Cerebrum: White matter

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White Matter (Medulla)
Cerebrum

• Dr. Zeenat Zaidi

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White Matter

• Underlies the cortex
• Contains
• Nerve fibers (predominantly myelinated)
• Neuroglia
• Blood vessels
• The nerve fibers originate, terminate or
  sometimes both, within the cortex

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• Depending on their origin termination, these
  nerve fibers are classified into three types

• Association
• B. Projection
• C. Commissural

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Association Fibers

• Unite different parts of the same hemisphere
• Are of two kinds
• Short association fibers those connecting
  adjacent gyri,
• Long association fibers those connecting more
  distant gyri

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Short Association Fibers

• Lie immediately beneath the gray substance of the
  cortex
• Connect together the adjacent gyri.

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Long Association Fibers

• Long fibers travel through white matter to
  connect distant areas of cerebral cortex
• Link the primary sensory areas in parietal,
  temporal and occipital lobes to the association
  areas of the cerebral cortex, and to each other

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Superior longitudinal fasciculus connects the
frontal, parietal, temporal and occipital lobes
Uncinate fasciculus connects frontal to temporal
lobe, contributing to the regulation of behavior
Arcuate Fasciculus
Brocas Area
Arcuate fasciculus connect gyri in frontal to
temporal lobes, important for language function
Wernickes Area
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Cingulum connects frontal parietal lobes to
the para-hippocampal gyrus and adjacent temporal
gyri
Inferior longitudinal fasciculus connects
occipital to temporal pole contributes to
visual recognition
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Commissural Fibers

• Connect the corresponding regions of the two
  hemispheres
• Include
• Corpus callosum
• Anterior commissure
• Hippocampal commissure (commissure of fornix)
• (Posterior commissure, not a cerebral
  commissure)

Corpus Callosum
F
P
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Corpus Callosum

• Is a fibrous bridge located in the depth of the
  median longitudinal fissure
• Connects the two cerebral hemispheres together
• Shorter craniocaudally than is the hemisphere
• Cranial end is nearer to the frontal pole of
  hemisphere as compared to caudal end to the
  occipital pole

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• The fibers in the corpus callosum connect the
  corresponding regions of the two hemispheres with
  each other (except the inferior part of the
  temporal lobes)

C C
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• Fibers linking the two frontal poles with each
  other, curve forward form u-shaped anterior
  forceps (forceps minor)
• Fibers linking the two occipital poles with each
  other, curve backward form u-shaped posterior
  forceps (forceps major)

Anterior forceps
F
C C
P
Posterior forceps
O
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Parts of Corpus Callosum
Body
Genu
Splenium
Rostrum
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Anterior Commissure

• Bundle of fibers runs transversely in front of
  the anterior columns of fornix
• Connects the inferior and middle temporal gyri
  the olfactory regions of the two hemispheres

fornix
IVF
Anterior column of fornix
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Hippocampal Commissure

• Bundle of fibers runs transversely between the
  crura of the fornix
• Connect the two hippocampi with each other
• (note that hippocampo-mamillary fibers do not
  cross)

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Posterior Commissure

• Rounded band of white fibers
• Crossing the midline on the dorsal aspect of the
  upper end of the cerebral aqueduct (located
  between superior colliculus pineal body)
• Connects the left and right midbrain. Plays
  important role in the bilateral pupillary reflex

P
SC
IC
Cerebral aqueduct
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Projection Fibers

• Fibers running vertically through the hemispheres
• Consist of
• Cortical afferent fibers conveying impulses to
  the cerebral cortex (mainly thalamo-cortical
  fibers)
• Cortical efferent fibers carrying impulses away
  from the cortex to the lower centers
  (corticostriate, corticobulbar, corticopontine,
  corticospinal, descending autonomic fibers)

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• Deeper to the cortex, these fibers are arranged
  radially as the corona radiata
• Then the fibers converge to form a sheath, called
  the internal capsule, that passes between the
  thalamus and the basal ganglia
• Continue in the
• Crus of the midbrain
• Basilar part of pons
• Pyramid of medulla oblongata
• Continue in the spinal cord as the corticospinal
  tracts

corona radiata
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Internal Capsule
BG

• Bundle of projection fibers, passes through the
  interval between the thalamus and the basal
  ganglia

Th
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• Has 5 parts
• Anterior limb between caudate (C) lentiform
  (L) nuclei
• Genu
• Posterior limb between thalamus (TH) lentiform
  nucleus (L)
• Retrolenticular part caudal to lentiform nucleus
• Sublenticular part below lentiform nucleus (can
  not be seen in this section)

C
1
2
L
3
Th
4
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• Anterior limb contains
• Thalamocortical projections that connect
  mediodorsal nucleus of thalamus with the
  prefrontal cortex
• Frontopontine fibers
• Genu contains
• Corticobulbar fibers which connect the cortex
  with cranial nerve motor nuclei in the brainstem

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• Posterior limb contains
• Corticospinal
• Corticobulbar
• Thalamocortical projections from
• VPN to the primary somatosensory cortex
• VAN VLN to motor regions of cortex

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• Retrolenticular part contains thalamocortical
  projections
• Geniculocalcarine fibers (visual radiation), from
  the lateral geniculate nucleus of thalamus to the
  visual cortex in the occipital lobe
• few Geniculotemporal fibers (auditory
  radiation) from the medial geniculate nucleus of
  thalamus to the auditory cortex in the temporal
  lobe

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• Sublenticular part contains thalamocortical
  projections geniculo-temporal fibers (auditory
  radiation) from the medial geniculate nucleus of
  thalamus to the auditory cortex in the temporal
  lobe

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Clinical Notes

• Bilateral lesion of the inferior longitudinal
  fasciculus (as in carbon monoxide poisoning),
  leads to
• Loss of identification of the
• Nature of objects (object agnosia)
• Individual faces (prosopagnosia)
• The elementary vision remains intact
• Damage to corpus callosum leads to split-brain
  syndrome. The two half of the brain behave
  relatively autonomously
• Damage to splenium of corpus callosum leads to
  posterior disconnection syndrome of alexia
  (cannot understand written material) without
  agraphia (can speak and write without difficulty)

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Thank You Good Luck