Anterolateral spinothalamic tract system

The anterolateral system carries pain, temperature, and crude touch sensations from the extremities and trunk.

Pain and temperature fibers have cell bodies in the dorsal root ganglia and enter the spinal cord via A-delta and C or class III and class IV dorsal root fibers (Figure IV-4-9). Their fibers ascend or descend a couple of segments in the dorsolateral tract of Lissauer before entering and synaps-ing in the dorsal hom. The second neuron cell bodies are located in the dorsal horn gray matter. Axons from these cells cross in the ventral white commissure just below the central canal of the spinal cord and coalesce to form the spinothalamic tract in the ventral part of the lateral funiculus. The spinothalamic tract courses through the entire length of the spinal cord and the brain stem to terminate in the VPL nucleus of the thalamus. Cells in the VPL nucleus send pain and temperature information to the primary somatosensory cortex in the postcentral gyrus.

Right

Left

Right

Left

Cerebral cortex

Thalamus

Ventre posterolateral nucleus (VPL)

Medulla

Spinal cord

Cerebral cortex

Thalamus

Ventre posterolateral nucleus (VPL)

Medulla

Brain stem

Lesion:

Anesthesia (loss of pain and temperature sensations)

Site of lesion: Affected side of body

A, B, C, and D: Contralateral below the lesion; tract intact rostral to the lesion

Spinal cord

Receptor

Clinical Correlate

Because the pain and temperature information crosses almost as soon as it enters the spinal cord, any unilateral lesion of the spinothalamic trad in the spinal cord or brain stem will result in a contralateral loss of pain and temperature. This is an extremely useful clinical sign because it means that if a patient presents with analgesia on one side of the trunk or limbs, the location of the lesion must be on the contralateral side of the spinal cord or brain stem. The analgesia begins I to 2 segments below the lesion and includes everything below that level (Figure IV-4-10).

Figure IV-4-9. Spinothalamic Tract (Anterolateral System)

The cell bodies of the dorsal spinocerebellar tract are found in Clarke's nucleus, which is situated in the spinal cord from T1 to L2. The cell bodies of the cuneocerebellar tract are found in the medulla in the external cuneate nucleus (Figure IV-4-11).

Clinical Correlate

Lesions that affect only the spinocerebellar tracts are uncommon, but there are a group of hereditary diseases in which degeneration of spinocerebellar pathways is a prominent feature. The most common of these is Friedreich ataxia, which is usually inherited as an autosomal recessive trait. The spinocerebellar tracts, dorsal columns, corticospinal tracts, and cerebellum may be involved. Ataxia of gait is the most common initial symptom of this disease.

medical 341

Was this article helpful?

0 0
Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment