Download 15. Cerebrum white matter

Cerebrum
White
Matter
(Medulla)
Dr. Zeenat Zaidi
White Matter
• Underlies the
cortex
• Contains:
• Nerve fibers
(predominantly
myelinated)
• Neuroglia
• Blood vessels
• The nerve fibers
originate, terminate
or sometimes both,
within the cortex
• Depending on their origin & termination, these
nerve fibers are classified into three types:
A. Association
B. Projection
C. Commissural
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
Short Association Fibers
• Lie immediately
beneath the
gray substance
of the cortex
• Connect
together the
adjacent gyri.
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
Superior
longitudinal
fasciculus:
connects the
frontal, parietal,
temporal and
occipital lobes
Uncinate
fasciculus:
connects frontal
to temporal lobe,
contributing to
the regulation of
behavior
Broca’s
Area
Arcuate
Fasciculus
Wernicke’s Area
Arcuate fasciculus:
connect gyri in
frontal to temporal
lobes, important for
language function
Cingulum: connects
frontal & parietal
lobes to the parahippocampal gyrus
and adjacent
temporal gyri
Inferior longitudinal
fasciculus: connects
occipital to temporal
pole & contributes to
visual recognition
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
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
• 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
• 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
O
Posterior
forceps
Parts of Corpus Callosum
Genu
Rostrum
Body
Splenium
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
Hippocampal Commissure
• Bundle of fibers
runs transversely
between the crura
of the fornix
• Connect the two
hippocampi with
each other
• (note that hippocampomamillary fibers do not
cross)
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
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)
• 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
Internal Capsule
• Bundle of
projection fibers,
passes through
the interval
between the
thalamus and the
basal ganglia
BG
Th
Has 5 parts:
1. Anterior limb: between caudate
(C) & lentiform (L) nuclei
2. Genu
3. Posterior limb: between
thalamus (TH) & lentiform
nucleus (L)
4. Retrolenticular part: caudal to
lentiform nucleus
5. Sublenticular part: below
lentiform nucleus (can not be
seen in this section)
C
1
2
L
3
Th
4
• 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
• Posterior limb
contains:
• Corticospinal
• Corticobulbar
• Thalamocortical
projections from:
• VPN to the
primary
somatosensory
cortex
• VAN & VLN to
motor regions of
cortex
• 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
• Sublenticular part
contains
thalamocortical
projections: geniculotemporal fibers
(auditory radiation)
from the medial
geniculate nucleus of
thalamus to the
auditory cortex in the
temporal lobe
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)
Thank You & Good Luck