7.5

• Lesions of the anterolateral system do not eliminate perception of pain or temperature.
• Dorsal-column medial-lemniscus system

  enter the spinal cord via a dorsal root, dorsal columns, dorsal column nuclei of the medulla, medial lemniscus, ventral posterior nuclei
• Most neurons of the ventral posterior nucleus project to the primary somatosensory cortex (SI)
• The anterolateral system comprises three different tracts: the spinothalamic tract, the spinoreticular tract, and the spinotectal tract.
• If both (dorsal-lateral medial-lemnicus system and anterolateral) ascending somatosensory paths are completely transected by a spinal injury, the patient can feel no body sensation from below the level of the cut.
• True or False, when it comes to spinal injuries, the lower, the better.

  True
• Penfield discovered that the human primary somatosensory cortex (SI) is somatotopic —organized according to a map of the body surface.
• The somatotopic map is commonly referred to as the somatosensory homunculus.
• The greatest proportion of SI is dedicated to receiving input from the parts of the body we use to make tactile discriminations (hands, lips, and tongue)
• Only small areas of SI receive input from large areas of the body, such as the back, that are not usually used to make somatosensory discriminations.
• SII receives most of its input from SI and is thus regarded as secondary somatosensory cortex.
• True or False, SII receives substantial input from both sides of the body.

  True
• Much of the output of SI and SII goes to the association cortex of the posterior parietal lobe.
• There are regions that specialize in processing sensations from the hands, feet, face, and so on. It means that different parts of that area are responsible for different parts of the body. By this we can say that the somatosensory system is somatotopically organized.
• It has been proposed that two streams of analysis proceed from SI:

  1. Dorsal Stream
  2. Ventral Stream
• A dorsal stream that projects to posterior parietal cortex and participates in multisensory integration and direction of attention (where).
• A dorsal stream that projects to posterior parietal cortex and participates in multisensory integration and direction of attention (where)
• A ventral stream that projects to SII and participates in the perception of objects’ shapes (what).
• The effects of damage to the primary somatosensory cortex are often remarkably mild — presumably because the somatosensory system features numerous parallel pathways.
• After a unilateral excision that included SI, patients displayed two minor contralateral deficits: a reduced ability to detect light touch and a reduced ability to identify objects by touch.