No. 27

1. 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 • Section 4 The Meninges and Blood Vessels of Brain and Spinal Cord, and the Circulation of Cerebrospinal Fluid

2. Ⅰ. The Meninges (or coverings) of Brain and Spinal Cord • 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 spiderweb-like 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.

3. 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.

4. 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.

6. 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.

7. 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.

9. 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.

10. 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.

11. 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.

13. 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

14. (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.

16. The drainage of the venoussinuses 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→→→→→→→→→→→→→→→→

17. 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

18. 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.

19. 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).

20. Ⅱ. The Blood Vessels of Brain and Spinal Cord 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.

21. 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 branchessupply the basal nuclei, the internal capsule and the diencephalon.

22. 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.

23. 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.

25. 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.

26. 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.

30. 3) The anterior choroidea artery 4) The posterior communicating artery • It runs backward and anastomoses with the posterior cerebral artery.

32. 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.

33. 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.

35. (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.

36. 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.

37. 3. The cerebral arterial circle (ofWillis) • 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.

39. 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.

42. 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.

44. Ⅲ. The Circulation of Cerebrospinal Fluid • 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.

45. Circulation route of cerebrospinal fluid: • Lateral ventricles • ↓(interventricular foramina) • third ventricle • ↓(cerebral aqueduct) • fourth ventricle • ↓(median foramen and lateral foramina) • subaracnoid space • ↓ • arachnoid granulations • ↓ • sinuses of dura mater (superior sagital sinus) • ↓ • internal jugular vein

47. 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.