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No. 27
1. The Meninges of Brain and Spinal Cord
2. The Blood Vessels of Brain and Spinal Cord
3. The Circulation of Cerebrospinal Fluid
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Section 4 The Meninges and Blood Vessels of
Brain and Spinal Cord, and the Circulation of
Cerebrospinal Fluid
Ⅰ. The Meninges (or coverings) of
Brain and Spinal Cord
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The brain and spinal cord are enclosed by three
layers of membranes, the meninges:
① The dura mater, an outer tough and dense
protective membrane.
② The arachnoid, and intermediate spiderweblike delicate one.
③ The pia mater, an innermost thin translucent,
more delicate and fibrous membrane, which is
rich in blood vessels and is adherent to the
surface of the brain and spinal cord.
The three membranes of the brain and spinal
cord are continuous at the foramen magnum.
Ⅰ) The meninges of spinal cord
1. The spinal dura mater (spinal dura)
 It is composed of dense connective tissue,
covering the spinal cord.
 The dura mater of the spinal cord is
continuous with the dura of the brain, and
is attached to the circumference of the
foramen magnum, so that the epidural
space is not open into the cranial cavity.
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The dural sac becomes thinner at the level
of the second sacral vertebra, and closely
invests the filum terminale to attach at the
back of the coccyx.
Laterally, the spinal dura is continuous
with the external membrane of the spinal
nerve at the intervertebral foramina.
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Epidural space and subdural space:
There is a space between the dura and the
periosteum of the vertebral canal, which is
called the epidural space. The epidural
space contains a quantity of loose areloar
tissue, lymphatic vessels and venous
plexuses. The spinal nerves on each side
pass through the epidural space which is
applicable for block anesthesia.
The space between the spinal dura and
arachnoid is subdural space.
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2. Spinal arachnoid
Spinal arachnoid is a delicate, avascular
membrane lying between the spinal dura and pia
maters, covering the surfaces of the spinal cord,
continuing with the cerebral arachnoid.
Spinal subarachnoid space and terminal cistern:
The spinal subarachnoid space is between the
spinal dura and pia maters. Upwards, it
communicates with the cerebral subarachnoid
space.
It becomes wider from the inferior end of the
spinal cord to about the level of the second sacral
vertebra, which is called terminal cistern and
contains the cauda equina.
It is the best site (between the 3rd and 4th
lumbar vertebrae or the 4th and 5th) for a
lumbar puncture because of avoiding injury to
the spinal cord.
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3. Spinal pia mater
It is a delicate vascular membrane, closely
attached to the surfaces of the spinal cord and
dips into the fissures and sulci of the spinal cord.
At the lower end of the spinal cord, it condensed
as the filum terminale which descends from the
conus medullaris to the level of the 2nd sacral
vertebra.
Denticulate ligament:
The denticulate ligament composed of spinal pia
mater, is attached along the lateral surface of the
spinal cord, midway between the dorsal and
ventral nerve roots. The lateral edge of this
ligament is sawtoothed and attached to the dura
at regular intervals.
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Ⅱ) The meninges of brain
They are named the cerebral dura mater, cerebral
arachnoid, and cerebral pia mater.
1. The cerebral dura mater
It is tightly used together with the inner
periosteum of the skull in one layer. The cerebral
dura mater is in loose contact with the calviria, so
that epidural hematoma often happens in this
area; while, the cerebral dura is closely attached
at the base of skull, and cerebrospinal fluid may
leak out from the nose or ear with a fracture of
the base of skull, because of accompanying
laceration of the cerebral dura mater and
arachnoid.
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The structures formed by the cerebral dura mater.
(1) Septa
The cerebral dura mater forms several septa
between the large divisions of the brain.
① The cerebral falx
A strong membrane extending down into the
cerebral longitudinal fissure between the two
cerebral hemispheres with the free inferior
margin just above the corpus callosum.
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② The cerebellar tentorium
A semilunar shelf of dura mater separating the
cerebellum from the cerebrum, attaches laterally
and posteriorly to the temporal and occipital
bones with the free anterior margin called
tentorial incisure surrounding the midbrain.
