NEUROANATOMY

Lecture : 2

The Cerebrum (The Cerebral Hemispheres)

Prepared and presented by:

Dr. Iyad Mousa Hussein ,

MD, Ph.D in Neurology

Head of Neurology Department

Nasser Hospital

1. Morphological subdivisions of the brain.

2. Lobes and sulci of each cerebral hemisphere.

3. The Important sulci, gyri, and functional areas of the frontal Lobe.

4. The Important Sulci, gyri, and functional areas of the parietal lobe.

5. The Important sulci, gyri, and functional areas of the temporal lobe.

6. The Important sulci, gyri, and functional areas of the occipital lobe.

7. The Internal structures of the cerebral hemispheres.

8. The layers of the cerebral cortex.

9. The white mater of the cerebral hemisphere.

LECTURE OBJECTIVES:

The Cranial FossaThe Cranial Fossa

The cranium is divided into The cranium is divided into

three regions (fossa):three regions (fossa):

1. Anterior Cranial Fossa: 1. Anterior Cranial Fossa:

house for frontal lobes.house for frontal lobes.

2. Middle Cranial Fossa: 2. Middle Cranial Fossa:

house for temporal lobes.house for temporal lobes.

3. Posterior Cranial Fossa: 3. Posterior Cranial Fossa:

house for occipital lobes, house for occipital lobes,

cerebellum and medulla cerebellum and medulla

oblongata. oblongata.

The brain is the intracranial part of the CNS and formed of:

1. The Cerebrum: formed of right and left cerebral hemisphere.

2. The Cerebellum: below the posterior part of the cerebrum.

3. The Brain Stem: formed of the following parts (from

downward):

1. Medulla oblongata.

2. Pons.

3. Midbrain.

Morphological Subdivisions of the Brain

The Cerebrum (Cerebral Hemisphere)

Site: occupies most of cranial cavity and it is the larges part

of the brain.

The cerebrum formed of two cerebral hemispheres,

connected to each other by:

1. The corpus callosum.

2. Right and left cerebral peduncles: connected to

upper part of the brain stem.

The Cerebrum (Cerebral Hemisphere)

The Cerebrum (Cerebral Hemisphere)

Each cerebral hemisphere has 3 poles:

1. Frontal pole: at the anterior end of the frontal lobe.

2. Temporal pole: at the anterior end of the temporal lobe.

3. Occipital pole: at the posterior end of the occipital lobe.

Poles of Each Cerebral Hemisphere

Poles of Each Cerebral Hemisphere

The surface of each cerebral hemisphere is divided by

three main sulci or fissures into four lobes (which have

been given the names of the skull bones under which they

lie).

These four lobes are:

1. The frontal.

2. The parietal.

3. The temporal.

4. The occipital.

Each surface of lobes is divided by sulci into gyri.

Lobes of Each Cerebral Hemisphere

Lobes of Each Cerebral Hemisphere

Lobes of Each Cerebral Hemisphere

1. The longitudinal fissure: divides the cerebrum into two

hemispheres.

2. The central sulcus (Roland sulcus): it separates the

frontal lobe (infront of it) from parietal lobe (behind it).

3. The lateral sulcus (Sylvian sulcus): between frontal and

parietal lobes (above) and temporal lobe (below).

4. The parieto-occipital sulcus: it found mainly on the

medial surface of the hemisphere between parietal and

occipital lobes.

Sulci of Each Cerebral Hemisphere

Sulci of the Cerebral Hemisphere

Sulci of the Cerebral Hemisphere

Sulci of the Cerebral Hemisphere

Sulci of the Cerebral Hemisphere

The Important Sulci of the Frontal Lobe:

1. The precentral sulcus.

2. The superior frontal sulcus.

3. The inferior frontal sulcus.

A. The Frontal Lobe

Sulci or Fissures of the Frontal Lobe

The Important Gyri of the Frontal Lobe

1. The precentral gyrus: lies between the central and

precentral sulci.

2. The superior frontal gyrus: lies above the superior

frontal sulcus.

3. The middle frontal gyrus: lies between the superior and

inferior frontal sulci.

