Brain

1. Leptomeninges(soft) = Pia & arachnoid
Pachymeninges (hard)= Dura
Meninges
Dr M Idris Siddiqui

2. MeningesMeninges
Skin
Bone
Dura mater
Arachnoid
Pia mater
Cerebral cortex

3.  The meninges are three connective tissue
membranes that lie just external to the
brain and spinal cord

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.  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. Meninges
 From external to internal, the meningeal layers
are
 Dura mater
 Arachnoid
 Pia mater

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. 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. 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. 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. 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. 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. The Dura Mater
 The falx cerebri dips into the longitudinal fissure
 It attaches to the crista galli of the ethmoid bone

14. The Dura Mater
 The falx cerebelli forms a midline partition that runs
along the vermis of the cerebellum

15. The Dura Mater
 The tentorium cerebelli extends into the transverse
fissure between the cerebral hemispheres and the
cerebellum

18. 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

19. Processes
 (1)Falx cerebri
 (2)Tentorium cerebelli
 (3) Falx cerebelli
 4) Diaphragma sellae
 (5) Cavum trigeminale

21. (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.

22. (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

24. (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.

25. (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

26. (5) Cavum trigeminale
Reduplication of dura containing trigeminale
ganglion.

28. 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.

29.  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

30. 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

32. 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

33. 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

34. 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.

35. 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.

36. 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

37. 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

39. PIAMATER(tender mother)
 Innermost vascular, thin delicate membrane
closely fits the surfaces of CNS. Blood
vessels lie on external surface of pia.

40. 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

41. 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

42. 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

43. 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

44. 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

45. Cerebrospinal fluidCerebrospinal fluid

46. 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

47. 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

48. Choroid Plexus
 The capillaries of
the choroid plexus
are fairly
permeable and
fluid filters
continuously from
the bloodstream
into the ventricles

49. 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

50. 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.

51. 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

52. 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

53. CSF Circulation
 The motion of the CSF is aided by the long microvilli of
the ependymal cells lining the ventricles

54. 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

55. 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

56. 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

57. 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

58. 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)

59. 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

60. 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