Because the parahippocampal gyrus and uncus
are located just above the tentorial incisure,
increased intracranial pressure can move the
parahipocampal gyrus and uncus downwards to
form the tentorial hernia. With the enlargement
of the homolateral pupil, paralyses of the
homolateral external ocular muscles and
contralateral hemiplegia will occur because the
hernia presses the oculomotor nerve and the
cerebral peduncle.
③ The cerebellar falx
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(2) Venous sinuses
At certain sites the cranial dura mater is
separated and forms large venous sinuses
called the sinuses of dura mater (dural
sinuses), into which the cerebral veins
are drained.
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The drainage of the venous sinuses of dura mater.
Superior sagittal s.→→→→→→→→→
↓
Inferior sagittal s. →Straight s. →Confluence of s.
→Transverse s. →Sigmoid s. →internal
↑
jugular v.
↑
↑
Cavernous s. →→→→→→Superior petrosal s.→→→→
↑
↓
↑
→→→→→→→→→→→→Inferior petrosal
sinus→→→→→→→→→→→→→→→→
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2.The cerebral arachnoid
Spinal arachnoid is a delicate, avascular
membrane lying between the cerebral
dura and pia maters.
Subarachnoid space and Subarachnoid
cisterns:
The subarachnoid space is between the
cerebral arachnoid and pia mater and
contains the cerebrospinal fluid.
The arachnoid bridges over some places
around the brain to form wide spaces
called
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the subarachnoid cisterns. They are as follows:
Cerebellomedullary cistern,
Pontine cistern,
Interpeduncular cistern,
Chiasmatic cistern,
Ambient cistern.
Arachnoid granulations:
The arachnoid granulations are berry-like tufts
of arachnoid which protrude into superior sagittal
sinus and other sinuses. The cerebrospinal fluid
in the subarachnoid cavity passes through this
thin membrane into the sinuses of dura mater
and is taken up by the venous blood stream.
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3. The cerebral pia mater
It is a delicate vascular membrane, closely
attached to the surfaces of the brain and
dips into the fissures and sulci of the brain.
Choroid plexuses:
At certain sites of the cerebral ventricular
walls, the cerebral pia mater and its blood
vessels combine with the ependyma to
form the choroid plexuses, which are
the main sources of cerebrospinal fluid
(CSF).
Ⅱ. The Blood Vessels of Brain and
Spinal Cord
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Ⅰ) The Arteries of Brain
The brain receives the blood from the internal
carotid artery and vertebral artery.
The anterior 2/3 of the cerebral hemisphere,
some portions of the diencephalon are supplied
by the internal carotid artery, and the posterior
1/3 of the cerebral hemisphere, some portions,
brain stem and cerebellum by the vertebral artery.
So the arteries of brain are summed up as the
internal carotid artery system and vertebral—
basilar artery system.
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The branches of the two systems are
divided into the cortical and the central
branches. The cortical branches supply
the cerebral cortex and part of the
medullary substances. The central
branches supply the basal nuclei, the
internal capsule and the diencephalon.
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1. The internal carotid artery
It arises from the common carotid artery,
passes upward through the carotid canal
to enter the cranial cavity and passes
through the cavernous sinus to the brain
after giving off the ophthalmic artery.
The internal carotid artery is divided into
carotid part, petrosal part, cavernous part,
and upper part of anterior clinoid process.
Its branches are the anterior cerebral,
middle cerebral, anterior choroidea and
posterior communicating arteries.
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1) The anterior cerebral artery
It passes forward and medially to enter
the cerebral longitudinal fissure and runs
backward along the dorsal surface of the
corpus callosum.
The cortical branches supply the medial
surface anterior to the parietoocipital
sulcus, part of basal surface of frontal lobe,
and the upper part of the dorsolateral
surface of the frontal and parietal lobes of
the cerebral hemisphere.
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The central branches arising from the
proximal segment of the anterior cerebral
artery, perforating through the anterior
perforated substance, supply the caudate
nucleus, anterior part of lentiform nucleus
and anterior limb of internal capsule.
The anterior comunicating artery
connects the anterior cerebral arteries of
each side at the place where they enter
the longitudinal fissure.
