No. 27 No. 27

1. The Meninges of Brain and Spinal Cord1. The Meninges of Brain and Spinal Cord 2. The Blood Vessels of Brain and Spinal Cord2. The Blood Vessels of Brain and Spinal Cord 3. The Circulation of Cerebrospinal Fluid3. The Circulation of Cerebrospinal Fluid

Section 4 The Meninges and Blood Vessels of Brain anSection 4 The Meninges and Blood Vessels of Brain and Spinal Cord, and the Circulation of Cerebrospinal Fld Spinal Cord, and the Circulation of Cerebrospinal Fluiduid

ⅠⅠ. The Meninges (or coverings) of . The Meninges (or coverings) of Brain and Spinal CordBrain and Spinal Cord

The brain and spinal cord are enclosed by three layers The brain and spinal cord are enclosed by three layers of membranes, the meninges:of membranes, the meninges:

① ① The dura mater, an outer tough and dense protectivThe dura mater, an outer tough and dense protective membrane.e membrane.

② ② The arachnoid, and intermediate spiderweb-like deliThe arachnoid, and intermediate spiderweb-like delicate one.cate one.

③ ③ The pia mater, an innermost thin translucent, more The pia mater, an innermost thin translucent, more delicate and fibrous membrane, which is rich in blood delicate and fibrous membrane, which is rich in blood vessels and is adherent to the surface of the brain and vessels and is adherent to the surface of the brain and spinal cord.spinal cord.

The three membranes of the brain and spinal cord are The three membranes of the brain and spinal cord are continuous at the foramen magnum.continuous at the foramen magnum.

Ⅰ Ⅰ) The meninges of spinal cord) The meninges of spinal cord 1. The 1. The spinal dura materspinal dura mater ( (spinal duraspinal dura)) It is composed of dense connective tissue, covIt is composed of dense connective tissue, cov

ering the spinal cord.ering the spinal cord. The dura mater of the spinal cord is continuouThe dura mater of the spinal cord is continuou

s with the dura of the brain, and is attached to s with the dura of the brain, and is attached to the circumference of the foramen magnum, so the circumference of the foramen magnum, so that the epidural space is not open into the crathat the epidural space is not open into the cranial cavity.nial cavity.

The dural sac becomes thinner at the level of tThe dural sac becomes thinner at the level of the second sacral vertebra, and closely invests he second sacral vertebra, and closely invests the filum terminale to attach at the back of the the filum terminale to attach at the back of the coccyx.coccyx.

Laterally, the spinal dura is continuous with thLaterally, the spinal dura is continuous with the external membrane of the spinal nerve at the e external membrane of the spinal nerve at the intervertebral foramina.intervertebral foramina.

Epidural space and subdural space:Epidural space and subdural space: There is a space between the dura and the periThere is a space between the dura and the peri

osteum of the vertebral canal, which is called tosteum of the vertebral canal, which is called the he epidural spaceepidural space. The epidural space contain. The epidural space contains a quantity of loose areloar tissue, lymphatic s a quantity of loose areloar tissue, lymphatic vessels and venous plexuses. The spinal nervevessels and venous plexuses. The spinal nerves on each side pass through the epidural space s on each side pass through the epidural space which is applicable for block anesthesia.which is applicable for block anesthesia.

The space between the spinal dura and arachnThe space between the spinal dura and arachnoid is oid is subdural spacesubdural space..

2. Spinal arachnoid2. Spinal arachnoid Spinal arachnoid is a delicate, avascular membrane lySpinal arachnoid is a delicate, avascular membrane ly

ing between the spinal dura and pia maters, covering ing between the spinal dura and pia maters, covering the surfaces of the spinal cord, continuing with the certhe surfaces of the spinal cord, continuing with the cerebral arachnoid.ebral arachnoid.

Spinal subarachnoid space Spinal subarachnoid space and and terminal cisternterminal cistern:: The The spinal subarachnoid spacespinal subarachnoid space is between the spinal is between the spinal

dura and pia maters. Upwards, it communicates with tdura and pia maters. Upwards, it communicates with the cerebral subarachnoid space.he cerebral subarachnoid space.

