CNS ascending tract

2. Spinal Cord
The Ascending Tracts
Dr
.Tawfeeg

3. The Ascending Tracts
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4. The Main Points
 Revision of the previous lecture
 The ascending tracts:
o Pain and temperature pathways.
o Light touch and pressure pathways.
o Discriminative Touch, Vibratory Sense, and Conscious
Muscle Joint Sense.
o Muscle joint sense pathways to the cerebellum.
o Some other ascending pathways.
o Visceral sensory tract.
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5.  The ascending tracts conduct afferent
informations.
 These informations are of two groups:
o Exteroceptive informations, which originates
from outside the body, such as pain, temperature
and touch.
o Proprioceptive informations, which originates
from inside the body,
e.g. from muscles and joints.
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6. Anatomical Organization
 1st
order neuron
has it cell body in the posterior root ganglion, a peripheral
process connects with a sensory receptor ending, whereas a
central process enter the spinal cord to synapse on the second
order neuron.
 2nd
order neuron
gives rise to an axon that decussates and ascends to a higher
level of the CNS, where it synapses with the third order neuron.
 3rd
order neuron
usually in the thalamus, gives rise to a projection fibers that
passes to a sensory region of the cerebral cortex.
 This is the most common, but some afferent pathways use
more or fewer neurons.
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7. Pain and Temperature
Pathways
LATERAL SPINOTHALAMIIC TRACT
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8.  Pain is a sensation that warns of potential injury
and alert the person to avoid or treat it.
 Receptors of pain and thermal sensation in the
skin and other tissues are free nerve ending.
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9. Pain and Temp. (Cont.)
1) The axons enter the spinal cord from the dorsal root
ganglion to the tip of the posterior gray column.
2) Divide into ascending and descending tracts that travel for
one or two segments forming the postero-lateral tract of
lissauer (fibers of 1st
order neuron).
3) Synapse with cells in the posterior gray column (2nd
order
neuron) substanitia gelatinosa
4) Cross the midline within one spinal segment.
5) Ascend in the contra-lateral white column as lateral
spinothalamic tract .
(Here it lies medial to the anterior spinocerebellar tract)
In the upper cervical segments the sacral fibers are lateral and the
cervical fibers are medial.
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10. 6) In the medulla oblongata, lateral spinothalamic tract:
• Lies near the lateral surface
• Lies between the inferior olivary nucleus and the nucleus of the
spinal tract of trigeminal nerve.
• accompanied by the anterior spinothalamic tract and the
spinotectal tract to form the spinal lemniscus.
7) In the pons the spinal lemniscus ascends throught it's
posterior part.
8) In the midbrain it lies in the tegmentum lateral to the
medial lemniscus.
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Pain and Temp. (Cont.)

11. 9) The fibers end by synapsing with the 3rd
order neuron in the
ventral postero-lateral nucleus of the thalamus. Some fiber
relay in the reticular formation
10) The axons now pass through the posterior limb of the
internal capsule and the corona radiata to reach post central
gyrus of cerebral cortex.
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Pain and Temp. (Cont.)

