04/11/2023 1

CEREBRUM-II

BYPROF. DR. ANSARI

(FOR BDS –II STUDENTS ONLY)

04/11/2023 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.

04/11/2023 3

04/11/2023 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.

04/11/2023 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.

04/11/2023 6

04/11/2023 7

04/11/2023 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.

04/11/2023 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.

04/11/2023 10

04/11/2023 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.

04/11/2023 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

04/11/2023 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.

04/11/2023 14

04/11/2023 15

04/11/2023 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

:

04/11/2023 17

04/11/2023 18

04/11/2023 19

04/11/2023 20

MRI-HORIZONTAL

04/11/2023 21

Identify A & B?

04/11/2023 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.

04/11/2023 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.

04/11/2023 24

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, genu (bend)].

• O = Optic radiations.• A = Auditory radiations.

04/11/2023 25

04/11/2023 26

04/11/2023 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.

04/11/2023 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.

04/11/2023 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.

04/11/2023 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.

04/11/2023 31

04/11/2023 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.

04/11/2023 33

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 Right BrainLogical

Sequential Rational

AnalyticalObjective

Looks at parts

Random IntuitiveHolistic

SynthesizingSubjective

Looks at wholes

The following illustrates the differences between left-brain and right-brain thinking:

04/11/2023 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,”

04/11/2023 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.

04/11/2023 36

04/11/2023 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.

04/11/2023 38

References

• http://healthpages.org/anatomy-function/brain-anatomy/

• http://library.thinkquest.org/4371/About%20the%20Brain.htm

• http://en.wikipedia.org/wiki/White_matter

04/11/2023 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