It becomes wider from the inferior end of the spinal coIt becomes wider from the inferior end of the spinal cord to about the level of the second sacral vertebra, whrd to about the level of the second sacral vertebra, which is called ich is called terminal cisternterminal cistern and contains the cauda and contains the cauda equina. equina.

It is the best site (between the 3rd and 4th lumbar vertIt is the best site (between the 3rd and 4th lumbar vertebrae or the 4th and 5th) for a lumbar puncture becauebrae or the 4th and 5th) for a lumbar puncture because of avoiding injury to the spinal cord.se of avoiding injury to the spinal cord.

3. Spinal pia mater3. Spinal pia mater It is a delicate vascular membrane, closely attached to It is a delicate vascular membrane, closely attached to

the surfaces of the spinal cord and dips into the fissurthe surfaces of the spinal cord and dips into the fissures and sulci of the spinal cord. At the lower end of the es and sulci of the spinal cord. At the lower end of the spinal cord, it condensed as the spinal cord, it condensed as the filum terminalefilum terminale whic which descends from the conus medullaris to the level of th descends from the conus medullaris to the level of the 2nd sacral vertebra.he 2nd sacral vertebra.

Denticulate ligamentDenticulate ligament:: The denticulate ligament composed of spinal pia matThe denticulate ligament composed of spinal pia mat

er, is attached along the lateral surface of the spinal cer, is attached along the lateral surface of the spinal cord, midway between the dorsal and ventral nerve rooord, midway between the dorsal and ventral nerve roots. The lateral edge of this ligament is sawtoothed and ts. The lateral edge of this ligament is sawtoothed and attached to the dura at regular intervals.attached to the dura at regular intervals.

Ⅱ Ⅱ) The meninges of brain) The meninges of brain They are named the cerebral dura mater, cerebral araThey are named the cerebral dura mater, cerebral ara

chnoid, and cerebral pia mater.chnoid, and cerebral pia mater. 1. The 1. The cerebral dura matercerebral dura mater It is tightly used together with the inner periosteum of It is tightly used together with the inner periosteum of

the skull in one layer. The cerebral dura mater is in loothe skull in one layer. The cerebral dura mater is in loose contact with the calviria, so that epidural hematomse contact with the calviria, so that epidural hematoma often happens in this area; while, the cerebral dura ia often happens in this area; while, the cerebral dura is closely attached at the base of skull, and cerebrospis closely attached at the base of skull, and cerebrospinal fluid may leak out from the nose or ear with a fractnal fluid may leak out from the nose or ear with a fracture of the base of skull, because of accompanying laceure of the base of skull, because of accompanying laceration of the cerebral dura mater and arachnoid.ration of the cerebral dura mater and arachnoid.

The structures formed by the cerebral dura materThe structures formed by the cerebral dura mater.. (1) Septa(1) Septa The cerebral dura mater forms several septa between The cerebral dura mater forms several septa between

the large divisions of the brain.the large divisions of the brain. ① ① The The cerebral falxcerebral falx A strong membrane extending down into the cerebral A strong membrane extending down into the cerebral

longitudinal fissure between the two cerebral hemisplongitudinal fissure between the two cerebral hemispheres with the free inferior margin just above the corpheres with the free inferior margin just above the corpus callosum.us callosum.

② ② The The cerebellar tentoriumcerebellar tentorium A semilunar shelf of dura mater separating the cerebelA semilunar shelf of dura mater separating the cerebel

lum from the cerebrum, attaches laterally and posterilum from the cerebrum, attaches laterally and posteriorly to the temporal and occipital bones with the free orly to the temporal and occipital bones with the free anterior margin called tentorial incisure surrounding tanterior margin called tentorial incisure surrounding the midbrain.he midbrain.

