Transcript Cortical Connections

White Matter Of Cerebrum
MYELINATED AXONS THAT
FORM BUNDLES OF FIBERS
BETWEEN DIFFÉRENT NUCLEAR
MASSES
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 Intracortical fibers
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short, project to nearby cortical areas
most from horizontal neurons in layer I
some from horizontal axon collaterals from pyramidal cells
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Association fibers
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gyrus to gyrus and lobe to
lobe in the same hemisphere
arcuate fibers connect
adjacent gyri
long association fibers
connect distant gyri
originate from pyramidal
neurons in layers II and III
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Short Association fibres
 Arcuate fibers
 “U” Cortical fibres
 Connect the Adjacent
gyri’s
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Long Association fibers
Long association fibers
 Connect the different
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lobes of the same
hemisphere
Cingulum
Superior longitudinal
Bundle
Inferior longitudinal
Bundle
Arcuate fasciculus
Uncinate fasciculus
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Superior longitudinal
fasciculus: connects sup. &
medial frontal gyri to
parietal & occipital lobe
Arcuate fasciculus: arches
around the insular region,
connects Broca’s and
Wernicke’s areas
Uncinate fasciculus:
connects orbital frontal gyri
to anterior parts of the
temporal lobe
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 Projection fibers connect cortex with subcortical
neurons
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corticofugal/efferent, project from cortex
corticopetal/afferent, project to cortex
 Corticofugal project to corpus striatum, brainstem, and
spinal cord
 Corticopetal projections arise mainly from the thalamus the thalamic radiations
 Internal capsule carries most of these connections
Clinical Case
 A patient presented with paralysis of the left side of
the limbs and left side of the lower face and deviation
of the tongue to the left with no atrophy and with no
loss of taste sensation. This constellation of deficits
most likely resulted from a lesion of the:
1. Left internal capsule
2. Right internal capsule
3. Left pontine tegmentum
4. Ventromedial medulla on the right side
5. Ventromedial medulla on the left side
Clinical Case
 A 35-year-old man suffered a stroke that did not
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cause paralysis. However, he discovered that he was
unable to perform complex learned movements. The
region of the cerebral cortex most likely affected by
the stroke was the:
Precentral gyrus
Postcentral gyrus
Premotor cortex
Temporal neocortex
Prefrontal cortex
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Projection fibers are deep to association fibers
 Corona Radiata: afferent & efferent fibers in
radially arranged bundles that converge towards the
brainstem
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form a compact band of fibers (Internal Capsule) between
the caudate nucleus and the thalamus
 Internal Capsule:
 Anterior limb: separates caudate nucleus from putamen
 Posterior limb: separates thalamus from lentiform nucleus ( =
putamen + globus pallidus)
 Both limbs meet at the genu of the internal capsule
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Internal Capsule Part 1
 Anterior limb
frontal lobe
connections
 cortex to striatum and
pontine nuclei
 anterior and medial
thalamus to frontal
lobe
 Genu
 Ventral anterior and
ventral lateral
thalamus to premotor
and motor cortex
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Internal Capsule Part 2
 Posterior limb
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corticospinal
retrolenticular =
optic radiations
sublenticular =
auditory radia.
Somatosensory
thalamocortical
fibers
Internal Capsule Clinical Illustration
 Posterior limb of internal capsule is most common site of
stroke (supplied by MCA)
 Capsular stroke
 contralateral spastic hemiplegia
 contralateral hemianesthesia
 contralateral lower facial paralysis
 if retrolenticular part is damaged then contralateral
homonymous hemianopsia will result (deficit in
contralateral half of visual field of both eyes)
 Anterior limb supplied by ACA
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Commissural fibers
 Connect homologous
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areas of the two
hemispheres
Corpus Callosum
Anterior Commissure
Posterior commissure
Hebelunar commissure
Hippocampal commissure
Corpus callosum
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connect homologous areas of the two hemispheres
Corpus callosum: rostrum, genu, trunk, splenium
 rostrum & genu connect frontal lobes
 trunk connects posterior frontal lobes, parietal lobes, and superior
temporal lobe
 splenium connects the occipital lobes
Originate with pyramidal neurons in layers II and III
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Split Brain Patients
 Transection of corpus callosum sometimes
performed for epilepsy treatment
 Separates 2 hemispheres except for anterior and
posterior commissures
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 Anterior commissure
connects the inferior and
middle temporal gyri in
opposite hemispheres;
also olfactory connections
 Posterior commissure
carries fibers from the
pretectal nuclei and other
nearby neurons