Parietal Lobes

Postcentral Central sulcus separates from frontal lobe anteriorly.

Postcentral Central sulcus separates from frontal lobe anteriorly.

gyrus notch

PARIETAL LOBE FUNCTION

1. Postcentral gyrus (granular cortex) The sensory cortex (representation similar to the motor cortex) receives afferent pathways for appreciation of posture, touch and passive movement.

2. Supramarginal and angular gyri (dominant hemisphere) make up part of Wernicke's language area.

This is the receptive area where auditory and visual aspects of comprehension are integrated.

The non-dominant parietal lobe is important in the concept of body image and the awareness of the external environment. The ability to construct shapes, etc. results from such visual/proprioceptive skills.

The dominant parietal lobe is implicated in the skills of handling numbers/calculation. The visual pathways - the fibres of the optic radiation (lower visual field) - pass deep through the parietal lobe.

IMPAIRMENT OF PARIETAL LOBE FUNCTION

1. Disease of either dominant or non-dominant sensory cortex (postcentral gyrus) will result in contralateral disturbance of cortical sensation: Postural sensation disturbed. Sensation of passive movement disturbed. Accurate localisation of light touch may be disturbed.

Discrimination between one and two points (normally 4 mm on finger tips) is lost. Appreciation of size, shape, texture and weight may be affected, with difficulty in distinguishing coins placed in hand, etc. (astereognosis).

Perceptual rivalry (sensory inattention) is characteristic of parietal lobe disease. Presented with two stimuli, one applied to each side (e.g. light touch to the palm of the hand) simultaneously, the patient is only aware of that one contralateral to the normal parietal lobe. As the gap between application of stimuli is increased (approaching 2-4 seconds) the patient becomes aware of both. 108 2. Supramarginal and angular gyri - Wernicke's dysphasia (see page 120).

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