Because the parahippocampal gyrus and uncus are loBecause the parahippocampal gyrus and uncus are located just above the tentorial incisure, increased intracated just above the tentorial incisure, increased intracranial pressure can move the parahipocampal gyrus cranial pressure can move the parahipocampal gyrus and uncus downwards to form the tentorial hernia. Wiand uncus downwards to form the tentorial hernia. With the enlargement of the homolateral pupil, paralyseth the enlargement of the homolateral pupil, paralyses of the homolateral external ocular muscles and conts of the homolateral external ocular muscles and contralateral hemiplegia will occur because the hernia preralateral hemiplegia will occur because the hernia presses the oculomotor nerve and the cerebral peduncle.sses the oculomotor nerve and the cerebral peduncle.

③ ③ The cerebellar falxThe cerebellar falx

(2) Venous sinuses(2) Venous sinuses At certain sites the cranial dura mater is separAt certain sites the cranial dura mater is separ

ated and forms large venous sinuses called the ated and forms large venous sinuses called the sinuses of dura mater (dural sinuses)sinuses of dura mater (dural sinuses),, into w into which the cerebral veins are drained.hich the cerebral veins are drained.

The drainage of the venousThe drainage of the venous sinuses of dura mater.sinuses of dura mater. Superior sagittal s.→→→→→→→→→Superior sagittal s.→→→→→→→→→ ↓ ↓ Inferior sagittal s. →Straight s. →Confluence of s. →TransverInferior sagittal s. →Straight s. →Confluence of s. →Transver

se s. →Sigmoid s. →internalse s. →Sigmoid s. →internal ↑ ↑ jugular v. jugular v. ↑ ↑ ↑ ↑ Cavernous s. →→→→→→Superior petrosal s.→→→→ Cavernous s. →→→→→→Superior petrosal s.→→→→

↑ ↑ ↓ ↑↓ ↑ →→→→→→→→→→→→ →→→→→→→→→→→→Inferior petrosal sinus→→→→→Inferior petrosal sinus→→→→→

→→→→→→→→→→→→→→→→→→→→→→

2.The cerebral arachnoid2.The cerebral arachnoid Spinal arachnoid is a delicate, avascular memSpinal arachnoid is a delicate, avascular mem

brane lying between the cerebral dura and pia brane lying between the cerebral dura and pia maters.maters.

Subarachnoid spaceSubarachnoid space and and Subarachnoid cisternSubarachnoid cisternss::

The The subarachnoid spacesubarachnoid space is between the cereb is between the cerebral arachnoid and pia mater and contains the cral arachnoid and pia mater and contains the cerebrospinal fluid.erebrospinal fluid.

The arachnoid bridges over some places arounThe arachnoid bridges over some places around the brain to form wide spaces called d the brain to form wide spaces called

the the subarachnoid cisternssubarachnoid cisterns. They are as follows:. They are as follows: Cerebellomedullary cistern,Cerebellomedullary cistern, Pontine cistern,Pontine cistern, Interpeduncular cistern,Interpeduncular cistern, Chiasmatic cistern,Chiasmatic cistern, Ambient cistern.Ambient cistern. Arachnoid granulationsArachnoid granulations:: The The arachnoid granulationsarachnoid granulations are berry-like tufts of ara are berry-like tufts of ara

chnoid which protrude into superior sagittal sinus and chnoid which protrude into superior sagittal sinus and other sinuses. The cerebrospinal fluid in the subarachother sinuses. The cerebrospinal fluid in the subarachnoid cavity passes through this thin membrane into thnoid cavity passes through this thin membrane into the sinuses of dura mater and is taken up by the venous e sinuses of dura mater and is taken up by the venous blood stream.blood stream.

3. The cerebral pia mater3. The cerebral pia mater It is a delicate vascular membrane, closely attaIt is a delicate vascular membrane, closely atta

ched to the surfaces of the brain and dips into ched to the surfaces of the brain and dips into the fissures and sulci of the brain.the fissures and sulci of the brain.

