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Leptomeninges(soft) = Pia & arachnoid
Pachymeninges (hard)= Dura
Meninges
Dr M Idris Siddiqui
MeningesMeninges
Skin
Bone
Dura mater
Arachnoid
Pia mater
Cerebral cortex
 The meninges are three connective tissue
membranes that lie just external to the
brain and spinal cord
Meninges
 CNS is covered by 3 membranes called
meninges which are separated by 2 spaces
 subdural &
 subarachnoid
 Men...
 The meningeal membranes
 Cover and protect the CNS structures
 Protect blood vessels and enclose venous sinuses
 Cont...
Meninges
 From external to internal, the meningeal layers
are
 Dura mater
 Arachnoid
 Pia mater
DURAMATER(hard mother)
(outermost & toughest)
 It is bilaminar membrane.
 Two layers :
 outer, periosteal or endosteal
...
DURAMATER(hard mother)
 Dural sheath lies loosely in vertebral
canal & separated from wall of canal by
extradural space.o...
The Dura Mater
 The leathery dura mater is by far the strongest of
the meninges
 Where it surrounds the brain it is a do...
The Dura Mater
 The periosteal layer is the superficial and lines
the inner surface (periostium) of the skull
 The deepe...
The Dura Mater
 The brain’s dural layers are fused together except
in certain areas where they enclose the blood filled
d...
The Dura Mater
 In several places the meningeal dura mater
extends inward to form flat septa (partitions) that
limit move...
The Dura Mater
 The falx cerebri dips into the longitudinal fissure
 It attaches to the crista galli of the ethmoid bone
The Dura Mater
 The falx cerebelli forms a midline partition that runs
along the vermis of the cerebellum
The Dura Mater
 The tentorium cerebelli extends into the transverse
fissure between the cerebral hemispheres and the
cere...
Spinal dura Cranial dura
Single layer consists of maeningeal
layer only
Two layered, consists of inner
meningeal & outer e...
Processes
 (1)Falx cerebri
 (2)Tentorium cerebelli
 (3) Falx cerebelli
 4) Diaphragma sellae
 (5) Cavum trigeminale
(1)Falx cerebri
Median sickle shaped dural fold between two
medial surfaces of cerebral hemispheres,
contains dural venous...
(2)Tentorium cerebelli
Semilunar reduplication of dura between cerebellum & occipital lobes of
cerebral hemispheres. It ro...
(3) Falx cerebelli:
Small fold of dura between two cerebellar
hemispheres. It lies below pos. part of
tenorium cerebelli. ...
(4) Diaphragma sellae:
Fold of dura stretches between 4 clinoid
processes. It roofs over pituitary fossa,
perforated by
1....
(5) Cavum trigeminale
Reduplication of dura containing trigeminale
ganglion.
SUBDURAL SPACE
 Internal surface of dura is smooth, glistening
(endothelial lined). It is separated from external
surface...
 Blood supply of dura in brain:
 Middle meningeal artery along with
ICA,maxillary, ascending pharyngeal, occipital,
vert...
The Arachnoid Mater
 The middle membrane forms a loose brain
covering over the surface of the cerebrum
 It is separated ...
The Arachnoid Mater
 The subarachnoid space is filled with
cerebrospinal fluid and contains the largest blood
vessels ser...
Processes:
 1)Arachnoid villi & granulation are finger like
processes which arise from surface of arachnoid,
push dura be...
Cisterns
 Cisterna magna: Cerebellomedullay cistern in angle
between medulla oblongata & cerebellum & occipital
bone.4th ...
ARACHNOID MATER(spiderlike)
 Thin transparent, avascular membrane,
separated from dura by a capillary space
(subdural). I...
The Arachnoid Mater
 Arachnoid villi protrude through the overlying
dura mater and into the dural sinuses overlying
the s...
The Pia Mater
 The pia mater is a delicate connective tissue that
is richly invested with tiny blood vessels
 It is the ...
PIAMATER(tender mother)
 Innermost vascular, thin delicate membrane
closely fits the surfaces of CNS. Blood
vessels lie o...
The Pia Mater
 Meningitis is an inflammation of the meningeal
layers that is caused by either a bacterial or viral
infect...
Processes:
 1) Perivascular space. Blood vessels to brain contains
perivascular cuff of subarachnoid space.
 2) Dips all...
