Cortical Areas and Internal Structure of the Cerebral Hemispheres pdf - Neuroanatomy

Lecture

- Cortical Areas

- Internal Structure of

the Cerebral

Hemispheres

Functional areas of Brain (Cortical Areas)

Frontal Lobe:

area:

precentral

-
which is divided into ant and post regions

- posterior region (motor area, primary motor area, or Brodmann area 4), the function of

the primary motor area is to carry out the individual movements of different parts of

the body

- anterior region (premotor area, secondary motor area, or Brodmann area 6 and

parts of areas 8, 44, and 45) the premotor area programs the activity of the primary

motor area

The supplementary motor area

Removal of the supplementary motor area produces no permanent loss of

movement

The frontal eye field

(parts of Brodmann areas 6, 8, and 9) Responsible for conjugate movements of the

eyes

Broca

The motor speech area of

Brodmann area 45, The ablation of this region in the nondominant hemisphere has

no effect on speech.

The prefrontal cortex

Brodmann areas 9, 10, 11, and 12, concerned with the makeup of the individual's

personality and emotion

Parietal Lobe

, and

areas

Brodmann

area ( primary sensory)

somesthetic

The primary

contralateral sensation

area

somesthetic

The secondary

). This area has many

and

areas

Brodmann

(

association area:

somesthetic

The

connections with other sensory areas of the cortex. It is believed that its main

function is to receive and integrate different sensory modalities.

Occipital Lobe

)

area

Brodmann

(

primary visual area

)

and

areas

Brodmann

(

secondary visual area

Temporal Lobe

)

area

Brodmann

(

primary auditory area

area

Brodmann

(auditory association cortex),

secondary auditory area

is localized in the left dominant hemisphere, The

Wernicke

The sensory speech area of

Wernicke area is connected to the Broca area by a bundle of nerve fibers called the

arcuate fasciculus, It receives fibers from the visual cortex in the occipital lobe and

the auditory cortex in the superior temporal gyrus.

The Wernicke area permits the understanding of the written and spoken language and

enables a person to read a sentence, understand it, and say it out loud

Functional
localization of
the cerebral
cortex.

A: Lateral view of
the left
cerebral
hemisphere.

B: Medial view of
the left
cerebral
hemisphere

Motor homunculus on the precentral gyrus.

Probable nerve pathways involved in reading a sentence and repeating it out loud

Probable nerve pathways involved with hearing a question and answering it

Internal Structure of the Cerebral

Hemispheres

Basal Nuclei

The term basal nuclei (basal ganglia) is applied to a collection of masses of
gray matter situated within each cerebral hemisphere.

They are:

- the corpus striatum,

- the amygdaloid nucleus

- claustrum

Corpus Striatum

The corpus striatum is situated lateral to the thalamus.

It is almost completely divided by a band of nerve fibers, the internal capsule,
into:

shaped mass of

The caudate nucleus is a large C

The caudate nucleus:

gray matter that is closely related to the lateral ventricle and lies lateral to
the thalamus

it can be divided into a head, a body, and a tail

shaped mass of gray matter whose

is a wedge

nucleus:

lentiform

The

broad convex base is directed laterally and whose blade is directed medially

A vertical plate of white matter divides the nucleus into: the putamen larger,
darker lateral portion,, and the globus pallidus an inner lighter portion,

Functions of corpus striatum
1- regulation of muscle tone
2- contral autonomic movement
3- contral voluntary movement

Clinical application
Lesion of corpus striatum lead to tremor due to loss of dopamine
(See functions of Basal n.)

Horizontal

section of

the

cerebrum,

as seen

from

above,

showing

the

relationshi

p between

the

lentiform

nucleus,

the

caudate

nucleus,

the

thalamus,

and the

internal

capsule

Amygdaloid Nucleus

The amygdaloid nucleus is situated in the temporal lobe close to the uncus
it can influence the body's response to environmental changes. In the sense of

fear, for example, it can change the heart rate, blood pressure, skin color,
and rate of respiration.

