Download Cranial contents

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Cranial contents
I.
Calvaria - skull cap
A. composed of three layers
1. outer table - compact bone
2. diploe - spongy bone
a. contains diploic veins and marrow
3. inner table - compact bone
B. emissary foramina for emissary veins
1. emissary veins connect dural venous sinuses within the cranium with the veins
external to it
II.
Meninges - coverings of the brain which are exposed when the calvaria is removed
A. dura mater (tough mother)
1. periosteal layer - fused to bone and fused to meningeal layer except where
meningeal vessels and dural sinuses are interposed
2. meningeal layer - the true layer of dura which reduplicates to form four
projecting folds
a. falx (sickle) cerebri - located between the cerebral hemispheres
b. falx cerebelli - between cerebellar hemispheres
c. tentorium cerebelli - separates occipital lobes of cerebrum from cerebellum
(1) attaches to the petrous ridge of the temporal bone on each side
(2) attaches along the occipital bone along the transverse sinus
(3) anteriorly at the sides of the anterior clinoid processes
(4) anterior concave margin is an open wrapping around the brainstem
d. diaphragma (septum) sellae (saddle) - forms roof of sella turcica
3. dural venous sinuses -lie between layers of dura mater and receive veins
draining the brain to ultimately leave the skull via the internal jugular vein
a. unpaired sinuses
(1) superior sagittal sinuses -along superior border of falx cerebri
(a) drains into the confluens of the sinuses -usually then draining into
the right transverse sinus
(2) inferior sagittal sinus - along the inferior border of the falx cerebri
(3) straight sinus -at junction of the falx cerebri and tentorium cerebelli
(a) receives the great cerebral vein of Galen which drains the choroid
plexus
(b) drains the inferior sagittal sinus
(c) empties into the confluens of the sinuses - usually into the left
transverse sinus
(4) intercavernous sinus -in the diaphragma sellae
(a) connects the left and right cavernous sinuses
(b) basilar sinus - on the clivus
(c) occipital sinus - bordering the foramen magnum and in the falx
cerebelli
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b. paired sinuses
(1) transverse sinuses - at attachment of the tentorium cerebelli to skull
(a) drains into the sigmoid sinus
(2) sigmoid sinuses - connect the anterior end of the transverse sinuses
with the internal jugular vein
(3) cavernous sinuses - on each side of the sella turcica
(4) superior petrosal sinuses - at the attachment of the tentorium
cerebelli to the petrous portion of the temporal bone
(a) connects the cavernous sinus to the sigmoid sinus
(5) inferior petrosal sinuses -connect the cavernous sinus to the internal
jugular vein
(6) sphenoparietal - along the lesser wing of the sphenoid bone
(a) drains into the cavernous sinus
c. cavernous sinus
(1) lies on either side of the body of the sphenoid bone (sella turcica)
(2) formed by dura on all sides (periosteal and meningeal)
(a) trabeculae from each layer cross the space giving it a cavernous
appearance
(3) extends from the petrous apex of the temporal bone posteriorly to the
superior orbital fissure anteriorly
(4) contents of the cavernous sinus and typical arrangement of its contents
(a) oculomotor nerve (CN3) - superiorly in the lateral wall
(b) trochlear nerve (CN4) - next one down in the lateral wall
(c) ophthalmic nerve (CN5 / V1) - below trochlear n. in the lateral wall
(d) maxillary nerve ( CN5 / V2) - lowest nerve in the lateral wall
(e) internal carotid artery - enters sinus after passing over the foramen
lacerum and it is medial to the above mentioned nerves
(f) abducens nerve (CN6) - passes in close relation lateral to the
internal carotid artery
(g) drains the superior ophthalmic veins, cerebral veins, and
sphenoparietal veins
(h) it drains into the superior and inferior petrosal sinus
(i) communicates with the pterygoid plexus of the infratemporal fossa
B. the subdural space
1. the space between the arachnoid and dura mater
2. it contains a very small amount of fluid
C. arachnoid (spider-like) mater - a delicate membrane attached to the pia
mater by trabeculae
1. arachnoid granulations - project into the dural sinuses to return
cerebrospinal fluid to the blood
D. subarachnoid space - actual space between the arachnoid and pia mater
(1) it is filled with about 150 ml of cerebrospinal fluid (CSF) that has a
turnover rate of three to four times every 24 hours
(a) the CSF is formed by the choroid plexus in the brain's ventricles
(2) it communicates with the fourth ventricle of the brain by the median
foramen of Magendie and the two lateral foramina of Luschka
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(3) major arteries and veins are located in this space
E. pia (tender) mater
(1) clings to the surface of the brain and follows all of its irregularities
F. meningeal arteries and veins - supply the dura and adjacent bone
(1) anterior cranial fossa - has small vessels of more than one source
(2) middle cranial fossa - the middle meningeal artery passes through
the foramen spinosum and it supplies four-fifths of the dura.
