Cerebrum

Cerebrum:


Location:
  • Anterior Cranial Fossa
  • Middle Cranial Fossa &
  • Supratentorial part of Posterior cranial fossa
 
Note: Below the tentorium cerebelli lie cerebellum in posterior cranial fossa.
 
Features
*  Cerebrum has two cerebral hemispheres.
*  Both hemispheres are incompletely separated by median longitudinal fissure.
*  Because below, both hemispheres are connected to each other by white matter called corpus callosum (a type of commissural fibers).
*  Each hemisphere contains a cavity called the lateral ventricle.
 
Note:
Contents of median longitudinal fissure is falx cerebri with superior sagittal sinus and inferior sagittal sinus.
The main composition of white matter is nerve fibers/ tract.
Corpus callosum (white matter) is the compact bundle of nerve fibers / consisting of million of axons connecting two hemispheres.

Tips:
Nerve fibers is axon or dendrites of nerve cell body.
Tract is the bundle of nerve fiber.
Thus, tract, nerve fibers are called white matter.
 
 
External Features of cerebral hemisphere:

Three surfaces:
1) Superolateral surface 
    * Related to cranial vault
2) Medial surface
   * Present on either side of the median longitudinal fissure
3) Inferior surface - divided into two parts by lateral sulcus
     * Orbital part and Tentorial part of inferior surface
 
Note: Tentorial part of inferior surface rest on the Tentorial cerebelli.
 
 
Four Borders
1) Superomedial border
Separate superolateral surface from medial surface

2) Inferolateral border
Separate superolateral surface from inferior surface

3) Medial orbital border
Separate medial surface from orbital part of inferior surface

4) Medial occipital border
Separate medial surface from the tentorial part of the inferior surface.
 
 
Three poles (Pointed end):
  1. Frontal pole
  2. Temporal pole
  3. Occipital pole
 
Fours lobes of Cerebral Hemisphere:
Frontal lobe:
Important for voluntary motor functions,
motivation, emotions, affect, awareness of self.
Parietal lobe:
Major center for interpretation
of all sensory information except smell, hearing, and vision.
Occipital lobe:
Center for the integration
of visual input.
Temporal lobe:
Center for smell and
hearing and plays an important role in memory.
 
 
How lobes are divided?
  1. Central sulcus
  2. Lateral sulcus
  3. 1st & 2nd imaginary lines
 
*  Central sulcus divides frontal and parietal lobe.
*  Lateral sulcus divides the frontal & temporal lobe.
*  2nd imaginary line which is drawn as the continuation of the posterior ramus of lateral sulcus divides parietal lobe & temporal lobe.
*  1st imaginary line drawn between parieto-occipital sulcus and preoccipital notch separate occipital lobe from parietal & temporal lobe.
 
Note:
Elevated part known as gyrus.
Depressed part known as the sulcus.
The cerebral cortex is folded into gyrus which are separated from each other by sulci.

 
Central Sulcus:
Central sulcus begins at the superomedial border, 1.25cm behind the midpoint of frontal pole and occipital pole.
*  Then it course obliquely downwards & forward.
*  And end a little above the posterior ramus of the lateral sulcus.
 
Note:
Central sulcus extends for a short distance on to the medial surface.
And the U-shaped gyrus around the central sulcus is called paracentral lobule [on medial surface].


Lateral Sulcus:
Lateral sulcus begins on the inferior surface.
*  It separates the inferior surface of cerebrum into the orbital part and the Tentorial part.
 
Laterally, this sulcus reaching the superolateral surface, it is divided into three ramus.
  • Anterior horizontal ramus
  • Anterior ascending ramus
  • Posterior ramus
Posterior ramus extends backward and slightly upward over the superolateral surface.
 
 
Parieto-occipital sulcus:
Parieto-occipital sulcus is the sulcus of the medial surface.
It’s upper end shortly cut the superomedial border about 5cm in front of the occipital pole.
 
Preoccipital notch:
This notch is present on the inferolateral border about 5cm in front of the occipital pole.
 
