Which spinal tract carries pain and temperature sensation?

Spinothalamic Tract Carries Pain and Temperature Sensation

The spinothalamic tract is the primary spinal pathway that carries pain and temperature sensation from the body to the brain. This tract originates in the dorsal horn of the spinal cord and terminates in the ventral posterior nucleus (VP) of the thalamus, including its posterior and inferior subnuclei 1.

Anatomical Pathway and Function

Origin and Course

• Pain and temperature signals travel from peripheral nociceptors to the spinal cord dorsal horn, where sensory information enters the central nervous system 2.
• The spinothalamic tract specifically conveys nociceptive (pain) and thermal information in a topographically organized manner 3.
• For cranial structures, the analogous pathway is the spinal division of the trigeminal nucleus, which serves similar functions for the face and head 1.

Fiber Types and Sensory Modalities

• Small sensory nerve fibers within the spinothalamic tract are involved in temperature and pain perception 2.
• The tract carries both noxious thermal stimulation and mechanical pain signals 4.
• Lamina I neurons in the spinal cord provide dense, topographic input to specific thalamic nuclei dedicated to pain and temperature processing 3.

Clinical Significance

Evidence from Lesion Studies

• Spinothalamic tract lesions result in loss of pain and temperature sensation on the contralateral side of the body 5, 6.
• Patients with lateral medullary infarcts affecting the spinothalamic tract demonstrate severe thermoalgic dissociation with preserved discriminative touch and motor function 4.
• Small strokes in the ventral posterior nucleus are associated with decreased painful and cold sensations 1.

Distinction from Other Sensory Pathways

• The spinothalamic tract is functionally and anatomically distinct from pathways carrying tactile and proprioceptive information 2.
• Large sensory nerves carrying touch, vibration, and proprioception travel via different pathways (dorsal column-medial lemniscal system), not the spinothalamic tract 2.
• General sensory information includes tactile, pain, and temperature sensations, but only pain and temperature specifically utilize the spinothalamic pathway 2.

Descending Modulation

Pain Control Mechanisms

• The periaqueductal gray (PAG) in the midbrain controls spinal nociceptive transmission through descending pathways that selectively target dorsal horn laminae containing nociceptive relay neurons 7.
• Serotonin and norepinephrine play critical roles in descending pain inhibitory pathways that modulate spinothalamic transmission 8.
• This descending control system can selectively modulate nociceptive transmission due to its anatomical proximity to primary afferent nociceptor terminals 7.

Important Clinical Caveats

• Reflex withdrawal from painful stimuli does not require intact spinothalamic pathways or conscious pain perception 2.
• Nociception (the physiological detection of noxious stimuli) is distinct from pain perception, which requires cortical processing 2.
• Even with severe spinothalamic injury, some residual pain perception may occur via alternative multisynaptic pathways such as the spinoreticulothalamic tract, though with altered characteristics and prolonged delays 4.
• Residual intact thermosensitive nociceptive afferents within partially lesioned spinothalamic pathways can distinguish patients who develop central pain from those who do not 6.