Spinal Cord & Spinal Nerves

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  1. 31 pairs of spinal nerves
    • Cervical - 8
    • Throacic - 12 
    • Lumbar - 5
    • Sacral - 5
    • Coccygeal - 1

    • All mixed in function
    • Emerge from intervertebral foramina
  2. Diameter of spinal cord
    • Varies
    • Generally narrows inferiorly
  3. Cervical Enlargement
    • Inferior cervical part of spinal cord 
    • Innervate upper limbs
  4. Lumbar Enlargement
    Extends through the lumbar and sacral parts of spinal cord and innervates the lower limbs
  5. Conus medullaris
    • Tapering inferior tip
    • Marks the official end of spinal cord proper
  6. Cuada Equina
    • Nerve roots from lumbar, sacral & Coccygeal region with vertebral cavity 
    • "Horses tail"
  7. Filum Terminale
    Thin strand of pia mater that helps anchor the conus medullaris to the coccyx
  8. Inner gray metter of spinal cord
    • Cell bodies, dendrites, unmyelinated axons
    • Horns & gray commissure
    • Synapses occur
  9. Outer white matter of spinal cord
    • Finiculi
    • White commissure
  10. Posterior root
    Sensory axons
  11. Posterior root ganglion
    • Cell bodies of sensory neurons 
    • attached to posterior root
  12. Anterior root
    Motor axons
  13. Posterior gray horns
    • Interneuron cell bodies
    • Sensory neuron axons
    • Synapses occur
  14. Anterior Gray Horns
    • Motor(Somatic) neuron cell bodies
    • Interneuron axons
    • Synapses Occur
  15. Lateral Gray Horns
    Lateral gray horns- Motor neuron cell bodies (ANS)Throacic & upper lumbar regions (t1-L2)
  16. Gray Commissure
    • Unmyelinated axons
    • Path between R&L sides of cord (Site of central canal)
  17. Cervical Plexus
    C1-C4: Neck, portions of head and shoulder
  18. Brachial Plexus
    C5-T1: Upper limbs
  19. Lumbar Plexus
    L1-L4: Anterior/medial thigh
  20. Sacral Plexus
    L4-S4: Most of lower limb & lower pelvis
  21. Posterior Ramus
    • Innervates deep muscle/skin of back 
    • Smallest of the 2 branches
  22. Anterior Ramus
    • Largest branch
    • Innervates limb muscles & structures, skin of anterior and lateral trunk 
    • May form spinal nerve plexus
  23. Rami Communicantes (ANS)
    • Between spinal nerve & sympathetic trunk ganglia 
    • Innervates glands, cardiac & smooth muscle
  24. Rami
    Spinal Nerves
  25. Dermatomes
    • Specific area of skin whose sensations are carried by a single spinal nerve 
    • Some overlap
    • Involved in referred visceral pain
    • Can be used diagnostically (indicate spinal damage or level or spinal cord injury)
  26. Nerve Plexus
    A network of interweaving anterior rami of spinal nerves 

    (posterior nerves are smaller and do not form plexus)
  27. Reflex arc
    • Shortest pathway; result in reflex
    • Fast automatic, involuntary response to a specific stimulus
  28. 5 Components of Reflex Arcs
    • Receptor - Excited by stimulus 
    • Sensory Neuron- Transmits to CNS
    • Interneuron- Integrates (in CNS)
    • Motor Neurons- Transmit to effector 
    • Effector- Performs reflexive action; muscle or gland
  29. Spinal Reflexes
    • Integration in spinal cord
    • Withdrawal 
    • Never reach the brain
  30. Cranial Reflexes
    • Integration in brainstem
    • Eye tracking movements during reading
  31. Somatic Reflexes
    Effects skeletal muscle
  32. Autonomic Reflexes
    Effects glands, cardiac & smooth muscle
  33. Ipsilateral vs Contralateral
    • Ipsilateral- When both receptor and effector are on the same side of spinal cord (pull hand from hot  object)
    • Contralateral- When sensory impuls from receptor cross over to activate effector on opposite limb
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Spinal Cord & Spinal Nerves
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