Our bodies constantly receive sensory information from the surrounding environment. This information, ranging from a gentle brush to the searing pain of a burn, is collected and transmitted to the brain. The brain then interprets these signals, allowing us to perceive, react, and navigate our world. This communication network forms the basis of our interaction with our surroundings.
The Body’s Sensory Highways
The spinothalamic tract is a major pathway for specific types of sensations. This pathway transmits signals related to pain, temperature, and crude touch from the body to the brain. It begins in the spinal cord and ascends towards the thalamus, a relay station within the brain.
The spinothalamic tract is composed of two main parts: the lateral spinothalamic tract, which carries pain and temperature information, and the anterior spinothalamic tract, responsible for crude touch and pressure sensations. These two divisions run closely together, functioning as a single pathway for these sensory inputs.
Where Signals Cross Over
A key feature of the spinothalamic tract is how its nerve signals “decussate,” meaning they cross over from one side of the body to the other. This crossing occurs early in the pathway, within the spinal cord itself, at or near the level where the sensory information first enters. Unlike some other sensory pathways that cross higher up in the brainstem, the spinothalamic tract’s crossing happens much lower down.
The axons of the second-order neurons, which receive initial sensory input in the spinal cord’s dorsal horn, are responsible for this crossing. They traverse the anterior white commissure, a small bundle of nerve fibers, to reach the opposite side. This decussation typically happens about one to two spinal nerve segments above the point of entry for the sensory signal. Sensory signals originating from one side of the body will then ascend the spinal cord on the contralateral, or opposite, side.
The Impact on Sensation
The early decussation of the spinothalamic tract has important implications for how we experience sensations. Because the pathway crosses over within the spinal cord, sensory information from one side of the body is ultimately processed by the opposite side of the brain. This contralateral processing is a core principle of nervous system organization.
This anatomical arrangement is important in clinical settings, especially for spinal cord injuries. If damage occurs to the spinothalamic tract in the spinal cord, loss of pain, temperature, or crude touch sensation will manifest on the side of the body opposite to the injury, and typically below the level of the lesion. This distinct pattern of sensory loss helps medical professionals pinpoint the location of spinal cord damage, such as in conditions like Brown-Séquard syndrome, where one side of the spinal cord is affected.