Cerebrum

Cerebrum ByDr.Anoop.V.Nair

Dept of Cons Dentistry & Endodontics

KVG Dental College, Sullia

The brainThe dental pulp

CONTENTS

• Anatomical and functional relationships

• Functions of specific cortical areas

• The association areas

• Functions of the brain in communication

• Function of corpus callosum

• Thoughts, consciousness and memory

• Immediate memory

• Short term and long term memory

• Consists of two cerebral hemispheres,

separated- in upper part falx cerebri invaginates

- in lower part two hemispheres connected by white commissure, corpus callosum

Each hemisphere,3 poles-Frontal pole anteriorlyOccipital pole posteriorlyTemporal pole

Surfaces-Superolateral surfaceMedial surfaceInferior surface

Borders-Superomedial borderInferolateral borderMedial border

Surface of a hemisphere-Covered by thin grey matter (2-4mm)Folded with intervening grooves of fissures,Folds or convolutions- gyriIntervening fissures- sulciAs a result of folding, cerebral cortex surface area, much larger

General Appearance

of

cerebral hemispheres:

Separated by a deep midline

sagittal fissure

– longitudinal cerebral fissure

The fissure contains

falx cerebri and the

anterior cerebral arteries

In the depth of the

fissure, the

corpus callosum

connects the

hemispheres across

the midline

Lobes-

• Each hemisphere- 4 lobes,

• Boundaries separating one lobe from another on the superolateralsurface are formed by three prominent sulci and two imaginary lines

• Sulci, separating lobes are-

- Central sulcus or fissure of Rolando

- Posterior ramus of lateral or Sylvian sulcus

- Parieto-occipital sulcus

• Imaginary lines-

- First line- connects upper end of parieto-occipital sulcus to parieto-occipital notch

- Second line- backward continuation of the posterior ramus of lateral sulcus to meet the first imaginary line

Parieto-occipital sulcus

Central sulcus/Fissure of Rolando

Posterior ramus of lateral sulcus(Sylvian sulcus)

Frontal pole

Temporal pole

Inferolateralborder

Occipital pole

Second imaginary line

First imaginary line

Motor functions

Sensory functions

Hearing

Vision

The Occipital Lobe-posterior end of cortexContains primary visual cortexThe Parietal Lobe-between occipital lobe & the central sulcus

Contains the primary somatosensory cortex-receiving touchsensation, muscle-stretch information and joint positioninformation

The Temporal Lobe-lateral portion of each hemisphere, near thetemples

Contains targets for audition, essential for understandingspoken language, complex visual processes, emotional andmotivational behaviors

The Frontal Lobe-extends from the central sulcus to the anteriorlimit of the brain

Contains Primary Motor Cortex-fine movementsContributes to shifting attention, planning of action, delayedresponse tasks as examples

Layers of the Cerebrum

Gray matter

Outer layer

Composed mostly

of neuron cell bodies

White matter

Fiber tracts inside the

gray matter

Example: corpus callosum connects hemispheres

Any man who can drive safely while kissing a pretty girl is simply not giving the kiss the attention it deserves.Albert Einstein

Why do women multitask better than men?

• The inferior-parietal lobe is larger in men than in women.• This area of the brain is thought to control characteristics that

make a person more prone to mechanical andanalytical thought.

• The corpus callosum, the space between the right and lefthemispheres of the brain is larger in women than in men andcontains more neural pathways. This is thought to makewomen superior in processing language, information,emotion and cognition.

• Hence, women are superior inunderstanding the subtleties ofrelationships, emotional overtones,and artistic expressions.

Cortical functional areas• Brodmann divided cortex into 47 areas, based on

cytoarchitecture(number & thickness of cortical lamellae & cell type)

Motor areas-

• Primary motor area( Brodmann’s area 4)

• Premotor area(area 6)

• Frontal eye field(area 8)

• Supplementary motor area

Sensory areas-

• Primary somaesthetic areas ( area 3,1 and 2)

• Secondary (supplementary) somaesthetic area

• Somaesthetic association areas (area 5,7 and higher association area 40)

Auditory areas-

• Primary auditory area (area 41) or auditory area I

• Auditory association area (area 42) or auditory area II

• Higher auditory association area (area 22)

Visual areas-

• Primary visual area (area 17) or visuostriate area of visual area I

• Visual association area 18 (peristriate area)

• Visual association area 19 ( parastriate area)

Speech areas-

- Motor speech area-

• Anterior area (Broca’s area) or

areas 44,45

• Superior area

- Sensory speech areas-

• Area 39 (reading centre)

• Area 40

• Area 22 (Wernicke’s area)

Smell area- area 28

Gustatory area- area 43

Phylogenetical divisions of cerebral cortex• Cerebral cortex- ‘Pallium’, divided into three-

1. Allocortex- old cortex

• Forms 10% of entire cortex

• Divided into-

Archipallium (ancient cortex)- hippocampus & dentate gyrus

Paleopallium (old cortex)- uncus, part of parahippocampal gyrus-belong to piriform area of olfactory cortex

• Allocortex- also called limbic cortex, as most of allocortex located around peripheral margin of the diencephalon in the form of a ring.