  • 1st imaginary line [on the superolateral surface] is drawn between parieto-occipital sulcus & preoccipital notch.

  • 2nd imaginary line is drawn as the continuation of the posterior ramus of lateral sulcus up to 1st imaginary line.
 
Note:
Central sulcus and lateral sulcus are the main sulcus of the superolateral surface.
But parieto-occipital sulcus is the sulcus of medial surface.
Content of lateral sulcus is the middle cerebral artery which is the continuation/ branch of the internal carotid artery.


 
Functional classification of Sulcus:
  • Limiting sulcus (Eg. Central sulcus)
  • Axial sulcus (e.g Postcalarine sulcus)
  • Operculated sulcus (Eg. Lunate sulcus)
 
Limiting sulcus
It separates two areas that are functionally and structurally different.
Example: Central sulcus
 
Limiting sulcus, as it limits the motor area from the sensory area.
*  In front of the central sulcus, it is the motor area.
*  Behind the area of central sulcus is sensory area.
 
Anterior to it lies motor cells that initiate the movements of the opposite side of the body.
Posterior to lies the general sensory cortex receives sensory information from the opposite side of the body.
 
Simply,
1) Frontal lobe - motor in function
2) Parietal lobe - mainly area of sensory impulse integration
3) Temporal lobe - for the sense of hearing
4) Occipital lobe - sense of vision
 
 
Sulci and gyrus of the cerebrum:
 
 
 
Note:
Central sulcus and lateral sulcus are not the sulci of the particular lobe.
They act as a partition between the lobes.
 
Note:
Anterior horizontal and anterior ascending rami of the lateral sulcus subdivide the inferior frontal gyrus into three parts:
Pars orbitalis
Pars triangularis
Pars opercularis
 
The area behind the postcentral gyrus is divided into the superior and inferior parietal lobules by the intraparietal sulcus.


 
 
The calcarine sulcus starts below the splenium and course forward towards the occipital pole.
It gives off the parieto-occipital sulcus which runs toward the superolateral surface.
Visual cortex lies above & below this sulcus.
The cingulate gyrus lies between the corpus callosum and the cingulate sulcus.
 
 
Frontal lobe:
Boundary of Frontal Lobe:
  • Superiorly - Superomedial border
  • Inferiorly - lateral sulcus
  • Posteriorly - central sulcus
 
Functional areas of Frontal Lobe:
 
Primary motor area (area no.4)
Located in precentral gyrus & extends up to the anterior part of the paracentral lobule.
*  About 30% of the corticospinal tract & corticonuclear tract (Pyramidal Tract) arises from here.
 
Control the voluntary activities of the opposite half of the body
Lesion in motor area:  
Contralateral paralysis (Hemiplegia of extremities of opposite side)
Premotor area (area no.6)
Control extrapyramidal system
*  Needed for perfect voluntary motor movements initiated by Primary motor area
Lesion in premotor area
Contralateral paralysis
*  Difficulty in the performance of skilled movements
Frontal eye field (area no.6,8) 
Controls horizontal conjugate movements of the eyes
Lesion in frontal eye field
Horizontal conjugate movements of eyes are lost
Motor speech area/ Broca’s area (area no.44,45) 
Control spoken speech
Lesion of Broca’s motor area
Aphasia (motor)/ inability to produce speech
Pre-frontal area (area no.9,10,11,12)
Controls emotion, concentration, attention, & judgement.
Lesion in pre-frontal area - Loss of orientation
Abnormality in ideas, judgment, emotional feeling & personality.
 