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2) The middle cerebral artery
It runs horizontally to the lateral and then
upward to the lateral sulcus in which it courses
laterally and backward to the dorsolateral surface
of the cerebral hemisphere.
Its cortical branches supply the most part of the
dorsolateral surface of the cerebral hemisphere
and insula which are the higher centers
concerned with motor, sensation, and language.
The central branches supply the caudate nucleus,
lentiform nucleus, genu and the anterior part of
posterior limb of internal capsule.
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3) The anterior choroidea artery
4) The posterior communicating artery
It runs backward and anastomoses with
the posterior cerebral artery.
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2. The vertebral artery
It arises from the subclavian artery and
runs upward through the foramina of the
transverse processes of the sixth to the
first cervical vertebrae to enter the cranial
cavity via the foramen magnum. At the
inferior border of the pons, it joins the
vertebral artery of the opposite side to
form the basilar artery, which runs
forward along the ventral surface of the
pons.
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At the upper border of the pons, the
basilar artery divides into two posterior
cerebral arteries, which supply most parts
of the occipital and temporal lobes.
(1) The main branches of vertebral artery
1) Anterior and posterior spinal arteries
2) Posterior inferior cerebellar artery
It supplies the posterior part of inferior
surface of cerebellum and the lateral part
of medulla oblongata.
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(2) The main branches of basilar artery
1) Anterior inferior cerebellar artery.
2) Labyrinthine artery
It supplies the labyrinthine of inner ear.
3) Pontine arteries
They supply the basilar part of pons.
4) Superior cerebellar artery
It supplies the superior part of cerebellum.
5) Posterior cerebral artery
It is the terminal branch of the basilar artery.
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The cortical branches supply the medial
and inferior surfaces of temporal lobe, and
the occipital lobe.
The central branches go into the cerebral
substance through the interpeduncular
fossa supplying dorsal thalamus, medial
geniculate body, hypothalamus, and
subthalamus.
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3. The cerebral arterial circle (of Willis)
It is formed by the anterior and posterior
cerebral arteries, the anterior and
posterior communicating arteries, and a
short segment of internal carotid arteries.
It encircles the optic chiasma, the tuber
cinereum, and the mammillary bodies.
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Ⅱ) The Veins of Brain
The cerebral veins do not run together with the
arteries, and usually are divided into superficial
and deep groups.
1. The superficial veins
They are situated on the surface of the brain and
drain the blood from the cerebral cortex to empty
into the adjacent sinuses of dura mater.
2. The deep veins
They drain the blood from the deep structures,
and terminate in the great cerebral vein which
empties into the straight sinus.
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Ⅲ) The Blood Vessels of Spinal Cord
The blood of the spinal cord comes from the
anterior and posterior spinal arteries of the
vertebral artery, and also from the posterior
intercostal and the lumbar arteries.
The posterior spinal artery descends along the
posterolateral sulcus.
The anterior spinal artery unites with its fellow of
the opposite side to form a trunk which descends
along the anterior median fissure to be
distributed to every part of the spinal cord.
The distribution of the spinal veins are similar to
that of the spinal arteries.
Ⅲ. The Circulation of
Cerebrospinal Fluid
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The cerebrospinal fluid (CSF) plays a role like
lymph in the central nervous system, has
nutritive functions and serves to remove the
waste products of neuronal metabolism.
CSF fills the subarachnoid space and supports
and cushions the central nervous system against
trauma.
The CSF can disperse the pressure on the brain
caused by a blow and regulate the intracranial
pressure.
Production:
The CSF is produced by the choroid plexuses of
the lateral, the third and the fourth ventricles.
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Circulation route of cerebrospinal fluid:
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Lateral ventricles
↓(interventricular foramina)
third ventricle
↓(cerebral aqueduct)
fourth ventricle
↓(median foramen and lateral foramina)
subaracnoid space
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arachnoid granulations
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sinuses of dura mater (superior sagital sinus)
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internal jugular vein
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An obstruction of the circulatory route
causes the increased intracranial pressure
of hydrocephalus in infants. The
displacement of the brain tissue due to the
elevated intracranial pressure, will cause a
cerebral hernia, such as the tentorial
herniation and the herniation of the
cerebellar tonsils.