The document is a lecture by Prof. Dr. Ansari for BDS-II students about the cerebrum. It discusses the objectives of understanding white matter, deep nuclei, and fiber tracts. It describes the composition and functions of the white matter including projection fibers that connect distant regions, commissural fibers that cross the midline, and association fibers that connect nearby regions within the same hemisphere. Important fiber tracts and structures are identified and explained such as the internal capsule, corpus callosum, and basal ganglia. The roles of the basal ganglia and dopamine in focusing attention are also summarized.

1. CEREBRUM-II
BY
PROF. DR. ANSARI
(FOR BDS –II STUDENTS ONLY)
1/7/2014
1

2. Objectives
• To know about white matter & deep nuclei.
• Internal capsule, corona radiata & projection
fibers.
• Corpus callosum and commissural fibers.
• Association fibers.
• Identification of structures in sections,
MRI/CT, their functions and connections.
1/7/2014
2

3. 1/7/2014
3

4. 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
have.
• By the time a person is 50 years old, about
10% of his or her neurons would have died.
1/7/2014
4

5. The medullary substance
• The structures below the surface cortex are
medullary substance, the white matter of the
brain.
• 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.
1/7/2014
5

6. 1/7/2014
6

7. 1/7/2014
7

8. The white matter
•
•
•
•
Classified as projection fibers,
Commissural fibers and
Association fibers.
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.
1/7/2014
8

9. Projection 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
wards.
• All ascending tracts and descending tracts are
projection fibers, corticospinal tract, middle
cerebellar peduncles, all lemnisci.
1/7/2014
9

10. 1/7/2014
10

11. Examples of projection fibers
•
•
•
•
•
•
•
•
Corona radiata
Internal capsule
Pyramidal tract
Optic radiation
Auditory radiation
Corticospinal tract
Spinothalamic tract
Medial, lateral, trigeminal and spinal lemnisci.
1/7/2014
11

12. 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
spinal cord.
• A tract is a population of fibers en route from one region to
another.
• 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
efferent
1/7/2014
12

13. Association fibers
• 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
fasciculus.
• Short association fibers connect one adjacent gyrus
with each other.
1/7/2014
13

14. 1/7/2014
14

15. 1/7/2014
15

16. :
The long association fibers include
the following
Name
From
To
•
uncinate fasciculus
frontal lobe
temporal lobe
•
cingulum
cingulate gyrus
entorhinal cortex
•
superior longitudinal
fasciculus
frontal lobe
occipital lobe
•
inferior longitudinal
fasciculus
occipital lobe
temporal lobe
•
perpendicular fasciculus
inferior parietal lobule
fusiform gyrus
•
occipitofrontal fasciculus
occipital lobe
frontal lobe
•
fornix
hippocampus
mammillary bodies
•
Arcuate fasciculus
frontal lobe
temporal lobe
1/7/2014
16

17. 1/7/2014
17

18. 1/7/2014
18

19. 1/7/2014
19

20. MRI-HORIZONTAL
1/7/2014
20

21. Identify A & B?
1/7/2014
21

22. 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.
1/7/2014
22

23. Internal capsule
• 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.
1/7/2014
23

24. The anterior horns and the posterior horns
are shown in this diagram.
•
•
•
•
•
•
•
•
•
•
•
1/7/2014
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,
genu (bend)].
O = Optic radiations.
A = Auditory radiations.
24

25. 1/7/2014
25

26. 1/7/2014
26

27. 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
opposite side.
1/7/2014
27

28. The anterior limb of internal capsule
contains:
• (1) fibers running from the thalamus to the
frontal lobe;
• (2) fibers connecting the lentiform and caudate
nuclei;
• (3) fibers connecting the cortex with the corpus
striatum; and
• (4) fibers passing from the frontal lobe through
the medial fifth of the base of the cerebral
peduncle to the nuclei pontis.
1/7/2014
28

29. 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
cerebral cortex.
1/7/2014
29

30. Commissural fibers
• These types of fibers cross the midline and
connect the same structures on either side of
brain.
• 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
either side.
• Habenular commissure connects one habenula
with other.
1/7/2014
30

31. 1/7/2014
31

32. Commissurotomy/split brain
• Patients with life-threating, intractable
epileptic seizures were treated in the past by
surgical commissurotomy or cutting of the
corpus callosum.
• Patients retained there original motor and
sensory functions, learning and memory,
personality, talents, emotional responding,
and so on, after split brain/commissurotomy.
1/7/2014
32

33. 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.
Left Brain
Logical
Sequential
Rational
Analytical
Objective
Looks at parts
1/7/2014
Right Brain
Random
Intuitive
Holistic
Synthesizing
Subjective
Looks at wholes
33

34. Basal ganglia
• The basal ganglia comprise several
interconnected brain areas deep in the
cerebral cortex.
• 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,”
1/7/2014
34

35. 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
problem-solving tasks.
1/7/2014
35

36. 1/7/2014
36

37. Applied anatomy of basal ganglia
• The basal ganglia are involved in Parkinson’s
disease.
• Neuroimaging studies have shown abnormal
activation of the striatum and other areas of
the basal ganglia in patients with
schizophrenia, attention-deficit/hyperactivity
disorder (ADHD), and anorexia nervosa, as
well as drug addiction.
1/7/2014
37

38. References
• http://healthpages.org/anatomyfunction/brain-anatomy/
• http://library.thinkquest.org/4371/About%20t
he%20Brain.htm
• http://en.wikipedia.org/wiki/White_matter
1/7/2014
38

39. Sample MCQS
• Which of the following is an example of
projection fibers?
• A. Uncinate fasciculus
• B. Cingulum
• C. Optic radiation
• D. Superior longitudinal fasciculus
• E. Front occipital fasciculus
1/7/2014
39