Generally, there are three grades neuron implicated In ascending pathway A chain of three long neurons and a number of interneurons conduct the nerve impulses generated in response to stimuli from an individual receptor to the somatosensory cortex First-order neuron: the cell bodies lie in a dorsal root ganglion or somatic afferent ganglia of cranial nn Second-order neurons: the cell bodies lie within the spinal cord or brain stem such as dorsal column nuclei(sensation of trunk limbs) or sensory nucleus of trigeminal nerve their axons usually decussate, ending in the thalamus Third-order neurons: the cell bodies lie in the thalamus project to the sensory cortex(center) Copy Right- Hongqi ZHANG-Department of Anatomy-Fudan UniversityCopy Right- Hongqi ZHANG-Department of Anatomy-Fudan University Copy Right- Hongqi ZHANG-Department of Anatomy-Fudan University A chain of three long neurons and a number of interneurons conduct the nerve impulses generated in response to stimuli from an individual receptor to the somatosensory cortex Generally,there are three grades neuron implicated In ascending pathway First-order neuron: the cell bodies lie in a dorsal root ganglion or somatic afferent ganglia of cranial nn. Second-order neurons: the cell bodies lie within the spinal cord or brain stem. such as dorsal column nuclei(sensation of trunk & limbs) or sensory nucleus of trigerminal nerve, their axons usually decussate, ending in the thalamus. Third-order neurons: the cell bodies lie in the thalamus. project to the sensory cortex (center)