• Ring of limbic cortex functions as a two way communication linkage between neocortex and lower limbic structures.

• Along with thalamus & hypothalamus, limbic cortex is concerned with emotional & instinctive behaviour.

2. Mesocortex- transitional zone between allocortex and neocortexand comprises the cingulate gyrus, part of parahippocampal gyrusand subiculum.

3. Neocortex-

• Isocortex

• 90% of cerebral cortex

• With evolution of mammals the extent of neocortex has increased

Areas, connections, functions and applied aspects of different lobes

I. Frontal lobe

• Lies in front of central sulcus and above posterior ramus of lateral sulcus

• 1/3rd of cortical surface.

• On basis of function, subdivided into-

a. Precentral cortex

b. Prefrontal cortex

a. Precentral cortex-

• Posterior part of frontal lobe

• Includes lip of central sulcus, precentral gyrus and posterior part of superior, middle and inferior frontal gyri.

• Stimulation at different points- activity of discrete skeletal muscles

• Excitomotor area of cortex

• Stimulation causes some sensory perception- ‘Sensorimotor cortex’

Areas-i. Primary motor area-Brodmann’s area 44, 45ii. Premotor area-Brodmann’s area 6,8,44 and 45iii. Supplementary motor area

i. Primary motor area-

- Area 4

- Presence of giant pyramidal

cells called Betz cells in

ganglionic layer and a thin

granular layer.

- Area is centre for volition

i.e, it is concerned with

initiation of voluntary

movements of the contra-

lateral half of the body

and initiation of speech

area 45 also called suppressor

area, forms a narrow strip

anterior to area 4.

- It inhibits movements

initiated by area 4.

ii. Premotor area-

• Lies anterior to primary

motor area

• Includes Brodmann’s area

6,8,44 and 45

• Absence of giant pyramidal

cells in ganglionic layer

• Involved in integration of

voluntary movements

• Thus, skilled movements

are accurate and smooth.

• Area 6- 6a (upper) and 6b (lower)

• (Electrical) Stimulation of area 6a causes generalized pattern of movements like rotation of head, eyes and trunk towards opposite side

• Stimulation of area 6b produces rhythmic, complex coordinated movements involving muscles of face, buccal cavity, larynx and pharynx

• Lesions lead to loss of skilled movements, recovery may occur but movements become awkward- grasping reflex

• Lesion of area 6 with area 4- hemiplegia with spastic paralysis

Area 8-

• Frontal eyelid

• Lies anterior to area 6

• Concerned with control of eye movements

• Electrical stimulation causes conjugate movements of eyeball to the opposite side, opening and closure of eyelids, pupillary dilatation and lacrimation

• Lesions of this area turns eye towards the affected side.

Area 44 and 45 or BROCA’s motor speech area-

• Movements of structures responsible for the production of voice and articulation of speech, activation of vocal cords simultaneously with movements of mouth and tongue during speech

• Lesions of this area causes motor aphasia i.e, inability to speak the word although vocalization is possible

iii. Supplementary motor area-

In association with premotor area provides attitudinal movements, fixation movement of different segments of the body and positional movements of head and eyes

b. Prefrontal cortex

• Prefrontal lobe or orbitofrontal cortex’

• Anterior part of frontal lobe lying anterior to area 8 and 44

• Major areas- Brodmann’s areas 9-14, 23, 24,29, 32, 44-47

• Centre for planned actions

• Centre for higher functions- emotions, learning, memory and social behaviour

• Responsible for various autonomic changes during emotional conditions because of connections with hypothalamus and brain stem

• Seat of intelligence/organ of mind- short term memories registered here

• Can keep track of many bits of information and ability to recall this information bit by bit for subsequent thoughts.

• Control of intellectual activities like prognosticate, plan future, allows to concentrate on central theme of thought- helps in depth and abstractness of thought and thereby in elaboration of thought.

• Allows to delay action in response to incoming sensory signals so sensory signals can be weighed until best response is obtained.

• Allows to consider the consequence of motor activites before their performance

• Plays role in solution of complicated mathematical, legal and philosophical problems

• Allows to correct avenues of information in diagnosis of rare diseases

• Allows to control ones activity according to the moral laws

Frontal lobe syndrome

• Symptom complex occurring due to injury or ablation of prefrontal cortex

• Prefrontal leucotomy- cutting the connection between thalamus and prefrontal lobe also results in frontal lobe syndrome.

