Anterolateral system of sensitive spinal tracts – (spinothalamic, spinoreticular and spinotectal tracts), pain pathways

anterolateral sensory pathway

Spinal cord tracts - ascending (sensory) and descending (motor)

Sensory pathways of the CNS are pathways that carry information from receptors in the skin, muscles, and tendons to the brain. The dendrite (not the axon!) of the first neuron is a sensory peripheral nerve and its body is located in a sensory ganglion on the dorsal root of the spinal cord or in the appropriate ganglion of a cranial nerve . The first neuron is always pseudounipolar.

spino-bulbo-thalamo-cortical tract

The spino-bulbo-thalamo-cortical tract (posterior spinal cord pathway, lemniscal system) is a pathway that carries fine cutaneous sensation and proprioception from the body. The first neuron, as in other sensory spinal pathways, is a pseudounipolar neuron in the spinal ganglion . Its fibers enter the spinal cord via the posterior roots and continue somatotopically in the posterior cords as the more medial fasciculus gracilis and the more lateral fasciculus cuneatus . The fibers from the sacral region run most medially, and the fibers from the cervical region most laterally. The fasciculus gracilis and cuneatus are separated from the outside of the spinal cord by the sulcus intermedius .

The body of the second neuron of this pathway is located in the nuclei in the medulla oblongata – ncl. gracilis and cuneatus. The axons of these neurons cross in the medulla oblongata ( decussatio lemniscorum ) and continue through the brainstem to the thalamus as lemniscus medialis . The third neuron is located in ncl. ventralis posterolateralis of the thalamus and runs as tr. thalamocorticalis to the cortex – Brodmann area 3, 1, 2 (primary somatosensory cortex).

This pathway sends collaterals at the second neuron level to the cerebellum ( tr. bulbocerebellaris ), tecta and ncl. ruber. Some fibers from the thalamus lead to the association areas of the cortex and to the SII area (area 40).

Anterolateral system

The anterolateral system includes three pathways that carry touch, heat, and pain from the body— the spinothalamic tract , the spinoreticular tract , and the spinotectal tract . They run through the spinal cord in the lateral and anterior spinal cords.

Spinothalamic tract

The spinothalamic tract carries gross skin sensation , "fast pain" and heat from skin receptors to the thalamus. The pathway has fewer synapses and pain is carried here mainly by fast-conducting myelinated Aδ fibers, which is why it is called fast. The first neuron has its body in the ggl. spinale.

The second neuron of this pathway are the cells of the posterior column of the proprius columnae of Rexed's laminae IV and V. The axons of the second neuron cross in the corresponding spinal segment, therefore they have the opposite somatotopic arrangement than the previous pathway - the most medial fibers are from the cervical regions. It passes through the trunk laterally from the medial lemniscus to the posterolateral thalamic nucleus ( third neuron ). From there the fibers continue to the cortex ( SI ).

Spinoreticular tract

The spinoreticular tract conducts mainly "slow pain" . It is a phylogenetically older pathway than the previous one and is dominated by unmyelinated C-type fibers. The pathway ends in the medial nuclei of the reticular formation and from there it is followed by the so-called ARAS - the ascending activation system of the reticular formation. The first neuron is the pseudounipolar neuron of the spinal ganglion.

The second neuron is located in the posterior spinal horn, part of its axons cross and run in the anterior and lateral spinal cords.

Spinotectal tract

The spinotectal tract conducts stimuli from the skin to the tectum, where they are integrated with visual and auditory information in the superior and inferior colliculi.

Sensory pathways of the cranial nerves

The sensitive pathways of the cranial nerves conduct sensitive information from the skin and muscles of the head and the mucous membranes of the oral cavity, nasal cavity, pharynx and larynx and cornea. This is mediated by the cranial nerves V , VII, IX and X. The connection occurs in the relevant ganglion – ggl.geniculi, ggl. trigeminale and ggl. superius n. IX and X. Here, as in ggl. spinale, there is a pseudounipolar cell. The axons of these cells together lead to the ncl. principalis (pontinus) and spinalis n. V.  From here, fibers such as the lemniscus trigeminalis lead to the ncl. ventralis posteromedialis of the thalamus. From here, the information is conducted to the lower third of the gyrus postcentralis .

Links

Související články

• Spinal cord

Použitá literatura

• DRUGA, Rastislav – GRIM, Miloš. Anatomy of central nervous system. 1. edition. Prague : Galén; Karolinum, 2011. 219 pp. ISBN 978-80-7262-706-6.

• GANONG, William F. Přehled lékařské fyziologie. 20. edition. Prague : Galén, 2005. 890 pp. ISBN 80-7262-311-7.