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CHAPTER 1 Sensory pathways and functional deficits There are three main spinal pathways that receive sensory information from the periphery and send it to the brain; the dorsal (posterior) column pathway, anterolateral system and the spinocerebellar pathways (Figure 1.2). Conscious somatosensory information is transmitted either through the dorsal columns or the anterolateral system. Posterior columns are responsible for the perception of fine touch, pressure, vibration and proprioception. First order neurons arise from the periphery, enter from the dorsal roots and ascend via the dorsal columns. Sensory information from the upper limbs travels in the cuneate fasciculus, while that from the lower limbs travels in the gracile fasciculus (Johns, 2014). These neurons terminate in the medulla oblongata in the dorsal column nuclei, where they synapse onto second order neurons in the cuneate and gracile nuclei respectively. The second order neurons cross the midline, then synapse contralaterally with third order neuron in the thalamus, after which signals are sent to the primary somatosensory cortex (Goetz, 2007). The anterolateral system can be simplified into three main pathways: spinothalamic, spinoreticular, and spinomesencephalic tracts (Yaksh and Luo, 2007). Spinothalamic tract carries pain/temperature and crude touch/pressure sensations (Rea, 2015). First order neurons enter the dorsal horn and immediately synapse with second order neurons. The second order neurons in the dorsal horn send their axons to the contralateral side of the spinal cord, then ascend along the anterolateral tract to synapse with the third order neuron in the thalamus. These third order neuron share some of the same thalamic region as the dorsal column pathway, and also send information to the cortex. The first order neurons in the spinoreticular tract and the spinomesencephalic tract share the same trajectory as those of the spinothalamic tract (Mai and Paxinos, 2011). The second order neurons then decussate and terminate in either the reticular formation of the medulla and pons (spinoreticular tract), or the periaqueductal grey in the midbrain (spinomesencephalic tract). The spinoreticular tract carries nociceptive signals from tissue injury and is likely to be involved in overall arousal (Darby and Frysztak, 2014; Sengul and W atson, 2012). The spinomesencephalic tract is involved in descending pain modulation and may be involved in the emotional component of pain (Patestas and Gartner, 2016). Unconscious proprioceptive information from muscle spindles and Golgi tendons is transmitted to the ipsilateral cerebellum via the spinocerebellar tracts (Rea, 2015). It is organised into a two-neuron system; the first order neuron receives peripheral input and enters the spinal cord through dorsal roots to synapse with the second order neuron in the dorsal horn. The second order neuron either sends axons to the ipsilateral, or contralateral spinocerebellar tracts (dorsal and ventral spinocerebellar tracts respectively). The second order neuron of the ventral spinocerebellar tract decussates twice; at the spinal cord level, then again above the cerebellum, thus both of the dorsal and ventral spinocerebellar tracts eventually terminate in the ipsilateral 10PDF Image | Effects of Red Light Treatment on Spinal Cord Injury
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