Choroid plexusesChoroid plexuses:: At certain sites of the cerebral ventricular wallAt certain sites of the cerebral ventricular wall

s, the cerebral pia mater and its blood vessels s, the cerebral pia mater and its blood vessels combine with the ependyma to form the combine with the ependyma to form the chorchoroid plexusesoid plexuses, which are the main sources of c, which are the main sources of cerebrospinal fluid (CSF).erebrospinal fluid (CSF).

ⅡⅡ. The Blood Vessels of Brain and . The Blood Vessels of Brain and Spinal CordSpinal Cord

Ⅰ Ⅰ) The Arteries of Brain) The Arteries of Brain The brain receives the blood from the The brain receives the blood from the internal carotid internal carotid

arteryartery and and vertebral arteryvertebral artery.. The anterior 2/3 of the cerebral hemisphere, some porThe anterior 2/3 of the cerebral hemisphere, some por

tions of the diencephalon are supplied by the internal tions of the diencephalon are supplied by the internal carotid artery, and the posterior 1/3 of the cerebral hecarotid artery, and the posterior 1/3 of the cerebral hemisphere, some portions, brain stem and cerebellum misphere, some portions, brain stem and cerebellum by the vertebral artery. So the arteries of brain are suby the vertebral artery. So the arteries of brain are summed up as the mmed up as the internal carotid artery systeminternal carotid artery system and and ververtebral—basilar artery systemtebral—basilar artery system..

The branches of the two systems are divided iThe branches of the two systems are divided into the nto the corticalcortical and and the central branchesthe central branches. The . The cortical branchescortical branches supply the cerebral cortex a supply the cerebral cortex and part of the medullary substances. The nd part of the medullary substances. The centcentral branchesral branches supply the basal nuclei, the intersupply the basal nuclei, the internal capsule and the diencephalon.nal capsule and the diencephalon.

1. The 1. The internal carotid arteryinternal carotid artery It arises from the common carotid artery, passIt arises from the common carotid artery, pass

es upward through the carotid canal to enter tes upward through the carotid canal to enter the cranial cavity and passes through the caverhe cranial cavity and passes through the cavernous sinus to the brain after giving off the nous sinus to the brain after giving off the ophophthalmic arterythalmic artery..

The internal carotid artery is divided into carotThe internal carotid artery is divided into carotid part, petrosal part, cavernous part, and uppid part, petrosal part, cavernous part, and upper part of anterior clinoid process.er part of anterior clinoid process.

Its branches are the anterior cerebral, middle Its branches are the anterior cerebral, middle cerebral, anterior choroidea and posterior cocerebral, anterior choroidea and posterior communicating arteries.mmunicating arteries.

1) The 1) The anterior cerebral arteryanterior cerebral artery It passes forward and medially to enter the cerIt passes forward and medially to enter the cer

ebral longitudinal fissure and runs backward aebral longitudinal fissure and runs backward along the dorsal surface of the corpus callosum.long the dorsal surface of the corpus callosum.

The The cortical branchescortical branches supply the medial surfac supply the medial surface anterior to the parietoocipital sulcus, part of e anterior to the parietoocipital sulcus, part of basal surface of frontal lobe, and the upper pabasal surface of frontal lobe, and the upper part of the dorsolateral surface of the frontal and rt of the dorsolateral surface of the frontal and parietal lobes of the cerebral hemisphere.parietal lobes of the cerebral hemisphere.

The central branches arising from the proximaThe central branches arising from the proximal segment of the anterior cerebral artery, perfol segment of the anterior cerebral artery, perforating through the anterior perforated substanrating through the anterior perforated substance, supply the caudate nucleus, anterior part oce, supply the caudate nucleus, anterior part of lentiform nucleus and anterior limb of internf lentiform nucleus and anterior limb of internal capsule.al capsule.

The The anterior comunicating arteryanterior comunicating artery connects t connects the anterior cerebral arteries of each side at the he anterior cerebral arteries of each side at the place where they enter the longitudinal fissure.place where they enter the longitudinal fissure.