4. The inferior frontal gyrus: lies below the inferior frontal

sulcus.

The Important Gyri of the Frontal Lobe

The Important Functional Areas of the Frontal LobeThe Important Functional Areas of the Frontal Lobe

AreasSiteFunctionLesion Primary motor area (4)Precentral gyrus

Voluntary motor activity of opposite 1/2 of the body

Irritative: contralateral motor Jaksonian fitDestructive: contralateral motor paresis usually affecting one limb (monoplegia)

Secondary motor (Premotor) area (6)

Anterior part of precentral gyrus

Gives extrapyramidal fibers

Contralateral muscle hypertonia & exaggerated deep reflexes+ve pathological reflex

Frontal eye field (8)

Middle frontal gyrusVoluntary conjugate deviation of eyes to opposite side

Irritative: conjugate deviation of eyes to the opposite sideDestructive: conjugate deviation of eyes to the same side.

Area (45)Inferior frontal gyrus in dominant hemisphere

Motor center of writing. In dominant hemisphere.

Agraphia: the pt. is unable to express ideas in written words

Brocca's area (44)

Inferior frontal gyrus in dominant hemisphere

Motor center of speech. In dominant hemisphere

Motor (expressive or Brocca's or verbal) aphasia: the pt. unable to express idea in spoken words

PrefrontalAreas(9, 10, 11 & 12)

Anterior poleHigher center of memory, orientation, thinking and intelligence

Amnesia (impaired of memory);Dementia;Sphencteric dysfunction;Loss of personal hygiene

Areas of the Frontal lobe

Areas of the Frontal lobe

Cortical Somatotopy

Cortical Somatotopy

The Important Sulci of the Parietal Lobe:

1. The postcentral sulcus.

2. The intraparietal sulcus.

B. The Parietal Lobe

1.The postcentral gyrus: its the main gyrus of parietal lobe, lies

between the central and postcentral sulci.

2.The superior parietal gyrus: lies above the intraparietal sulcus.

3.The inferior parietal gyrus: lies below the intraparietal sulcus.

4.The supramarginal gyrus: small gyrus surrounding the upper end

of lateral sulcus.

5.The angular: small gyrus surrounding the upper end of the

temporal sulcus.

Important Gyri of the Parietal Lobe

Sulci of the parietal lobe

The Important Gyri of the Parietal Lobe

The Important Functional Areas of the Parietal LobeThe Important Functional Areas of the Parietal Lobe

AreasSiteFunctionLesion

Primary sensory area (1,2,3)

Post central gyrus

Perception of cortical sensation from opposite 1/2 of the body

Irritative: contralateral sensory Jaksonian fit (numbness, paresthesia)Destructive: contralateral sensory loss of cortical sensation usually affecting one limb (monoanesthesia)

Areas 5& 7Superior parietal gyrus

Knowing the meaning of the sensations felt (by associating the visual, auditory and tactile sensation)

Asteriognosis: inability to recognize the felt objects

Angular gyrus, area (39)

Surround the upper end of superior temporal sulcus in dominant hemisphere

Visual psychic area for speech (recognition of letters & numbers). In dominant hemisphere.

Visual aphasia (alexia): the pt. can not read because he does not understand letter & number (word blindness)

Supramarginalgyrus,area (40)

Surround the upper end of lateral sulcus

Center for complex movement. In dominant hemisphere

Apraxia: inability to perform complex motor activity in absence of paresis and sensory loss or incoordination

Areas of the Parietal lobe

Areas of the Parietal lobe

The Important Sulci of the Temporal Lobe:

1. The superior temporal sulcus.

2. The middle temporal sulcus.

C. The Temporal Lobe

1. The superior temporal gyrus: lies between the lateral

sulcus and the superior temporal sulcus.

2. The middle temporal gyrus: lies between the superior

and middle temporal sulcus.

3. The inferior temporal gyrus: lies below the middle

temporal sulcus.

