- Spinothalamic tract
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Caption = Spinothalamic tract is 5, in blue at right.
Caption2 = Diagram of the principal fasciculi of the spinal cord. (Anterior and posterior spinothalamic fasciculus is labeled at bottom left.)
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The spinothalamic tract is a sensory pathway originating in the spinal cord. It transmits information to the
thalamusabout pain, temperature, itchand crude touch. The pathway decussatesat the level of the spinal cord, rather than in the brainstemlike the posterior column-medial lemniscus pathwayand corticospinal tract.
The cell bodies of neurons that make up the spinothalamic tract are located principally within the dorsal horn of the spinal cord. These neurons receive input from sensory fibers that innervate the skin and internal organs.
There are two main parts of the spinothalamic tract (STT):
lateral spinothalamic tracttransmits painand temperature.
anterior spinothalamic tract(or "ventral" spinothalamic tract) transmits light touch and pressure.
The types of sensory information transmitted via the spinothalamic tract are described as "
affective sensation". This means that the sensation is accompanied by a compulsion to act. For instance, an itch is accompanied by a need to scratch, and a painful stimulus makes us want to withdraw from the pain.
There are two sub-systems identified:
* Direct (for direct conscious appreciation of pain)
* Indirect (for affective and arousal impact of pain). Indirect projections include
** Spino-Reticulo-Thalamo-Cortical (part of the
ascending reticular arousal system, aka ARAS)
** Spino-Mesencephalo-Limbic (for affective impact of pain).
Path of sensation
The Spinothalamic Tract, like the
Dorsal Column-Medial Lemniscus Tract, use three neurons to convey sensory information from the periphery to conscious level at the cerebral cortex. Pseudounipolar neurons (those with only one long process) in the dorsal root ganglionhave axons that lead from the skininto the dorsal spinal cordwhere they synapsewith secondary neurons in the marginal nucleus. These secondary neurons are called "tract cells".
The axons of the tract cells cross over (decussate) to the other side of the spinal cord via the
anterior white commissure, and to the anterolateral corner of the spinal cord (hence the spinothalamic tract being part of the anterolateral system). The axons travel up the length of the spinal cord into the brainstem. Pain travels through spinothalamic tracts, and crosses over in the spinal cord at the point it enters, and then travels up contralaterally.
Traveling up the brainstem, the tract moves dorsally. The neurons ultimately synapse with third-order neurons in several nuclei of the thalamus -- including the medial dorsal, ventral posterior lateral, and ventral medial posterior nuclei. From there, signals go to the
cingulate cortex, the primary somatosensory cortex, and insular cortexrespectively.
Unilateral lesion usually causes contralateral
anaesthesia(loss of pain) and temperature. Anaesthesia will normally begin 1-2 segments below the level of lesion, affecting all caudal body areas. This is clinically tested by using pin pricks.
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