2) The 2) The middle cerebral arterymiddle cerebral artery It runs horizontally to the lateral and then upward to tIt runs horizontally to the lateral and then upward to t

he lateral sulcus in which it courses laterally and backhe lateral sulcus in which it courses laterally and backward to the dorsolateral surface of the cerebral hemisward to the dorsolateral surface of the cerebral hemisphere.phere.

Its Its cortical branchescortical branches supply the most part of the dorso supply the most part of the dorsolateral surface of the cerebral hemisphere and insula lateral surface of the cerebral hemisphere and insula which are the higher centers concerned with motor, swhich are the higher centers concerned with motor, sensation, and language.ensation, and language.

The central branches supply the caudate nucleus, lentThe central branches supply the caudate nucleus, lentiform nucleus, genu and the anterior part of posterior iform nucleus, genu and the anterior part of posterior limb of internal capsule.limb of internal capsule.

3) The anterior choroidea artery3) The anterior choroidea artery 4) The 4) The posterior communicating arteryposterior communicating artery It runs backward and anastomoses with the pIt runs backward and anastomoses with the p

osterior cerebral artery.osterior cerebral artery.

2. The 2. The vertebral arteryvertebral artery It arises from the subclavian artery and runs uIt arises from the subclavian artery and runs u

pward through the foramina of the transverse pward through the foramina of the transverse processes of the sixth to the first cervical verteprocesses of the sixth to the first cervical vertebrae to enter the cranial cavity via the foramebrae to enter the cranial cavity via the foramen magnum. At the inferior border of the pons, in magnum. At the inferior border of the pons, it joins the vertebral artery of the opposite side t joins the vertebral artery of the opposite side to form the to form the basilar arterybasilar artery, which runs forward , which runs forward along the ventral surface of the pons.along the ventral surface of the pons.

At the upper border of the pons, the basilar artAt the upper border of the pons, the basilar artery divides into two posterior cerebral arteries,ery divides into two posterior cerebral arteries, which supply most parts of the occipital and t which supply most parts of the occipital and temporal lobes.emporal lobes.

(1) The main branches of vertebral artery(1) The main branches of vertebral artery 1) Anterior and posterior spinal arteries1) Anterior and posterior spinal arteries 2) 2) Posterior inferior cerebellar arteryPosterior inferior cerebellar artery It supplies the posterior part of inferior surface It supplies the posterior part of inferior surface

of cerebellum and the lateral part of medulla oof cerebellum and the lateral part of medulla oblongata.blongata.

(2) The main branches of basilar artery(2) The main branches of basilar artery 1) Anterior inferior cerebellar artery.1) Anterior inferior cerebellar artery. 2) Labyrinthine artery2) Labyrinthine artery It supplies the labyrinthine of inner ear.It supplies the labyrinthine of inner ear. 3) Pontine arteries3) Pontine arteries They supply the basilar part of pons.They supply the basilar part of pons. 4) Superior cerebellar artery4) Superior cerebellar artery It supplies the superior part of cerebellum.It supplies the superior part of cerebellum. 5) Posterior cerebral artery5) Posterior cerebral artery It is the terminal branch of the basilar artery.It is the terminal branch of the basilar artery.

The The cortical branchescortical branches supply the medial and in supply the medial and inferior surfaces of temporal lobe, and the occipiferior surfaces of temporal lobe, and the occipital lobe.tal lobe.

The central branches go into the cerebral subsThe central branches go into the cerebral substance through the interpeduncular fossa suppltance through the interpeduncular fossa supplying dorsal thalamus, medial geniculate body, ying dorsal thalamus, medial geniculate body, hypothalamus, and subthalamus.hypothalamus, and subthalamus.

3. The 3. The cerebral arterial circlecerebral arterial circle (of (of WillisWillis)) It is formed by the anterior and posterior cereIt is formed by the anterior and posterior cere

bral arteries, the anterior and posterior commbral arteries, the anterior and posterior communicating arteries, and a short segment of inteunicating arteries, and a short segment of internal carotid arteries.rnal carotid arteries.