• Flight of ideas- difficulty in planning

• Emotional instability

• Euphoria- false sense of well being, failure to realize or indifference to seriousness of others feelings or emotions

• Impairment of memory- recent memory only

• Loss of moral and social sense

• Lack of attention and power of concentration

• Lack of initiative following marked depression of intellectual activity

• Functional abnormalities like hyperphagia, loss of control over urinary or rectal sphincters

• Disturbances in orientation

• Slight tremor

Further Investigation

Phineas Gage: Phineas Gage was a railroad worker in the 19th century living inCavendish, Vermont. One of his jobs was to set off explosive charges in large rock inorder to break them into smaller pieces. On one of these instances, the detonationoccurred prior to his expectations, resulting in a 42 inch long, 1.2 inch wide, metalrod to be blown right up through his skull and out the top. The rod entered his skullbelow his left cheek bone and exited after passing through the anterior frontal lobeof his brain.

Remarkably, Gage never lost consciousness, or quickly regained it (there isstill some debate), suffered little to no pain, and was awake and alert whenhe reached a doctor approximately 45 minutes later. He had a normal pulseand normal vision, and following a short period of rest, returned to workseveral days later. However, he was not unaffected by this accident.

Learn more about Phineas Gage: http://en.wikipedia.org/wiki/Phineas_Gage

Gage’s personality, reasoning, and capacity to understand and follow social norms had been diminished or destroyed. He illustrated little to no interest in hobbies or other involvements that at one time he cared for greatly. ‘After the accident, Gage became a nasty, vulgar, irresponsible vagrant. His former employer, who regarded him as "the most efficient and capable foreman in their employ previous to his injury," refused to rehire him because he was so different.’

The first identified (2009) portrait of Gage,shown here with his "constant companion forthe remainder of his life"—his inscribedtamping iron

Gage is a fixture in the curricula of neurology, psychology and relateddisciplines, and is frequently mentioned in books and academic papers; heeven has a minor place in popular culture. Despite this celebrity the body ofestablished fact about Gage and what he was like (whether before or afterhis accident) is remarkably small, which has allowed "the fitting of almostany theory to the small number of facts we have"—Gage having been cited,over the years, by proponents of various theories of the brain wholly contra-dictory to one another.

II. Parietal lobe• Lies between central sulcus and parieto-occipital sulcus and upper

part of first imaginary line

• Divided into three parts functionally,

• Primary sensory area(corresponds to Brodmann’s area 3,1 & 2), also called primary somatosensory area or first somatosensory area, SI

• Secondary sensory area or second somatic sensory area SII

• Sensory association areas (Brodmann’s area 5,7)

i. Primary sensory area/ first somatic sensory area/SI

• Occupies posterior wall of central sulcus, postcentral gyrus and postcentral part of paracentral lobule

• Includes Brodmann’s area 3,1 and 2

• Granular cortex densely packed with stellate cells, with few small and medium sized pyramidal cells

• Recieves sensory inputs from opposite half of the body

• Sensations derived from skin are appreciated in anterior part of the area and proprioceptive sensations in posterior part of the area

• Electrical stimulation of area produces vague sensations like numbness and tingling

• If lesions occur without involving thalamus, sensations are perceived but discriminative functions are lost. If thalamus also affected, loss of sensations in opposite side of body

ii. Secondary sensory area/ SII

• Situated in post central gyrus below first somatic sensory area, most of it buried in the superior wall of the sylvian fissure

• Recieves sensory impulses from primary sensory area as well as thalamus

• Neurons in anterior part respond to touch whereas neurons in posterior part can be excited by touch, auditory, visual and nociceptive stimuli

• Lesions produce deficits in discriminative power whereas sensory processing in SI not affected.

iii. Sensory association areas

• Include area 5 and 7, also area 40- higher association area

• Area 5- lies posterior to area SI in parietal lobe and contains neurons which react to passive or active rotation of a joint or joints

• Area 7- concerned with more elaborate process of discrimination between stimuli

• Area 40- higher association area, concerned with stereognosis i.e, recognition of common objects placed in the hand without looking at them.

• Lesion affecting this area produces tactile agnosia

Functions of parietal lobe

• SI localizes, analyzes and discriminates different cutaneous and proprioceptive senses

• Area 3- receives cutaneous sensations of touch, pressure, position and vibratory senses

• Area 1- receives projections from cutaneous and joint senses

• Area 2- primarily concerned with deep senses from muscles and joints

• SII receives sensory impulses from SI and thalamus, concerned with perception of sensation. Thus sensory parts of the body have two representation in area SI and SII.

• Sensory assoc. areas (5,7)- assoc. with more elaborate process of discrimination between the stimuli, thus helps in differentiating the relative intensity of different stimuli. Eg:- warm objects from warmer, cold from colder etc

• Higher association areas (40)- stereognosis- recognition of common familiar objects placed in hand without looking at them

III. Temporal lobe• Lies below posterior ramus of lateral sulcus and its continuation,

the second imaginary line.

