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Ascending tracts (1.tracts in the dorsal (posterior) WC (both of these…

- - - - extent
        
        majority of the fibers
        end in
        medulla
        in necleus gracilis &
        nucleus cuneatus respectively
        (1st relay station)
        
        2nd order neuron
        arises frm here
        whose axons are divided
        into 2 groups
        
        external arcuate fibers
        
        dorasal group
        
        the dorsal fibers
        pass via inferior cerebellar peduncle
        of the same side-to end in the
        cerebellum
        
        ventral group
        
        the ventral group fibers
        cross to the opposite side
        via inferior cerebellar peduncle
        & end in the cerebellum
        
        internal arcuate fibers
        
        cross to the opposite side
        & pass through mid brain
        in the medial lemniscus
        to end in
        specific relay nuclei of the thalamus
        (venteroposterior nucleus)
        
        this forms 2nd relay station
        
        1 more item...
    - - 1.after entering the SC,-fasc.gracilis fibers
        run in dorsal (posterior) column
        of same segment
        occupying the whole of its width
        upto the mid-thoracic region.
        
        above this level,
        its fibers are pushed medially by
        the fasc.cuneatus.
        
        so in this ascending system,
        the fibers are represented as
        sacral to cervical segments
        frm medial to lateral
        in the SC
    - - it conveys these info
        frm various parts of the body
        to the higher center
        
        fine touch ( touch with low threshold)
        
        tactile localization & discrimination
        
        proprioceptive & kinesthetic sensation
        ie sensation of body position in space
        & joint movements
        
        vibration sense
        
        sense of deep pressure
        
        some unconscious kinesthetic impulses
        to the cerebellum via external arcuate fibers
        which are essential for control of body posture
        
        constitutes sensory pathway for some
        superficial reflexes
- - - - situation,extent & termination
        
        1.after entering the spinal cord,
        fibers of all segments end around
        nociceptive neurons
        *ie.cells in dorsal horn cells of
        grey matter of spinal cord*
        
        2.most of the axons of 2nd order neurons
        cross in ant white comissure obliquely to
        opposite side of the same segment
        & ascend in the lateral spinothalamic tract
        to end in the thalamus
        (venteroposterior nucleus)
        
        some axons of the 2nd order neurons
        before crossing,
        run up & down for a few segments
        & then cross in anterior white comissure
        to reach the lateral column
        of the opposite side of the SC
        
        axons frm the sacral & lumbar segments
        of the body are pushed laterally
        by axons crossing the mid line
        at successive higher levels
        
        so the fibers are represented as
        cervical to sacral segments
        frm medial to lateral
        in the spinal cord
        
        at higher brain stem level,
        this tract sends several collaterals
        into the reticular formation & tegmentum
        before ending in the thalamus
        
        in the thalamus ,
        3rd order neuron via
        posterior limb of internal capsule
        end in sensory cortex
        ( postcentral gyrus)
- - - - these nuclei receive info like that
        carried by the dorsal column system
        such as touch,vibration & proprioception
        
        axons frm the 2nd neuron decussate & ascend
        to the thalamus along the
        trigemiothalamic tract
        
        in the thalamus,
        each axon synapses with the 3rd neuron
        in it's respective pathway
        
        axons frm the 3rd neuron
        then project frm the thalamus
        to the primary somatosensory cortex
        of the cerebrum
- - - - situation,extent & termination
        
        after entering the SC,
        the fibers end round the cells
        which are situated at the median part
        in the dorsal horn
        ( 1st relay station)
        
        2nd order neuron arises here
        
        most of the axons of 2nd order neurons
        cross in ant white comissure obliquely
        to opposite side of the
        same segment,
        & ascend in the ant column of spinal cord
        to end in the thalamus
        (venteroposterior nucleus)
        
        small no.of axons of the 2nd order neurons are
        uncrossed & may ascend homolaterally as
        anterior spinothalamic tract runs
        in parallel with the
        lateral spinothalamic tract
        & together they constitute the
        spinal lemniscus
        or anterolateral system of ascending fibers.
        
        in upper medulla or lower pons,
        spinal lemniscus joins with the
        fibers frm gracilis & cuneatus nucleus
        to form -media lemniscus
        
        at higher brain stem level,
        this tract sends several colleterals
        into the reticular formation & tegmentum
        before ending in the thalamus.
        
        in thalamus,
        3rd order neuron starts
        & axons of this neuron
        via posterior limb of internal capsule
        ends in the sensory cortex
        ( postcentral gyrus)
    - - It conveys
        
        gross/crude touch sensation
        ie with high threshold
        
        tactile localization