1. The Spinal Cord
Basic Neuroscience
James H. Baños, Ph.D.

2. Grey and White Matter

3. Grey and White Matter Grey Matter = Cell Body
White Matter = Myelinated axon

4. Grey and White Matter Grey matter Cortex Nucleus (CNS)
Ganglion (PNS) Exception: Basal Ganglia

5. Grey and White Matter White Matter Nerve (PNS) Tract (CNS)
Fasciculus/Funiculus -- Group of fibers with common origin and destination
Lemniscus -- Ribbon-like fiber tract
Peduncle -- Massive group of fibers -- usually several tracts

6. Grey and White Matter
Tracts are named with origin first, then destination
Corticospinal tract -- cortex to spinal cord
Mammilothalamic tract -- Mammilary bodies to thalamus
Spinocerebellar tract -- Spinal cord to cerebellum
Corticobulbar tract -- Cortex to brain stem

7. The Spinal Cord

8. General Organization Spinal cord is SMALL!
42-45 cm long
1 CM wide at widest point
Does not extend all the way to the bottom of the spinal column
Pattern of grey/white matter is reversed in the cord
White matter tracts on outside
Grey matter on the inside
Staining reverses this!!!

9. General Organization White matter (tracts of axons) Grey Matter
(cell bodies)

10. General Organization Spinal cord is segmented anatomically
Input and output occurs in groups of rootlets arranged in a series longitudinally along the cord
Dorsal rootlets -- Input -- carry sensory information
Ventral rootlets -- Output -- motor neurons

11. General Organization
Each set of rootlets forms a spinal nerve that innervates a corresponding segment of the body, called a dermatome

12. General Organization

13. There are 31 segments in the spinal cord:
General Organization
There are 31 segments in the spinal cord:
8 cervical (C1 - C8)
12 Thoracic (T1 - T12)
5 Lumbar (L1 - L5)
5 Sacral (S1 - S5)
1 Coccygeal

14. General Organization
The spinal cord is housed within the vertebral column

15. General Organization
Each cord segment has a corresponding vertebra of the same name (e.g., C3)
Spinal nerves enter/exit underneath their corresponding vertebral segment

16. But wait! Something doesn’t add up!
General Organization
But wait! Something doesn’t add up!
How can spinal nerves exit below their corresponding vertebral segment if the cord is only 42cm-45cm long?
Answer: Spinal nerves extend down to the appropriate vertebral segment forming the cauda equina
This means cord segments and vertebral segments don’t line up

17. General Organization

18. General Organization
Cord is not of uniform thickness throughout its length. Why not?

19. Cord is not of uniform thickness throughout its length. Why not?
General Organization
Cord is not of uniform thickness throughout its length. Why not?
Answer:
Segments of the cord innervate parts of the body that differ in complexity
There are fewer white matter tracts lower in the cord.

20. General Organization Cervical enlargement C5 - T1 Lumbar enlargement
L2 - S3

21. The Spinal Cord in Cross Section

22. Cord Sections
Segments of the spinal cord have a similar organization, but vary in appearance.
Always know where you are in the cord (i.e., cervical, thoracic, lumbar, sacral)

23. Cord Sections -- Cervical
Cervical cord is wide, flat, almost oval in appearance. Why?

24. Cord Sections -- Cervical Enlargement
What’s different about the cervical enlargement . Why?
Cervical
Cervical Enlargement

25. Cord Section -- Thoracic
Less White matter than cervical
Rounder appearance
Less prominent ventral horns than cervical enlargement

26. Less White matter than thoracic Rounder appearance
Cord Section -- Lumbar
Less White matter than thoracic
Rounder appearance
Larger ventral horns, especially in lumbar enlargement
Lumbar
Lumbar Enlargement

27. Cord Section -- Sacral
Not much white matter
Mostly grey, although not much of that either

29. Cross Sectional Organization
Posterior intermediate sulcus
Posterior median sulcus
Tract of
Lissauer
Anterior white commissure
Anterior median fissure

30. Grey Matter
Laminar
Laminae of Rexed

31. Grey Matter Posterior (dorsal) Horn Intermediate Grey
Anterior (ventral) Horn

32. Grey Matter: Posterior Horn
Mostly Interneurons
Substantia gelatinosa
Pain/temp proc
Body of the posterior horn
Sensory proc

33. Grey Matter: Intermediate Grey
Clarke’s Column
T1-L3
Balance/proprio.
Intermediolateral Column
Sympathetic neurons

34. Grey Matter: Anterior Horn
Lower Motor Neurons

35. White Matter: The “Big Four” Pathways
Corticospinal tract
Dorsal Columns
Spinothalamic tract
Spinocerebellar tracts

36. The Big Four Corticospinal tract Dorsal columns/ medial lemniscus
Voluntary motor
Dorsal columns/ medial lemniscus
Discriminative touch
Conscious proprioception
Spinocerebellar tract (dorsal and ventral)
Unconscious proprioception
Spinothalamic tract
Pain/temperature

37. Corticospinal Tract
Voluntary Motor

38. Corticospinal Tract
First order neuron (upper motor neuron) originates in precentral gyrus
Passes through internal capsule
90% decussates in caudal medulla
Lateral corticospinal tract
10% undecussated
Anterior corticospinal tract
Synapses on second order neuron (lower motor neuron) in ventral gray of the cord
Second order neuron innervates muscle

