Periosteum

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Periosteum
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Periosteum

• Central nervous system is protected by the bone
  structure (skull and vertebral column) as well as
  meninges. Meninges include dura mater, arachnoid
  and pia mater. These layers are continuous
  linings in both spinal cord and brain.
• Periosteum, consists of collagenous connective
  tissue and arteries, covers the inner side of the
  skull. It also continues with the periosteum on
  the external surface of the cranium at the exit
  of foramen magnum and smaller foramina for nerves
  and blood vessels.

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Periosteum

• Periosteum and cranial bones are supplied by
  meningeal arteries. The largest is called middle
  meningeal artery, which splits into anterior and
  posterior branches after it enters the cranial
  cavity, supplies lateral surface of the cranium.

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Dura Reflections

• Dura Mater
• Unlike dura mater in spinal cord, cranial dura
  mater is firmly attached to the periosteum.
  Subdural space, between the dura and arachnoid,
  is occupied by simple squamous epithelium and
  some fluid.
• Dura reflections
• The cranial dura is reflected along certain lines
  to form the dural reflections or dural septa

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Dura Reflections

• 1. The Falx Cerebri
• a longitudinal fissure between the cerebral
  hemispheres. In front, it attaches to the crista
  galli of the ethmoid bone and goes back to
  tentorium cerebeli, hanging above corpus callosum
• 2. The tentorium cerebelli
• lies between occipital lobes and the cerebellum,
  the free border bounds incisura of the tentorium.
• 3. The falx cerebelli
• small dural fold in the posterior cranial fossa,
  extending vertically between the cerebellar
  hemispheres.

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Transtentorial hernias

• Expanding lesion of supratentorial compartment
  (tumor, hematoma) can push temporal lobe down
  into the incisura of the tentrium, causing
  impaired ipsilateral oculomotor nerve, first sign
  of this is impaired light reflex ipsilaterally.
  (dilated pupil). Further herniation can damage
  descending motor pathway causing upper neuron
  damage, with exaggerated reflexes (Barbinskis
  Sign positive), either side or both
  (contralaterally)

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Dural venous sinuses

• Veins draining the brain empty into the venous
  sinuses of the dura mater, from which blood flows
  into the internal jugular veins. The wall of the
  sinus consists of dura mater, periosteum and
  endothelium
• Dural venous sinus is formed by the outer
  periosteal and inner meningeal layer

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Superior sagittal sinus

• Lies along the attached border of falx cerebri
• communication with nasal vein in the front
• superior cerebral veins drain into it
• continues with right transverse sinus

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Inferior sagittal sinus

• runs along the free border of falx cerebri
• receives vein from medial aspects of the cerebral
  hemispheres
• opens into straight sinus, which also receives
  great cerebral sinus
• straight sinus usually continues with left
  transverse sinus
• the sinus configuration around the internal
  occipital protuberance is referred as confluence
  of the sinuses.

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Transverse sinus

• Right (left) transverse sinus
• lies in a groove on the occipital bone along the
  attached margin of tentorium cerebelli.
• Becomes sigmoid sinus when reaches the petrous
  part of the temporal bone and continues with
  internal jugular vein

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Other sinuses

• The cavernous sinuses
• on side of the sphenoid bone
• receives the ophthalmic vein and the superficial
  middle cerebral vein
• drains into transverse sinus via superior
  petrosal sinus

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Other sinuses

• inferior petrosal sinus
• between the petrous part of the temporal bone and
  the basilar portion of the occipital bone
• communication between the cavernous sinus and
  internal jugular vein
• basilar sinus
• connects cavernous and inferior petrosal sinus

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Other sinuses

• sphenoparietal sinus
• small venous channel under the lesser wing of the
  sphenoid bone
• drains into cavernous sinus

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Emissary veins

• connect dural sinuses with veins outside the
  cranial cavity
• blood may flow either way

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Pia and arachnoid layer

• leptomeninges (slender membranes) pia mater and
  arachnoid
• The arachnoid contains fibroblasts, collagen
  fibers, and some elastic fibers

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Subarachnoid cisterns

• regions of subarachnoid space that contain
  substantial amounts of cerebrospinal fluid (CSF)

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CSF

• Production
• generated mainly by the choroid plexuses of the
  lateral (largest and most important), third and
  fourth ventricles.
• Choroid plexuses are formed by vascular pia mater

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Function of CSF

• Shock Absorbtion. Because the brain and spinal
  cord are suspended within the CSF, it cushions
  the CNS and protects it from traumatic injury.
• Nutrition. The CSF contains sugars and other
  elements that are used by central nervous system
  cells, specifically neurons and glial cells.
• Waste disposal. The CSF removes waste products
  produced by the metabolism of the cells in the
  CNS.
• Communication. The CSF also acts as a messaging
  medium. Because the CSF contains a lot of active
  biochemicals (cytokines , hormones,
  neurotransmitters, metabolites and the like) the
  CSF provides information about the state of the
  CNS, whether it is running normally or whether
  there are any infections or dysfunctions.

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CSF Circulation

• lateral ventricles gt through interventricular
  foramina to third ventricle gt via cerebral
  aqueduct to fourth ventricle

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CSF Circulation

• From forth ventricle ? median aperture into
  cerebellomedullary cistern (cistern of magna)
  lateral aperture into pontine cistern ?
  interpeduncular cistern ? cistern of optic
  chiasma ? cistern of lamina terminalis ? cistern
  of corpus callosum

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CSF absorption

• Main site
• Arachnoid villi that project into the dural sinus

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CSF properties

• Volume 80 - 150 ml
• Pressure 80 - 180 cmH2O (recumbent, higher in
  lumbar area when sitting)
• Clear and colorless, few cells (lymphocytes gt 10
  ?disease)
• Glucose half of plasma
• Protein very low

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Hydrocephalus

• Excess CSF
• External CSF in subarachnoid space
• Internal enlarged ventricles

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