Ascending Tracts of the Spinal cord. Dr Rania Gabr. Objectives. Define the meaning of a tract. Distinguish between the different types of tracts. Locate the position of each tract. Describe the sensory pathway.
Dr Rania Gabr
1-Ascending (sensory or afferent).
2-Descending (motor or efferent).
- First order neurone- Second order neurone- Third order neurone
The main fibers remain on the ipsilateral side of the cord and terminate by syapses with the second neuroneeither in the spinal grey matter or in the medulla oblongata of the brain stem.
SECOND ORDER NEURON
1- Dorsal column tracts:
(Gracile & Cuneate)
These senses reach a Consciouslevel (cerebral cortex).
Transmit impulses concerned with specific sensory modalities:
pain, temperature, touch, that reach a Consciouslevel (cerebral cortex).
3- Spinocerebellar tracts:
Carries unconsciousinformation from muscles, joints, skin, subcutaneous tissues
Transmit impulses from tactile and stretch receptors to Subconsciouscenters (cerebellum) for muscle tone and coordinations.
Axon of 1st order neuron enter the spinal cord through the dorsal roots of the spinal nerves.
upper 6 thoracic segments
lower 6 thoracic segments
destruction of fasciculus gracilis and cuneatus
(extremely rare to have a lesion of the spinal cord to be localized as to affect one sensory tract only )
Spinothalamic tracts lie lateral and ventral to the ventral horn of the spinal grey matter.
2- Spinothalamic tracts
( input from free nerve endings, thermal receptors )
synapse with cell body of 2nd order neuron
in substantiagelatinosa of posterior gray column of the spinal cord
cross to the opposite side
in the anterior white commissure and ascend in contralateralwhite column as lateral spinothalamic tract
destruction of LSTT
patient will not
respond to pinprick
recognize hot and cold
Medium sized cells in the dorsal root ganglia.
Cells of main sensory nucleus or (nucleus proprius). cross to the opposite side (decussate)
Cells of VPL nucleus of thalamus project to cerebral cortex ( area 3, 1 and 2 )
Loss of crude touch sensation below the level of the lesion. on the contralateral side of the body
Axons carrying pain and temperaturedecussate within one segment of their origin,
It is highly organisedsomatotopically;consequently, the origin of sensory stimuli can be accurately localised.
Both tracts carry information derived from muscle spindles, Golgi tendon organs and tactile receptorsto the cerebellum for the control of posture & coordination of movement.
The spinoreticulothalamic system is thought to be the route via which dull, aching pain (sometimes called \'slow\' pain) is transmitted to a conscious level.