Filum terminale
) Pial extension from conus medullaris to back of
coccyx. 20 cm long,consists of mostly nonneural
tissue(o...
Cerebrospinal Fluid (CSF)
 CSF is a watery “ broth”found in and around
the brain and spinal cord
 It forms a liquid cush...
Cerebrospinal Fluid CSF
 CSF also helps to nourish the brain
 It also helps to remove wastes produced by neurons
 Final...
Cerebrospinal fluidCerebrospinal fluid
Cerebrospinal Fluid (CSF)
 The figure at the
right depicts the
sites of CSF
production and its
circulation
 Most CSF is ...
Choroid Plexus
 Choroid plexus
hang from the roof
of each ventricle
 The plexuses are
clusters of thin
walled capillarie...
Choroid Plexus
 The capillaries of
the choroid plexus
are fairly
permeable and
fluid filters
continuously from
the bloods...
Choroid Plexus
 The choroid plexus
cells are joined by
tight junctions and
have ion pumps
that allow them to
modify this ...
TELA CHOROIDAE
 At certain places wall of ventricles is thin,
consists of ependyma only. This piamater
invaginates into c...
Choroid Plexus
 After entering the ventricles, the CSF
moves freely through these chambers
 Some CSF enters the central ...
The Choroid Plexus
 Cerebrospinal fluid arises from the blood and
returns to it at a rate of about 500 ml a day
 The cho...
CSF Circulation
 The motion of the CSF is aided by the long microvilli of
the ependymal cells lining the ventricles
Blood-Brain Barrier
 The brain has a rich supply of capillaries that
provide its nervous tissues with nutrients,
oxygen, ...
Blood-Brain Barrier
 Blood-borne toxins, such are urea, mild
toxins from food, bacterial toxins, are
prevented from enter...
Blood-Brain Barrier
 The brain is very dependent on a constant
internal environment
 Fluctuations in the concentration o...
Blood-Brain Barrier
 Blood-borne substances within the brain’s
capillaries are separated from the extra-
cellular space a...
Blood-Brain Barrier
 The capillary endothelial cells are joined almost
seamlessly by tight junctions
 They are the least...
Blood-Brain Barrier
 The blood-brain barrier is a selective, rather
than absolute barrier
 Nutrients, such as glucose, e...
Blood-Brain Barrier
 The barrier is ineffective against fats, fatty acids,
oxygen, and carbon dioxide, and other fat-solu...
Meninges
Meninges
Meninges
Meninges
Meninges
Meninges
Meninges
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Meninges

  1. 1. Leptomeninges(soft) = Pia & arachnoid Pachymeninges (hard)= Dura Meninges Dr M Idris Siddiqui
  2. 2. MeningesMeninges Skin Bone Dura mater Arachnoid Pia mater Cerebral cortex
  3. 3.  The meninges are three connective tissue membranes that lie just external to the brain and spinal cord
  4. 4. Meninges  CNS is covered by 3 membranes called meninges which are separated by 2 spaces  subdural &  subarachnoid  Meninges of brain are continuous with spinal meninges at foramen magnum.  In skull, dura is fused with periosteum of skull.
  5. 5.  The meningeal membranes  Cover and protect the CNS structures  Protect blood vessels and enclose venous sinuses  Contain cerebrospinal fluid  Form partitions within the skull
  6. 6. Meninges  From external to internal, the meningeal layers are  Dura mater  Arachnoid  Pia mater
  7. 7. DURAMATER(hard mother) (outermost & toughest)  It is bilaminar membrane.  Two layers :  outer, periosteal or endosteal  Inner, investing, dura proper, meningeal proper  Outer dura is thick, firm membrane covers the bone from inside. It stops at foramina & blends with periosteum of margins. It is nothing but periosteum.  Inner dura is strong fibrous membrane covering the brain & continuous through foramen magnum, with spinal dura and ends at S2.. It provides tubular sheah for cranial nerves through foramina of skull & outside skull fuses with epineuria of nerves.The dural root sheath or sleeve surround anterior or posterior nerve roots as dural sac fuses with periostium The two layers are firmly adherent except  Where these split to enclose venous sinuses (endothelium lined spaces lie either in folds of dura or between investing layer & endocranium)  Where inner layer reduplicates to to form folds
  8. 8. DURAMATER(hard mother)  Dural sheath lies loosely in vertebral canal & separated from wall of canal by extradural space.or epidural space which is occupied by internal vertebral venous plexusemedded in fatty matix- epidural fat  The space between dura & arachnoid mater is called subdural space.It contains capillary layer of fluid.
