recent posts

Ascending tracts

 Lecture as Text
They are located in the white matter Conduct afferent information (May or may not reach consciousness) There are 2 types of information Exteroceptive : Originates from outside the body (Pain, temperature & touch) Proprioceptive : Originates from inside the body (From muscles & joints) Normally there are 3 neurons in an ascending pathway 1st order neuron : Cell body is in the posterior root ganglion 2nd order neuron : Decussates (Crosses to the opposite side) & ascends to a higher level of the CNS 3rd neuron : Located in the thalamus & passes to a sensory region of the cortex Pain & temperature pathway :Lateral spinothalmic tract Pain & temperature pathway :Lateral spinothalmic tract 1st order neuron Peripheral process extends to skin or other tissues & ends as free nerve endings (Receptors) Cell body is situated in the posterior root ganglion Central process extends into the posterior grey column & synapses with the 2nd order neuron 2nd order neuron The axon crosses obliquely to the opposite side in the anterior grey & white commissures within one spinal segment of the cord It ascends in the contra – lateral white column as the lateral spinothalamic tract (LSTT) As the LSTT ascends through the spinal cord new fibers are added to the antero – medial aspect of the tract (Sacral fibers are lateral & cervical fibers are medial) The fibers carrying pain are situated anterior to those conducting temperature As the LSTT ascends through the medulla oblongata, it’s joined by the anterior spinothalamic tract & the spinotectal tract and forms the spinal lemniscus Spinal lemniscus ascends through the pons & the mid brain Fibers of the LSTT end by synapsing with the 3rd order neurons in the ventral posterolateral nucleus of the thalamus (Here crude pain & temperature sensations are appreciated) 3rd order neuron Axons pass through the posterior limb of the internal capsule & corona radiata to reach the somesthetic area in the post central gyrus of the cerebral cortex From here information is transmitted to other regions of the cerebral cortex to be used by motor areas The role of the cerebral cortex is interpreting the quality of the sensory information at the level of the consciousness Light (Crude) touch & pressure pathway : Anterior spinothalamic tract (ASTT) 1st order neuron : It is similar to the pain & temperature pathway 2nd order neuron The axon crosses obliquely to the opposite side in the anterior grey & white commissures within several spinal segments It ascends in the contra – lateral white column as the anterior spinothalamic tract (ASTT) As the ASTT ascends through the spinal cord new fibers are added to the antero – medial aspect of the tract (Sacral fibers are lateral & cervical fibers are medial) As the ASTT ascends through the medulla oblongata, it’s joined by the lateral spinothalamic tract & the spinotectal tract and forms the spinal lemniscus Spinal lemniscus ascends through the pons & the mid brain Fibers of the ASTT end by synapsing with the 3rd order neurons in the ventral posterolateral nucleus of the thalamus (Here crude awareness of touch & pressure sensations are appreciated) 3rd order neuron Axons pass through the posterior limb of the internal capsule & corona radiata to reach the somesthetic area in the post central gyrus of the cerebral cortex The sensations can be crudely localized Very little discrimination is possible
Ascending tracts Ascending tracts Reviewed by Ucfm on March 01, 2012 Rating: 5
Powered by Blogger.