MYELINATED AXONS THAT FORM BUNDLES OF FIBERS BETWEEN DIFFÉRENT NUCLEAR MASSES
White Matter Of Cerebrum
White Matter Of Cerebrum
Intracortical fibers short, project to nearby cortical areas most from horizontal neurons in layer I some from horizontal axon collaterals from
pyramidal cells
Association fibersAssociation fibers
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
White Matter Of Cerebrum
Short Association fibresShort Association fibres
Arcuate fibers“U” Cortical fibresConnect the
Adjacent gyri’s
White Matter Of Cerebrum
Long Association fibersLong Association fibers Long association fibersLong association fibers
Connect the different lobes of the same hemisphere
CingulumSuperior longitudinal
BundleInferior longitudinal
BundleArcuate fasciculusUncinate fasciculus
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
White Matter Of Cerebrum
White Matter Of Cerebrum
Projection fibers connect cortex with subcortical neurons 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 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
White Matter Of Cerebrum
Projection fibers are deep to association fibers
Corona Radiata: afferent & efferent fibers in radially arranged bundles that converge towards the brainstem form a compact band of fibers (Internal Capsule)
between the caudate nucleus and the thalamusInternal 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
White Matter Of Cerebrum
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
Internal Capsule Part 2
Posterior limb 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
Commissural fibersCommissural fibers Corpus callosumCorpus callosum
Connect homologous areas of the two hemispheres
Corpus Callosum Anterior CommissurePosterior commissureHebelunar commissureHippocampal
commissure
White Matter Of Cerebrum
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
White Matter Of Cerebrum
White Matter Of Cerebrum
Split Brain Patients
Transection of corpus callosum sometimes performed for epilepsy treatment
Separates 2 hemispheres except for anterior and posterior commissures
White Matter Of Cerebrum
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