Title: Cerebrum: White matter
1(No Transcript)
2White Matter (Medulla)
Cerebrum
3White Matter
- Underlies the cortex
- Contains
- Nerve fibers (predominantly myelinated)
- Neuroglia
- Blood vessels
- The nerve fibers originate, terminate or
sometimes both, within the cortex
4- Depending on their origin termination, these
nerve fibers are classified into three types
- Association
- B. Projection
- C. Commissural
5Association 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
6Short Association Fibers
- Lie immediately beneath the gray substance of the
cortex - Connect together the adjacent gyri.
7Long 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
8Superior 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
9Cingulum 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
10Commissural 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
11Corpus 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
12- 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
13- 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
14Parts of Corpus Callosum
Body
Genu
Splenium
Rostrum
15Anterior 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
16Hippocampal 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)
17Posterior 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
18Projection 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)
19- 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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21Internal Capsule
BG
- Bundle of projection fibers, passes through the
interval between the thalamus and the basal
ganglia
Th
22- 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
23- 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
24- Posterior limb contains
- Corticospinal
- Corticobulbar
- Thalamocortical projections from
- VPN to the primary somatosensory cortex
- VAN VLN to motor regions of cortex
25- 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
26- 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
27Clinical 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)
28Thank You Good Luck