TB3 Lecture 4; Basic facts re; sensory perception

The somatosensory cortex is a band across the middle of the brain adjacent to the motor *****. In line with the visual cortex, the somatosensory cortex is abbreiviated to S1.

• When cells from S1 are recorded, they reveal a property similar to visual cortical neurons. 
  • In their receptive field, they have an excitatory and inhibitory input area. Simultaenously touching both areas therefore results in little signal change.

In S1, cortical magnification occurs. There are more receptors in some parts of the body than others, for example the lips have more receptors than the thigh, so the cortical representation is over a wider area. This is similar in the visual cortex.

  This is a visual representation of cortical magnifaction with regards to size of physical area. (below)                                                                                    

• All sensory modalities require a physical stimulus to be converted into an electrical signal.
  • This process is called transduction and is served by sensory receptors.

• Sensory receptors often respond with graded potentials which in turn are converted to action potentials such that signalling in the central nervous system can occur.

• The cortical representation of most senses is in the form of a map, which are magnified on the cortex in terms of density of the receptors (e.g there are more receptors on the lips than the thigh, therefore more of the cortex is mapped to the lip)
  • Visual and tactile stimuli are mapped according to their locations (on the body)
  • Auditory stimuli is mapped according to its tone/frequency.