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Neuro-Anatomy
lec: 1 Prof Dr. Al-Hubaity
THE MENINGES
Three membranes cover the brain & spinal cord. They are arranged as
outer dura, then arachnoid & inner layer is pia mater.
The cranial dura mater is formed of 2 layers, an endosteal & meningeal.
(The dura of spinal cord is only one layer). The 2 layers are firmly fused
together, except at certain sites where they separate to enclose between
them venous sinus.
The inner layer of dura is thick, fibrous, tough and strong, being stretched
at certain places to form the dural folds (4 in number) they divide the
intercranial cavity into a freely communicating compartments, which
contain the different parts of the brain.
These folds are:
(1) Flax cerebri
Is sickle shaped fold occupying the median longitudinal cerebral fissure
between the 2 cerebral hemispheres, its pointed anterior end attaches to
cristagalli & internal frontal crest, while its broad posterior extremity
fuses with the superior layer of tentorium cereblli. The flax cerebri has an
outer fixed convex border related to the inner aspect of sagittal suture,
while its inner border is free and related to corpus callosum (which
connects the 2 cerebral hemispheres) at the bottom of the cerebral fissure.
The flax cerebri encloses 3 venous sinuses:
1- Superior sagittal sinus, on the fixed outer border of falx cerebri.
2- Inferior sagittal sinus, on the inner free border of falx cerebri.
3- Straight (rectus) sinus along the line of fusion of posterior
extremity of falx cerebri & tentorium cerebelli.
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(2) Tentorium cerebelli
Is a tent shaped fold which roofs the posterior cranial fossa & its contents,
it separates the superior surface of the cerebellum from inferior surface of
the occipital lobe of cerebrum.
It has 2 borders (attached & free)
The attached border extend from the posterior clinoid process, apex
of the petrous bone, superior border of petrous bone and along the
groove for the transverse sinus on the circumference of the
occipital bone on each side.
The free border is U shaped and surrounds the mid brain, it is
called the tentorial hiatus (or tentorial notch). The 2 ends of U
cross the fixed part at the posterior clinoid Process on each side to
be affixed at the anterior clinoid process, between the 2 parts there
is a slit like gap for the passage of occulomotor & trochlear nerves
to reach the cavernous sinus on their way to the superior orbital
fissre.
Three venous sinuses are enclosed within the tentorium cerebelli
includes:
1- Rectus (straight) sinus.
2- Superior petrosal sinus on the attached border of petrous bone
(superior petrosal sulcus).
3- Transverse sinus, lies in the attached border in the groove for
transverse sinus on the circumference of occipital bone from
inside.
(3) Falx cerebelli
Is a small median sickle shaped fold attached to the internal occipital
crest and fuses to the inferior layer of tentotrium cerebelli. It indents the
cerebellum from behind between the 2 cerebellar hemispheres. It encloses
the occipital venous sinus.
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(4) Diaphragm sellae
Is a circular fold that roofs the sella turcica (as a diaphragm) where it
covers the pituitary gland. It is perforated at its centre by the
infundibulum (pituitary stalk) which connects the pituitary gland to the
hypothalamus. The diaphragm sellae encloses the anterior and posterior
inter cavernous sinuses.
The dura mater of spinal cord is separated from the wall of the vertebral
canal by the epidural (extradural) space and from the arachnoid mater by
subdural space.
It is attached to the following areas:
1- Circumference of foramen magnum.
2- Bodies of 2
nd
& 3
rd
cervical vertebrae.
3- Back of the coccyx.
4- Intervertebral foramina (loose attachment).
5- Posterior longitudinal ligament (loose attachment).
The spinal dural tube is continuous above with the cranial dura mater &
ends below at the 2
nd
sacral vertebra where it forms a dural sheath around
the filum terminale.
It sends sleeves around the roots of the spinal nerves as they approach the
intervertebral foramina. The epidural space lies between it and the wall of
the vertebral canal it contains:
Loose areolar tissue.
Internal vertebral plexus of veins.
Fine arterial branches.
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VENOUS SINUSES
These are venous spaces either between the outer & inner layers of the
dura mater or within the meningeal layer only (i.e. related to folds of the
dura).
They receive the venous blood from the brain, meninges & diploi veins of
skull bones & drain them eventually in to the bulb of the internal jugular
vein.
They possess no valves. They include singled & paired sinuses.
Paired includes:
1- Sphenoparietal related to the lesser wing of sphenoid.
2- Cavernous sinus: on either side of body of sphenoid, extending
from medial end of S.O.F to apex of the petrous bone.
3- Superior petrosal sinus (S.P.S) on the upper border of petrous bone.
4- Inferior petrosal sinus (I.P.S) runs on the petro-occipital sulcus.
5- Transverse Sinus: runs transversely from internal occipital
protuberance in a groove within the circumference of the occipital
bone.
6- Sigmoid sinus (S-Shaped): starts at the base of the petrous
temporal bone, as a continuity of the transverse sinus.
Singled includes:
1- Superior sagittal sinus (S.S.S) on the convex, outer fixed margin of
the falx cerebri.
2- Inferior sagittal sinus (I.S.S) on the inner free border of falx
cerebri.
3- Straight (rectus) sinus at the line of fusion of broad posterior end of
falx cerebri with the superior layer of tentorium cerebelli.
4- Occipital sinus: in the attached margin of falx cerebelli at the
internal occipital crest. It communicates with the internal vertebral
venous plexus (in the vertebral canal) & also communicates with
the confluence of sinuses at the internal occipital protuberance.
5- Confluence of venous sinuses.
6- Basilar venous Plexus.
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THE CAVERNOUS SINUS
It contains the following structures
Within the lumen:
1- Internal Carotid Artery.
2- Internal Carotid Sympathetic Plexus.
3- Abducent nerve.
On the wall of the cavernous sinus:
1- Occulomotor nerve.
2- Trochlear nerve.
3- Ophthalmic division of trigeminal.
4- Maxillary division of trigeminal.