Final answer:
The dorsal column system is a key sensory pathway in the spinal cord responsible for transmitting fine touch, vibration, and proprioception to the brain, distinct from the spinothalamic tract that carries pain and temperature. It includes fasciculus gracilis for lower body and fasciculus cuneatus for upper body information, with fibers decussating in the medial lemniscus.
Step-by-step explanation:
Summary of Dorsal Column / Medial Lemniscus Pathways
The dorsal column system, also known as the dorsal column-medial lemniscus pathway, is one of the two major pathways that transmit sensory information to the brain, with the other being the spinothalamic tract. Within the spinal cord, sensory information from the body is carried via three successive neurons. The dorsal column system initiates from the axon of a dorsal root ganglion neuron, which enters the spinal cord and sorts itself within the dorsal column based on the body's positional arrangement. As such, axons from lower body regions are situated medially in the fasciculus gracilis, whereas axons from the upper body lateralize into the fasciculus cuneatus.
The medial lemniscus is a fiber tract within the dorsal column system that runs from the nuclei gracilis and cuneatus to the thalamus. It also houses the decussating fibers from these nuclei. This tract is responsible for conveying fine touch, vibration, and proprioception, while the spinothalamic pathway carries pain and temperature sensations. These pathways segregate in the spinal cord, allowing specific testing to determine the function and potential damage to these sensory tracts.
In cases of spinal cord damage, sensory discrimination is crucial in pinpointing the level of the injury. For instance, with certain types of damage, pain stimuli might be perceived on one side but not fine touch, depending on where the trauma is located and which pathways it affects. By understanding how these fibers cross and where they ascend, clinicians are better suited to diagnose and locate injuries within the spinal cord.