1. Long Sensory Pathways (Somatic Sensation) David A. Morton, Ph.D. Thursday January 31 st, 2013 - Anterolateral System (Pain and Temperature Pathway) - DCML (Vibration and Proprioception)

2. Objectives Somatic (general) sensation ALS and DCML pathways Identify pathways on sections

3. Somatic Sensation Pathway Overview How many neurons are involved in somatic sensation?

4. Somatic Sensation Pathway Overview What structures are involved in these pathways?

5. Somatic Sensation Pathway Overview Will decussation occur? If so, where?

6. Somatic Sensation Pathway Overview Describe the neurons involved:

7. Somatic Sensation General sensation.

8. Somatic Sensation General sensation. Crude (non-discriminative) touch. Cannot localize sensation. Temperature Pain Proprioception Vibration Fine (discriminative) touch. Can localize sensation. Anterior lateral system (ALS) Dorsal column-Medial Lemniscus (DCML) Receptor distribution is NOT uniform over the body surface; receptor density varies, as does receptive field size. Results in distorted cortical maps representing different parts of the body.

9. Anterior Lateral System (ALS) General sensation. Crude (non-discriminative) touch. Cannot localize sensation. Temperature Pain

10. 1° Order neuron Location of cell body. Location of synapse. Collaterals. Reflex connections. Anterior Lateral System (ALS)

11. 1° Order neuron Location of cell body. Location of synapse. Collaterals. Reflex connections. Anterior Lateral System (ALS)

12. 2° Order neuron Location of cell body. Decussation. Course of axons. Location of synapse. Anterior Lateral System (ALS)

13. 2° Order neuron Location of cell body. Decussation. Course of axons. Location of synapse. Anterior Lateral System (ALS)

14. VPL Internal capsule Post-central gyrus Thalamus 3° Order neuron Location of cell body. Course of axons. Location of synapse. Anterior Lateral System (ALS)

15. Primary Somatosensory Cortex Brodmann’s areas. Somatotopic organization. Homunculus. Contrast cortex area for hand to elbow.

16. A vascular lesion of which cerebral artery would result in loss of somatic sensation from the hand? From the foot? * * Medial view Lateral view Anterior view

18. Ascending visceral afferent input travels in the anterolateral system (dashed) and through multisynaptic circuits via the reticular formation of the brain stem (spino-reticulo-thalamic pathway) (solid). These fibers influence both specific and diverse areas of the cerebral cortex. Thalamic relays include intralaminar and midline nuclei and cortical areas include orbitofrontal cortex, insula and anterior cingulate gyrus.

19. Explain the sensory loss with a pathological enlargement of the central canal at the level of C 5,6,7. Why might there be atrophy of the hand muscles?

20. Define a dermatome and explain why they are useful. Know the dermatomes represented at the level of the back of the head, shoulder, thumb, middle finger, small finger, nipple, umbilicus, inguinal ligament, big toe, small toe and anus.

21. Somatic Sensation Part II: DCML

22. Proprioception, vibration, fine touch Dorsal column 1° Order neuron Location of cell body. Location of synapse. Dorsal Column-Medial Lemniscus (DCML)

23. Gracile tract Cuneate tract 1° Order neuron Location of cell body. Location of synapse. Dorsal Column-Medial Lemniscus (DCML)

24. 2° Order neuron Location of cell body. Location of synapse. Dorsal Column-Medial Lemniscus (DCML)

25. Medulla oblongata (caudal) ALS Medial lemniscus Gracile nucleus Cuneate nucleus 2° Order neuron Location of cell body. Location of synapse. Dorsal Column-Medial Lemniscus (DCML) Sensory dissociation

26. The somatotopic organization of the Medial Lemniscus (ML): "Feet down" in medulla. "Feet lateral" in pons. "Feet up" in midbrain Dorsal Column-Medial Lemniscus (DCML)

27. 3° Order neuron Location of cell body. Course of axons. Location of synapse. Dorsal Column-Medial Lemniscus (DCML)

28. Trace. Dorsal Column-Medial Lemniscus (DCML)

29. Locate the ALS and DCML on the following sections:

30. ALS Spinal Cord DCML

31. Olivary nucleus Pyramid 4 th ventricle XII X IX, X ALS Med lem Medulla

32. ALS Med lem V CN V Pons What happened in the Pons?

33. Cerebral peduncle AQ III Red nucleus Substantia nigra ALS ML Midbrain

34. Diencephalon Midbrain IC Cereb ped RN Mamillary bodies 3 rd ventricle

36. The yellow represents area of a lesion. What sensory loss would you expect? R L

37. R L Below the lesion: Loss of pain and temp from left side Loss of proprioception/vibration from right side

38. The right side of the pons is lesioned. What sensory loss would you expect?