It encircles the optic chiasma, the tuber cinereIt encircles the optic chiasma, the tuber cinereum, and the mammillary bodies.um, and the mammillary bodies.

Ⅱ Ⅱ) The Veins of Brain) The Veins of Brain The cerebral veins do not run together with the arterieThe cerebral veins do not run together with the arterie

s, and usually are divided into superficial and deep grs, and usually are divided into superficial and deep groups.oups.

1. The superficial veins1. The superficial veins They are situated on the surface of the brain and drain They are situated on the surface of the brain and drain

the blood from the cerebral cortex to empty into the athe blood from the cerebral cortex to empty into the adjacent sinuses of dura mater.djacent sinuses of dura mater.

2. The deep veins2. The deep veins They drain the blood from the deep structures, and teThey drain the blood from the deep structures, and te

rminate in the rminate in the great cerebral veingreat cerebral vein which empties into which empties into the straight sinus.the straight sinus.

Ⅲ Ⅲ) The Blood Vessels of Spinal Cord) The Blood Vessels of Spinal Cord The blood of the spinal cord comes from the The blood of the spinal cord comes from the anterioranterior

and and posterior spinal arteriesposterior spinal arteries of the of the vertebral arteryvertebral artery, , and also from the and also from the posterior intercostalposterior intercostal and the and the lumblumbar arteriesar arteries..

The posterior spinal artery descends along the posterThe posterior spinal artery descends along the posterolateral sulcus.olateral sulcus.

The anterior spinal artery unites with its fellow of the The anterior spinal artery unites with its fellow of the opposite side to form a trunk which descends along thopposite side to form a trunk which descends along the anterior median fissure to be distributed to every pae anterior median fissure to be distributed to every part of the spinal cord.rt of the spinal cord.

The distribution of the spinal veins are similar to that The distribution of the spinal veins are similar to that of the spinal arteries.of the spinal arteries.

ⅢⅢ. The Circulation of Cerebrospinal . The Circulation of Cerebrospinal FluidFluid

The The cerebrospinal fluidcerebrospinal fluid (CSF) plays a role like lymph i (CSF) plays a role like lymph in the central nervous system, has nutritive functions an the central nervous system, has nutritive functions and serves to remove the waste products of neuronal nd serves to remove the waste products of neuronal metabolism.metabolism.

CSF fills the subarachnoid space and supports and cusCSF fills the subarachnoid space and supports and cushions the central nervous system against trauma.hions the central nervous system against trauma.

The CSF can disperse the pressure on the brain causeThe CSF can disperse the pressure on the brain caused by a blow and regulate the intracranial pressure.d by a blow and regulate the intracranial pressure.

Production:Production: The CSF is produced by the choroid plexuses of the latThe CSF is produced by the choroid plexuses of the lat

eral, the third and the fourth ventricles.eral, the third and the fourth ventricles.

Circulation route of cerebrospinal fluidCirculation route of cerebrospinal fluid:: Lateral ventriclesLateral ventricles ↓ ↓(interventricular foramina)(interventricular foramina) third ventriclethird ventricle ↓ ↓(cerebral aqueduct)(cerebral aqueduct) fourth ventriclefourth ventricle ↓ ↓(median foramen and lateral foramina)(median foramen and lateral foramina) subaracnoid spacesubaracnoid space ↓↓ arachnoid granulationsarachnoid granulations ↓↓ sinuses of dura mater (superior sagital sinus)sinuses of dura mater (superior sagital sinus) ↓↓ internal jugular veininternal jugular vein

An obstruction of the circulatory route causes An obstruction of the circulatory route causes the increased intracranial pressure of hydrocethe increased intracranial pressure of hydrocephalus in infants. The displacement of the braiphalus in infants. The displacement of the brain tissue due to the elevated intracranial pressn tissue due to the elevated intracranial pressure, will cause a cerebral hernia, such as the teure, will cause a cerebral hernia, such as the tentorial herniation and the herniation of the cerntorial herniation and the herniation of the cerebellar tonsils.ebellar tonsils.