 
 
Parietal lobe:

Boundary of Parietal Lobe:
  • Anteriorly - Central sulcus
  • Posteriorly - 1st imaginary line from preoccipital notch to parieto-occipital sulcus
  • Superiorly - Superomedial border
  • Inferiorly - 2nd imaginary line drawn as the continuation of the posterior ramus of the lateral sulcus
 
Functional areas of Parietal Lobe:

Primary somatosensory area (area no.3,1,2)
Situated in postcentral gyrus & extends up to the posterior part of the paracentral lobule

Primary Center for Exteroceptive Sense (Pain, Temperature, Pressure, Touch)
*  and Proprioceptive Sense (Movements of Joints, muscles, Vibration) from the opposite side
Lesion:
Loss of Proprioceptive & Exteroceptive sense from the opposite side.
Sensory association area (area no.5,7)
Responsible for Prediction of shape, size, structures of objects.

One can recognize what has been placed in their hands without seeing.
This capability of a person is called stereognosis.
Lesion:
Loss of stereognosis
Wernicke’s area/ Sensory speech area (area no.22)
Responsible for understanding the spoken speech
Lesion:
Sensory Aphasia
 


Note:
Aphasia means impairment of language, affecting the production or understanding(sense) of speech and ability to read & write.
It could occur due to stroke, brain tumor.
Broca’s motor speech area lesion:
One loses the ability to produce proper speech. A person finds difficulty in expressing words he/she wants, but could understand the speech.
Wernicke’s sensory speech area:
Loss of ability to understand the speech & written word, but can speak fluently.



 
Temporal lobe:

Boundary of Temporal Lobe:
  • Superiorly- Posterior ramus of the lateral sulcus
  • Inferiorly - Inferolateral border
  • Anteriorly - Temporal pole
  • Posteriorly - 1st imaginary line from preoccipital notch to parieto-occipital sulcus
 
Functional Areas of Temporal Lobe
 
Primary Auditory Area (area no. 41, 42)
Reception & Perception of Auditory impulses
Lesion:
Impaired Hearing
Secondary Auditory Area (area no. 22)
Correlate the auditory impulses to the past memory
Lesion;
Auditory Agnosia
(Lost of past auditory memory)
One cannot recognize or identify the sound.
 
 
Occipital lobe:

Boundary of occipital lobe
  • Superiorly - superomedial border
  • Inferiorly - Inferolateral border
  • Anteriorly - 1st imaginary line from preoccipital notch to parieto-occipital sulcus
  • Posteriorly - Occipital lobe
 
Functional areas of Occipital Lobe
 
Primary visual area (visuosensory area) - (area no.17)
Receives and integrate the visual impulses
Lesion:
Homonymous Hemianopia
(Defect in nasal field of vision of one eye & Temporal field of vision of another eye)
Secondary visual area (area no.18,19)
Correlate the recent visual impulses with the past memory.
Lesion:
Visual Agnosia
(Lost of past Visual memory)
One cannot correlate the visual impulses with a past memory, so fail to recognize the seen objects.
 
 
 
Paracentral lobule:
It is the U-shaped gyrus on the medial surface around the extended end of the central sulcus.
It is the lobe on the medial surface of the cerebral hemisphere.
 
Subdivision:
Central sulcus extends shortly on the medial surface and divide the paracentral lobule into:
  • Anterior part - continuous with precentral gyrus of the frontal lobe
  • Posterior part - continuous with postcentral gyrus of the parietal lobe
Function of paracentral lobule:
  1. Control the motor and sensory innervation of the opposite side of the lower extremities.
  2. It is the chief center for micturition & defecation.
Anterior part -
*  Regulates movement of the contralateral lower extremity
*  Voluntary control of micturition & defecation
 
Posterior part -
*  Receives sensation from contralateral lower extremity.
*  Sense of distention from bladder & rectum.
 
Note
Micturition is the parasympathetic function.
Lower spinal level Center of micturition located on the S2-S4 segment of spinal cord and parasympathetic fibers are carried by pelvic splanchnic nerves.


 
 
White matter of cerebrum/ Fibers of Cerebrum:

Main component of white matter of cerebrum is myelinated nerve fibers
 
Subdivision of white matter
  1. Association (Arcuate Fibers)
  2. Commissural Fibers
  3. Projection Fibers
Association (Arcuate Fibers):
Fibers which connect different area of the same hemisphere
 
Two types:
1) Short association fibers
*  These fibers connects the adjacent area of the same lobe
 
2) Long association fibers
*  Connect distant areas of different lobes of the same hemisphere.
 
