Sensory and Spinocerebellar Pathways

The ascending sensory pathways carry information from the body to the brain, and the spinocerebellar pathways carry proprioceptive information to the cerebellum for the unconscious coordination of movement. The two principal conscious-sensation systems are the dorsal column-medial lemniscus pathway, which conveys fine touch, vibration, and conscious proprioception, and the anterolateral (spinothalamic) system, which conveys pain, temperature, and crude touch; they differ in where they cross the midline.

Definition

The ascending sensory pathways are projection fibre systems that convey somatosensory information from peripheral receptors through the spinal cord and brainstem to the thalamus and cortex (dorsal column-medial lemniscus and anterolateral systems) or to the cerebellum (spinocerebellar tracts).

Scope

This entry covers the ascending somatosensory tracts of the spinal cord and brainstem, the dorsal column-medial lemniscus and anterolateral (spinothalamic) systems, and the dorsal and ventral spinocerebellar tracts, treated as reference anatomy. It does not address the clinical examination of sensation or the management of sensory disorders.

Key concepts

• Dorsal column-medial lemniscus pathway
• Anterolateral (spinothalamic) system
• Fasciculus gracilis and fasciculus cuneatus
• Decussation site (medulla versus spinal cord)
• Three-neuron sensory relay
• Dorsal and ventral spinocerebellar tracts
• Somatotopic organisation

Mechanisms

Conscious somatosensation is generally carried by three-neuron chains. In the dorsal column-medial lemniscus pathway, first-order fibres carrying fine touch, vibration, and conscious proprioception ascend uncrossed in the fasciculus gracilis and fasciculus cuneatus to the dorsal column nuclei of the medulla, where second-order neurons cross as the internal arcuate fibres to form the medial lemniscus, ascend to the thalamus, and project to the somatosensory cortex. In the anterolateral system, first-order fibres for pain and temperature synapse in the dorsal horn, and second-order neurons cross within the spinal cord to ascend as the spinothalamic tract; Craig reviews how this system also conveys information about the physiological condition of the body. Because the two systems cross at different levels, a spinal lesion can dissociate the modalities on the two sides. The spinocerebellar tracts carry unconscious proprioception to the cerebellum, the dorsal tract conveying largely uncrossed information from the lower limb and trunk and the ventral tract following a more complex double-crossing course.

Clinical relevance

The different crossing points of the dorsal column and anterolateral systems explain why some spinal lesions affect touch and proprioception on one side but pain and temperature on the other. The entry describes this anatomy for reference and does not constitute clinical guidance.

Evidence & guidelines

The organisation of the sensory tracts is established from histology, experimental tracing, and clinical-anatomical correlation, and is described in reference texts. Diffusion MRI tractography can reconstruct components of these pathways in vivo, as shown in early fibre-tracking work and tract atlases, with the usual caveats about resolving small or crossing fibres.

History

The dorsal columns and the spinothalamic system were defined through nineteenth- and twentieth-century clinical-anatomical correlation and experimental work, which established that conscious touch and proprioception ascend uncrossed to the medulla while pain and temperature cross within the cord. Later anatomical and physiological studies refined the role of the anterolateral system in conveying the body's physiological state.

Key figures

• Arthur D. Craig
• Susumu Mori

Seminal works

• craig2002
• mori1999
• wakana2004

Frequently asked questions

What is the main difference between the dorsal column and spinothalamic pathways?

The dorsal column-medial lemniscus pathway carries fine touch, vibration, and conscious proprioception and crosses in the medulla, whereas the anterolateral (spinothalamic) system carries pain and temperature and crosses within the spinal cord.

What do the spinocerebellar tracts carry?

They carry unconscious proprioceptive information from muscles and joints to the cerebellum, contributing to the coordination of posture and movement rather than to conscious sensation.