PROF. DR. ANSARI
(FOR BDS –II STUDENTS ONLY)
• To know about white matter & deep nuclei.
• Internal capsule, corona radiata & projection
• Corpus callosum and commissural fibers.
• Association fibers.
• Identification of structures in sections,
MRI/CT, their functions and connections.
The human brain
• The human brain makes up only 2% of the
body’s total weight but it uses 20% of the
body’s volume of oxygen and glucose.
• Neurons do not reproduce themselves. The
neurons you are born with are all you will ever
• By the time a person is 50 years old, about
10% of his or her neurons would have died.
The medullary substance
• The structures below the surface cortex are
medullary substance, the white matter of the
• There are submerged deep nuclei in the
medullary substance, like caudate
nucleus, thalamus and lentiform nucleus.
• The white matter is mainly formed by
fibers/axons originating from the neurons
placed in the gray matter.
The white matter
Classified as projection fibers,
Commissural fibers and
The fibers run from one side to opposite
side, from one pole to another pole, or they
connect one area below to another area above.
• White matter is so called because there are no
neurones, among them, they have comparatively
less vascularity and they are myelinated fibers.
• These fibers arise from neurones present at
one place and they project their axons to
those neurones placed somewhere else.
• There are projection fibers from one nucleus
to other, below upwards or above down
• All ascending tracts and descending tracts are
projection fibers, corticospinal tract, middle
cerebellar peduncles, all lemnisci.
White matter is white from the myelin sheaths of
axons, which are the principal components of this tissue
A nerve is a thread- or cord-like bundle of axons passing among
organs made of non-nervous tissue.
• A funiculus is a major bundle of myelinated fibers in the
• A tract is a population of fibers en route from one region to
• A capsule is a conspicuous sheet of white matter in the brain.
Many axons cross the midline of the body.
• If they connect symmetrical structures, the crossing fibers
constitute a commissure.
• A decussation is the site at which a tract connecting
asymmetric structures crosses the midline. Axons coming to a
region are afferent. Axons projecting from a region are
• The association fibers are those which connect one
lobe/region/area to another lobe/region/area of brain.
• The fibers run same side, right sided structures are
connected with each other.
• They never cross the midline.
• They never leave the area.
• Examples are cingulum, superior/inferior longitudinal
• Short association fibers connect one adjacent gyrus
with each other.
The long association fibers include
inferior parietal lobule
Identify A & B?
What types of fibers arise from A?
What types of fibers are running in B?
• A= Nucleus gracilis, internal arcuate fibers arise
from here and will form medial lemniscus,
projection fibers, to VPL of thalamus.
• B= corticospinal fibers, they arise from motor
cortex, pyramidal tract, pass through the internal
capsule, crus cerebri, basilar part of pons and
pyramids. They are projection fibers, UMN from
motor cortex projected to LMN at ventral horn
cells of spinal cord.
• They are projection fibers arising from motor
cortex, precentral gyrus, & post central gyrus.
• They run in posterior limb of internal capsule.
• There is anterior limb of internal capsule and a
bend part called as genu.
• In a horizontal section of cerebral hemisphere
the internal capsule can be seen.
The anterior horns and the posterior horns
are shown in this diagram.
L = Lateral ventricles.
3 = Third ventricle.
CC = Corpus callosum.
C = Caudate nucleus.
P = Putamen
G = Globus Pallidus.
The putamen and globus
pallidus together form the
lenticular (lentiform) nucleus.
T = Thalamus
Arrows = Internal Capsule
[anterior limb, posterior limb,
O = Optic radiations.
A = Auditory radiations.
Genu of internal capsule
• Is the flexure of the internal capsule.
• The fibers in the region of the genu are named
the geniculate fibers; they originate in the
motor part of the cerebral cortex, and, after
passing downward through the base of the
cerebral peduncle with the cerebrospinal
fibers, undergo decussation and end in the
motor nuclei of the cranial nerves of the
The anterior limb of internal capsule
• (1) fibers running from the thalamus to the
• (2) fibers connecting the lentiform and caudate
• (3) fibers connecting the cortex with the corpus
• (4) fibers passing from the frontal lobe through
the medial fifth of the base of the cerebral
peduncle to the nuclei pontis.
The posterior limb of internal capsule
• The part of the internal capsule separating the
thalamus from the basal ganglia.
• Contains fibers destined for and leaving the
• These types of fibers cross the midline and
connect the same structures on either side of
• The great commissure is corpus callosum, it
connects right side of brain with left half.
• Anterior commissure connects right sided
olfactory tract with left side.
• Posterior commissure connects equal areas on
• Habenular commissure connects one habenula
• Patients with life-threating, intractable
epileptic seizures were treated in the past by
surgical commissurotomy or cutting of the
• Patients retained there original motor and
sensory functions, learning and memory,
personality, talents, emotional responding,
and so on, after split brain/commissurotomy.
The following illustrates the differences between left-brain and right-brain thinking:
Left Vs. right brain
Left brain has control on “science & maths”.
right brain has control on “Fine arts brain.
Right half of brain is mute, no language in it.
Left half has language centre on it.
Looks at parts
Looks at wholes
• The basal ganglia comprise several
interconnected brain areas deep in the
• First believed to be mainly involved in
movement, the basal ganglia are now known
to be active in learning, habit formation, and
certain psychiatric disorders.
• “The basal ganglia help you focus,”
Dopamine is the neurotransmitter
• It is likely that the dopamine released in the
basal ganglia system communicates with the
brain areas in the prefrontal cortex to allow
people to pay attention to critical
tasks, ignore distracting information, and
update only the most relevant task
information in working memory during
Applied anatomy of basal ganglia
• The basal ganglia are involved in Parkinson’s
• Neuroimaging studies have shown abnormal
activation of the striatum and other areas of
the basal ganglia in patients with
disorder (ADHD), and anorexia nervosa, as
well as drug addiction.
• Which of the following is an example of
• A. Uncinate fasciculus
• B. Cingulum
• C. Optic radiation
• D. Superior longitudinal fasciculus
• E. Front occipital fasciculus