PANTOMATH

Cerebral Cortex synopsis:

•  Embryology.
• Sectional anatomy.
• Gross anatomy.
• Evolutionary aspects.
• Lobes, white matter of cerebral cortex.
• Functional areas of cerebral cortex.
• Review on Clinical anatomy and lesions of cortex.

Cerebral Cortex    

Numerical Data :

• Total surface area: 2200 cm2 (2.5 ft2).            
  • about 1/3 ------ surface area.             
  • about 2/3 ------ hidden in the sulci .      
• Thickness: 1.5 mm.       
• Weight: 600 gm (40 % of total brain weight).             
  • 180 gm --------- neurons.            
  • 420 gm --------- glial cells.

Surfaces of brain Evolution of human brain Allocortex

• Most primitive.             
• First species with cerebral cortex had allocortex only.            
• 3 layered - dentate gyrus, piriform cortex, hippocampus. 

Mesocortex (paleocortex)

• Transitional position in between these two has 4-5 layers. 
• Cingulate gyrus.

These two are found only around the hilum of each cerebral hemispheres, i.e.at the point of junction with the brainstem. Lobes of cortex

Four lobes, each one is specialised for different activities.

• occipital lobe: initial processing of visual input.
• Temporal lobe: primary auditory cortex, Integration of multiple sensory inputs, Wernicke’s area.
• Parietal lobe: Somatosensory processing mostly from opposite side of the body.
• Frontal lobe: Voluntary motor activity, broca’s area and elobration of thoughts.

 The motor cortex
 Motor area-4

• Location: pre-central gyrus in frontal lobe. It contains large excitable Betz cells. It gives origin to the pyramidal tract
• Representation of body: controls the opposite side of the body
  •  inverted manner 
  •  The upper face, respiratory  and abdominal         
  •  muscles are bilaterally represented.
• Function:
  • initiates fine voluntary movements.
  • initiates gross movements in combination with area-6.
  • Facilitate spinal motor neurons (increase stretch reflex).

  Effect of lesion to area - 4

The manifestation occurs on  the opposite side of the lesion.

• 1-Paralysis of the muscles usually in localized form (monoplegia…), with permanent loss of fine skilled movements and partial recovery to gross movements.
• 2-inhibition to stretch reflex leading to flaccid paralysis (hypotonia and hyporeflexia).
• 4-Babinski’s sign (only dorsiflexion of big toe without fanning of the other toes).

Premotor cortex: area - 6

Premotor area - 6

Location: anterior to area - 4.

• it is less excitable and gives 30% of pyramidal fibers and major part to extrapyramidal tracts.

Body representation: similar to area - 6 .

Function:

• Plans for the voluntary movements.
• Initiates gross movements.
• Initiates subconsciously automatic movements as moving the arms during walking.

Lesion of area - 6

• Muscle paresis (weakness).
• pasticity (increased muscle tone).
• Grasp reflex.
• Babinski’s sign (only fanning of lateral toes)
• Motor apraxia : it is inability to perform previously learned motor act (light a match) in absence of paralysis due to loss of the plan of the motor act.

Supplementary motor area

Location: in frontal lobe anterior and superior to area-6.

Body representation:  head anterior, while leg posterior (horizontally).

Function:

• Plans and programs and keep memory for the motor act.
• Its activity starts just before the beginning of the motor act.
• 2- Bimanual tasks.

Imagine being unable to say, "I am hungry," "I am in pain," "thank you," or "I love you.“ Being trapped inside your body, a body that doesn't respond to commands. Surrounded by people, yet utterly alone. Wishing you could reach out, to connect, to comfort, to participate. For 13 long years, that was my reality. Most of us never think twice about talking, about communicating.

Area-8:Frontal eye field

Location: above Broca’s area

Function:

• conjugate eye deviation.
• direct the eyes toward the desired object voluntarily.
• control movements of eye lids (blinking).

Head rotation area

Location: above area-8.

Function: rotate the head towards the objects.

Hand skill area

Location: anterior to hand area in primary cortex.

Function: performs skilled movement of the hand.

PREFRONTALLOBE PREFRONTALLESION

• Inability to perform two works at a time.
• Inability to follow the proper sequence to achieve a task  - cooking which requires sequential steps.
• Lack of initiative.
• Impairment of moral sense.
• Impairment of social sense.
• Failure  to realise the gravity of situation.
• Anosmia.
• Prefrontal lobe responsible for personality ,social behaviour,   ability to analyse  a situation, restraint etc.

