DISCRIMINATIVE TOUCH, VIBRATORY SENSE, AND CONSCIOUS MUSCLE JOINT SENSE (Dorsal column-medial leminiscus tract/system) Lufukuja G.

Dorsal column-medial lemniscus tract/system This pathway transmits information from mechanoreceptors and proprioceptors. Lufukuja G.

Dorsal column… First order neurons from the periphery enter the spinal cord through the dorsal root. The main axons ascend the spinal cord in the ipsilateral dorsal column and end in the dorsal column nuclei in the medulla oblongata where they synapse with second-order neurons. Lufukuja G.

Dorsal column … The axons enter the spinal cord from the posterior root ganglion and pass directly to the posterior white column of the same side. Here, the fibers divide into long ascending and short descending branches. The descending branches pass down a variable number of segments, giving off collateral branches that synapse with cells in the posterior gray horn, with internuncial neurons, and with anterior horn cells. It is clear that these short descending fibers are involved with intersegmental reflexes Lufukuja G.

Dorsal column … If the primary axon enters below spinal level T6, the axon travels in the fasciculus gracilis, the medial part of the column. If the axon enters above level T6, then it travels in the fasciculus cuneatus, which is lateral to the fasiculus gracilis. Lufukuja G.

Lufukuja G.

4/27/2017 G.LUFUKUJA

Dorsal column-medial leminiscus …. The fibers of the fasciculus gracilis and fasciculus cuneatus ascend ipsilaterally and terminate by synapsing on the second-order neurons in the nuclei gracilis and cuneatus of the medulla oblongata Lufukuja G.

Dorsal column-medial leminiscus tract/system The axons of the second-order neurons, called the internal arcuate fibers, sweep anteromedially around the central gray matter and cross the median plane, decussating with the corresponding fibers of the opposite side in the sensory decussation. The fibers then ascend as a single compact bundle, the medial lemniscus, through the medulla oblongata, the pons, and the midbrain. Lufukuja G.

Lufukuja G.

Lufukuja G.

Lufukuja G.

Medial lemniscus tract/system Secondary axons from the medial lemniscus finally terminate in the ventral posterolateral nucleus (VPL) of the thalamus, where they synapse with tertiary neurons. From there, tertiary neurons ascend via the posterior limb of the internal capsule, and end in the primary somatosensory cortex. Lufukuja G.

MUSCLE JOINT SENSE PATHWAYS TO THE CEREBELLUM (Spinocerebellar tracts ) Lufukuja G.

Lufukuja G.

Spinocerebellar tract… The spinocerebellar tract is a set of axonal fibers originating in the spinal cord and terminating in the ipsilateral cerebellum. This tract conveys information to the cerebellum about limb and joint position (proprioception). Lufukuja G.

Spinocerebellar tract… This is important for the cerebellum to integrate neuronal inputs from the cerebral cortex with activities in the peripheral and for body balance Proprioceptive information is obtained by Golgi tendon organs and muscle spindles. Golgi tendon organs consist of a fibrous capsule enclosing tendon fasciculi and bare nerve endings that respond to tension in the tendon by causing action potentials Muscle spindle fibres are complicated systems of tension monitoring nerve endings within muscles which result in information being carried via larger and faster neurons Lufukuja G.

Lufukuja G.

Dorsal S-C tract… The secondary neuronal axons (dorsal spinocerebella tract) continue to ascend ipsilaterally and then pass into the cerebellum via the inferior cerebellar peduncle. The second-order neurons from the dorsal nucleus of Clarke form the dorsal spinocerebellar tract; second-order neurons from the lateral cuneate nucleus form the cuneocerebellar tract. Both tracts remain on the ipsilateral side of the spinal cord, ascending via the inferior cerebellar peduncle to terminate in the paleocerebellar cortex Lufukuja G.