Transcript Periosteum - Maryville University

Periosteum
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.
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.
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
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.
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 (Barbinski’s Sign positive),
either side or both (contralaterally)
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
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
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.
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
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
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
Other sinuses
• sphenoparietal sinus
– small venous channel under the lesser wing of
the sphenoid bone
– drains into cavernous sinus
Emissary veins
• connect dural sinuses with veins outside the
cranial cavity
• blood may flow either way
Pia and arachnoid layer
• leptomeninges (slender membranes) : pia
mater and arachnoid
• The arachnoid contains fibroblasts, collagen
fibers, and some elastic fibers
Subarachnoid cisterns
• regions of subarachnoid space that contain
substantial amounts of cerebrospinal fluid
(CSF)
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
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.
CSF Circulation
• lateral ventricles => through interventricular
foramina to third ventricle => via cerebral
aqueduct to fourth ventricle
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
CSF absorption
• Main site
– Arachnoid villi that project into the dural sinus
CSF properties
• Volume : 80 - 150 ml
• Pressure: 80 - 180 cmH2O (recumbent, higher
in lumbar area when sitting)
• Clear and colorless, few cells (lymphocytes >
10 disease)
• Glucose: half of plasma
• Protein: very low
Hydrocephalus
• Excess CSF
– External: CSF in subarachnoid space
– Internal: enlarged ventricles