CEREBRUM AND BASE OF THE SKULL BY DR MANAH CHANDRA CHANGMAI IMS
Able to describe the general structure of the Cerebrum and Cerebral Cortex. Able to identify the Cerebrum, the Lobes of the Brain, the Cerebral Cortex, and its major regions/divisions. Able to describe the primary functions of the Lobes and the Cortical Regions of the Brain. Objectives
The cerebrum is the largest part of the brain with two hemisphere.The two cerebral hemisphere are linked by commisural fibres of corpus callosum.
Each cerebral hemisphere contains externally highly convulated cortex of grey matter and internal mass of white matter or medulla .
Each cerebral hemisphere contains lateral venticle continous with the third ventricle through interventricular foramen.
The cerebral hemispheres contains motor and sensory areas and the limbic system.
Each cerebral cortex is often divided phylogenetically into old allocortex,consisting of archicortex and paleocortex and a newer neocortex.
Longitudinal Fissure Cerebral hemisphere
Cortex and medulla
Surfaces of cerebral hemisphere
Each cerebral hemisphere has three surfaces
Inferior surface .
Inferior surface further divided into two
Surfaces of cerebral hemisphere………contd.
It follows the concavity of the cranial vault
It is flat and vertical and seperated from its fellow by the great longitudinal fissure and falx cerebri.
Inferior surface or the basal surface is irregular and divided into orbital and tentorial surface.
Superolateral Medial surface Surfaces of the brain
Inferior surface Orbital surface Tentorial surface
Borders of cerebral hemisphere Superomedial border Inferior border
Occipital pole Frontal pole Temporal pole Poles of the brain
Lobes of the brain
Four lobes are present
Occasionally insula is considered as the fifth lobe
Gyrus and sulcuses
Each cerebral hemisphere shows a complex pattern of convulation called Gyrus
The gyruses are separated by furrows of varying length called Sulci.
The convulated structure increases the cortical volume to three times what it would be if the surface is smooth.
It has a stem which divides into three rami:anterior,ascending,p-osterior.
The floor of the posterior ramus is the insula which is hidden cortex.
Lateral sulcus Central sulcus
Important sulcus and gyrus…….contd .
ii. The central sulcus
It is the boundary between frontal and parietal lobes
It starts at the superomedial border, a little behind the midpoint between frontal and occipital poles.It runs downards and forwards for about 8-10cm to end little above the posterior ramus of lateral sulcus.
It demarcates the motor and sensory area of the cerebral cortex.
iii. The other known sulcuses are
superior frontal sulcus
Inferior frontal sulcus
In the medial surface
The commisural fibres of the corpus callosum lies in the depth of longitudinal fissure
Parts of corpus callosum
Trunk or body
The anterior part divided into outer and inner zone by cingulate sulcus
splenium Body or trunk Genu Rostrum Medial surface with corpus callosum
Cingulate sulcus Parieto-occipital sulcus Calcarine sulcus Collateral sulcus Sulcus in the medial surface
Sulcus and gyrus………contd.
The posterior region of the medial surface is traversed by parieto-occipital and calcarine sulcus .The parieto-occipital sulcus marks the boundary between parietal and occipital lobes.
The visual cortex lies above and below the calcarine sulcus.
In the inferior cerebral surface
Orbital sulcus Occipitotemporal sulcus Collateral sulcus Rhinal sulcus Sulcus and important structures on inferior surface of cerebral hemisphere Olfactory sulcus
Insula -Present within the lateral sulcus Between temporal and frontal Lobe. -The overlying cortical areas are called opercula formed from the parts of frontal,temporal and parietal lobe -Functions linked to emotion and body’s homeostasis -i.e perception,motor control,self awarness,congnitive functioning interpersonal experience Insula
Cerebral cortex is an intricate blend of nerve cells and fibres,neuroglia and blood vessels.
Microscopically the cortex consists of six layers or laminae lying parallel to the surface.
From outside to inside
Molecular or plexiform layer
The external granular layer
External pyramidal lamina
Internal granular layer
Internal pyramidal cell layer
Multiform or pleiomorphic layer
Neocortex has 6 layers designated I, II, III, IV, V, VI Pyramidal cells predominate in layers III and V Granule cells in layers II and IV Pyramidal cells Granule cells Cerebral cortex
Pyramidal cells have large apical dendrite and basal dendrites
Axon projects downward into subcortical white matter; may have collaterals
Pyramidal cell is the primary output neuron
Pyramidal cell Pyramidal cell
These areas were defined and numbered by korbinian broadmann
The areas are based on the cortical cytoarchitectonic organisation of neurons
Many of the broadmann’s areas are defined on neurological function coorelated closely to diverse cortical functions.
