The spinal cord is a major communication route between the brain and the rest of the body. Signals travelling upward through it carry information about sensations such as touch, pressure, temperature, pain, and body position. Signals travelling downward carry commands that help control movement and automatic functions.
Ascending spinal tracts are bundles of nerve fibres that move sensory information toward the brain. Their routes differ according to the kind of information being carried and the level of processing required.
Types of sensory neurons in the spinal tract
Sensory information begins when receptors detect a change inside or outside the body. Somatic sensory neurons collect information from the skin, joints, and skeletal muscles. Visceral sensory neurons monitor internal organs.
Key idea: An ascending pathway usually carries information toward the brain, while a descending pathway carries commands from the brain toward the spinal cord and muscles.
Sensory neurons
A typical sensory signal begins at a receptor. The signal enters a spinal nerve and passes through the dorsal root into the dorsal horn of the spinal cord. There it may connect with another neuron before crossing to the opposite side and continuing upward.
Not every response needs the brain. Some signals are processed locally in the spinal cord and produce a rapid reflex. The brain can later receive information about the event, but the immediate protective movement can occur through a shorter spinal reflex pathway.
A brief overview of motor neurons
Motor neurons carry instructions away from the central nervous system. Somatic motor neurons help control skeletal muscles, including voluntary movements and many reflexes. Autonomic motor pathways regulate internal organs and smooth muscle.
The spinothalamic tract
The spinothalamic tract is part of the anterolateral system. It carries information mainly related to pain, temperature, crude touch, and pressure. The name describes its route: “spino” refers to the spinal cord and “thalamic” refers to the thalamus, a major relay station in the brain.
Receptors of the spinothalamic tract
Nociceptors detect potentially damaging stimuli and contribute to pain signals. A-delta fibres generally carry faster, sharper pain and some temperature information. C fibres conduct more slowly and contribute to longer-lasting pain, temperature, and chemical signals.
Other sensory endings contribute information about touch and pressure. These include Merkel discs, hair-associated nerve endings, and free nerve endings. Together, these receptors provide the first stage in a chain that continues through peripheral nerves and the spinal cord.
The pathway of sensory information
After entering the spinal cord, sensory fibres connect with neurons in defined regions of the dorsal horn. These regions are often described using the Rexed laminae, layers that receive and organise different kinds of sensory input.
- C fibres commonly connect in deeper dorsal-horn layers and contribute to slower pain pathways.
- A-delta fibres connect in other dorsal-horn layers and contribute to faster pain and temperature pathways.
- Touch and pressure fibres follow routes that can extend farther into the anterior part of the spinal cord.
Many fibres cross the midline through the anterior white commissure before ascending in the anterolateral region. Some fibres travel briefly in the tract of Lissauer before reaching their next spinal connection.
The anterolateral system
The anterolateral system is a group of ascending pathways that carry several forms of protective and crude sensory information. As fibres move upward, they send signals to different parts of the brain, including the thalamus and reticular formation.
From the thalamus, information can continue toward the cerebral cortex, where the sensation can be identified and interpreted. Other connections help coordinate attention, alertness, and the emotional aspects of pain. The exact experience depends on the stimulus, the pathway involved, and how the brain processes the information.
Remember: A spinal tract is not just a single wire. It is an organised route involving receptors, peripheral nerves, spinal neurons, crossings, relay stations, and brain regions.
Further reading
Continue with related Brain Made Simple guides on the spinal cord, spinothalamic tracts, spinocerebellar tracts, ascending pathways, and the central nervous system.