Brain Topography

Dr. NimirDr. 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

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.

Superolateral surfaceFrontal lobe:Is anterior to the central sulcus

and superior to the lateral sulcus.

Its superolateral surface is divided by three sulci into four gyri.

Precentral sulcus runs parallel to central sulcus, and precentral gyrus lies between them.

Extending anteriorly from precentral sulcus are superior and inferior frontal sulci.

Superior frontal gyrus lies above superior sulcus.

Middle frontal gyrus lies between superior and inferior sulci.

Inferior frontal gyrus lies below inferior sulcus.

Parietal lobe:Is posterior to central

sulcus, superior to lateral sulcus and anterior to parieto-occipital sulcus.

Its lateral surface is divided by two sulci into three gyri.

Postcentral sulcus runs parallel to central sulcus, and postcentral gyrus lies between them.

Running posteriorly from the middle of the postcentral sulcus is intraparietal sulcus. 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 surfacesCorpus callosum is the

largest commissure.Cingulate gyrus is above

corpus callosum,separated from it by callosal sulcus and from medial frontal gyrus by cingulate sulcus.

Paracentral lobule anteriorly is part of precentral gyrus posteriorly is part of postcentral gyrus.

Precuneus is part of parietal lobe.

Cuneus which is part of occipital lobe, is between parieto-occipita & calcrine sulci.

Inferior surfaceCollateral sulcus runs

anteriorly below the calcarine sulcus.

Between collateral sulcus and calcarine sulcus is lingual gyrus.

Anterior to lingual gyrus is parahippocampal gyrus which terminates in front as uncus.

Medial occipitotemporal gyrus is bounded medially by collateral and rhinal sulci and laterally by occipitotemporal sulcus which separate it from lateral occipitotemporal gyrus.

On inferior surface of frontal lobe is olfactory sulcus with 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.Habenular

commissure.

2. Association fibers:Connect various

cortical regions within the same hemisphere and may be divided into short and long.

Short association fibers connect adjacent gyri.

Long association fibers:

Uncinate fasciculus connects motor speech area & inferior surface of the frontal lobe to temporal lobe.

Cingulum within 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 fibers are 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 & lentiform nucleus laterally.

The fibers radiate to cortical areas as corona radiata.