Spinal Cord Ascending Tracts

1. Spinal CordAscending Tracts Dr. Sama-ul-Haque

2. Objectives • Describe lateral spinothalamic tract and pathways for pain and temperature from the limbs and trunk. • Describe ventral spinothalamic tract and pathways for simple touch from the limbs and trunk. • Describe gracile and cuneate tracts and pathways for conscious proprioception, touch, pressure and vibration from the limbs and trunk. • Describe dorsal and ventral spinocerebellar tracts and pathways for unconscious proprioception from the limbs and trunk.

3. Tracts • Bundles or fasciculi of Nerve fibers present in white matter is called a Tract. • The bundles of ascending fibers are called Ascending tracts. • Theyconnect brain to the spinal cord. • They are classified into: 1: Ascending (Sensory or Afferent) 2: Descending (Motor or Efferent)

4. Ascending Tracts of Spinal Cord • Ascending tracts conduct Afferent information. • Exteroceptive: Information which originates from outside the body (Pain, Temperature and Touch). • Proprioceptive: Information which originates from inside the body (Muscles and Joints). • Some information reaches to conscious level (cerebral cortex). • Some information reaches to subconscious centers (cerebellum).

5. Ascending Tracts of Spinal Cord • Ascending sensory pathways between the peripheral receptorsand the cerebral cortex, are organized in a three neuronal chain: • First-order Neuron: • (Cell body lies in the dorsal root ganglion). • Peripheral process: Sensory receptor ending • Central process: Enters in the spinal cord through its posterior root.

6. Ascending Tracts of Spinal Cord • First-order Neuron: • Terminate by synapses with the second neuron either in the spinal gray matterOR in the medulla oblongata of the brain stem.

7. Ascending Tracts of Spinal Cord • Second-order Neuron: • Has its cell bodies in thespinal cord OR medulla oblongata. • Axon of 2nd order neuron decussates & ascend to CNS (Thalamus) • Synapse with 3rd order neuron

8. Second Order Neuron

9. Ascending Tracts of Spinal Cord • Third-order Neuron: (Lies in the thalamus) • Gives rise to projection fiber that reach to sensory area of cerebral cortex

10. First-orderSecond-orderandThird-order Neurons

11. Ascending Tracts • Lateral Spinothalamic Tract • Anterior Spinothalamic Tract • Posterior Spinocerebellar Tract • Anterior Spinocerebellar Tract • Posterior White Column: • Fasciculus Gracilis • Fasciculus Cuneatus • Cuneocerebellar Tract • Spinotectal Tract • Spinoreticular Tract • Spino-olivary Tract

12. Ascending Tracts of Spinal Cord

13. Lateral Spinothalamic Tract(Pain and Temperature Pathways)

14. Lateral Spinothalamic Tract • Pain and thermal receptors lie in the skin. • Through Posterior root ganglion Axons enter spinal cord and divide into ascending and descending branches. • These branches with one or two segments form Posterolateral Tract of Lissauer. • 1st order neuron fibers terminate by synapsing with cells in the posterior gray column (Substantia Gelatinosa). • Axons of 2nd order neuron cross obliquely to the opposite side in the anterior gray and white commissures within one spinal segment of the cord.

15. Lateral Spinothalamic Tract • Axons ascend in the contralateral white column as Lateral Spinothalamic tract. • Reaching medulla oblongata it is accompanied by anterior spinothalamic tract and Spinotectal tract (Spinal Leminscus). • Many fibers of this tracts end by synapsing with the 3rd order neuron (VPN: Ventral Posterolateral Nucleus) of thalamus. • Pain and temperature sensations are appreciated here. • The axons of 3rd order neuron of VPN now pass through the posterior limb of internal capsule and the corona radiata to reach postcentral gyrus of the cerebral cortex(Conscious level).

16. Lateral Spinothalamic Tract(Pain and Temperature Pathway)

17. Anterior Spinothalamic TractLight (Crude) Touch and Pressure Pathways

18. Anterior Spinothalamic Tract • Through Posterior root ganglion Axons enter spinal cord and divide into ascending and descending branches. • These branches with one or two segments form Posterolateral Tract of Lissauer. • 1st order neuron fibers terminate by synapsing with cells in the posterior gray column (Substantia Gelatinosa). • Axons of 2nd order neuron cross obliquely to the opposite side in the anterior gray and white commissures within several spinal segment of the cord.

19. Anterior Spinothalamic Tract • Axons ascend in the opposite white column as Anterior Spinothalamic tract. • Reaching medulla oblongata it is accompanied by lateral spinothalamic tract and Spinotectal tract (Spinal Leminscus). • This tract terminate by synapsing with the 3rd order neuron (VPN: Ventral Posterolateral Nucleus) of thalamus. • Crude awareness of touch and pressure is appreciated here. • The axons of 3rd order neuron of VPN now pass through the posterior limb of internal capsule and the corona radiata to reach postcentral gyrus of the cerebral cortex(Conscious level).