  9. 9. The Dura Mater  The leathery dura mater is by far the strongest of the meninges  Where it surrounds the brain it is a double layer membrane
  10. 10. The Dura Mater  The periosteal layer is the superficial and lines the inner surface (periostium) of the skull  The deeper meningeal layer forms the true external covering of the brain
  11. 11. The Dura Mater  The brain’s dural layers are fused together except in certain areas where they enclose the blood filled dural sinuses  The dural sinuses collect venous blood and direct it into the internal jugular veins of the neck
  12. 12. The Dura Mater  In several places the meningeal dura mater extends inward to form flat septa (partitions) that limit movement of the brain within the skull
  13. 13. The Dura Mater  The falx cerebri dips into the longitudinal fissure  It attaches to the crista galli of the ethmoid bone
  14. 14. The Dura Mater  The falx cerebelli forms a midline partition that runs along the vermis of the cerebellum
  15. 15. The Dura Mater  The tentorium cerebelli extends into the transverse fissure between the cerebral hemispheres and the cerebellum
  16. 16. Spinal dura Cranial dura Single layer consists of maeningeal layer only Two layered, consists of inner meningeal & outer endosteal layers Does not form folds Forms folds e.g.falx cerebri& cerebelli,tentorium cerebelli Epidural space exists No epidural space
  17. 17. Processes  (1)Falx cerebri  (2)Tentorium cerebelli  (3) Falx cerebelli  4) Diaphragma sellae  (5) Cavum trigeminale
  18. 18. (1)Falx cerebri Median sickle shaped dural fold between two medial surfaces of cerebral hemispheres, contains dural venous sinuses. It is narrow & shallow in front and deeper posteriorly. It contains dural venous sinuses.  Apex: attached to crista galli & frontal crest  Base: attached to upper part of tentorium cerebelli containing straight sinus.  Upper border: convex, fixed to lips of groove for superior Sagittal sinus  Lower border: concave, free, rests on corpus callosum, contains inf. sagittal sinus which joins great cerebral vein to form straight sinus.
  19. 19. (2)Tentorium cerebelli Semilunar reduplication of dura between cerebellum & occipital lobes of cerebral hemispheres. It roofs in posterior cranial fossa & divides the cavity in two compartments i.e. supratentorial & infratentorial, stretches horizontally. Tent like has a beak, outer & inner border. Base of Falx cerebri is attached to beak of tentorium cerebelli. At its attachments lies straight sinus.  Inner free border U-shaped which attaches to anterior clinoid process on either side leaving a wide gap in center __ tentorial notch for passage of midbrain.  The attached outer border on either side is connected to posterior clinoid process (at a higher level than occipital side) & superior border of petrous part of temporal bone, mastoid bone, lips of transverse sinus in occipital bone.  Sinuses, in relation, are straight sinus, superior petrosal sinus, and transverse sinus.  Near clinoid process, both borders cross each other, attached border passes deep to free border.  III nerve in front of decussation  IV nerve at point of decussation  V nerve behind decussation
  20. 20. (3) Falx cerebelli: Small fold of dura between two cerebellar hemispheres. It lies below pos. part of tenorium cerebelli. Is ant. border projects forwards between two cerebellar hemispheres & post. border is attached to internal occipital crest which encloses occipital sinus. It is continuous down with margins of foramen magnum.
  21. 21. (4) Diaphragma sellae: Fold of dura stretches between 4 clinoid processes. It roofs over pituitary fossa, perforated by 1. Infundibulum 2. III nerve 3.optic nerve 4.posterior cerebral artery 5. Great cerebral vein  It encloses inercavernous sinus
  22. 22. (5) Cavum trigeminale Reduplication of dura containing trigeminale ganglion.
  23. 23. SUBDURAL SPACE  Internal surface of dura is smooth, glistening (endothelial lined). It is separated from external surface of arachnoid by a capillary space____Subdural space. This space persists throughout but absent only where structures pierce. , where arachnoid villi are present, where lig. Denticulatum is attached to dura. It contains film of fluid.