14. Types of Pain
Fast pain Slow pain
Fast conducting A-type fibers Slow conducting C-type fibers
Felt within about 0.1 sec. after stimulation Felt within about 1 sec. after stimulation
Sharp, acute or pricking Burning, aching and throbbing
Confined to skin Due to tissue destruction
Precisely localized Poorly localized due to multiple
relays
Relayed to the cerebral cortex Terminate in the reticular formation
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15. Light (Crude) Touch and
Pressure Pathways
ANTERIOR SPINOTHALAMIC TRACT
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16. Light (Crude) Touch and Pressure
Pathways
1) The axons enter the spinal cord from the dorsal root
ganglion to the tip of the posterior gray column.
2) Divide into ascending and descending tracts that travel for
one or two segments forming the postero-lateral tract of
lissauer (fibers of 1st
order neuron).
3) Synapse with cells in the posterior gray column (2nd
order
neuron)( nucleus proprius)
4) Cross the midline within several spinal segment.
5) Ascend in the contra-lateral white column as Anterior
spinothalamic tract .
(In the upper cervical segments the sacral fibers are lateral and
the cervical fibers are medial).
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17. Light (Crude) Touch and Pressure Pathways
(Cont.)
6) In the medulla oblongata, the anterior spinothalamic tract
accompanies the lateral spinothalamic tract and the
spinotectal tract to form the spinal lemniscus.
7) In the pons the spinal lemniscus ascends throught it's
posterior part.
8) In the midbrain it lies in the tegmentum lateral to the
medial lemniscus.
9) The fibers end by synapsing with the 3rd
order neuron in the
ventral postero-lateral nucleus of the thalamus.
10) The axons now pass through the posterior limb of the
internal capsule and the corona radiata to reach post central
gyrus of cerebral cortex.
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19. Discriminative Touch, Vibratory
Sense, and Conscious Muscle
Joint Sense
FASCICULUS GRACILIS
AND
FASICULUS CUNEATUS
(POSTERIOR WHITE COLUMN)

20. Discriminative Touch, Vibratory Sense, and
Conscious Muscle Joint Sense
1) The axons enter the spinal cord from the dorsal root
ganglion and pass directly to the posterior white
column.
2) The fibers divide into long ascending and short
descending branches.
3) The descending branches and some of the ascending
branches end by synapsing with cells in the posterior
gray horn and anterior horn cells. They are involved
with intersegmental reflexes.
4) Many of the ascending branches travel upward in the
posterior white columns as the fasciculus gracilis and
cuneatus.
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21. Discriminative Touch, Vibratory Sense,… (Cont.)
5) The fasciculus gracilis is present throughout the spinal
cord and contains fibers from sacral, lumbar and lower six
thoracic spinal nerves.
6) The fasiculus cuneatus is present in the upper thracic and
cervical segments and contains fibers from the upper six
thoracic and all cervical spinal nerves. It is situated
laterally and separated from the fasciculus gracilis by a
septum.
7) Both types of fibers ascend ipsilaterally
8) In the medulla oblongata they terminate by synapsing in
the 2nd
order neuron in the nuclei gracilis and cuneatus.
9) the axons of the 2nd
order neuron now known as internal
arcuate fibers .
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22. Discriminative Touch, Vibratory Sense,… (Cont.)
10) The internal arcuate fibers decussate and ascend as one
compact bundle, the medial lemniscus.
11) The fibers end by synapsing with the 3rd
order neuron in the
ventral postero-lateral nucleus of the thalamus.
12) The axons now pass through the posterior limb of the
internal capsule and the corona radiata to reach post central
gyrus of cerebral cortex.
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25. Spinocervical thalamic tract
- For proprioceptive sensation
- it locates through length spinal cord
- The axon of dorsal root ganglia travel within the posterior funiculus for
several segments before entering the posterior horn gray matter to
synapse on neurons there.
- Axons of neurons in the posterior horn ascend in the lateral funiculus
to the upper two or three cervical segments, where they synapse on
neurons of the lateral cervical nucleus
- Axons of this nucleus cross to the opposite lateral funiculus and ascend
to the thalamus

26. MUSCLE JOINT SENSE
PATHWAYS TO THE
CEREBELLUM
o POSTERIOR SPINOCEREBELLAR TRACT
o ANTERIOR SPINOCEREBELLAR TRACT
o CUNEOCEREBELLAR TRACT