(3) posterior cranial fossa - has small vessels from several sources
G. meningeal nerves
(1) the ones superior or above the tentorium cerebelli have branches
from all three divisions of the trigeminal nerve: V1, V2, V3.
(2) the ones that are inferior to the tentorium cerebelli are supplied by
the upper cervical nerves
III.
Brain
A. its divisions
1. telencephalon or cerebral hemispheres with the frontal, parietal,
temporal, and occipital lobes.
(a) the olfactory bulb and tract are attached to the frontal lobe and
are associated with the olfactory nerve (CN1)
2. diencephalon - located superior to the sella turcica
(a) it includes the thalamus, hypothalamus, optic chiasma (CN2),
pituitary and pineal glands
3. mesencephalon (mid-brain) - gives the origin to oculomotor (CN3)
and trochlear nerves (CN4)
4. metencephalon -consists of the pons and cerebellum
a. pons lies on the clivus and gives origin to the trigeminal nerve (CN5)
b. the pontomedullary junction is the location of the abducens (CN6),
facial (CN7), and vestibulocochlear (CN8) nerves
5. myelencephalon (medulla)
a. origins of the glossopharyngeal (CN9), vagus (CN10) and the
cranial portion of accessory (CN11) nerves are immediately
posterior (dorsal) to the inferior olive and the hypoglossal nerve
(CN12) is immediately anterior (ventral) to the inferior olive.
B. the brain itself is insensitive to pain, but vasomotor and sensory fibers from
the plexuses on the internal carotid and vertebral arteries supplying blood
vessels to the brain do sense pain.
C. blood supply to the brain
1. vertebral arteries
a. gives off branches as they enter the cranial cavity through the
foramen magnum
b. vessels from both sides join to form the basilar artery on the front
of the pons
c. branches
(1) posterior spinal arteries - descend to supply the dorsal side of
the spinal cord
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(2) anterior spinal arteries - join and descend to supply the ventral
surface of the spinal cord as a single artery
(3) posterior inferior cerebellar arteries - supply the cerebellum
2. basilar artery gives off several pairs of arteries before dividing into its
larger paired terminal branches, the posterior cerebral arteries
a. pontine branches - numerous branches along the length of the
basilar artery
b. labyrinthine artery -enters the internal acoustic meatus and
supplies the internal ear
c. anterior inferior cerebellar artery -supplies the cerebellum
d. superior cerebellar artery -supplies the cerebellum
e. posterior cerebral artery - supplies the cerebral cortex
(1) terminal branches of the basilar artery
(2) communicates with the ipsilateral internal carotid artery by
way of the posterior communicating artery
3. internal carotid artery
a. enters the cranial cavity by passing through the carotid canal and
then lying superior to the foramen lacerum
b. then passes through the cavernous sinus, pierces the dura as it gives
off the ophthalmic artery, then proceeds to the lateral cerebral fissure
c. branches
(1) ophthalmic artery - enters the orbit through the optic foramen
with the optic nerve
(2) posterior communicating artery-communicates with the
posterior cerebral artery (branch of the basilar artery).
(3) anterior cerebral artery - smaller of the two terminal branches.
Goes medial then superior to the optic nerves, communicating with
each other by way of the unpaired anterior communicating
artery.
(4) middle cerebral artery -the largest of the two terminal branches
4. cerebral circle of Willis
a. anterior and posterior communicating arteries indirectly link up
the basilar artery with the internal carotid arteries of both sides
(1) equalizes the blood flow under fluctuating pressure through major
vessels.
b. arteries that make up the circle of Willis
(1) posterior cerebral arteries
(2) posterior communicating arteries
(3) internal carotid arteries
(4) middle cerebral arteries
(5) anterior cerebral arteries
(6) anterior communicating artery
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