A. Skeletal Anatomy [1]

1. Four Divisions of Vertebrae
   1. Cervical (C1-7)
   2. Thoracic (T1-12)
   3. Lumbar (L1-5)
   4. Sacral (S1-5 including fused)
2. Anterior Column
   1. Anterior longitudinal ligament
   2. Anterior portion of the verbegbral body
   3. Anterior portion of the intervertebral disc
3. Middle Column
   1. Posterior longitudinal ligament
   2. Posterior body
   3. Posterior intervertebral disc
4. Posterior Column
   1. Ligamentum flavum
   2. Posterior elements which include:
   3. Facet joints, pedicles, transverse processes, laminae, spinous processes
5. Intervertebral Disc
   1. Outer annulus fibrosus: lamelliform (layered) connective tissue bands
   2. Inner nucleus pulposus: mucinous colloidal gel (proteoglycan/collagen), 75% water content
   3. Absorbs shock, provides resistance to compression, allows flexibility

B. Types of Nerve Fibers

1. Type A
   1. Alpha - motor, proprioception (6-14µm axon diameter)
   2. Beta - touch
   3. Gamma - muscle tone
   4. Delta - Pain, temperature, touch
2. Type B - autonomic
3. Type C - pain (0.5-1.5µm axon diameter)

C. Corticospinal Tract (CST)
[Figure] "Schematic of Upper Spinal Cord"

1. Most important decending (motor) tract
2. Originates from pyramidal cells in contralateral cerebral cortex (motor area)
3. Motor Area (Precentral) Axons ±> hemispheric white matter ±>
4. Internal Capsule ±>
5. Cerebral Peduncles (midbrain basis pedunculi) ±>
6. Pontine Corticospinal Tracts ±>
7. Medullary Pyramids ±> 8. Decussation of the Pyramids (Junction of Medulla and Cervical Cord) ±>
8. Corticospinal Tracts (Lateral Spinal Cord)
9. Lesions in CST produce Upper Motor Neuron (UMN) Syndromes
10. Need to injure motor nuclei or motor axons from anterior horn cells to get LMN syndromes
11. Pure pyramidal tract lesions also possible, though very rare

D. Upper Motor Neuron Syndrome

1. Weakness
2. Muscle bulk is preserved until very late in course
3. Increased Muscle Tone
4. Increased reflexes; may see clonus
5. Babinski Sign
   1. Noxious stimulus applied to lateral plantar surface of foot (around big toe)
   2. Extension (dorsiflexion, upgoing) of big toe (and usually others) is abnormal
   3. This test is rarely upgoing (abnormal) in normal persons due to "tickling" reflex
6. Hoffman Sign
   1. Use similar to Babinski Sign
   2. Running smooth object down along anterior fibia (shin bone) can elicit toe response
   3. Upgoing toe is an abnormal response, likely upper motor neuron lesion

E. Lower Motor Neuron Syndrome

1. Weakness
2. Muscle Atrophy - severe reduction in bulk early in course
3. Reduced muscle tone
4. Decreased reflexes
5. Fasciculations and Fibrillations
6. Lack of clonus
7. Normal plantarflexion (flexor) of toes (downgoing)

F. Pyramidal Tract Lesion

1. Pyramidal Weakness
   1. Very characteristic findings
   2. Strength of anti-gravity muscles (eg. biceps, quadriceps) is largely (~80%) preserved
   3. Non-anti-gravity muscles (eg. triceps, arm extensors, hamstrings) severely affected
   4. Hemiparetic posture: tonic spastic flexion of the arm and spastic extension of legs
   5. Loss of independent finger control and other fine motor movements
2. Increased reflexes and muscle tone
3. Babinski or Hoffman Sign: upgoing toes present (hyperactive deep reflexes)

G. Lateral Spinothalamic Tract (LST)

1. One of the two important ascending (sensory) tracts
2. Pain and temperature information from spinal cord to thalamus
3. Sensory nerve fibers originate from cell bodies in dorsal root ganlion (DRG)
4. Central processes of the DRG neuron enter spinal cord via the dorsal root/horn
5. Synapse with 2nd order neuron in dorsal horn
6. Second order Axons
   1. Traverse Anterior White Commissure while ascending 1-3 vertebral segments
   2. Thus, axons arisig from second order neurons usually ascend several segements before crossing to the other side
7. Fibers in LST are leg lateral and arm medial
8. Lesions in spinal cord cause loss of pain and temperature sensation contralaterally below the lesion
9. Lesions in Anterior Commissure will destroy pain and temperature sensation bilaterally 1-3 segments below the lesion

