The Human Brain : From Neurone to Nervous System
DISCRIMINATIVE TOUCH SENSATION
- Low threshold slowly and rapidly adapting receptors in skin mediate the sensation of touch; impulses from these receptors are carried by the dorsal column-medial lemniscal pathway to the contralateral thalamus and sensory cortex. Precise discrimination is enhanced by sharpening the contrast around the edges of objects at each relay station in the pathway.
Low threshold mechanoreceptors in skin mediate the sensation of touch: collaterals of their axons enter the dorsal column-medial lemniscal system, and communicate with the primary somatosensory receiving area of the cortex.
Areas of the body surface with precise two-point discrimination have higher densities of afferent innervation and are represented by larger numbers of cortical columns. Discriminative touch sensation also depends on sensory processing at each relay station in the pathway
- Contrast enhancement is achieved by process called lateral inhibition, mediated by interneurones in the relay stations - the dorsal column nuclei and thalamus.
The preservation of modality specificity from sensory receptor through to the cortex, accompanied by sensory processing that enhances the discriminative aspects of touch is a characteristic property of this pathway. Each type of cutaneous sensory receptor projects to a column of neurones in the somatosensory cortex concerned primarily with the activity in that class of receptor.
Key Words: Low threshold receptors, dorsal column-medial lemniscal system, fine two-point discrimination, high innervation density, contrast enhancement, lateral inhibition, modality specific pathways.