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CEREBRAL TRACTS
Categories of Tracts

Association:
Confined to a given hemisphere.
Connect regions of the same hemisphere.

Commissural:
Interconnect the two hemispheres.
Categories of Tracts

Projection Tracts:
Form internal capsule.
Make up ascending and descending tracts.
Connect hemispheres to other parts of brain
and spinal cord.
Association Tracts: Examples
Arcuate
 Cingulum
 Superior longitudinal fasciculus
 Superior occipitofrontal fasciculus
 Inferior occipitofrontal fasciculus
 Uncinate fasciculus

Arcuate Tracts

Interconnect adjacent gyri.
Cingulum

Connects frontal, parietal and temporal
cortical areas on the medial side of each
hemisphere.
Superior Longitudinal
Fasciculus

Interconnects areas within the frontal,
parietal, occipital, and temporal lobes.
Superior Occipitofrontal
Fasciculus

Located in medial part of hemisphere
underneath lateral extension of corpus
callosum.

Interconnects the frontal lobe with more
posterior parts of hemisphere.
Inferior Occipitofrontal
Fasciculus

Runs between the occipital and frontal
lobes in the lateral part of each
hemisphere under the insula.
Uncinate Fasciculus

Makes a sharp bend around the lateral
fissure.

Interconnects the orbital surface of the
frontal lobe with the rostral part of the
temporal lobe.
Commissural Tracts: Examples
Corpus callosum
 Anterior commissure
 Posterior commissure
 Hippocampal commissure

Corpus Callosum
Contains about 300 million fibers.
 Interconnects neocortical areas in all
lobes.
 Unifies awareness and attention between
the two lobes.
 Permits a sharing of learning and memory.

Corpus Callosum: Subdivisions
Splenium = Wide caudal part.
 Body = Large midportion.
 Genu = Anterior part.
 Rostrum is continuous with lamina
terminalis.

Anterior Commissure

Interconnects areas within the two
temporal lobes.
Posterior Commissure

Connects cerebral hemispheres with
superior colliculi.
Hippocampal Commissure

Interconnects two hippocampal
formations.
Projection Tracts: Types

Corticopetal:
To cerebral cortex.

Corticofugal:
From cerebral cortex.
Corticopetal Projection Fibers
Mostly from thalamus.
 Form part of internal capsule.
 Diverge toward cerebral cortex.
 Form part of corona radiata.

Corticofugal Projection Fibers
Originate in different parts of cerebral
cortex.
 Converge toward:

Basal nuclei.
Thalamus.
Form part of corona radiata.
 Form part of internal capsule.

Projection Tract Examples
Thalamic radiation
 Corticopontine
 Corticobulbar
 Corticospinal
 Corticoreticular
 Optic radiation
 Fornix

Thalamic Radiation

Corticothalamic fibers project within
internal capsule from cerebral cortex to
thalamus.

Thalamocortical fibers project within
internal capsule from thalamus to cerebral
cortex.
Corticopontine Projections

Corticopontine fibers projects to pontine
nuclei in the pons.

Pontine nuclei project to cerebrellum.
Corticobulbar Projections

Part of pyramidal tracts.

Originate mostly in motor cortex.

Project to cranial nerve nuclei in
brainstem.
Corticospinal Projections

Part of pyramidal tracts.

Originate mostly in motor cortex.

Project to cell groups throughout all parts
of spinal cord.
Corticoreticular Projections

Originate in motor and somatosensory
cortex.

Project to brainstem reticular formations.
Optic Radiation
= Geniculocalcarine tract.
 Originates in lateral geniculate body.
 Runs in lateral direction in the internal
capsule.
 Makes a sharp bend (= Meyer’s loop).
 Runs in caudal direction toward calcarine
fissure in occipital lobe.

Fornix

Major projection system between the
hippocampus in temporal lobe and the
diencephalon.