Brain Topography

The largest division of the forebrain. It is divided into two hemispheres, each of which is divided into four lobes.

Cerebrum Cerebrum

Cerebellum

Cerebrum

Right hemisphere Left hemisphere

Corpus callosum

Median Longitudinal fissure

Divided into two halves, the cerebral hemispheres, which are separated by a deep Median longitudinal fissure which lodges a dural fold called falx cerebri.

In the depth of the fissure, the hemispheres are connected by a bundle of fibers called the corpus callosum.

The structure of cerebral hemispheres includes:Superficial layer of grey

matter, the cerebral cortex.Deeper to the cortex, axons

running to and from the cells of the cortex form an extensive mass of white matter (WM).

Burried within the white matter lie a number of nuclear masses (caudate, putamen, globus pallidus) collectively known as the basal ganglia.

The cavity of hemisphere is called the lateral ventricle.

CortexBasal

ganglia

WM

Lateral ventricle

Cerebral Cortex

Cerebral Cortex

The outermost layer of gray matter making up the superficial aspect of the cerebrum.

Cerebral Cortex

Cerebral Features

• Sulci – Small grooves dividing the gyri– Central Sulcus – Divides the Frontal Lobe

from the Parietal Lobe

• Fissures – Deep grooves, generally dividing large regions/lobes of the brain – Longitudinal Fissure – Divides the two

Cerebral Hemispheres– Transverse Fissure – Separates the

Cerebrum from the Cerebellum– Sylvian/Lateral Fissure – Divides the

Temporal Lobe from the Frontal and Parietal Lobes

• Gyri – Elevated ridges “winding” around the brain.

Highly convoluted arrangement. This arrangement maximize the surface area of the cerebral cortex (about 70% is hidden within the depths of sulci).

Gyri (ridge)

Fissure

(deep groove)

Sulci (groove)

Longitudinal Fissure

Transverse Fissure

Sylvian/Lateral Fissure

Central Sulcus

Specific Sulci/Fissures:

Three sulci, consistent in their position (central, lateral & parieto-occipital) are used to divide each hemisphere into lobes. Each hemisphere is divided into FOUR lobes (named after overlying bones).

motor function, motivation, aggression, smell and mood

reception and evaluation of sensory information

smell, hearing, memory and abstract thought

visual processing

Lobes of the Brain (4)

• Frontal• Parietal• Occipital• Temporal

* Note: Occasionally, the Insula is considered the fifth lobe. It is located deep to the Temporal Lobe.

Lobes of the Brain - Frontal

• The Frontal Lobe of the brain is located deep to the Frontal Bone of the skull.

• It plays an integral role in the following functions/actions:

- Memory Formation

- Emotions

- Decision Making/Reasoning

- Personality

- In addition to its major role in motor functions

Frontal lobe• Precentral gyrus.• Superior & inferior

frontal sulci divide the lobe into superior, middle & inferior frontal gyri.

Frontal Lobe

Primary motor cortex: Located in precentral gyrus (Brodmann area 4).

Premotor cortex: Located in the region immediately anterior to the precentral gyrus (Brodmann’s area 6).

Frontal eye field: Located in the middle frontal gyrus immediately in front of motor cortex (Brodmann’s area 8).

Broca’s (motor speech) area: Located in the inferior frontal gyrus of the dominant hemisphere, usually left (Brodmann’s area 44 & 45).

Prefrontal cortex: Extensive region of the frontal lobe anterior to premotor area.

Lateral SurfacePrecentral Gyrus --- primary motor area:

Superior Frontal Gyrus Middle Frontal GyrusInferior Frontal Gyrus

Pars Opercularis Pars Triangularis

Pars Orbitalis Medial SurfaceMedial Frontal Gyrus Paracentral Lobule

Basal SurfaceRectus Gyrus

Orbital GyrusInferior Frontal Gyrus

Gyri of the Frontal Lobe

]Broca’s area (dominant hemisphere)

Gyri of the Cerebral Cortex (Lateral Surface)

Gyri of the Cerebral Cortex (basal surface)

Basal Surface

Rectus Gyrus Orbital Gyrus

Inferior Frontal Gyrus

Gyri of the Cerebral Cortex (Medial Surface)

Medial Surface

Medial Frontal Gyrus Paracentral Lobule

Lobes of the Brain - Parietal Lobe• The Parietal Lobe of the brain is located deep to the

Parietal Bone of the skull.

