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