Areas of temporal lobe-

Major areas-

• Primary auditory area- area 41, 42

• Auditory association area- area 22,21,20

i. Primary auditory area

• Audiosensory area- Brodmann’s area 41, 42 and forms centre for hearing

• Situated in middle of superior temporal gyrus on the upper margin and on its deep or insular aspect (Heschl’s or transverse temporal gyrus).

ii. Auditory association area

• Corresponds to Brodmann’s area 22, 21, 20

• Area 22- Wernicke’s area, sensory speech centre

• Functions are interpretation of the meaning of what is heard and comprehension of spoken languages and the formation of ideas that are articulated in speech

• Area 21, 20- located in the middle and inferior temporal gyrusrespectively

• Receive impulses from primary area and are concerned with interpretation and integration of auditory impulses

• Lesions of these areas impair auditory, short term memory without impairing visual memory.

Primary Auditory Cortex

Wernicke’s Area

Primary Olfactory Cortex (Deep)

Conducted from Olfactory Bulb

• Lies behind parieto-occipital sulcus and its continuation down an imaginary line, concerned with vision

• Mostly formed of sensory and association areas and has only slight motor function.

Contains visual cortex having three areas-

• Primary visual cortex (area 17)- striate area, receives fibres of optic radiations which bring impulses from parts of both retinae, constitutes the centre of vision

• Visual association area (area 18)- peristriate area

• Visual association area or occipital eyefield (area 19)- parastriatearea

IV. Occipital lobe

Functions-

• Primary visual area (area 17) is concerned with perception of visual impulses

• Visual association areas (area 18 and area 19) are concerned with interpretation of visual impulses. These are involved in the recognition and identification of objects in the light of past experience.

• Occipital eyefield area (area 19) is concerned with the movements of eyeball.

White matter of cerebrum• Passing through, between and around the subcortical masses of

grey matter of cerebrum are tracts of white fibres.

3 types-

• Association fibres

• Commissural fibres

• Projection fibres

Association fibres

• Connect different gyri of the same hemisphere.

2 types-

• Short association fibres- connect adjacent gyri

• Long association fibres- connect widely separated gyri-

Five groups-

• Superior longitudinal fasciculus

• Inferior longitudinal fasciculus

• Cingulum

• Fronto-occipital fasciculus

• Uncinate fasciculus

Commissural fibres

• Connect corresponding parts of two cerebral hemispheres with each other. There are five bundles of commissural fibres.

• Corpus callosum

• Anterior commissure

• Posterior commissure

• Habenular commissure

• Hippocampal commissure

Projection fibres

• Connect cerebral hemispheres with other parts of CNS eg:-thalamus, brain stem and spinal cord

• Afferent and efferent

• Corona radiata (fountain of fibres)- refers to that part of projection fibres that radiates from the upper end of internal capsule to cerebral cortex. Contains both ascending and descending fibres.

• Internal capsule- thick curved band of projection fibres that occupy the space between thalamus and caudate nucleus medially and the lentiform nucleus laterally.

Internal capsule• Thick curved band of projection fibres that occupy the space

between thalamus and caudate nucleus medially and the lentiformnucleus laterally.

Subdivisions-

• Anterior limb-

• Genu

• Posterior limb

• Retrolenticular or caudal part

• Sublentiform part

Applied aspect-

• Vulnerable to effects of even a pinpoint vascular lesion, as pyramidal fibres are compressed in a little space

• Damage to internal capsule from infarction and haemorrhage is a common form of stroke, resulting in loss or decrease in sensations and movements of the opposite half of the body

• Most common cause of hemiplegia- thrombosis or rupture of one of the striate branches of middle cerebral artery which passes through the anterior perforated substance to supply the internal capsule.

• Charcot’s artery- one of the lateral striate arteries, largest of the perforating branches, particularly prone to such pathological conditions

• Heubner artery- thrombosis of recurrent branch of anterior cerebral artery results in contralateral paralysis of the face and upper limbs on account of the involvement of corticonuclearfibres and adjacent pyramidal fibres for the superior extremity.

• Think of a number from 1-9

• Multiply by 9

• Add the individual digits

• Subtract the result by 5

• Think of the corresponding english alphabet

• Think of a country that starts with the alphabet

• Think of an animal that starts with the last alphabet of the country you thought of

• Think of a fruit with the last alphabet of the animal you thought of

• Did you think of-

• DENMARK

• KANGAROO

• ORANGE…

• Only 2 % of us think different..

• ‘Think different’- Steve Jobs, Apple

ReferencesMedical physiology- Guyton

Medical physiology- Indu Khurana

Various internet sources