• It plays a major role in the following functions/actions:

- Senses and integrates sensation(s)

- Spatial awareness and perception(Proprioception - Awareness of body/ body parts in space and in relation to each other)

Parietal Lobe

Parietal lobe: Postcentral gyrus.Intraparietal

sulcus dividing the lobe into superior & inferior parietal lobules.

Primary Somatosensory Cortex/ Postcentral Gyrus

Primary Gustatory Cortex

Somatosensory Association Cortex

Parietal Lobe

• Primary Somatosensory Cortex (Postcentral Gyrus) – Site involved with processing of tactile and proprioceptive information.

• Somatosensory Association Cortex - Assists with the integration and interpretation of sensations relative to body position and orientation in space. May assist with visuo-motor coordination.

• Primary Gustatory Cortex – Primary site involved with the interpretation of the sensation of Taste.

Parietal lobe

Parietal association cortex: located posterior to primary somatosensory cortex.

Primary somatosensory cortex: located in postcentral gyrus (Brodmann’s area 1, 2, 3).

Gyri of the Parietal Lobe• Lateral Surface • Postcentral Gyrus

----• Superior Parietal

Lobule • Inferior Parietal

Lobule ---- Wernicke’s area ??

Supramarginal Gyrus Angular Gyrus

• Medial Surface• Paracentral Lobule• Precuneus

Lobes of the Brain – Occipital Lobe

• The Occipital Lobe of the Brain is located deep to the Occipital Bone of the Skull.

• Its primary function is the processing, integration, interpretation, etc. of VISION and visual stimuli.

Occipital Lobe • Primary Visual Cortex – This is

the primary area of the brain responsible for sight -recognition of size, color, light, motion, dimensions, etc.

• located on the medial surface of the hemisphere, in the gyri surrounding the calcarine sulcus (Brodmann’s area 17).

• Visual Association Area – Interprets information acquired through the primary visual cortex. located around the primary visual cortex.

Primary Visual Cortex

Visual Association Area

Gyri of the Occipital LobeLateral Surface:Lateral Occipital Gyrus Superior Occipital Gyrus Inferior Occipital Gyrus Medial Surface

CuneusLingual Gyrus

Basal SurfaceLingual GyrusOccipitotemporal Gyrus

Lobes of the Brain – Temporal Lobe

• The Temporal Lobes are located on the sides of the brain, deep to the Temporal Bones of the skull.

• They play an integral role in the following functions:

- Hearing- Organization/Comprehension

of language

- Information Retrieval (Memory and Memory Formation)

Temporal lobe: Superior & inferior

temporal sulci giving rise to superior, middle & inferior temporal gyri.

Insula: the gyri in the depth of lateral fissure, covered by parts of frontal, parietal & temporal lobes called the opercula (removed in lower picture.).

Superior, middle & inferior temporal gyri

insula

stsits

Temporal Lobe • Primary Auditory Cortex – Responsible for hearinglocated in the superior surface of the superior temporal gyrus (Brodmann’s area 41, 42)• Primary Olfactory Cortex – Interprets the sense of smell once it reaches the cortex via the olfactory bulbs. (Not visible on the superficial cortex)

• Wernicke’s Area – Language comprehension. Located on the Left Temporal Lobe.

Auditory association cortex: located immediately around the primary auditory cortex (also includes Wernick’s area)

Primary Auditory Cortex

Wernike’s Area

Primary Olfactory Cortex (Deep)Conducted from Olfactory Bulb

• Parahippocampal gyrus:

• located in the inferomedial part of temporal lobe.

• Deep to this gyrus lies the hippocampus and the amygdala, which are parts of limbic system

Temporal Lobe

Language Area Organized around the lateral

fissure. Broca’s area: concerned with

expressive aspects of language. Wernick’s area: responsible for

comprehension of the spoken words.

Nearby regions of temporal lobe and parietal lobe (angular gyrus & supramarginal gyrus of the inferior parietal lobule) are important in naming, reading, writing, and calculation.

• Arcuate Fasciculus - A white matter tract that connects Broca’s Area and Wernicke’s Area through the Temporal, Parietal and Frontal Lobes. Allows for coordinated, comprehensible speech. Damage may result in:- Conduction Aphasia - Where auditory comprehension and speech articulation are preserved, but people find it difficult to repeat heard speech.

