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Brain Topography. Dr. Nimir Dr. Safaa. Objectives Demarcate the major lobes, gyri and sulci of the cerebral hemisphere . Describe the organization of the cerebral hemisphere into cerebral cortex ,white matter and nuclei

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brain topography
Brain Topography
  • Dr. Nimir
  • Dr. Safaa


  • Demarcate the major lobes, gyri and sulci of the cerebral hemisphere.
  • Describe the organization of the cerebral hemisphere into cerebral cortex ,white matter and nuclei
  • Describe the types of fibers in the white matter of the cerebral hemisphere: projection (internal capsule), commissural and association fibers.

The brain is divided into:

  • 1- Forebrain (Telencephalon= cerebrum & diencephalon).
  • 2- Midbrain.
  • 3- Hindbrain (pons ,medulla oblongata, cerebellum).
  • Cerebrum (cerebral hemispheres & basal ganglia ).
  • Cerebral hemispheres are seperated by longitudinal fissure into left & right which are connected by corpus callosum.

Each cerebral hemisphere has 3 surfaces:

  • Superolateral.
  • Medial.
  • Inferior.
  • Each cerebral hemisphere has 3 poles:
  • Frontal pole.
  • Temporal pole.
  • Occipital pole.

To increase the surface area the cerebral cortex is thrown into folds or gyri, which are separated from each other by sulci or fissures.

  • Each cerebral hemisphere is divided by central, parieto-occipital,lateral and calcarine sulci into frontal, parietal, temporal, and occipital lobes.


  • Frontal lobe:
  • Is anterior to the central sulcus and superior to the lateral sulcus.
  • Its superolateral surface is divided by three sulciinto four gyri.
  • Precentralsulcusruns parallel to central sulcus, and precentralgyruslies between them.
  • Extending anteriorly from precentralsulcus are superior and inferior frontal sulci.
  • Superior frontal gyruslies above superior sulcus.
  • Middle frontal gyruslies between superior and inferior sulci.
  • Inferior frontal gyruslies below inferior sulcus.

Parietal lobe:

  • Is posterior to central sulcus, superior to lateral sulcusand anterior to parieto-occipital sulcus.
  • Its lateral surface is divided by two sulci into three gyri.
  • Postcentralsulcus runs parallel to central sulcus, and postcentralgyruslies between them.
  • Running posteriorly from the middle of the postcentral sulcus is intraparietalsulcus. Superior to intraparietal sulcus is superior parietal lobule (gyrus).
  • Inferior to the intraparietal sulcus is the inferior parietal lobule (gyrus).

Temporal lobe:

  • Is inferior to the lateral sulcus.
  • Its lateral surface is divided into three gyri by two sulci.
  • The superior and middle temporal sulci run parallel to lateral sulcus and divide temporal lobe into superior, middle, and inferior temporal gyri.
  • Occipital lobe:
  • Is behind the parieto-occipital sulcus.

Medial surfaces

  • Corpus callosum is the largest commissure.
  • Cingulate gyrusis above corpus callosum,separatedfrom it by callosalsulcus and from medial frontal gyrusby cingulate sulcus.
  • Paracentral lobule anteriorly is part of precentralgyrusposteriorly is part of postcentralgyrus.
  • Precuneus is part of parietal lobe.
  • Cuneuswhich is part of occipital lobe, is between parieto-occipita & calcrinesulci.

Inferior surface

  • Collateral sulcus runs anteriorly below the calcarine sulcus.
  • Between collateral sulcus and calcarine sulcus is lingual gyrus.
  • Anterior to lingual gyrus is parahippocampalgyrus which terminates in front as uncus.
  • Medial occipitotemporalgyrusis bounded medially by collateraland rhinal sulci and laterally by occipitotemporalsulcus which separate it from lateral occipitotemporalgyrus.
  • On inferior surface of frontal lobe is olfactory sulcuswith olfactory bulb and orbital gyri.

Gray matter consists of nerve cells(neurons) embedded in neuroglia.

  • White matter consists of nerve fibers (axons) embedded in neuroglia.
  • In cerebral hemispheres gray mater is seen in cerebral cortex & basal ganglia.

White mater fibers are classified into three groups according to their connections:

  • 1. Commissural fibers.
  • 2. Association fibers.
  • 3. Projection fibers.

1. Commissural fibers:

  • Connect corresponding regions of the two hemispheres. They are:
  • Corpus callosum(splenium ,body, genu, rostrum).
  • Anterior commissure.
  • Posterior commissure.
  • Fornix.
  • Habenularcommissure.

2. Association fibers:

  • Connect various cortical regions within the same hemisphere and may be divided into short and long.
  • Shortassociation fibers connect adjacent gyri.
  • Longassociation fibers:
  • Uncinatefasciculus connects motor speech area & inferior surface of the frontal lobe to temporal lobe.

Cingulumwithin cingulate gyrus connects frontal and parietal lobes to parahippocampal and temporal cortical regions.

  • Superior longitudinal fasciculus connects anterior part of the frontal lobe to the occipital and temporal lobes.
  • Inferior longitudinal fasciculus connects occipital lobe to temporal lobe.
  • Fronto-occipital fasciculus connects frontal lobe to occipital and temporal lobes.

3. Projection fibersare afferent and efferent nerve fibers passing to and from the brainstem & spinal cord to the entire cerebral cortex.

  • Mainly pass within the internal capsule between caudate nucleus &thalamus medially &lentiformnucleus laterally.
  • The fibers radiate to cortical areas as corona radiata.