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Cortical areas

The frontal lobes: the cortex contains motor areas and the personality center.

The parietal, temporal and occipital lobes contain all the sensory areas and sensory association

The motor areas:

1. Primary motor area (area 4)

2. Premotor area (secondary motor area,area6)

3. Frontal eye field (motor eye field area, area 8)

4. Motor speech (Broaca’s area, areas 44 and 45)

The sensory areas:

1. General sensory area (primary somatic sensory area ) (area 3,1,2)

2. Somatic sensory association area (areas 5,7,40)

3. Primary visual area (area 17)

4. Visual association areas (areas 18,19,39)

5. Primary auditory area ( areas 41,42)

6. Auditory association area (Wernicke’s area (area 22)

7. Primary gustatory area (taste area) (area 43)

8. primary vestibular area

9. Primary olfactory area and olfactory association area.10. Sensory language areas (sensory speech areas) (areas 22, 39, 40)

1. Primary motor area (area 4)

Site: 1. precentral gyrus,

2. anterior wall of the central sulcus,

3. anterior part of the paracentral lobule

Representation of the body: The opposite half of the body is represented upside down.

1. Lower 1/3 : head region

2. upper 2/3 : neck, upper limb, trunk, hip, high, knee and then the leg, foot and

 perineum in the paracentral lobule.

Functions:

1. Gives origin to 40% of the corticospinal and corticobulbar fibres (pyramidal tract)2. Initiation of the highly skilled fine movements such as playing piano and typing.

Arterial supply:

1. upper ¼ and paracentral lobule: anterior cerebral artery

2. lower ¾; middle cerebral artery

Lesion: contralateral hemiplegia with all signs of upper motor neuron lesion. There is no

 pure area 4 lesion and area 6 is usually affected with area 4. Signs appear in two stages:1. stage of shock: flaccid paralysis and loss of all reflexes 9hours to days)

2. After recovery from shock:

a. recovery of gross movements at the proximal joints

 b. skilled movements at the distal joints remain impaired

c. hypotonia changes to hypertonia and areflexia changes hyperreflexia

d. spasticity, Babinski sign and clonuse. loss of superficial abdominal reflexes and cremastric reflex

2. Premotor area (area 6):

Site: anterior to the motor area

Function:

1. Gross or stereotyped movements of group of muscles through connections with the basal

ganglia

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2. Execution of learned motor activity by storing the programs of motor activity learned by

experience such as walking, dancing, opening the door, saluting.

Arterial Supply: Similar to the area 4.

Lesion: Apaxia; Apraxia is difficulty in performing a learned movement without paralysis.

3. Motor speech area ( Broca’s Area, 44 & 45:

Site: posterior part of the inferior gyrus.Functions: it coordinates actions of the muscles used in speech (lips, tongue and larynx)

Arterial supply: middle cerebral artery.

Lesions:

a. Aphasia: is paralysis of speech

 b. The patient is unable to express himself by speaking. He can not form words.

c. The patient understands and can point at objects

d. Lesion in non dominant hemisphere (right) has no effect.

4. Frontal eye field area (area 8):

Site: posterior part of the middle frontal gyrus.

  Function: horizontal movements of both eyes to the opposite side.

  Arterial supply: middle cerebral artery.  Lesion: ipsilateral deviation of both eyes due to the unopposed action of the intact area 8.

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