Covers the three main ascending sensory pathways of the spinal cord: the dorsal column medial lemniscal route, the spinothalamic (anterolateral) route with its spinoreticular and spinomesencephalic branches, and the spinocerebellar pathways. It opens with a comparison table of the three pathways and general principles of first to third order neurons, then traces each tract's course from ganglion to cortex, cerebellum or brainstem, and notes where the fibres cross the midline.
Topic 7 of 34 in the MU Sofia syllabus for Anatomy (CNS) (Medicine, Year 2). The free AceMed note covers it in 4 sections, about 776 words (6 min of reading), with 10 flashcards.
In this note
ASCENDING TRACTS
Dorsal column - medial lemniscal pathway:
Spinothalamic - Antolateral pathway:
Spino-cereberall pathway: "no 3rd order axon !! "
ASCENDING TRACTS
- Ascending tract carry sensory information from the body up the spinal cord to the brain.
General principles of sensory pathways:
1st order neuron: it is the sensory neuron that delivers the sensation to the CNS. It is located in the dorsal root ganglion or cranial nerve ganglion.
2nd order neuron: it is an interneuron within the CNS on which the axons of the 1st order neuron synapse. It may be located in spinal cord or brain stem. → medulla oblongata
3rd order neuron: it is located in the thalamus on which the axons of 2nd order neuron synapse, so the sensation reaches our awareness.
Somewhere along its length, the axons of the 2nd order neuron cross over to the opposite side. As a result, the right side of thalamus receives sensations from the left side of body and vice versa.
Axons of the 3rd order neuron ascend (without crossing back again) and synapse on neurons of the 1ry sensory cortex of the cerebral hemisphere.
← The base of all tracts.
* Important !!
body → so nucleus !!
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