Lemniscal system (dorsal column tract), proprioceptive and tactile sensation, sensory loss in spinal cord lesions

Lemniscal pathway

The lemniscal system (posterior spinal cord pathway, tr. spino-bulbo-thalamo-corticalis) is a three-neuron sensory spinal pathway. Its function is to transmit information from skin and musculoskeletal receptors:

1. from Meissner's corpuscles (touch, discriminatory sensation)
2. from Vater-Pacini corpuscles (vibration)
3. from muscle spindles and tendon bodies (static part of proprioception – pull, pressure, perception of weight, position and body in space)

Information is conducted through the spinal cord , brainstem, and thalamus to the cortex. The fibers of the pathway are somatotopically arranged in all sections and belong to the category of strong and fast conducting fibers.

Pathway

1st cell – pseudounipolar cell of the spinal ganglion (tr. spinobulbaris)

It begins as a receptor in the periphery, runs through the sensory spinal nerve to the posterior spinal root. It passes through the spinal ganglion without interruption and as an axon heads towards the spinal cord , where the ascending collaterals on the ncl. gracilis and ncl. cuneatus end. The fibers have a somatotopic arrangement according to Kahler's rule :

1. fibers of the sacral, lumbar and lower thoracic spinal ganglia ascend in the fasciculus gracilis (medially)
2. fibers of the upper thoracic and cervical ganglia ascend in the fasciculus cuneatus (laterally)

2nd cell – cell in ncl. gracilis and ncl. cuneatus (tr. bulbothalamicus)

Tr. bulbothalamicus (= lemniscus medialis ) is formed by axons of neurons from ncl. gracilis and ncl. cuneatus. The fibers cross in the oblongata ( decussatio lemniscorum ), pass through the pontine and mesencephalon to the thalamus . In the thalamus it ends in ncl. ventralis posterolateralis.

3rd cell – cell in the ventral posterolateral nucleus of the thalamus (tr. thalamocortical)

The axons of these cells pass through the posterior branch of the internal capsule (radiatio thalami centralis) and end in the primary sensitive cortical area (gyrus postcentralis area 3, 1 and 2).

Sensory loss in spinal cord lesions

1. tactile impairment (the patient is unable to distinguish the size, shape and surface of the held object)
2. Discriminative sensory disorder (inability to distinguish the distance between two points on the skin surface)
3. Vibrating sensation disorder (the patient does not feel the vibrations of the tuning fork on the skin)
4. ataxia (lack of information about muscle tension)
5. perception of pain and heat preserved

Links

Related articles

• Sensitive pathways of the CNS
• Traumatic spinal cord syndromes
• Spinal Cord Function
• Spinal cord

References

• PETROVICKÝ, Pavel – DRUGA, Rastislav. Systematická, topografická a klinická anatomie : VIII. periferní nervový systém. 1. edition. Nakladatelství Karolinum, 1997. ISBN 80-7184-108-0.

• GRIM Miloš, DRUGA Rastislav et al. Základy anatomie, 4a Centrální nervový systém. 2.vydání. Galén, 2014. ISBN 978-80-7262-938-1