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Cerebrum: White matter

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* White Matter (Medulla) Dr. Zeenat Zaidi Cerebrum White Matter Underlies the cortex Contains: Nerve fibers (predominantly myelinated) Neuroglia Blood vessels The ... – PowerPoint PPT presentation

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Title: Cerebrum: White matter


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(No Transcript)
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White Matter (Medulla)
Cerebrum
  • Dr. Zeenat Zaidi

3
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
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