The Human Brain : From Neurone to Nervous System


  1. Primary somatosensory cortex (SI) is located in the post central gyrus (Brodmann's areas 1,2,3). This contains a somatotopic map, as does the thalamus, and in both structures the map of the body surface is distorted, depending on the density of sensory innervation in each part of the body. The hands, feet, genitalia and lips are the most sensitive areas of the body surface and have a relatively huge representaion on the cortex.

  2. As a result the sensory homunculus is grossly distorted with large areas of cortex given over to handling information arising in the most sensitive ares of the body. Damage to the sensory cortex results in decreased sensory thresholds, an inability to discriminate the properties of tactile stimuli or to identify objects by touch.

  3. In addition to SI, there is another representation of the body surface on the cerebral cortex - the secondary somatosensory cortex (SII) which is in Brodmann's area 40. It has inputs from both sides of the body - via SI and some less specific thalamic nuclei, but the map is less discrimintive. Some aspects of sensory experience are affected by damage to these areas.

  4. This tutorial also contains a brief reference to the visual and auditory pathways, for purposes of comparison between the systems.