Gyri of the Temporal Lobe

Lateral SurfaceSuperior Temporal GyrusMiddle Temporal Gyrus Inferior Temporal Gyrus Basal Surface

Lingual Gyrus Occipitotemporal Gyrus

Medial Occipitotemporal GyrusLateral Occipitotemporal

Supplementary motor area(programming of complex movement) Primary motor cortex

(Voluntary movement)

Centralsulcus

Somatosensory cortex(Somesthetic sensation and

proprioception)

Posterior parietal cortex(integration of somatosensory and

visual input)

Wernicke’s area(speech

understanding)

Parietal lobe

Parietal-temporal-occipitalassociation cortex

(integraton of all sensory input-imp in language)

Occipital lobe

Primary visual cortex

Temporal lobeLimbic association cortex(motivation, emotion, memory)

Primary auditory cortex

Broca’s area(speech formation)

Frontal lobe

Premotor cortex(coordination of complex

movements)

Prefrontal association cortex

(planning for voluntary activity; decision making;personality traits)

Lobes and Structures of the Brain

B. A. (groove)

C. (groove)

D. E.

F.

G.

B. Frontal Lobe

G. Parietal Lobe

F. Occipital Lobe

D. Temporal Lobe

A. Central Sulcus

(groove)

E. Transverse Fissure

C. Sylvian/Lateral Fissure

Hemispheric Dominance The localization of speech

centers & mathematical ability is the criterion for defining the dominant cerebral hemisphere.

In 96% of normal right-handed individuals and 70% of normal left-handed individuals, the left hemisphere contains the language centers. These are left hemisphere dominant.

Cerebral dominance becomes established during the first few years after birth.

Verbal Memory

Shape Memory

Hemispheres communicate via the corpus callosum

White MatterUnderlies the cortex and contains:

Nerve fibers, Neuroglia cells & Blood vessels. The nerve fibers run in different directions and originate,

terminate or sometimes both, within the cortex.

Depending on their origin & termination, the nerve fibers in the cerebral white matter are classified into three types: Association, Commissural & Projection

Association fibers: Unite different parts of the same hemisphere

Commissural fibers: Connect the corresponding regions of the two hemispheresProjection fibers: Consisting of Afferent fibers conveying impulses to the cerebral cortex. Efferent fibers conveying impulses away from the cortex.

Association Fibers Unite different parts

of the same hemisphere.

Are of two kinds: Those connecting

adjacent gyri, short association fibers

Those connecting more distant parts, long association fibers.

Short association fibers

Long association fibers

1. Uncinate fasciculus: connects frontal to temporal lobe

2. Superior longitudinal fasciculus: connects the frontal, occipital, parietal, and temporal lobes

3. Arcuate fasciculus: connect gyri in frontal to temporal lobes

4. Inferior longitudinal fasciculus: connects occipital to temporal pole

13

2

4

5

5 .Cingulum: connects frontal & parietal lobes to the para-hippocampal gyrus and adjacent temporal gyri

Long Association Fibers

Commissural Fibers

Connect the corresponding regions of the two hemispheres.

Include: Corpus callosum. Anterior

commissure. Hippocampal

commissure (commissure of fornix).

Posterior commissure.

Corpus Callosum Connects the corresponding

regions of the two hemispheres except the temporal lobes, that are connected by anterior commissure

It is shorter craniocaudally than is the hemisphere

The callosal fibers linking the frontal poles curve forward forming anterior forceps (forceps minor)

The callosal fibers linking the occipital poles curve backward forming posterior forceps (forceps major)

O

F

P

CC

Anterior forceps

Posterior forceps

Parts of Corpus Callosum

Rostrum

Genu

Body

Splenium

Anterior commissure: connects the inferior and middle temporal gyri & the olfactory regions of the two hemispheres

Hippocampal Commissure: connects the two hippocampi with each other

Posterior Commissure: connects the left and right midbrain. Important in the bilateral pupillary reflex

Projection Fibers Consist of:

Afferent fibers conveying impulses to the cerebral cortex.

Efferent fibers conveying impulses away from the cortex.

Deeper to the cortex, these fibers are arranged radially as the corona radiata.

Then the fibers converge downward, form internal capsule, between thalamus and basal ganglia.

Continue in the crus cerebri of the midbrain, basilar part of pons, & pyramid of medulla oblongata.

crus cerebri

Internal capsule

corona radiata

pyramidal decussation

pyramid

Corticospinal tract

Internal Capsule

• Bundle of projection fibers, passes through the interval between the Thalamus (T) and the basal ganglia: Caudate (C) & Lentiform nucleus (L)

Has 5 parts: 1-Anterior limb: Thalamocortical &

Frontopontine fibers 2-Genu: corticobulbar fibers 3-Posterior limb: Corticospinal,

Corticobulbar & Thalamocortical fibers 4-Retrolenticular part: Geniculocalcarine

fibers 5-Sublenticular part (not shown): geniculo-

temporal fibers

C

T

L

12

3

4