39. Motor Homunculus
HAL

40. Motor Homonculus
HAL:
Arms
Legs
Head

41. Corticospinal Tract
Spinal Cord
Medulla
Pons
Midbrain

42. Corticospinal Tract
Spinal Cord
Medulla
Pons
Midbrain

43. Upper & Lower Motor Neurons
Upper Motor Neuron
Motor Cortex to Ventral Grey Horn
Modulatory influence on stretch reflex arc
Lower Motor Neuron
Ventral Grey Horn to Neuromuscular Junction
Efferent of stretch reflex arc
Helps maintain tone
Sensory Neuron
Stretch receptors in muscle and tendons
Afferent of basic stretch reflex arc
Motor Ctx
UMN
Ventral
Grey Horn
LMN

44. Upper & Lower Motor Neurons
Maintenance of Tone
Input from stretch receptors causes lower motor neuron to supply tonic stimulation to the muscle
The upper motor neuron modulates this -- will tend to “override” the tonic signal from the sensory neuron
UMN
LMN

45. Upper & Lower Motor Neurons
Reflex Arc
Afferent is sensory neuron detecting a sudden stretch
Signal is strong and results in a strong response by the lower motor neuron
Strong signal usually overcomes mild cortical input from the UMN
UMN
LMN

46. Upper & Lower Motor Neurons
Upper Motor Neuron Signs
Spastic paresis
Hypertonia
Hyperreflexia
No muscle atrophy (until perhaps late in the course)
Positive Babinski
Why?
Loss of voluntary UMN signal
Loss of modulation of tone and reflexes by UMN -- the circuit runs unchecked
Motor Ctx
UMN
Ventral
Grey Horn
LMN

47. Upper & Lower Motor Neurons
Lower Motor Neuron Signs
Flaccid paresis/paralysis
Muscle fasciculations
Hypotonia
Hyporeflexia
Muscle atrophy
Negative Babinski
Why?
Loss of LMN for voluntary movement
Loss of efferent component of reflex arc and tone pathway
Motor Ctx
UMN
Ventral
Grey Horn
LMN

48. Babinski’s Sign
In response to stimulation of the sole of the foot, the toes will usually curl downward.
When UMN inhibition is removed, the toes will curl upward (Dorsiflexion). This is referred to as a positive Babinski or presence of Babinski’s sign.

49. Related Terms…
Spasticity -- Increased muscle tone and increased reflex contraction (UMN)
Clonus -- Rythmic contractions and relaxations seen when a spastic muscle is stretched (UMN)

50. Basics of Localization
If all limbs are checked for upper and lower motor neuron signs, you can begin to localize lesions
Left-right differences are also very important

51. Dorsal Column/ Medial Lemniscus
Discriminative Touch
Conscious Proprioception

52. Dorsal Columns/Medial Lemniscus
First order neuron begins in receptor
Enters cord at tract of Lissauer
Legs run in fasciculus gracilis (medial dorsal)
Arms run in fasciculus cuneatus (lateral dorsal)
Synapse on nucleus gracilis and nucleus cuneatus (caudal medulla)
2nd order neuron decussates and runs from NG & NC to thalamus (as medial lemniscus)
3rd order neuron runs from thalamus to postcentral gyrus

53. Dorsal Columns/Medial Lemniscus
Spinal Cord
Medulla
Pons
Midbrain

54. Spinocerebellar Tracts
Unconscious Proprioception

55. Dorsal (Posterior) Spinocerebellar Tract
Involves Clark’s Column, a longitudinal gray matter body from about T1 to L3
Below Clark’s Column:
Runs with f. gracilis, synapses in Clark’s Column, joins dorsal spinocerebellar tract
Level of Clark’s Column
Synapses in Clark’s Column, joins dorsal spinocerebellar tract
Above Clark’s Column
Runs with f. cuneatus, synapses in lateral cuneate nucleus (caudal medulla), projects to ipsilateral cerebellum

56. Dorsal (Posterior) Spinocerebellar Tract
Spinal Cord
Medulla
Pons
Midbrain
To Cerebellum

57. Ventral (Anterior) Spinocerebellar Tract
Supplements Dorsal Spinocerebellar Tract
Information from more diverse array or receptors
Originates from scattered cells in the intermediate grey caudal to L1 (which in turn have input from proprioceptive axons or their collaterals
Crosses twice, to end up in ipsilateral cerebellum

58. Ventral (Anterior) Spinocerebellar Tract
Spinal Cord
Medulla
Pons
Midbrain

59. Spinothalamic Tract
Pain and Temperature

60. Spinothalamic Tract
First order neurons originate in pain receptors, enter cord at tract of Lissauer, and synapse in substantia gelatinosa or nucleus proprius
Second order neurons cross at the anterior white commissure, rising 1 or 2 cord levels in the process, and form contralateral spinothalamic tract
A third order neuron (not technically spinothalamic tract) projects to the cortex

61. Spinothalamic Tract

62. Spinothalamic Tract
Spinal Cord
Medulla
Pons
Midbrain

63. L1 L1 L2 L2 L3 L3 L4 L4 L5 L5

64. Coming Up…
Lab Week Overview
Virtual Lab
Wet Lab