Examples
  • Uncinate Fasciculus
  • Cingulum
  • Inferior longitudinal Fasciculus
  • Superior longitudinal Fasciculus
Note
Superior longitudinal Fasciculus:
Connect occipital lobe with frontal lobe; form pathway of accommodation reflex; occipital cortex to frontal eye field
 
Commissural fibers:
Fibers that connect corresponding parts of two hemispheres.
 
Example
  • Corpus callosum
  • Anterior commissure
  • Posterior commissure
  • Commissure of fornix (hippocampal commissure)
  • Habenular commissure
 
Corpus Callosum:
Corpus callosum is the largest commissural fibers of the brain.
*  The central part of the medial aspect of the hemisphere is occupied by the corpus callosum.
*  It is made up of nerve fibers connecting the two cerebral hemispheres.
 
Parts of corpus callosum:
  • Rostrum
  • Genu
  • Trunk/Body
  • Splenium (Posterior end)
Function of corpus callosum:
Responsible for the transfer of information that is essential for bilateral response.
 
Tips
Below the corpus callosum, there are the septum pellucidum, the fornix and the thalamus.
*  Lateral to septum pellucidum, lies the central portion of the lateral ventricle.
 
 
Projection Fibers:
Connect the cerebral cortex to other parts of CNS like brainstem, spinal cord
Example
  • Internal capsule
  • Corona Radiata
  • Optic radiation
  • Fornix
 
Internal capsule:

The internal capsule is the compact bundle of nerve fibers (a part of white matter) present between the thalamus & lentiform nucleus.
*  It consists of ascending and descending nerve fibers that connect the cerebral cortex to the spinal cord & brain stem.
*  Almost all fibers going to the cerebral cortex or fibers coming from the cerebral cortex, all pass through internal capsules.
 
Continuation:
* Upward with corona radiata
* Downward with crus cerebri of midbrain
 
Division of internal capsule:
  • Anterior limb
  • Genu
  • Posterior limb
  • Retrolentiform part- lie behind lentiform nucleus
  • Sublentiform part - lie below lentiform nucleus
 
Boundary of internal capsule:
* Medially- Head of caudate nucleus & thalamus
** Laterally- Lentiform nucleus
 
 
Artery supply of internal capsule:
 
Anterior limb by:
* Recurrent branch of anterior cerebral artery
* Direct brach from anterior cerebral artery
Genu by
* Direct branch from the internal carotid artery
* Branches from posterior communicating artery
Posterior limb by:
* Medial & lateral striate arteries of middle cerebral artery
Sublentiform part & retrolentiform part by:
* Branches from posterior cerebral artery
 
 
Fibers of Internal capsule
 
Parts Motor fibers Sensory fibers
Anterior limb Corticopontine fibers Anterior thalamic radiation
Genu Corticopontine fibers
Corticospinal fibers
Superior thalamic radiation
Posterior limb Corticopontine fibers
Corticospinal fibers
Superior thalamic radiation
Retrolentiform part Corticopontine fibers Optic radiation
Sublentiform part Corticopontine fibers Auditory radiation
  
Note:
All parts of the internal capsule contain corticopontine fibers.
**  Because of widely pass of motor and sensory nerve fibers within the internal capsule, even a small lesion in the internal capsule could cause paralysis and sensory loss in the opposite half of the body.
 
 
Clinical importance of internal capsule:
The lesion of the internal capsule is usually vascular.
*  Posterior limb of the internal capsule is supplied by lateral & medial striate branches of the middle cerebral arteries. These are end arteries.
*  These arteries are vulnerable to rupture leading to loss of sensation & spastic paralysis of the opposite half of the body (contralateral hemiplegia).
*  It comes under the category of upper motor neuron type of paralysis.
 