27. Posterior Spinocerebellar Tract
1) The axons enter the spinal cord from the dorsal root
ganglion to the base of the posterior gray column.
2) They terminate by synapsing in the 2nd
order neuron in the
posterior grey column, the nucleus dorsalis.
3) The nucleus dorsalis (Clark's columns) extend from the 3rd
or
4th
lumbar segment to the 8th
cervical segment.
4) The axons of the 2nd
order neuron enter the postero-lateral
part of the lateral white column on the same side and ascend
as the posterior spinocerebellar tract.
5) In the medulla oblongata the tract joins the inferior
cerebellar peduncle and terminates in the cerebellar cortex.
6) This tract conveys the informations from the muscle spindles
and joints receptors in the trunk and lower limb to the
cerebellum.
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28. Anterior Spinocerebellar Tract
1) The axons enter the spinal cord from the dorsal root ganglion to the
base of the posterior gray column.
2) They terminate by synapsing in the 2nd
order neuron in the
posterior grey column, the nucleus dorsalis. (laminae V to VII????)
3) The nucleus dorsalis (Clark's columns) extend from the 3rd
or 4th
lumbar segment to the 8th
cervical segment.
4) The majority of the axons of the 2nd
order neuron cross to enter the
antero-lateral part of the lateral white column of the opposite side
and ascend as the anterior spinocerebellar tract.
5) The minority ascends as the anterior spinocerebellar tract of the
same side of the lateral white column..
6) After ascending through the medulla oblongata and pons the
tract joins the superior cerebellar peduncle and terminates in the
cerebellar cortex.
7) This tract conveys the informations from the muscle spindles and
joints receptors in the trunk and upper and lower limbs to the
cerebellum.
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31. Cuneocerebellar Tract
 Originates from the accessory cuneatus nucleus
and enter the cerebellum through the inferior
cerebellar peduncle of the same side.
 It conveys the informations about muscle joint
sense to the cerebellum.
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33. OTHER ASCENDING
PATHWAYS
o SPINOTECTAL TRACT
o SPINORETICULAR TRACT
o SPINO-OLIVARY TRACT

34. Spinotectal Tract
 The axons enter the spinal cord from the dorsal root
ganglion.
 They synapse with unknown 2nd
order neuron in the grey
matter.
 The fibers of the 2nd
order neuron cross the midline and
ascend as spinotectal tract.
 This tract lying in the antero-lateral column of white
matter, close to the lateral spinothalamic tract.
 After passing through the medulla and pons, they
terminate by synapsing with neurons in the superior
colliculus of the mid brain.
 This pathway provides afferent informations for
spinovisual reflexes.
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35. Spinoreticular Tract
 The axons enter the spinal cord from the dorsal root
ganglion.
 They synapse with unknown 2nd
order neuron in the grey
matter.
 The fibers of the 2nd
order neuron ascend in the lateral
white column as spinoreticular tract, lying mixed with the
lateral spinothalamic tract.
 Most of the fibers are uncrossed and terminate by
synapsing with neurons in the reticular formation of the
medulla oblongata, pons and mid brain.
 This pathway provides afferent informations for reticular
formation, which play an important role in influencing
levels of cosciousness.
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36. Spino-olivary Tract
 The axons enter the spinal cord from the dorsal root
ganglion.
 They synapse with unknown 2nd
order neuron in the
posterior grey column.
 The fibers of the 2nd
order neuron cross the midline and
ascend in the junction between the anterior and lateral
white column as spino-olivary tract.
 The axons end by synapsing on 3rd
order neuron in the
inferior olivary nucleus of the medulla oblongata.
 The axons of the 3rd
order neuron cross the midline and
enter the cerebellum through the inferior cerebellar
peduncle.
 This tract conveys informations from cutaneous and
proprioceptive organs.
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37. VISCERAL SENSORY TRACT

38. 38
 Pain and stretch receptors in viscera situated in
the thorax and abdomen send information to the
cell bodies of the 1st
order neuron in the
posterior root ganglion.
 Cells of the 2nd
order neurons situated in the gray
column, the fibers then join the spinothalamic
tracts to the post central gyrus.

39. SUMMARY
CARRIED SENSATION TRACT
Pain and temperature pathways. Lateral spinothalamic tract
Light touch and pressure pathways.
Anterior spinothalamic tract
Discriminative Touch, Vibratory
Sense, and Conscious Muscle Joint
Sense. Fasciculus cuneatus and gracilis
Muscle joint sense pathways to the
cerebellum. Anterior and posterior spinocerebellar
tract
Some other ascending pathways.
Spinotectal, spinoreticular and spino-
olivary tracts
Visceral sensory tract.
-
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40. Thanks