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scalp | Main Anatomy
Index | Blood supply to the head
Last updated 30 March 2006
The Main Parts of the Brain
Cerebral Hemispheres (p. 693)
- The cerebral hemispheres form the
largest part of the brain.
- They occupy the anterior and middle
cranial fossae and extend posteriorly over the tentorium cerebelli and the
cerebellum to the internal
- They comprise of the cerebral cortex, the basal nuclei,
their fibre connections, and the lateral
- These are the cavities in each cerebral hemisphere and
are part of the ventricular system.
- There are four main lobes of the cerebral hemispheres:
frontal, parietal, temporal, and occipital.
The Frontal Lobe
- These are the largest of all the lobes and they form the anterior part of the cerebral hemispheres.
- They are located anterior to the central
sulci and superior to the lateral
Lobes (p. 693)
- These lobes are related to the internal aspects of the
posterior and anterior parts of the parietal bone.
- Each lobe is bound anteriorly by the central
sulcus and posterior by the superior
part of the line joining the parieto-occipital sulcus and
the preoccipital notch.
Lobes (p. 693)
- These lobes lie inferior to the lateral
Lobes (p. 693)
- These lobes are relatively small and are located
posterior to the parieto-occipital
- The rest on the tentorium cerebelli.
- This is the smallest part of the brain.
- It is located at the junction of the middle and posterior
cranial fossae, lying partly in each.
- The cavity of the midbrain is represented by a narrow
canal, called the cerebral aqueduct.
- It conducts CSF from the lateral and third ventricles to
the fourth ventricle.
The Pons (p. 696)
- The pons lies in the anterior part of the posterior
cranial fossa, posterior to the
superior part of the clivus and posterior surface of the
- The part of it that is visible from the inferior surface
is a wide, bridge-like transverse
band of nerve fibres.
Medulla Oblongata (p. 696)
- This is the most caudal part
of the brainstem.
- It is located in the posterior cranial fossa with its
ventral aspect facing the clivus.
- The medulla is continuous with the spinal cord at the
foramen magnum, but the transition is gradual.
- The distinctive characteristics on its ventral surface
are the elongated pyramids
and the olives beside
Cerebellum (pp. 696-7)
- This "little brain" (L. cerebellum)
overlies the posterior aspect of the pons and medulla and
extends laterally beneath the
- It occupies most of the posterior cranial fossa.
Blood Supply of the Brain
- The brain is supplied through an extensive system of
branches from two pairs of vessels, the
internal carotid arteries and the vertebral arteries.
Internal Carotid Artery (p. 701)
- The petrous part of the
artery enters the middle cranial fossa through the
superior part of the foramen
lacerum and then runs anteriorly in the cavernous sinus.
- At the anterior end of the cavernous sinus, the artery
makes a hairpin turn and
leaves the sinus to enter the subarachnoid
- The cerebral part of the
artery immediately gives off the ophthalmic
artery that supplies the eye.
- The internal carotid artery passes superior
to the optic nerve.
- Lateral to the optic nerve, it branches into the middle and anterior cerebral arteries.
- The sinuous course taken by the cavernous and cerebral
parts of the internal carotid artery forms a U-shaped bend, often called
the "carotid siphon".
- Within the cranial cavity, the internal carotid artery
and its branches supply the hypophysis
cerebri (pituitary gland), the
orbit, and much of the supratentorial
part of the brain.
Vertebral Arteries (p. 701)
- They arise from the superior aspect of the first part of
the subclavian artery.
- The vertebral arteries ascend through the transverse foramina of the
cervical vertebrae, except for C7 vertebrae.
- After winding around the lateral
mass of the atlas, the vertebral artery enters
the skull though the foramen magnum.
- At the inferior border of the pons, the vertebral
arteries join to form a median vessel called the basilar artery, which is an
important arterial supplier to the brain.
The Basilar Artery (p. 701)
- This artery is formed by the union of the two vertebral
- It runs through the pontine cistern
to the superior border of the pons, where it ends by
dividing into the two posterior
The Cerebral Arterial Circle of Willis (pp.
Click here for a
schematic of the arterial circle.
- This circle is an important anastomosis between the four
arteries that supply the brain.
- It is formed by the posterior
cerebral, and anterior
- The circle is located at the base of the brain,
principally in the interpeduncular
- The cerebral arterial circle encircles
the optic chiasma, the infundibulum,
and the mamillary bodies.
- In general, each of the cerebral arteries supplies a
surface and a pole of the brain.
Anterior Cerebral Artery (p. 701)
- It supplies most of the medial and superior surfaces of
the frontal pole.
Middle Cerebral Artery (pp. 701-2)
- It supplies the lateral surface and temporal pole.
Posterior Cerebral Artery (p. 702)
- It supplies the inferior surface and the occipital pole.
Dura Septa or Reflections
- The dura mater is the
outermost and toughest of the membranes covering the
central nervous system.
- These septa divide the cranial cavity into three intercommunicating compartments,
one subtentorial and two supratentorial.
- The dura septa provide support for
parts of the brain, particularly the cerebral
Cerebri (p. 686)
- The falx cerebri (L. falx, a sickle) is a large
sickle-shaped vertical partition in the longitudinal
fissure between the two cerebral hemispheres.
- This thick, tough dural fold is attached in the medial
plane to the internal surfaces of the cranium from the frontal crest of the frontal
bone and the crista galli
of the ethmoid bone anteriorly to the internal
occipital protuberance posteriorly.