  24. 24.  Blood supply of dura in brain:  Middle meningeal artery along with ICA,maxillary, ascending pharyngeal, occipital, vertebral aa.  Nerve supply:  Supratentrial____________ V nerve  Infratentorial____________ C1,C2,C3  Autonomic via cervical ganglion & vagus
  25. 25. The Arachnoid Mater  The middle membrane forms a loose brain covering over the surface of the cerebrum  It is separated from the dura mater by a narrow serous cavity, the subdural space  Beneath the arachnoid membrane is the wide subarachnoid space
  26. 26. The Arachnoid Mater  The subarachnoid space is filled with cerebrospinal fluid and contains the largest blood vessels serving the brain  Since the arachnoid is fine and elastic, these blood vessels are rather poorly protected
  27. 27. Processes:  1)Arachnoid villi & granulation are finger like processes which arise from surface of arachnoid, push dura before them eventually perforating it & project into venous sinuses convey, CSF to blood stream. These are valvular structures. Granulations are just aggregation of arachnoid villi clumped together, found in adults. In old age may erode bone, most numerous in sup. Sagittal sinus.  2)Subarachnoid space is crossed by connective tissue-subarachnoid trabeculae.  3)Down distal to termination of spinal cord subarachnoid space around filum terminale becomes roomy forming a pool of CSF.-Lumbar cistern
  28. 28. Cisterns  Cisterna magna: Cerebellomedullay cistern in angle between medulla oblongata & cerebellum & occipital bone.4th ventricle opens into it by 3 apertures. Cisternal puncture is done here.  Cisterna pontis: on front of pons containing vertebrobasillary artery  Interpeduncular cistern  Some unimportant cisterns  Down distal to termination of spinal cord subarachnoid space around filum terminale becomes roomy forming a pool of CSF.-Lumbar cistern  Cisternal puncture: In sitting position with head flexed forward needle is introduced in midline just above 1st palpable cervical spinous process parallel to line joining external auditory meatus to nasion.
  29. 29. ARACHNOID MATER(spiderlike)  Thin transparent, avascular membrane, separated from dura by a capillary space (subdural). I does not enter sulci.It is separated from pia by a subarachnoid space. Fine filaments connect arachnoid with piamater called TRABECULAE. Subarachnoid space is fluid filled sponge (CSF). Cerebral vessels lie in subarachnoid space.
  30. 30. The Arachnoid Mater  Arachnoid villi protrude through the overlying dura mater and into the dural sinuses overlying the superior aspect of the brain  Cerebrospinal fluid is absorbed into the venous blood sinuses through these valvelike villi
  31. 31. The Pia Mater  The pia mater is a delicate connective tissue that is richly invested with tiny blood vessels  It is the only membrane that clings tightly to the brain, following its every convolution
  32. 32. PIAMATER(tender mother)  Innermost vascular, thin delicate membrane closely fits the surfaces of CNS. Blood vessels lie on external surface of pia.
  33. 33. The Pia Mater  Meningitis is an inflammation of the meningeal layers that is caused by either a bacterial or viral infection that can spread to the underlying nerve tissue  Brain inflammation is called encephalitis
  34. 34. Processes:  1) Perivascular space. Blood vessels to brain contains perivascular cuff of subarachnoid space.  2) Dips all sulci & fissures  3) Sheath to all cervical spinal nerve fuses with epineurium  4) A septum in ant. median fissure__Linea splendens  5) Ligamentum Denticulatum: 21 tooth like processes extend from pia to dura pushing arachnoid before them midway between ventral & dorsal nerve roots. Highest projection at foramen magnum & lowest between T12 & L1.  6) At certain places wall of ventricles is thin, consists of ependyma only. This piamater invaginates into cavities as a series of vascular tufts which carry ependyma before them to form choroids plexus. Pial element of this is called TELA CHOROIDAE, found in medial wall of lateral ventricle, roofs of 3rd & 4th ventricles.  7) Subarachnoid septum:It is midsagittal fenestrated pial septum which connects dorsal surface of spinal cord with arachnoid.  8. Filum terminale
  35. 35. Filum terminale ) Pial extension from conus medullaris to back of coccyx. 20 cm long,consists of mostly nonneural tissue(only in upper part some rudiments of S1,S2,S3,S4 exist). Central canal of spinal cord extends into upper part of of filum terminale for about 5mm.There are two parts  i) Dural part(filum terminale externum), extends 5 cm length, lie outside dural sac i.e. below level of S2 vertebrae via sacral hiatus also called “coccygeal ligament”  Ii) Pial part (filum terminale internum)15 cm long lies within dural sac