[Figure]: "Schematic of Dorsal Root Ganglion"

H. Dorsal Columns

1. Fibers in these columns are from 1st order neurons (DRG cell bodies)
2. Mediate proprioception (joint position) and vibration
3. Fibers enter through dorsal root/horn and do not synapse until the medulla.
4. The fibers travel up as leg medial (Fasciculus gracilis) and arm lateral (F. cuneatus)
5. The fibers synapse in the N. Gracilis or N. Cuneatus in the dorsal medulla
6. 2nd order fibers cross (decussate) as part of the contralateral Medial Lemniscus ±>
7. Ascent to Ventral Posterolateral Thalamus.
8. Damage to columns destroys ipsilateral proprioception, joint inputs
9. Damaged
   1. Extramedulary: Dorsal midline posterior compression - eg. Meningioma
   2. Tubulomedulary - demyelination, AIDS, B12 deficiency, Tabes Dorsalis (Syphilis), ataxias, vasculitis or infarction

I. Spinocerebellar Tracts

1. Dorsal and Ventral Tracts located in lateral areas of spinal cord
2. Convey information on joints, tendons, muscles, and muscle spindles
3. First order neuron lies in DRG ±> synapse on Dorsal Horn 2nd neuron ±>
4. 2nd neuron fibers up tracts (ipsilateral) ±> Cerebellar Peduncles
5. Ventral Tract (partially crossed) ±> Superior Cerebellar Peduncle
6. Dorsal Tract (uncrossed) ±> Inferior Cerebellar Peduncle

J. Ventral Horn

1. Motor Neurons and Associated Interneurons
2. Lesions give Lower Motor neuron syndrome

K. Intermediate (Lateral) Horn

1. Cells of Preganglionic Sympathetics levels T1 through L2
2. Lesions in this region cause ipsilateral loss of sweating and cause vasodilation
3. T1 Lesion will cause Horner Syndrome [2]:
   1. Ptosis - lid droop
   2. Miosis - pupillary constriction
   3. Anhidrosis - absence of sweating

L. Spinal Cord Dysfunction

1. Grouped into those affecting a portion of the width versus entire width of cord
2. Partial Cord Dysfunction Syndromes
   1. Brown-Sequard Syndrome
   2. Central Cord Syndrome
3. Brown-Sequard Syndrome
   1. Lesions cause loss of function on one side of spinal cord
   2. Contralateral pain and temperature loss with ipsilateral paralysis
   3. Tactile sensitibility remains intact in regions of pain and temperature sensory loss
   4. Called dissociated sensory loss
   5. Posterolateral (Lissauer's) axons, which give rise to spinothalamic tract, are affected
   6. Thus, spinal cord lesion is several segments above the level where sensory loss occurs
4. Central Cord Syndrome
   1. May arise from acute trauma, tumors, syringomyelia
   2. Anterior horn cell dysfunction at spinal level leads to loss of motor function
   3. Motor function loss occurs in a lower motor neuron pattern
   4. Generally affects local areas, with variable effects outside of local area
   5. Thus, cervical central lesion can affect hands but not legs
   6. Spinothalamic tracts cross midline within core of spinal cord, so these are affected
   7. Sensory effects are dissociated (as above)
5. Radicular (Nerve Root) Disease
   1. Nerve roots pass through thecal sac to neural foramina
   2. Narrowing of the neural foramina can lead to root dysfunction
   3. Bone spurs, disk prolapse or herniation are the most common causes of radiculopathy
   4. Cervical C5, C6, and C7, lumbar L4 and L5, and sacral S1 are most commonly affected
6. Spina Bifida
   1. Congenital anomaly of the spinal cord
   2. Refers to nonfusion of the embryonic halves of the vertebral arches
   3. Occurs during the fourth week of fetal development
   4. Considered a "dysraphic" disease
   5. Sometimes allows the brain or spinal cord to herniate through the opening

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References

1. Arce D, Sass P, Abul-Khoudoud H. 2001. Am Fam Phys. 64(4):631
2. Miller NR and Newman NJ. 2004. Lancet. 364(9450):2045