Major somatosenosory pathways

Vivian Imbriotis | May 26, 2026

These pathways involve transduction of a signal from the peripheries, which causes a primary sensory neuron (a pseudounipolar neuron with cell body in the dorsal root ganglion) to fire. Signals ascend via the spinal cord and ultimately converge on the thalamus for processing and distribution to the cortex.

Light touch, vibration, and conscious proprioception sensory pathway

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Mechanoreceptors \(\to\) primarily \(A\beta\) fibers \(\to\) pseudounipolar cell body in DRG \(\to\) ascends in ipselateral dorsal column of spinal cord (without synapsing in the dorsal horn) \(\xrightarrow{synapse}\) nucleus cuneatus + gracilis \(\xrightarrow{\text{great sensory decussation}}\) contralateral medial lemniscus \(\to\) thalamus \(\to\) parietal cortex

Pain and temperature sensory pathway

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Polymodal nociceptors \(\to\) C-fibers. Mechanosensitive and thermosensitive \(\to \ A\delta\) fibers

Both have cell bodies in DRG. Synapse onto interneuron in dorsal horn of spinal cord \(\xrightarrow{synapse}\) secondary nociceptor \(\xrightarrow{\text{immediate decussation}}\) \to contralateral spinothalamic tract of spinal cord (lateral STT carries pain/temperature, anterior carries course touch); continues laterally up through brainstem \(\xrightarrow{synapse}\) thalamus.

Thalamus signals frontal cortex and cinguate gyrus (affective component) and parietal cortex (discriminatory component).

Unconscious proprioception sensory pathway

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Muscle spindles + joint position receptors \(\to\) A\(\gamma\) fibers \(\to\) Cell bodies in DRG \(\xrightarrow{synapse}\) secondary sensory neurons.

These form two tracts

The dorsal spinocerebellar tract ascends to the ipselateral cerebellum via the inferior cerebellar peduncle
The anterior spinocerebellar tract decussates immediately, travels up to the brainstem, then decussates again and enters the ipselateral cerebellum via the superior cerebellar peduncle.