 
Inability to store a programme:

Memory storage

• Fail to keep track of bits of information even in temporary memory, because they are distracted so easily they cannot hold thoughts long enough for memory storage to take place.
• Prefrontal  areas are divided into separate segments for storing different types of temporary memory – for storing shape and form of an object or apart of the body, for storing movement etc.

Inable to

• Plan for the future.
• Delay action in response to incoming sensory signals so that the sensory information can be weighed until the best course of response is decided.
• Consider the consequences of motor actions even before they are performed.
• Solve complicated mathematical, legal or philisophical problems.
• Correlate all avenues of information in diagnosing diseaseas.
• Control our activities in accord with moral laws.

PREFRONTALLESION

• The patient could still talk and comprehend language, but unable to carry through any long trains of thought.
• Their moods changed rapidly from sweetness to rage to exhiliration to madness.
• Could still perform most of he usual patterns of motor functions that they had performed throughout life ,but often without purpose.

Sensory Areas

•   Somesthetic Area (Somesthesia)  S I, S II.
•   Visual Area (vision)  V I, V II.
•   Auditory Area (Hearing)  A I, A II.
•   Vestibular Area (Equilibrium).
•   Gustatory Area (Taste).
•   Olfactory Area (Smell) .

Sensory cortex

Somatic sensory area I (area 3,1,2)

Location: in parietal lobe at postcentral gyrus.

Body representation: opposite half in inverted manner  (head down, while legs up) area of higher sensation represented in wide area (lips).

Function: It is responsible for perception of Tactile localization, discrimination, proprioception, vibration, stereognosis, pressure, muscle tension, fast pain (localization), fine temperature.

Somatic sensory area - II

Location: at supramarginal gyrus above the lateral fissure.

Body representation: bilaterally represented, head anterior, while leg posterior.

Function: 

• It receives signals from sensory area-I, visual and auditory association areas, thalamus and brain stem nuclei.
• It collects these sensory signals to give a meaning to  the sensation perceived. 
• It increases the acuity of the action of sensory area-I.

Somatosensory association area

Location: at parietal lobe behind sensory area-I.
It receives signals from sensory area I and II, thalamus visual and auditory areas.

Function:

• It gives meaning to the somatic sensory signals, visual and auditory signals.
• integration of general sensation with past experience.
• Deciphering the sensory information that enters the somatosensory area.

Lesion: Astereognosis (absence of stereognosis) and amorphosynthesis, the patient neglects the opposite half of the body as if it is not present. Parieto - occipito - temporal association area

• Bounded by somatosensory cortex anteriorly.
• visual cortex posteriorly and auditory cortex laterally.
• High level of interpretive meaning for the signals from all the surrounding sensory areas.
• Analysis of the spatial coordinates of the body.
• Area for language comprehension.
• Area for initial processing  of visual language (reading).
• Area for naming objects.

Prefrontal Association Areas

Frontal Granular Cortex

Lateral Prefrontal Association Area 

• ------ 9, 10, 46.        
• judgement, foresight, problem solving.

Orbitofrontal Cortex

• ------ 11, 12, 47.        
• emotion, olfaction, personality.

Case of Phineas Gage.
 Prefrontal Leucotomy of Moniz and Freeman. Disorders of Association Cortex      

• Agnosia.
  • Tactile agnosia.
  • Visual agnosia.
  • Auditory agnosia.
• Apraxia.       
• Aphasia.
  • Wernicke’s (receptive) aphasia.
  • Broca’s (Motor) aphasia.
  • conduction aphasia.
  • global aphasia.

Visual Cortex

• V I ----- 17 (striate cortex - line of Gennari).                
  • greatly thickened outer band of Baillarger heterotypical isocortex.          
  • afferent: LG of thalamus.          
  • visual field defect: homonymous quadranopia and macular sparing. 
• V II ---- 18, 19 (visual association area).          
  • afferents: V I, pulvinar of thalamus.          
  • integration of vision with past experience.          
  • visual agnosia.

Auditory Cortex

• A I ----- 41, 42 (transverse temporal gyrus of Heschl).               
  • afferents: MG of thalamus - core projection  slight diminution in auditory acuity.   
• A II ---- 22 (Wernike's area).     
  • afferents: non-laminar part (MG) – belt projection - A I auditory agnosia - sensory aphasia.

Cerebral Dominance (Lateralization, Asymmetry)    

Dominant Hemisphere            

• Language:                
  • speech, writing.           
• Calculation.    

Non-dominant Hemisphere    
        

• Spatial Perception (3D subject).             
• Singing.    
• Playing musical instrument.