Cutaneous Innervation - Pathways To The CNS

Pathways To The CNS

The sensory modality that is detected by the afferent fibers is an important factor to consider because it determines the pathway that the dorsal root ganglion neurons will take within the central nervous system. The sensory neurons coming from the body synapse in the dorsal horn of the spinal cord, bringing in information about touch sensations (epicritic), or modalities of pain (protopathic). While both types of sensory neurons must first synapse in the dorsal horn of the spinal cord, the area of the dorsal horn where they synapse is different. Their pathway to the thalamus is also different.

Neurons that carry information about touch, vibration, and proprioception sensations from the lower body enter the spinal cord below spinal level T6, where they synapse in the dorsal horn to form reflex circuits, but also send axon branches through the gracile fascicle to the brainstem. Similarly, information from the upper body enters the spinal cord at level T6 and above, and ascend toward the brainstem in the Cuneate_fasciculus. Together the gracile and cuneate form the dorsal column in the spine.

Neurons that carry information about pain and temperature synapse in the dorsal horn at the anterolateral fascicles.

While the neurons for touch sensations ascend ipsilaterally through the dorsal column-medial lemniscal system to the thalamus; neurons for pain and temperature ascend contralaterally to the thalamus through the anterolateral system.

When both sensory pathways reach the integrating center that is the thalamus, they make their final assent to the somatosensory areas in the postcentral gyrus of the cerebral cortex.