The spinothalamic tract conducts the sensations of pain, temperature, itch, and touch from various parts of the body to the thalamus. There are two parts of the spinothalamic tract; the lateral tract and the anterior tract. The lateral tract conducts sensations to the brain and creates sensations of pain and temperature, and the anterior tracts’ impulses are interpreted as pressure and touch.
When a sensation, such as pain or temperature, is conducted through the spinothalamic tract, it arrives in the thalamus and creates an impulse to act. This is what is known as affective sensation. For example, if you are pricked by a pin on your finger tip, the sensation is conducted up through the spinothalamic tract and into the brain, and your brain sends the signal to withdraw from the source of pain in order to reduce it. If you have an itch, the brain sends the impulse to scratch.
A typical pathway of an impulse conducted through the spinothamalic tract begins in the skin, often in the extremities such as the hands or feet. For example, if you get pricked by a pin a neuron, known as a psuedounipolar neuron, connects the skin and the dorsal aspect of the spinal cord. The impulse that comes from the skin goes through these pseudounipolar neurons, and then reaches a secondary neuron, known as a tract cell. These tract cells cross over, or deccusate, to the anterolateral, or frontside, of the spinal cord. From the tract cells, the spinothalamic tract carries the impulse up the spinal cord to the brainstem and to the thalamus, which contains third-order neurons that carry the impulse to several areas of the brain.
Clinically speaking, the spinothalamic tract can be involved in injuries of the spinal cord. Since it deccusates on the level of the spine, it creates different responses than some of the other nerve pathways, which deccusate in the brain. For instance, if there is an injury sustained to the spinothalamic tract, it can create damaged tissue called a lesion. If the lesion is on one side of the spine, there will be loss of the sensations of both pressure and touch below the lesion on that side. Since the spinothalamic tract pathway deccusates on the spine and ascends on the opposite side of the spinal cord, it results in pain below the lesion but on the opposite side of the body, which is known as dissociated sensory loss.