1. Lecture VIII. The Spinal Cord, Reflexes and Brain Pathways Bio 3411 Monday September 27, 2010

2. Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 2 Readings NEUROSCIENCE 4 th ed: Review Chapter 1 pp. 11-22; Read Chapter 9 pp. 207-212, 218 Study Box 9A, Figure 9.8 & Refer to Table 9.1; Read Chapter 16 pp. 399–414 Study figures 16.2,16.3,16.4, 16.14 Read Chapter 17 pp. 432–436 Study figure 17.9 THE BRAIN ATLAS 3 rd ed: Read pp. 4-17 on class web site Look at pp 36, 43, 49, 75-76, 140, 151, 154, 170-171, 182-183, 200- 201.

3. What the last Lecture was about September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 3 The Initiation of the Central Nervous System CNS Growth and Pattern Development Bug Brains Several Mechanisms for Directing the Show (scripts conserved) How did vertebrate and invertebrate patterns arise? Reprise and overview the discussions of developmental sequences and mechanisms in the nervous system

4. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 4 Overview for this Lecture Spinal Cord Columns, Horns, Spinal Segments Spinal Nerves Dermatomes, Motor Units Reflexes “Knee Jerk”- Myotatic or Stretch Reflex Withdrawal & Crossed Extensor Reflexes Two Spinal Pathways Sensory - Dorsal Column/ Medial lemniscus Motor - Cortico-spinal Tract

5. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 5 Segments of spinal cord, spinal nerves and vertebrae Cervical (C) - Neck Thoracic (T) - Chest Lumbar (L) - Back Sacral (S) - Pelvis (The Brain Atlas 3 rd ed, p. 8)

6. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 6 Human spinal cord from side, front and back ≈ 50 cm

7. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 7 Internal Structure Canal = tube White Matter - columns, tracts anterior up and down to and from brain lateral down from brain (>>up) posterior mainly up to brain Gray Matter - posterior (dorsal) horn “sensory”, anterior (ventral) horn “motor”

8. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 8 Section of human spinal cord (C8) myelin stain Back (posterior/dorsal) Front (anterior/ventral) Anterior Horn (gray matter) Posterior Horn (gray matter) Posterior Column (white matter) Anterior Column (white matter) Lateral Column (white matter)

9. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 9 Section of human spinal cord (C8) cell body stain Anterior Horn Posterior Horn Posterior Column Anterior Column Lateral Column Back (posterior/dorsal) Front (anterior/ventral)

10. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 10 Sacral Cord (The Brain Atlas 3 rd ed, p.154) Cervical Cord (The Brain Atlas 3 rd ed, p.151) The size of white matter tracts (posterior, lateral and anterior columns) increases as more axons are added on the way TO the brain and decreases as axons end on the way FROM the the brain.

11. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 11 Spinal Nerves Intervertebral foramen Segmental spinal nerve Compound action potential

12. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 12 The Brain Atlas 3 rd ed, p. 49. Spinal canal Intervertebral foramen Left - Vertebral bones. Right - Human spinal cord in cross–section showing anterior (ventral) and posterior (dorsal) spinal roots and spinal or posterior (dorsal) root ganglion (posterior to right).

13. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 13 Mixed spinal nerve Periphery (skin, muscle, etc.) Segmental nerve: (posterior (dorsal) root = sensory - touch; anterior (ventral) root = motor -movement; spinal or posterior (dorsal) root ganglion = sensory nerve cell bodies) Spinal cord back = posterior front = anterior

14. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 14 Joseph Erlanger 1874 - 1965 (Prix Nobel 1944) Herbert Spencer Gasser 1888 - 1965 (Prix Nobel 1944) George H. Bishop 1889 - 1973

15. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 15 Periphery (skin, muscle, etc.) Spinal cord front = anterior back = posterior Mixed spinal nerve Stimulate (Shock) Record

16. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 16 Compound action potential Erlanger, Gasser (Bishop) Conduction Velocity m/s Discriminative Touch Fast pain & Temperature (cold) Slow pain & Temperature (warm)

17. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 17 Cross section of human muscle (motor) nerve – myelin stain Cross section of human sensory nerve – myelin stain Axon diameters differ in motor and sensory nerves

18. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 18

19. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 19 Segmental Nerves Spinal or Posterior (dorsal) Root, Ganglion Cells & Sensory Nerves (axons in from posterior (dorsal) root ganglia) Dermatomes Anterior (ventral) Root & Motor Nerves (axons out from motor neurons) Motor Units

20. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 20 Spinal or Posterior (dorsal) Root Ganglion Cells Pseudo-Unipolar Neurons (neurons start as bipolar cells and become “unipolar” during development) Single sensory endings light & crude touch, pain, temperature and muscle senses Axons diverge to multiple spinal targets motor neurons - c, interneurons - c, spinal cord - b, and brain -a

21. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 21 Periphery (skin, muscle, etc.) Segmental nerve (posterior (dorsal) root = sensory - touch; ventral root = motor -movement; spinal or posterior (dorsal) root ganglion = sensory nerve cell bodies) Spinal cord back = dorsal front = ventral Mixed spinal nerve

22. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 22 Dermatome = The region (slice) of skin innervated by a single spinal or posterior (dorsal) root ganglion

23. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 23 Motor Units, Motor Neuron Pools & Somatotopy

24. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 24 Spinal Motor Neurons Multipolar Output Diverges to - several or many muscle cells: motor unit Input Converges from – spinal or posterior (dorsal) root ganglion cells spinal interneurons long tracts from from brain Integrate Map flexors, extensors, proximal, distal

25. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 25 Section of human spinal cord (C8) myelin stain – anterior horn Section of human spinal cord (C8) cell body stain – anterior horn

26. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 26 Motor Unit - A motor neuron and the muscle fibers it innervates.

27. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 27 Motor neuron pools (nuclei) are organized systematically according to the body plan - somatotopically Motor Neurons to Proximal (nearer) Flexor muscles Motor Neurons to Proximal (nearer) Extensor muscles Motor Neurons to Distal (farther) Extensor muscles Motor Neurons to Distal (farther) Flexor muscles “Quads” Proximal (nearer) Extensor muscles “Shin” Distal (farther) Extensor muscles “Hamstrings” Proximal (nearer) Flexor muscles “Calf” Distal (farther) Flexor muscles

28. Demonstration

29. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 29 “Knee Jerk” Stretch Reflex & Antagonist Inhibition

30. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 30 When the knee is struck… Ia muscle afferents fire… there is monosynaptic activation of the extensor  -motor neuron… and the (agonist) muscle(s) contracts.

31. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 31 …which inhibit motor neurons to the flexor (antagonist) muscle. When the knee is struck… Ia muscle afferents fire… there is monosynaptic activation of the extensor  -motor neuron… and the (agonist) muscle(s) contracts. The knee extends. Glycinergic (inhibitory) interneurons are also activated…

32. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 32 “Stepping on a Nail” Withdrawal & Crossed Extensor Reflexes

33. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 33 that excite flexors and inhibit extensors… Stepping on a sharp object activates pain afferents in the skin… activating interneurons in the dorsal horn…

34. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 34 and the leg flexes “withdraws.” that excite flexors and inhibit extensors… Stepping on a sharp object activates pain afferents in the skin… activating interneurons in the dorsal horn…

35. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 35 and the crossed flexors weren’t inhibited to extend the other (contralateral) leg to stand on. if the crossed extensors weren’t activated… But the person would fall…

36. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 36 Pathways Subserve a particular function Axons travel together in specific locations (i.e., tracts) in a particular order (topography) Always consider: cell body (soma) location, axon course, synapses and side relative to origin and destination Nomenclature often origin and target, i.e., Cortico- Spinal Tract = from cortex to spinal cord

37. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 37 Path Finding Loss of a particular function after damage (lesion) Stimulation (natural/electrical) with recording Pathology - degeneration of cells and axons with secondary loss of myelin Experiments - special stains and tracers that take advantage of physiological processes

38. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 38 Pathway Conventions Related to whole brain through “sections” – gross, histological, imaging Related to fiber bundles (fasciculi; i.e., lateral columns, internal capsule, corpus callosum) Related to nuclei, ganglia, areas, layers Related to transmitters and effects: excitatory, inhibitory, modulatory; fast, slower, slow

39. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 39 THE BRAIN ATLAS 3 nd ed, pp. 5, 7

40. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 40 Midline Knee Jerk 1 Antagonist Inhibition 2 Intraspinal “Pathways” 11 Pathways - “Primitive” ––––> “Evolved’ (Synapse & Synapse Number) 2

41. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 41 BrainstemCerebellum THE BRAIN ATLAS 3 nd ed, p. 8

42. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 42 THE BRAIN ATLAS 3 nd ed, p. 151

43. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 43 THE BRAIN ATLAS 3 nd ed, p. 140

44. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 44 THE BRAIN ATLAS 3 nd ed, p. 75-76

45. Dorsal Column/Medial Lemniscus (a ribbon) Pathway This pathway carries fine discriminative and active touch, body and joint position, and vibration sense.

46. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 46 THE BRAIN ATLAS 3 nd ed, p. 185 Foot Hand Face Body

47. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 47 Midline Knee Jerk 1 Antagonist Inhibition 2 Dosal Column/ Medial Lemniscus Pathway 2 Intraspinal “Pathways” Ascending Sensory Pathway 11 1 2 2 Pathways - “Primitive” ––––> “Evolved” (Synapse & Synapse Number)

48. Corticospinal (Pyramidal) Pathway This is the direct connection from the cerebral cortex for control of fine movements in the face and distal extremities, e.g., buttoning a jacket or playing at trumpet.

49. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 49 THE BRAIN ATLAS 3 nd ed, pp. 36, 43 Corticospinal Tract (Pyramid) at Medulla

50. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 50 THE BRAIN ATLAS 3 nd ed, p. 201 FootHandFaceAll

51. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 51 THE BRAIN ATLAS 3 nd ed, p. 201

52. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 52 Midline Knee Jerk 1 Antagonist Inhibition 2 Dosal Column/ Medial Lemniscus Pathway 2 Corticospinal Pathway 1 Intraspinal “Pathways” Ascending Sensory Pathway Descending Motor Pathway 11 1 1 2 2 Pathways - “Primitive” ––––> “Evolved’ (Synapse & Synapse Number)

53. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 53 The left hemisphere of the monkey brain - Motor (Ms) and Somatosens ory (Sm) maps

54. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 54 What this lecture was about: Spinal Cord - Segmental organization Peripheral Nerves - Compound action potential (Erlanger & Gasser Prix Nobel 1944) Spinal Nerves - Dermatomes, motor neuron pools (nuclei) and motor units Spinal reflexes - stretch (knee jerk); withdrawal/ crossed extensor Introduction to Pathways - 1 sensory (DC-ML); 1 motor (CST)

55. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 55 For Review Use the Bio 3411 Work Sheet 082809 (handout and posted on the course web site) to get comfortable with the neuroanatomy. It’s neither rocket science nor is it neurosurgery, it just takes a little practice!

56. September 27, 2010Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 56 The New Yorker, 7/10-17/2006, p. 110