Important Gyri of the Temporal Lobe

The Important Gyri of the Temporal Lobe

The Important Gyri of the Temporal Lobe

The Important Functional Areas of the Temporal LobeThe Important Functional Areas of the Temporal Lobe

AreasSiteFunctionLesionPrimary (area 41,42) and secondary (area 22) auditory center

In the middle part of the superior temporal gyrus

Auditory sensory area

Irritative: auditory hallucinationDestructive: Unilateral lesion of temporal lobe does not cause deafness as the sense of hearing is bilaterally represented

Sensory speech area or Wernicke's center

In the superior temporal lobe of dominant hemisphere

Auditory association area (recognition & recall of sounds). In dominant hemisphere.

Auditory agnosia (sensory or Wernicke's aphasia): the pt. hears but does not understand sound

Limbic system

Uncus and hypocampus in the medial and inferior surface of the temporal lobe

Uncus: sense of smell

Hipocampus: mood & memory

a. Uncus: Irritative: olfactory hallucinationDestructive: Unilateral lesion of

temporal lobe does not cause anosmia as the sense of smell is bilaterally represented

b. Hipocampus: Temporal epilepsy and amnesia to recent events

Areas of the Temporal lobe

Areas of the Temporal lobe

The main part of the occipital lobe lies on the medial

surface.

Only a small part appears on the lateral surface and

presents one sulcus called the transverse occipital

(calcarine) sulcus.

D. The Occipital Lobe

The Occipital Lobe

The Occipital lobe

The Occipital lobe

The Important Functional Areas of the Occipital LobeThe Important Functional Areas of the Occipital Lobe

AreasSiteFunctionLesion

Primary visual

sensory

area (17)

Posterior medial

part of occipital

lobe (surrounds

calcarine sulcus)

Visual sensory area

(perception of visual

impulses)

Irritative: visual

hallucination

Destructive:

contralateral

homonymous

hemianopia with

macular sparing

Secondary

(psychic)

visual area

(18, 19)

Anterior to area

17 in dominant

hemisphere

Visual association

area (Recognition &

recall of image). In

dominant hemisphere

Visual agnosia:

patient can see

but does not

recognize objects

Areas of the Occipital Lobe

Areas of the Occipital Lobe

The cerebral hemispheres consists of :

1.Gray Mater (outer): composed of nerve cells (cerebral

cortex). The cells of each area has specific functions.

2.White Mater (inner): composed of nerve fibers

conducting impulses to and from the cortex.

3.Basal Ganglia: there are several groups of nuclei situated

at various levels within the white mater.

4.Lateral Ventricle: the cavity of the cerebral hemisphere.

Internal Structures of the Cerebral Hemispheres

Internal Structures of the Cerebral Hemispheres

1. Molecular layer.

2. External granular layer.

3. External pyramidal layer.

4. Internal granular layer.

5. Internal pyramidal layer.

6. Multiform layer.

The Layers of the Cerebral Cortex

The Layers of the Cerebral Cortex

Consists of myelinated nerve fibers .

There are three types of fibers in the white mater:

1. Projection fibers.

2. Commissural fibers.

3. Association fibers.

The White Mater of the Cerebral Hemisphere

Definition: they are afferent and efferent fibers of the

cerebral cortex which pass through the internal capsule

and connect the cerebral cortex with lower centers.

Types of the Projection Fibers:

1. Ascending (afferent or sensory): to the cerebral

cortex from the thalamus.

2. Descending (efferent or motor): from the cerebral

cortex to lower centers.

The Projection Fibers

Definition and function: is a band of white mater (nerve

fibers) connecting and coordinating of activates of the right

and left hemisphere.

The Commissural Fibers Include:

1. The corpus callosum: connect the two cerebral

hemisphere.

2. The anterior commissure: connect the two cerebral

hemisphere.

3. The posterior commissure: between the two side of

the midbrain.

4. The habenular commissure: between the right and

left habenular nuclei and epithalamus.

The Commissural Fibers

The Commissural Fibers

Definition: they are fibers which connect the different

cortical areas in the same hemisphere.

Function: they interrelate the functions of the different areas

of the cortex and integrate the activities of cortex as a whole.

Types of Association Fibers:

1. Short association fibers: they connect adjacent gyri

with one another.

2. Long association fibers: connect the different lobes

of the hemisphere together.

The Association Fibers