Cranial cavity

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Neurocranium

Definition

  • The part of the skull that houses the brain
  • Contains three tiers:
    1. anterior cranial fossa - contains the frontal lobes of the brain
    2. middle cranial fossa - contains the temporal lobes
    3. posterior cranial fossa - contains the cerebellum and brain stem

Bones

Side view of the skull
Left infratemporal fossa
The skull from the front
Base of the skull. Upper surface.

Sutures

  • Coronal
  • Lambdoidal
  • Saggital

Meninges

Cranial nerves

Blood supply to the brain

Internal carotid arteries

  • bilateral branches of the common carotid arteries in the neck
  • At the base of the skull, each artery enters its own carotid canal, within the petrous part of the temporal bone and passes into the cranial cavity at the foramen lacerum
  • Here the artery passes forward, through the cavernous sinus, then upwards, through the roof of the sinus (diaphragma sellae)
  • At this point, the artery pierces the arachnoid mater, and enters the subarachnoid space

Vertebral arteries

  • branches of the subclavian arteries
  • Each one:
    • ascends the neck through the foramina transversaria of the upper six cervical vertebrae
    • enters the subarachnoid space by piercing the dura and arachnoid just below the foramen magnum
  • They enter the cranial cavity through the foramen magnum and pass on to the anterior surface of the brainstem
  • they unite to form the basilar artery
  • The basilar artery later divides into two terminal posterior cerebral arteries

Intracranial arteries

Diagram of the arterial circulation at the base of the brain.

Basilar arteries

Anterior inferior cerebellar arteries (AICA)

  • each gives branches to the pons and cerebellum
  • The labyrinthine artery is either a branch of either the AICA or basilar artery
    • It supplies the structures of the inner ear, via the internal auditory meatus

Pontine arteries

  • enter the pons along its length

Superior cerebellar arteries

  • usually arise just proximal to the termination of the basilar artery, at the junction of the pons and midbrain
  • Each one supplies the dorsal surface of the cerebellum and midbrain

Posterior cerebral artery

  • terminal branches of the basilar artery
  • Each one curves dorsolaterally around the midbrain to the medial surface of the cerebral hemisphere
  • gives branches to the medial and 5 inferior surfaces of the temporal and occipital lobes and a narrow strip on the lateral surface of the occipital lobe
  • One of the latter branches, the calcarine artery, supplies the visual cortex

Internal carotid arteries

Ophthalmic arteries

  • accompany the optic nerves into the orbits
  • Each supplies the contents of the orbit, including the eye

Anterior cerebral artery

  • pass medially towards the midline where they meet, via the anterior communicating artery
  • Each anterior cerebral artery then enters the longitudinal fissure and curves posteriorly, around the corpus callosum
  • supplyies the inferior (orbital) and medial surfaces of the frontal lobe, olfactory bulb and tract, the medial side of the parietal lobe and the corpus callosum
  • A few of its branches extend just on to the lateral surfaces of the frontal and parietal lobes.

Middle cerebral artery

  • each enters the lateral fissure, passing between the temporal and frontal lobes
  • Frontal, parietal and temporal branches leave the fissure to supply much of the lateral surfaces of the corresponding lobes.

Vertebral arteries

Posterior inferior cerebellar arteries (PICA)

  • each passes laterally to supply the medulla, posterior part of the cerebellum and choroid plexus of the fourth ventricle

Circle of Willis

  • aka circulus arteriosus cerebri
  • arterial anastomosis encircling the pituitary stalk and optic chiasma on the undersurface of the brain
  • Formed by:
    1. the two anterior cerebral arteries, united by a short anterior communicating artery
    2. the two posterior cerebral arteries, which are joined to their respective internal carotid arteries by posterior communicating arteries
  • Often, one of the anastomotic channels is functional and the appropriate communicating artery is enlarged, to accommodate the increased blood flow

Central arteries

  • The anterior choroidal (from the internal carotid or middle cerebral) and posterior choroidal (from posterior cerebral) arteries are also considered central arteries
  • The anterior ones supply choroid plexus in the lateral ventricles, as well as the hippocampus, posteror limb of the internal capsule and thalamus
  • The posterior choroidal arteries supply the dorsal thalamus and choroid plexus in the third ventricle

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