Claustrum

The claustrum is a thin sheet of gray matter that is separated from the lateral

surface of the lentiform nucleus by the external capsule

Connections of the Corpus Striatum

Afferent Fibers

- Thalamostriate Fibers

- Nigrostriate Fibers

- Brainstem Striatal Fibers

Efferent Fibers

- Striatopallidal Fibers

- Striatonigral Fibers

Pallidus

Globus

Connections of the

Afferent Fibers

Striatopallidal Fibers

Efferent Fibers



Pallidofugal Fibers can be divided into groups: (1) the ansa lenticularis, (2)
the fasciculus lenticularis, (3) the pallidotegmental fibers and (4) the
pallidosubthalamic fibers

Functions of the Basal Nuclei

the basal nuclei control muscular movements by influencing the cerebral cortex

and have no direct control through descending pathways to the brainstem
and spinal cord. In this way, the basal nuclei assist in the regulation of
voluntary movement and the learning of motor skills.

Writing the letters of the alphabet, drawing a diagram, passing a football, using

the vocal cords in talking and singing, and using the eye muscles when
looking at an object are a few examples where the basal nuclei influence
the skilled cortical motor activities.

White Matter of the Cerebral Hemispheres

The white matter is composed of myelinated nerve fibers of different diameters

supported by neuroglia. The nerve fibers may be classified into three groups

according to their connections:

(1) commissural fibers: Commissure fibers essentially connect corresponding

regions of the two hemispheres. They are as follows: the corpus callosum,

the anterior commissure, the posterior commissure, the fornix, optic

chiasma and the habenular commissure

(2) association fibers: Association fibers are nerve fibers that essentially

connect various cortical regions within the same hemisphere and may be

divided into short and long groups ex: cingulate gyrus.

(3) projection fibers: Afferent and efferent nerve fibers passing to and from the

brainstem to the entire cerebral cortex must travel between large nuclear

masses of gray matter within the cerebral hemisphere ex: corona radiata,

internal capsule, external capsule and corticospinal tract.

callosum

The corpus

the largest

commissure of the

brain, connects the

two cerebral

hemispheres.It lies

at the bottom of the

longitudinal fissure.

For purposes of

description, it is

divided into:

the rostrum (connect

both temporal

lobes),

the genu (connect both

frontal lobes),

the body (connect part

of frontal parietal

and occipital lobes)

the splenium (connect

the occipital lobes).

The septum pellucidum

The septum pellucidum is a thin vertical sheet of nervous tissue consisting of
white and gray matter covered on either side by ependyma

The septum pellucidum forms a partition between the anterior horns of the
lateral ventricles.

Medial view of the right cerebral hemisphere, which has been dissected to
show the internal capsule and the corona radiata. The thalamus has been
removed

Structure of the Cerebral Cortex

The cerebral cortex forms a complete covering of the cerebral hemisphere. It is
composed of gray matter and has been estimated to contain approximately
10 billion neurons. The surface area of the cortex has been increased by
throwing it into convolutions, or gyri, which are separated by fissures or
sulci. The thickness of the cortex varies from 1.5 to 4.5 mm. The cortex is
thickest over the crest of a gyrus and thinnest in the depth of a sulcus. The
cerebral cortex, like gray matter elsewhere in the central nervous system,
consists of a mixture of nerve cells, nerve fibers, neuroglia, and blood
vessels.

The following types of nerve cells are present in the cerebral cortex:

(1) pyramidal cells, (2) stellate cells, (3) fusiform cells, (4) horizontal cells of
Cajal, and (5) cells of Martinotti

Main types of neurons found
in the cerebral cortex

Layers of the Cerebral Cortex

1- Molecular layer (plexiform layer).

2- External granular layer.

3- External pyramidal layer.

4- Internal granular layer.

5- Ganglionic layer (internal
pyramidal layer).

The insula

is an area of the cortex that is buried within the lateral sulcus and forms its
floor

It can be examined only when the lips of the lateral sulcus are separated
widely.

Histologically, the posterior part is granular and the anterior part is agranular,
thus resembling the adjoining cortical areas.

Its fiber connections are incompletely known. It is believed that this area is
important for planning or coordinating the articulatory movements
necessary for speech.