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Lab 5 - Somatosensory, Viscerosensory and Spinocerebellar Pathways

Purpose:

Recall that afferent pathways carry information arising from the body and face and include peripherally located neurons and neurons in the central nervous system. The somatosensory systems (i.e., their anatomical pathways) are a subset of afferent systems that include neurons in the posterior root and cranial nerve ganglia, spinal cord, brain stem, thalamus and cerebral cortex. As the somatosensory pathways include the cerebral cortex, stimulation of somatosensory neurons results in the conscious perception of tactile, proprioceptive, painful or temperature sensations. Other afferent pathways, e.g., the spinocerebellar pathways, do not include the thalamus and cerebral cortex, and, when stimulated, do not give rise to conscious sensations. In addition, the somatosensory systems processing information about crude touch, pain and temperature involve anatomical pathways that differ from those processing information used in discriminative touch and proprioception.

Objectives:

In this Exercise, we will examine the following afferent pathways:

  1. Spinothalamic Pathways - Pain, temperature and simple touch from the body and viscera
    • Neospinothalamic Pathway - Conveys “sharp/cutting” pain sensation associated with tissue damage. Fast.
    • Paleospinothalamic Pathway - Conveys “dull/burning,” crude touch, and temperature. Slower than the neospinothalamic pathway.
    • Archeospinothalamic Pathway - Poorly defined.
  2. Trigeminal pathways - processing somatosensory information from the face and consisting of three parts:
    • The Spinal Sensory Trigeminal Pathway - mediating crude touch, pain and temperature information.
    • The Main Sensory Trigeminal Pathway - a precisely topographically organized pathway mediating fine tactile discrimination and proprioception
    • The Mesencephalic Trigeminal System - monitoring jaw position and movement.
  3. Viscerosensory Pathways - slow conducting, barely topographically organized, sensitive to mechanical, thermal and chemical stimulation of the viscera (i.e., internal body organs such as the heart and gastrointestinal tract).
  4. Spinocerebellar Pathways - “nonsensory” afferent pathways which include the posterior and anterior spinocerebellar pathways and cuneocerebellar pathway.

At the end of this Exercise you should be able to:

  1. Describe the course of major somatosensory and viscerosensory pathways from the receptors to the thalamus.
  2. Describe the course of the spinocerebellar pathways.
  3. Identify the relevant tracts and nuclei on the photomicrograph images.
  4. Identify the location of the cell bodies and synapses of each pathway.
  5. Identify where each pathway crosses the midline.
  6. Name the sensory modalities carried by each pathway.

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