Chapter 2: Spinal Cord

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dmshaw9
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297792
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Chapter 2: Spinal Cord
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2015-03-06 23:13:24
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Spinal Cord
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NPTE: Chapter 2
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  1. Spinal Cord: General Structure
    • Cylindrical has of nerve tissue
    • Extends from foramen magnum in skull continuous with medulla to lower border of 1st lumbar vertebra in conus medullaris
    • Divided into 30 segments → 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and a few coccygeal
  2. Central Gray Matter
    • 2 anterior (ventral) and 2 posterior (dorsal) horns
    • United by gray commissure with central canal
    • 2 enlargements (cervical and lumbosacral) for origins of nerves of upper and lower extremities
  3. Central Gray Matter: Anterior Horns
    • Contain cell bodies that give rise to efferent (motor) neurons 
    • Alpha motor neurons to affect muscles
    • Gamma motor neurons to affect muscle spindles
  4. Central Gray Matter: Posterior Horn
    Contain afferent (sensory) neurons with cell bodies located in dorsal root ganglia
  5. Central Gray Matter: Lateral Horn
    • Found in thoracic and upper lumbar segments
    • For preganglionic fibers of ANS
  6. White Matter
    • Anterior (ventral), lateral, and posterior (dorsal) white columns or funiculi
    • Ascending fiber systems
    • Descending fiber systems
  7. Anterior Fiber Systems (Sensory Pathways)
    • DCML
    • Spinothalamic
    • Spinocerebellar
    • Spinoreticular
  8. Dorsal Columns/Medial Lemniscal System
    • Proprioception
    • Vibration
    • Tactile discrimination

    Divided into fascicles cuneatus (UE tracts, laterally located) and fasciculus gracilis (LE tracts, medially located)

    Neurons ascend to medulla → fibers cross (lemniscal decussation) → form medial lemniscus → ascend to thalamus → somatosensory cortex
  9. Spinothalamic Tracts
    • Lateral: pain and temperature 
    • Anterior: crude touch

    Tracts ascend 1-2 ipsilateral SC segments (Lissauer's tract) → synapse and cross in SC → ascend in ventrolateral spinothalamic system
  10. Spinocerebellar Tracts
    • Proprioception from muscle spindles and GTO's (unconscious proprioception)
    • Touch and pressure receptors to cerebellam for control of voluntary movements

    • Dorsal: ascends to ipsilateral inferior cerebellar peduncle
    • Ventrospinocerebellar: ascends to contralateral and ipsilateral superior cerebellar peduncle
  11. Spinoreticular Tracts
    • Deep and chronic pain
    • To reticular formation of brainstem via diffuse, polysynaptic pathways
  12. Descending Fiber Systems (Motor Pathways)
    • Corticospinal 
    • Vestibulospinal 
    • Rubrospinal 
    • Reticulospinal 
    • Tectospinal
  13. Corticospinal Tracts
    Arise from primary motor cortex → descend in brainstem → cross in medulla (pyramidal decussation) → via lateral corticospinal tract to ventral gray matter (anterior horn cells)

    10% of fibers do not cross and travel in anterior corticospinal tract to cervical and upper thoracic segments 

    Important for voluntary motor control
  14. Vestibulospinal Tracts
    Arise from vestibular nucleus → descend to SC in lateral (uncrossed) and medial (crossed and uncrossed) vestibulospinal tracts

    Control of muscle tone, antigravity muscles and postural reflexes
  15. Rubrospinal Tracts
    Arise in contralateral red nucleus → descend in lateral white columns to spinal gray

    Assist in motor function
  16. Reticulospinal System
    Arises in reticular formation of brainstem → descends (crossed and uncrossed) in ventral and lateral columns → terminates both on dorsal gray and ventral gray

    • Dorsal gray: modifies transmission of sensation (especially pain)
    • Ventral gray: influences gamma motor neurons and spinal reflexes
  17. Tectospinal Tract
    Arises from superior colliculus (midbrain) → descends to ventral gray

    Head turning responses to visual stimuli
  18. Autonomic Nervous System (ANS): Function
    • Innervation of involuntary structures: smooth muscle, heart, glands
    • Helps maintain homeostasis (constant internal body environment)
  19. ANS Divisions
    • Sympathetic
    • Parasympathetic

    • Both have afferent and efferent nerve fibers
    • Preganglionic and postganglionic fibers
  20. Sympathetic Nervous System
    • Thoracolumbar division, T1-L2
    • Prepares the body for fight of flight, emergency responses
    • Increases HR and BP
    • Constricts peripheral blood vessels 
    • Redistributes blood
    • Inhibits peristalsis
  21. Parasympathetic Nervous System
    • Craniosacral Division, CN III, VI, IX, X, pelvic nerves 
    • Conserves and restores homeostasis
    • Slows heart rate and reduces BP
    • Increases peristalsis and glandular activity
  22. Autonomic Plexuses
    • Cardiac
    • Pulmonary
    • Celiac (Solar)
    • Hypogastric
    • Pelvic
  23. The ANS is modulated by brain centers
    Descending autonomic system: arises from control centers in hypothalamus and lower brainstem (cardiac, respiratory, vasomotor) and projects to preganglionic ANS segments in thoracolumbar (sympathetic) and craniosacral (parasympathetic) segments

    Cranial nerves: visceral afferent sensations via glossopharyngeal and vagus nerves; efferent outflow via oculomotor, facial, glossopharyngeal, and vagus nerves

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