Ascending and descending spinal tracts are pathways that carry information up and down the spinal cord between brain and body.
The ascending tracts carry sensory information from the body, like pain, for example, up the spinal cord to the brain.
Descending tracts carry motor information, like instructions to move the arm, from the brain down the spinal cord to the body.
Both types of tracts are made up of neuronal axons that gather into long columns called funiculi, meaning long ropes, which are found inside the ventral, lateral and dorsal parts of the spinal cord.
Ascending tracts are sensory pathways that begin at the spinal cord and stretch all the way up to the cerebral cortex.
There are three types of ascending tracts, dorsal column-medial lemniscus system, spinothalamic (or anterolateral) system, and spinocerebellar system. They are made up of four successively connected neurons.
First order neurons are found inside dorsal root ganglions from where they gather sensory input and send it to the second order neurons, usually found inside the spinal cord or brainstem.
They further transmit it to the third order neurons found inside the thalamus, and then the fourth order neurons in the cerebral cortex.
While ascending through the spinal cord these tracts cross over to the opposite side of the central nervous system, or CNS, meaning that the left side of the brain receives sensory input from the right side of the body and vice versa.
These crossings are called decussations and they happen at different levels of the CNS for each of these tracts.
Let’s start with the dorsal column-medial lemniscus system which is a sensory pathway that transmits delicate sensations like vibration, proprioception or sensation of the position of bodyparts, two-point discrimination, and touch.