20. Anterior Spinothalamic TractLight (Crude) Touch and Pressure Pathways

21. Posterior White ColumnFasciculus Gracilis and Fasciculus Cuneatus(Discriminative Touch, Vibratory sense and conscious muscle joint sense)

22. Posterior White ColumnFasciculus Gracilis and Fasciculus Cuneatus • Paciniancorpuscles, Messiner’s corpuscles, joint receptors, muscle spindles and Golgi tendon organs. • Through Posterior root ganglion Axons enter spinal cord and pass directly to the posterior white column of the same side. • Fibers divide into long ascending and short descending branches. • Descending fibers are involved in intersegmental reflexes. • Most of the Long ascending fibers travel upward in the Posterior white column asFasciculus Gracilis and Fasciculus Cuneatus.

23. Posterior White ColumnFasciculus Gracilis and Fasciculus Cuneatus • Fasciculus Gracilis is present throughout the length of spinal cord (fibers from sacral, lumbar, and lower six thoracic nerves. • Fasciculus Cuneatus is present laterally in the upper six thoracic and cervical segments. • Fibers from both the tracts ascends ipsilaterally. • 1st order neuron fibers terminate by synapsing with nuclei gracilis and cuneatus of the medulla oblongata.

24. Posterior White ColumnFasciculus Gracilis and Fasciculus Cuneatus • Axons of 2nd order neuron (Internal actuate fibers) cross the median plane, decussating with the corresponding fibers of opposite side (Sensory decussation). • Now the fibers ascends as Medial Leminscus. • The fibers terminate by synapsing on the 3rd order neuron in VPS (Ventral Posterolateral Nucleus) of thalamus. • The axons of 3rd order neuron now pass through the posterior limb of internal capsule and the corona radiata to reach postcentral gyrus of the cerebral cortex.

25. Posterior White ColumnFasciculus Gracilis and Fasciculus Cuneatus(Discriminative Touch, Vibratory sense and conscious muscle joint sense)

26. Posterior Spinocerebellar TractUnconsciousMuscle joint sense pathway

27. Posterior Spinocerebellar Tract • Through Posterior root ganglion Axons enter spinal cord. • 1st order neuron fibers terminate by synapsing with cells in the posterior gray column (Nucleus Dorsalis or Clarke’s Column). • Axons of 2nd order neuron enter Posterolateral part of white column on the same side. • Axons ascend as Posterior Spinocerebellar Tract.

28. Posterior Spinocerebellar Tract • Reaching medulla oblongata tract joins inferior cerebellar peduncle and terminates in the cerebellar cortex. • This tract receives muscle joint information from the muscle spindle, tendon organs and joint receptors of trunk and lower limb. • This information of tension of muscle tendons and movements of muscles and joints is used by cerebellum (For coordination of limb movements and maintenance of posture).

29. Posterior Spinocerebellar TractUnconscious Muscle joint sense pathway

30. Anterior Spinocerebellar TractUnconsciousMuscle joint sense pathway

31. Anterior Spinocerebellar Tract • Through Posterior root ganglion Axons enter spinal cord. • 1st order neuron fibers terminate by synapsing with cells in the posterior gray column (Nucleus Dorsalis or Clarke’s Column). • Majority of Axons of 2nd order neuron cross to the opposite side. Axons ascend as Anterior Spinocerebellar Tract in the contralateral white column.

32. Anterior Spinocerebellar Tract • Minority of Axons ascend as Anterior Spinocerebellar Tract in the same side lateral white column. • Reaching medulla oblongata the fibers enter cerebellum through the superior cerebellar peduncle and terminates in the cerebellar cortex. • It is believed the fibers crossed to the opposite side cross back with in the cerebellum. • This tract conveys muscle joint information from the muscle spindle, tendon organs and joint receptors of trunk and lower limb.

33. Anterior Spinocerebellar TractUnconscious Muscle joint sense pathway

36. Spinotectal Tract • Through Posterior root ganglion Axons enter spinal cord. • 1st order neuron fibers terminate by synapsing with unknown cells in the posterior gray column. • Axons of 2nd order neuron cross the median plane. • Axons ascend as Spinotectal tract in the anterolateral white column. • They terminate by synapsing in the superior Colliculus of the midbrain. • Provides afferent information for spinovisual reflexes.

37. Spinotectal Tract

38. Spinoreticular Tract • Through Posterior root ganglion Axons enter spinal cord. • 1st order neuron fibers terminate by synapsing with unknown cells in the posterior gray column. • Most fiber remain uncrossed. • Axons ascend as Spinoreticular tract in the lateral white column. • They terminate by synapsing with the neurons of reticular formation in the medulla, pons and midbrain. • Have a role in influencing levels the consciousness.

39. Spinoreticular Tract

40. Spino-olivary Tract • Through Posterior root ganglion Axons enter spinal cord. • 1st order neuron fibers terminate by synapsing with unknown cells in the posterior gray column. • Axons of 2nd order neuron cross the midline. • Axons ascend as Spino-olivary tract in the white matter. • They terminate by synapsing in the inferior olivary nuclei in the medulla. • Coveys information to cerebellum for cutaneous and proprioceptive organs.

41. Spino-olivary Tract

42. Thank you