The Central Nervous System
In several places, the meningeal dura mater extends inward
to form ﬂat partitions that subdivide the cranial cavity. Tese
, which limit excessive movement of the brain within
the cranium, include the following (Figure 12.23a):
ĕ-bri). A large sickle-shaped (
sickle) fold that dips into the longitudinal ﬁssure between the
cerebral hemispheres. Anteriorly, it attaches to the crista galli
of the ethmoid bone.
i). Continuing inferiorly from the
posterior falx cerebri, this small midline partition runs along
the vermis of the cerebellum.
re-um; “tent”). Resembling a
tent over the cerebellum, this nearly horizontal dural fold ex-
tends into the transverse ﬁssure between the cerebral hemi-
spheres (which it helps to support) and the cerebellum.
Te middle meninx, the
a loose brain covering, never dipping into the sulci at the cerebral
surface. It is separated from the dura mater by a narrow serous
, which contains a ﬁlm of ﬂuid. Beneath
the arachnoid membrane is the wide
web-like extensions span this space and secure the arachnoid mater
to the underlying pia mater (
means “spider”). Te sub-
arachnoid space is ﬁlled with cerebrospinal ﬂuid and also contains
the largest blood vessels serving the brain. Because the arachnoid
mater is ﬁne and elastic, these blood vessels are poorly protected.
Knoblike projections of the arachnoid mater called
i) protrude superiorly through the dura mater
and into the superior sagittal sinus (see Figure 12.22). Tese villi
absorb cerebrospinal ﬂuid into the venous blood of the sinus.
(cerebrospinal ﬂuid). Furthermore, the blood brain barrier pro-
tects the brain from harmful substances in the blood. We de-
scribed the cranium, the brain’s bony encasement, in Chapter 7.
Here we will consider the other protective elements.
membrane) are three
connective tissue membranes that lie just external to the CNS
organs. Te meninges:
Cover and protect the CNS
Protect blood vessels and enclose venous sinuses
Contain cerebrospinal ﬂuid
Form partitions in the skull
From external to internal, the meninges (singular:
the dura mater, arachnoid mater, and pia mater
ter), meaning “tough
mother,” is the strongest meninx. Where it surrounds the brain,
it is a two-layered sheet of ﬁbrous connective tissue. Te more
attaches to the inner surface of the
skull (the periosteum). (Tere is no dural periosteal layer sur-
rounding the spinal cord.) Te deeper
the true external covering of the brain and continues caudally in
the vertebral canal as the spinal dura mater. Te brain’s two du-
ral layers are fused together except in certain areas, where they
separate to enclose
dural venous sinuses
that collect venous
blood from the brain and direct it into the internal jugular veins
of the neck
Superior sagittal sinus
Skin of scalp
• Meningeal la
Bone of skull
Meninges: dura mater, arachnoid mater, and pia mater.
dura forms the falx cerebri fold. A dural sinus, the superior sagittal sinus, is enclosed by the
dural membranes superiorly. Arachnoid villi return cerebrospinal ﬂuid to the dural sinus. (Frontal