Area 1,2,3 – primary somatosensory area
Area 4 – Motor area
Area 41,42 – Auditory area
Area 44,45 – Broca’s area,etc
Mapping of sensory and motor areas to the body
Primary Motor Cortex ( Precentral Gyrus) – Cortical site involved with controlling movements of the body.
Broca’s Area – Controls facial neurons, speech, and language comprehension. Located on Left Frontal Lobe.
Broca’s Aphasia – Results in the ability to comprehend speech, but the decreased motor ability (or inability) to speak and form words. Orbitofrontal Cortex – Site of Frontal Lobotomies
* Desired Effects:
- Diminished Rage
- Decreased Aggression
- Poor Emotional Responses
* Possible Side Effects: - Epilepsy - Poor Emotional Responses - Perseveration (Uncontrolled, repetitive actions, gestures, or words) Frontal lobes cortical regions Primary motor cortex Broca’s area Orbitofrontal cortex
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 cortical areas Associated somatosensory area(7) Primary gustatory area (40) Primary somatosensory area (3, 1, 2)
Primary Visual Cortex – This is the primary area of the brain responsible for sight -recognition of size, color, light, motion, dimensions, etc. Visual Association Area – Interprets information acquired through the primary visual cortex. Occipital lobe and cortical regions
White matter of cerebrum
Consists of myelinated nerve fibres which are categorized on the basis of their course and connections
It links different cortical areas of the same hemisphere
Short association fibres
They are entirely intracotical
Some merely pass from one wall of the sulcus to othe r.
Commisural fibres cross the midline,linking corresponding areas in the two cerebral hemisphere.
The largest commissure is the corpus callosum . Other commisures are
Commissure of the fornix .
White matter of cerebrum……..contd.
Projection fibres connect cerebral cortex with lower levels in the brain and spinal cord.
Consists of both coticofugal and corticopetal fibres
Corticofugal fibres converge from all directions to form corona radiata.Corona radiata continous with the internal capsule.
Corpus callosum Anterior commissure Habenular commissure Posterior commissure Commissures of brain Commissure of fornix
CT SCAN OF THE BRAIN
CT scan of the brain showing a tumour in the right cerebral hemisphere CT scan of brain…….contd
MRI OF BRAIN
. A non-progressive disorder • Caused by brain injury pre (70-80%), peri, or post natally • Injure occurs before CNS reaches maturity • Patients often have great potential masked by their connections Cerebral palsy • Malfunction of motor centers • Postural and balance difficulties • Normal life expectancy possible • Early death respiratory Manifestation
Spastic • 52-70% of all CPs • Hyperirritability of muscles • Arms flexed, legs internally rotated • Difficulty bending into a sitting position • Difficulty with head control • Postural difficulty • May not have protective extension Athetoid or Dyskinetic Type
• 25- 30% of CPs
• Uncontrollable writhing movements of
opposing muscle groups
• All four extremities involved
• Neck and face involved
• Voluntary movements are flailing
• Difficulty uprighting and balancing
• Tremors (rare form) of CP • Rigid 5 -10% of CPs • Flaccid (Hypotonicity) • Mixed 15 - 40% of CPs • 5 to 10 % • Affects balance and coordination. • They may walk with an unsteady gait with feet far apart, and they have difficulty with motions that require precise coordination, such as writing. Ataxic cerebral palsy Other types
BASE OF THE SKULL
SKULL BASE Skull base boundaries : Upper surface of the ethmoid bone,orbital plate of the frontal bone upto the ethmoid bo ne
Orbital Plate of frontal bone
Skull base……contd. Divided into three cranial fossa: a. Anterior cranial fossa b. Middle cranial fossa c. Posterior cranial fossa
Key openings in base of the skull
Superior orbital fissure
Inferior orbital fissure
Present at the anterior and medial part of sphenoid bone.
Located in the anterior part of sphenoid bone,posterolateral to foramen rotundum
Accessory meningeal artey
Lesser petrosal nerve
Foramen spinosum may be absent in 2% of the cases.
Situated posterolateral to foramen ovale
Transmits following structures
Middle meningeal artery
Nervous spinosus from mandibular nerve
Middle meninigeal vein
Latin ”great hole” is present in the occipital bone
Medulla oblongata,vertebral arteries
Anterior and Posterior spinal arteries
Spinal accessory nerve
Membrana tectoria,Alar ligaments.
Superior Orbital Fissure
CN III, IV, V 1 , VI
Middle meningeal artery- orbital branch
Recurrent meningeal artery
Superior opthalmic vein
Inferior petrosal sinus
Cranial nerve IX,X,XI
Internal jogular vein
Meningeal branches of occipital and ascending pharyngeal artery