid bone. Numerous trabeculae cross inside, which gives it a spongy appearance, hence its name. Each sinus extends from the superior orbital fissure in front to the apex of the petrous temporal bone behind.
The internal carotid artery, surrounded by sympathetic nerve plexus, runs forward through the breast. The abducens nerve also passes through the breast. The internal carotid artery and nerve separated from the blood by an endothelial lining.
The third and fourth cranial nerves and the ophthalmic branch and maxillary trigeminal nerve running forward in the lateral sinus wall. They are located between the endothelial lining and the dura. Tributaries are the superior and inferior ophthalmic veins, cerebral veins inferior parietal and spheno within the central retinal vein. The sinus drains
later in the superior and inferior petrosal sinus, and inferiorly into the pterygoid venous plexus.
The two sinuses communicate with each other through both breasts intercavernous front and back running in the diaphragm sellae in front and behind the pituitary stalk. Each breast has a significant communication with the facial vein via the superior ophthalmic vein (this is a route by which infection can spread from the skin of the face to the sinus).
petrosal sinuses upper and lower small breasts are located on the top and bottom edges of the petrous temporal bone on either side of the skull. Each sinus drains into the cavernous sinus than in the transverse sinus and draining each breast below the cavernous sinus in the internal jugular vein. Arachnoid
brain
The arachnoid is a delicate waterproofing membrane covering the brain and lies between the pia mater internally and the dura mater externally. She is separated from the dura by a potential space subdural space, filled with a liquid film, and the pia mater by the subarachnoid space, which is filled with cerebrospinal fluid. The external and internal surfaces of the arachnoid are covered with flattened mesothelial cells.
The arachnoid bridges over the grooves form the surface of the brain and, in certain situations, the arachnoid and pia mater are widely separated to form the subarachnoid cisterns.
cerebellomedullary The tank is located between the lower surface of the cerebellum and roof of the fourth ventricle. The interpeduncular cistern is located between the two pendulums brain. All tanks communicate freely among themselves and with the rest of the space subcaroideo.
arachnoid In some areas the project into the venous sinuses forming arachnoid villi. These are more numerous along the superior sagittal sinus. The groups are called arachnoid villus arachnoid granulations. Arachnoid villi serve as sites from which the cerebrospinal fluid diffuses into the bloodstream.
The arachnoid is connected with the pia mater through the fluid-filled subarachnoid space by delicate bands of fibrous tissue.
is important to remember that the structures that pass into the brain and down into the skull or holes must traverse the subarachnoid space. All arteries and veins brain located in space, like the cranial nerves. The arachnoid membrane fuses with the epineurium of the nerves at their point of exit from the skull. In the case of the optic nerve, the arachnoid forms a sheath that extends into the orbital cavity through the optic foramen and fuses with the sclera of the eyeball. Thus, the subarachnoid space extends around the optic nerve to the eyeball.
Arachnoid Spinal Cord
The arachnoid is a waterproof membrane, which covers the delicate spinal cord and pia mater is located between the inside and outside the dura mater. The pia mater, separated by a wide space, the subarachnoid space, that is filled with cerebrospinal fluid.
The subarachnoid space is crossed by some thin bands of connective tissue. The arachnoid is continued upward through the foramen magnum with the arachnoid membrane covering the brain. At the bottom, ending in the filum terminale at the bottom of the second sacral vertebra. The arachnoid continues along the spinal nerve roots and forms small lateral extensions of the subarachnoid space.
Pia mater of the brain.
The pia mater is a vascular membrane covered by flattened mesothelial cells. Of closely covering the brain convolutions and down in the grooves deeper. It stretches out over the cranial nerves and merged with its epineurium. Cerebral arteries entering the brain substance are pial sheath with them.
The pia mater velum forms the roof of the third and fourth ventricles of the brain and fuses with the ependyma to form the choroid plexus in the lateral ventricles, third and fourth of the brain.
spinal part in its jagged walls arranged in a festoon, called denticulate ligaments. Between the arachnoid and pia mater is the subarachnoid space containing cerebrospinal fluid and appears crossed by a large number of thin trabeculae. Pia Mater
Spinal Cord.
is a vascular membrane that lines closely the spinal cord is thickened on each side between the nerve roots to form the denticulate ligament that runs laterally to join the arachnoid and dura. In this way the spinal cord is suspended in the middle of the dural sheath. The pia mater extending along each nerve root and is continuous with the connective tissue surrounding each nerve cord.
Blogalaxiatags: meninges meninges + cranial dura pia arachnoid + dural venous sinuses +
0 comments:
Post a Comment