Animation 5.3: Somatosensory Receptive Fields
Sensory information travels from the sensory surface to the highest levels of the brain, and each sensory system has its own distinctive pathway. Pathways from receptors lead into the spinal cord or brainstem, where they connect to distinct clusters of nerve cells. These cells, in turn, have axons that connect to other nerve cell groups. Each sensory modality has a distinct hierarchy of tracts and stations in the brain that are collectively known as the sensory pathway for that modality. Each station in the pathway accomplishes a basic aspect of information processing. Eventually sensory pathways terminate in the cerebral cortex, where the most complex aspects of sensory processing take place.
The receptive field of a cell in a sensory system is the area of the periphery whose stimulation influences the response of a sensory nerve cell. The receptive fields of cortical neurons differ in important ways from those of primary afferent neurons. The receptive field of a primary touch afferent neuron is simply the area of skin where stimulation causes excitation. The receptive field of a cortical neuron, however, is more complex. Thus, stimulation of appropriate areas of skin give rise to excitation or inhibition of a cortical neuron.
The receptive field of a somatic sensory neuron is the region of the skin within which a tactile stimulus evokes a sensory response in the cell or its axon. The accuracy with which tactile stimuli can be sensed varies from one region of the body to another. Analysis of the human hand shows that the receptive fields of mechanosensory neurons are 1-2 mm in diameter on the fingertips but 5-10 mm on the palms. The receptive fields on the arm are larger still. The importance of receptive field size is easy to envision. If, for instance, the receptive fields of all cutaneous receptor neurons covered the entire digital pad, it would be impossible to discriminate two spatially separate stimuli applied to the fingertip (since all of the receptive fields would be returning the same spatial information.)
Textbook Reference: : Sensory Information Processing Is Selective and Analytical, p. 113