 
Artery supply of Cerebrum
According to surfaces :
 
On the superolateral surface:
The main artery is the middle cerebral artery, (continuation or terminal branch of internal carotid artery)
 
Superior part of superolateral surface extending 2.5cm width from superomedial border up to parietals-occipital sulcus
*  Supplied by anterior cerebral artery
Lower part of the temporal lobe (excluding temporal pole) and occipital lobe
*  Supplied by posterior cerebral artery
The rest of all (maximum) areas 
*  Supplied by the middle cerebral artery.

[Including Broca’s area, Wernicke’s area, temporal pole.]
 
 
On the medial surface:
The main artery is the anterior cerebral artery, terminal small branch of internal carotid artery
 
Temporal pole of temporal lobe
*  Supplied by middle cerebral artery
Rest of temporal (excluding temporal pole) & occipital lobe
*  Supplied by posterior cerebral artery
Rest of upper maximum part area including paracentral lobule
*  Supplied by anterior cerebral artery
 
 
On the inferior surface:
The main artery is the posterior cerebral artery, a branch of the basilar artery.
 
Most part of the temporal lobe (except temporal pole) & occipital lobe
*  Supplied by posterior cerebral artery
Temporal pole & lateral part of the orbital surface of the frontal lobe
*  Supplied by middle cerebral artery
Medial small part of the orbital surface of the frontal pole
*  Supplied by anterior cerebral artery.

Tips:
Always remember
Temporal pole - by middle cerebral artery
* Occipital lobe - by posterior cerebral artery
 
 
Note:
Course of anterior cerebral artery
Anterior cerebral artery runs along above like the course of the corpus callosum on either side of the median longitudinal fissure - middle surface.
Course of middle cerebral artery
Middle cerebral artery course along the lateral surface which begins from the inferior surface and runs laterally in the superomedial surface and runs along the posterior ramus of the lateral sulcus.
Content of lateral sulcus: Middle cerebral artery
Lateral sulcus - start from inferior surface
* Divide the inferior surface into orbital part & Tentorial part
* On coming on superolateral surface
Lateral sulcus give 3 rami:
 1) Anterior horizontal ramus
 2) Anterior ascending ramus
 3) Posterior ramus
Anterior horizontal & ascending rami divide the inferior frontal gyrus into:
 a) Pars triangularis
 b) Pars opercularis
 c) Pars orbitalis
Location of Broca’s motor speech area:
 I) Pars triangularis (area no .45)
II) Pars opercularis (area no. 44)
Stroke is related to the brain, not heart.
 
 
Histology of Cerebrum:
The cerebrum consists of outer grey matter knowns as the cerebral cortex & inner white matter made of bundles of nerve fibers.
 
Within the white matter of its basal parts, the embedded mass of grey matter is found called Basal Nuclei.
 
 
Difference in arrangement of White matter & Grey matter In Brain & Spinal Cord
Both the spinal cord & brain contains of grey and white matter.
In Brain
Cerebrum:
Outer cortex of Grey matterInner core of White matter
Brainstem(Midbrain, Pons, Medulla)
Outer White matter
Within
the white matter, embedded masses of Grey matter called nuclei. 
Numerous nuclei are present in the brainstem within white matter.
 
In Spinal Cord
Outer white matter
Inner H-shaped Grey matter
 
Note:
The grey matter consists of nerve cell bodies & dendrites.
White matter consists predominantly of myelinated nerve fibers.
 
 
Development of cerebrum:
Simply, Brain & Spinal cord develops from Neural Tube.
The cranial part of the neural tube differentiates into 3 main enlarge vesicles.
 
Parts  Subdivision

Forebrain
(Prosencephalon)

Telencephalon(Cerebrum)

Diencephalon

Midbrain
(Mesencephalon)

Midbrain

Hindbrain
(Rhombencephalon)

Metencephalon (Pons& Cerebellum)

Myelencephalon (Medulla)
 
Simply, Cerebrum develops from the most cranial part of the forebrain which develops from the neural tube. (Ectodermal In origin)