  36. 36. Cerebrospinal Fluid (CSF)  CSF is a watery “ broth”found in and around the brain and spinal cord  It forms a liquid cushion that gives buoyancy to the CNS organs  With the brain floating, CSF reduces brain weight by 97% and thus prevents the brain from crushing under its own weight  CSF also protects the brain and spinal cord from trauma
  37. 37. Cerebrospinal Fluid CSF  CSF also helps to nourish the brain  It also helps to remove wastes produced by neurons  Finally, it carries chemical signals between different parts of the CNS  Although it performs many functions there is 100-160 ml of fluid (about a half cup) present in the body at any one time  CSF is a similar in composition to blood plasma, from which it arises  It contains less protein and more sodium and chloride ions
  38. 38. Cerebrospinal fluidCerebrospinal fluid
  39. 39. Cerebrospinal Fluid (CSF)  The figure at the right depicts the sites of CSF production and its circulation  Most CSF is made in the choroid plexuses which are membranes on the roofs of the four brain ventricles
  40. 40. Choroid Plexus  Choroid plexus hang from the roof of each ventricle  The plexuses are clusters of thin walled capillaries enclosed by a layer of ependymal cells
  41. 41. Choroid Plexus  The capillaries of the choroid plexus are fairly permeable and fluid filters continuously from the bloodstream into the ventricles
  42. 42. Choroid Plexus  The choroid plexus cells are joined by tight junctions and have ion pumps that allow them to modify this filtrate by actively transporting only certain ions across their membranes into the CSF pool
  43. 43. TELA CHOROIDAE  At certain places wall of ventricles is thin, consists of ependyma only. This piamater invaginates into cavities as a series of vascular tufts which carry ependyma before them to form choroids plexus. Pial element of this is called TELA CHOROIDAE, found in medial wall of lateral ventricle, roofs of 3rd & 4th ventricles.
  44. 44. Choroid Plexus  After entering the ventricles, the CSF moves freely through these chambers  Some CSF enters the central canal of the spinal cord, but most enters the subarachnoid space through the lateral and median apertures in the walls of the fourth ventricle  In the subarachnoid space, the CSF bathes the outer surface of the brain and cord
  45. 45. The Choroid Plexus  Cerebrospinal fluid arises from the blood and returns to it at a rate of about 500 ml a day  The choroid plexus also helps to cleanse the CSF by removing waste products and other unnecessary solutes
  46. 46. CSF Circulation  The motion of the CSF is aided by the long microvilli of the ependymal cells lining the ventricles
  47. 47. Blood-Brain Barrier  The brain has a rich supply of capillaries that provide its nervous tissues with nutrients, oxygen, and all other vital molecules  However, some blood-borne molecules that can cross other capillaries of the body cannot cross the brain capillaries
  48. 48. Blood-Brain Barrier  Blood-borne toxins, such are urea, mild toxins from food, bacterial toxins, are prevented from entering brain tissue by the blood-brain barrier  The barrier is a protective mechanism that helps maintain a stable internal environment for the brain
  49. 49. Blood-Brain Barrier  The brain is very dependent on a constant internal environment  Fluctuations in the concentration of ions, hormones, or amino acids, would alter the brain’s function  Hormones and amino acids can influence neurotransmitters  Ions (K+) can affect neuron thresholds
  50. 50. Blood-Brain Barrier  Blood-borne substances within the brain’s capillaries are separated from the extra- cellular space and neurons by  Continuous endothelium of the capillary walls  Relatively thick basal lamina surrounding the external face of the capillary  To a limited extend the “feet” of the astrocytes that cling to the capillaries
  51. 51. Blood-Brain Barrier  The capillary endothelial cells are joined almost seamlessly by tight junctions  They are the least permeable capillaries in the body  The relative impermeability of brain capillaries accounts for most of the blood brain barrier Basal lamina (cut)
  52. 52. Blood-Brain Barrier  The blood-brain barrier is a selective, rather than absolute barrier  Nutrients, such as glucose, essential amino acids, and some electrolytes, move passively by facilitated diffusion through the endothelial cell membranes
  53. 53. Blood-Brain Barrier  The barrier is ineffective against fats, fatty acids, oxygen, and carbon dioxide, and other fat-soluble molecules that diffuse easily through all plasma membranes  This explains why blood-borne alcohol, nicotine, and anesthetics can affect the brain  The barrier is not completely uniform and not completely developed in infants
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