Lateral spinothalamic tract

The lateral spinothalamic tract is an example of an ascending sensory tract. It transmits sensory information of pain and temperature from free nerve ending receptors in the skin and other tissues. The pain and temperature information is carried by fast conducting delta A-type fibers and slow conducting C-type fibers.

These are first order neurons whose cell bodies reside within the dorsal root ganglion. From here, the axons of first order neurons enter the apex of the posterior gray column of the spinal cord, where they ascend and descend for a few spinal segments. These ascending and descending fibers constitute the posterolateral trat of Lissauer, which synapse with cell bodies of the second order neurons in the posterior gray column, mainly the nucleus of substantia gelatinosa. Here they release a synaptic neurotransmitter, called substance P.

Next, the axons of these second order neurons cross obliquely–in front–via the anterior gray and white commissures of the spinal cord, to ascend in the contralateral white column. The nerve fibers which ascend in the lateral funiculus constitute the lateral spinothalamic tract, while those which ascend in the anterior funiculus constitute the anterior spinothalamic tract.

In the spinal cord, the lateral spinothalamic tract lies medial to the anterior spinocerebellar tract. In the medulla oblongata, the lateral spinothalamic tract ascends behind the inferior olivary nucleus, where it joins with the anterior spinothalamic and spinotectal tracts to constitute the spinal leminiscus. Next, the spinal leminiscus (containing the lateral spinothalamic tract) passes through the posterior pons to enter the tegmentum of the mid-brain. Afterwards, the second order neurons of lateral spinothalamic tract relay the pain and temperature information into the VPL (ventral posterior lateral) nucleus of the thalamus.

The VPL nucleus contains cell bodies of third order neurons which project–as thalamocortical projections–through the corona radiata to reach the post-central gyrus (area 3, 1, 2, a.k.a. the primary sensory area). The sensory representation of the body is ‘inverted’ in the primary sensory cortex (a.k.a. sensory homunculus) with the face and upper limbs being represented on the posterolateral surface of cortex, while the legs being represented on the inner or medial surface.