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Left lateral ventricle
VetBooks.ir
4th ventricle
3rd ventricle Lateral aperture
Lateral ventricles Mesencephalic aqueduct
4th ventricle
Lateral apertures
Figure 10-10. Ventricular system of the brain. Arrows indicate the direction of flow of cerebrospinal
fluid, which is produced in the ventricles and flows via the lateral apertures into the subarachnoid space
surrounding the brain and spinal cord. Top, lateral view; bottom, dorsal view.
valves for the return of CSF from the suba- does not visibly enlarge the head; the
rachnoid space to the venous blood. elevated pressure inside the cranial
Reabsorption of CSF is passive, driven by vault, however, can profoundly affect
the pressure gradient across the arachnoid the brain within.
granulations (i.e., the higher pressure of
CSF within the subarachnoid space drives
the CSF into the low pressure sinus). Meninges
Any obstruction in cerebrospinal
circulation can injure the brain, since The connective tissue coverings of the brain
the choroid plexuses produce CSF inde- and spinal cord are the meninges (singular
pendent of the pressure within the meninx). They include, from deep to super-
ventricular system. Buildup of CSF will ficial, the pia mater, the arachnoid, and
expand the affected ventricular spaces the dura mater (Fig. 10‐11).
at the expense of nervous tissue, which The pia mater, the deepest of the menin-
can be markedly compressed as a result. ges, is a delicate membrane that invests the
If this occurs during development (as brain and spinal cord, following the grooves
often happens when the mesencephalic and depressions closely. The pia mater
aqueduct is inadequately formed), the forms a sheath around the blood vessels and
head can become markedly enlarged follows them into the substance of the CNS.
and the cerebral tissue extremely com- The middle meninx arises embryologi-
pressed. This is the condition called cally from the same layer as the pia mater
hydrocephalus. In an older individual but separates from it during development
whose cranial bones are fully formed so that a space forms between them.
and fused at the sutures, buildup of CSF Remnants of their former connection in
