Al-Chalabi Mustafa, Reddy Vamsi, Gupta Sonu
McKinsey & Company
Campbell University
The spinothalamic tract (STT) is a sensory tract that carries nociceptive, temperature, crude touch, and pressure from our skin to the somatosensory area of the thalamus. It is responsible for our quick withdraw reaction to a painful stimulus such as touching the stove burner. The spinothalamic tract is composed of two adjacent pathways: anterior and lateral. The anterior spinothalamic tract carries sensory input about crude touch. The lateral spinothalamic tract carries information about pain and temperature. These two divisions of the spinothalamic tract run next to each other indistinctly. Thus, they can be considered one pathway. The spinothalamic tract is part of the anterolateral system, which also encompasses the spinoreticulothalamic tract (SRTT) and the spinotectal tract (SpTT). Three types of sensory fibers are associated with the spinothalamic tract: type III fibers, unmyelinated c-fibers, and myelinated A-delta fibers. Peripheral receptors having associations with the spinothalamic tract pathway are nociceptors, thermal receptors, and thermal nociceptors. Nociceptors are associated with A-delta and type III fibers, which are small, lightly myelinated axons for the transmission of fast, sharp pain. Thermal receptors and thermal nociceptors are associated with A-delta and C fibers, which are small, unmyelinated axons that conduction the transmission of slow-burning pain. The pathway of the spinothalamic tract to the cerebral cortex starts with the dorsal root ganglions, which are composed of pseudounipolar neurons with the peripheral (distal) and central (proximal) axonal processes. These dorsal root ganglia lie adjacent to the spinal cord and represent the first-order neuron of the spinothalamic tract pathway. The axons of the central process of the first-order neurons enter the spinal cord through the lateral dorsal root entry zone to enter the Lissauer tract and synapses with second-order neurons in the substantia gelatinosa, located in the grey matter of the spinal cord. The axons of the second-order neurons cross over the spinal cord to the opposite side two segments above the level of entry via the anterior white commissure, unlike the posterior medial lemniscus pathway, which decussates in the brainstem. The decussating second-neuron fibers enter the anterolateral portion of the spinal cord and then enter the brainstem as the spinal lemniscus. The spinothalamic tract ascends in the ventrolateral aspect of the spinal white matter over the length of the spinal cord. The anterolateral system in the rostral medulla runs between the inferior olivary nucleus and the nucleus of the spinal trigeminal tract, whereas, in the pons and midbrain, the anterolateral system runs dorsolaterally to the medial lemniscus. The spinothalamic tract of the anterolateral system terminates in the ventral posterolateral nucleus (VPL) of the thalamus, the third-order neurons of this pathway. From the thalamus, axons of VPL neurons project out of the thalamus laterally and course somatotopically through the internal capsule's posterior limb of the and terminate in the postcentral gyrus primary somatosensory. In the spinal cord, the spinothalamic tract pathway has a certain somatotopic organization. The medial part of the track receives cervical input while the lateral part receives sacral input. Other pathways, such as cortical spinal tract and posterior medial lemniscus pathway, have a reversed somatotopy in comparison to the spinothalamic tract.
脊髓丘脑束（STT）是一条感觉传导束，它将伤害性刺激、温度、粗略触觉和压力从我们的皮肤传递到丘脑的躯体感觉区。它负责我们对疼痛刺激（如触摸炉灶燃烧器）的快速退缩反应。脊髓丘脑束由两条相邻的通路组成：前束和侧束。脊髓丘脑前束传导有关粗略触觉的感觉输入。脊髓丘脑侧束传导有关疼痛和温度的信息。脊髓丘脑束的这两个分支彼此相邻且界限不明显。因此，它们可被视为一条通路。脊髓丘脑束是前外侧系统的一部分，该系统还包括脊髓网状丘脑束（SRTT）和脊髓顶盖束（SpTT）。与脊髓丘脑束相关的有三种感觉纤维：III型纤维、无髓鞘C纤维和有髓鞘Aδ纤维。与脊髓丘脑束通路相关的外周感受器是伤害感受器、热感受器和热伤害感受器。伤害感受器与Aδ纤维和III型纤维相关，它们是细小的、轻度有髓鞘的轴突，用于传递快速、尖锐的疼痛。热感受器和热伤害感受器与Aδ纤维和C纤维相关，它们是细小的、无髓鞘的轴突，传导缓慢灼痛的传递。脊髓丘脑束通向大脑皮层的通路始于背根神经节，背根神经节由具有外周（远端）和中枢（近端）轴突的假单极神经元组成。这些背根神经节位于脊髓附近，代表脊髓丘脑束通路的一级神经元。一级神经元中枢突的轴突通过外侧背根进入区进入脊髓，进入脊髓后索，并在位于脊髓灰质的胶状质中与二级神经元形成突触。与在脑干交叉的后内侧丘系通路不同，二级神经元的轴突通过前白连合在进入水平上方两个节段处交叉到脊髓的对侧。交叉的二级神经元纤维进入脊髓的前外侧部分，然后作为脊髓丘系进入脑干。脊髓丘脑束在脊髓全长的脊髓白质腹外侧上升。延髓上部的前外侧系统在下橄榄核和脊髓三叉神经束核之间运行，而在脑桥和中脑，前外侧系统向背外侧延伸至内侧丘系。前外侧系统的脊髓丘脑束终止于丘脑的腹后外侧核（VPL），这是该通路的三级神经元。来自丘脑的VPL神经元的轴突从丘脑外侧伸出，沿躯体定位穿过内囊后肢，终止于中央后回的初级躯体感觉区。在脊髓中，脊髓丘脑束通路有一定的躯体定位组织。该束的内侧部分接收颈部输入，而外侧部分接收骶部输入。与脊髓丘脑束相比，其他通路，如皮质脊髓束和后内侧丘系通路，具有相反的躯体定位。