- The falx cerebri is also attached to the midline of the tentorium cerebelli.
- At the superior coven border of the falx cerebri, its two
layers separate to enclose the superior
- The inferior sagittal sinus
is enclosed within the free edge of the falx cerebri.
- The falx cerebri forms a rigid partition between the
cerebral hemispheres that reduces side-to-side movement.
Tentorium Cerebelli (p. 686)
- The tentorium cerebelli (L. tentorium, tent) is a
wide crescentic, arched fold of dura that separates the occipital lobes of the
cerebral hemispheres from the cerebellum.
- The attachment of the falx cerebri to the medial portion
of the tentorium cerebelli holds the latter fold up.
- The tentorium cerebelli is attached anterolaterally to
the superior edges of the petromastoid
parts of the temporal bones and the anterior
and posterior clinoid processes.
- Posteriorly, the tentorium is attached to the occipital
bone along the groove for the transverse
sinuses, which it encloses.
- Its concave anteromedial border is
- The oval opening surrounds the midbrain
as it passes from the middle to the posterior cranial
Cerebelli (p. 687)
- This is a small, sickle-shaped, median dural fold in the
posterior part of the posterior cranial fossa.
- It extends almost vertically, inferior to the inferior
surface of the tentorium cerebelli.
- Its free edge projects slightly between the cerebellar
The Diaphragma Sellae (p. 687)
- This is a small, circular, horizontal sheet of dura that
forms a roof for the hypophyseal
fossa in the sella turcica.
- This fold is formed by the dura surrounding the hypophysis cerebri (pituitary
gland) and encircling the stalk of this gland.
- The diaphragma sellae has a central aperture for the
hypophyseal stalk (or infundibulum).
Venous Sinuses of Dura Mater
- These sinuses are venous channels located between the
dura and the internal periosteum lining the cranium.
- The venous sinuses drain all the
blood from the brain.
- These sinuses have no valves or muscles in their walls.
Superior Sagittal Sinus (p. 689)
- This lies in the median plane, along the attached border
of the falx cerebri.
- It begins at the crista galli,
runs the entire length of the superior attached border of
the falx cerebri, and ends at the internal
- In 60% of cases the superior sagittal sinus ends by
becoming the right transverse sinus.
- At the termination of the superior sagittal since is a
dilation, known as the confluence
- Occasionally, this dilation is referred to as the sinus confluens or the torcular Herophili (L.
winepress of Herophilus, an early anatomist and surgeon).
- This sinus is triangular in cross-section.
Inferior Sagittal Sinus (p. 690)
- It occupies the posterior 2/3 of the free inferior edge
of the falx cerebri.
- It ends by joining the great
cerebral vein (of Galen) to form the straight sinus.
Straight Sinus (p. 690)
- This is formed by the union of the inferior sagittal
sinus with the great cerebral vein.
- It runs inferoposteriorly along the line of attachment of
the falx cerebri to the tentorium cerebelli.
- It ends by becoming continuous with one of the transverse
sinuses, usually the left.
Transverse Sinuses (p. 690)
- These pass laterally from the confluence of the sinuses
in the attached border of the tentorium cerebelli.
- They groove the occipital bone
and the posteroinferior angle of the parietal bones.
- They then leave the tentorium and become the sigmoid sinuses.
Sigmoid Sinuses (p. 690)
- These are shaped like the Greek letter sigma.
- They follow S-shaped courses in the posterior cranial
fossa, forming deep grooves in the inner surface of the
posterior part of the mastoid parts
of the temporal bones, and in the lateral
surfaces of the jugular tubercles
of the occipital bone.
- The sigmoid sinuses then turn anteriorly and enter venous
enlargements called the superior
bulbs of the internal jugular veins, which
occupy the jugular foramina.
- These large bulbs receive the inferior
petrosal sinuses and continue as the internal
Cavernous Sinuses (p. 690)
- The cavernous sinuses (L. caverna, cave) are
located on each side of the sella
turcica and the body of the sphenoid bone.
- Each cavernous sinus extends from the superior
orbital fissure anteriorly, to the apex of the petrous part of the temporal
- Each cavernous sinus receives blood from the superior and inferior ophthalmic veins, the
superficial middle cerebral vein
and the sphenoparietal sinus.
- The cavernous sinuses communicate with each other through
the intercavernous sinuses,
which pass anterior and posterior to the hypophyseal stalk.
- The cavernous sinuses drain posteriorly and inferiorly
through the superior and
inferior petrosal sinuses
and the pterygoid plexuses.
Superior Petrosal Sinuses (p. 609)
- These are small channels that drain
the cavernous sinuses.
- They run from the posterior ends of the cavernous sinuses
to the transverse sinuses
at the points where they curve inferiorly to form the
- Each superior petrosal sinus lies in the attached margin
of the tentorium cerebelli,
running in a small groove on the superior margin of the
petrous part of the temporal bone.
Inferior Petrosal Sinuses (p. 609)
- These are small venous sinuses that drain the cavernous
sinuses directly into the inferior
- From the posterior end of the cavernous sinus, each
inferior petrosal sinus runs posteriorly, laterally, and
inferiorly in a groove between the
petrous part of the temporal bone and the basilar part of the occipital bone.
- This sinus enters the jugular foramen and joints the superior bulb of the internal jugular
vein, usually just inferior to the base of the