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The Spinal Cord & Peripheral Nervous System

This lecture covers the anatomy of the spinal cord and peripheral nervous system, including the dorsal root ganglion, sensory input, ventral root, motor output, and important spinal cord tracts. It also discusses the cranial nerves and their functions.

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The Spinal Cord & Peripheral Nervous System

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  1. The Spinal Cord & PeripheralNervous System Lecture 4

  2. Spinal Cord • Dorsal root ganglion • sensory input • ventral root • motor output • Caudal spinal cord • Cauda equina ~

  3. Spinal Cord Tracts • Clinically important anatomy • Descending & ascending tracts • Motor 1. corticospinal tract • distal muscles • only descending tract with overt effects ~

  4. Spinal Cord Tracts • Sensory 2. Dorsal column-medial lemniscal tract • touch, vibration, & proprioception • axons ascend ipsilaterally • synapse then decussate at medulla 3. Spinothalamic tract (lateral) • pain & temperature • decussate at SC entry level • ascends contralaterally ~

  5. Spinal Cord Tracts 4. Spinocerebellar tract • position of body in space & relative position of limbs • affected in hereditary ataxias • no symptoms in other diseases ~

  6. Corticospinal trct Spinothalamic path Medulla Dorsal column-medial lemniscal path

  7. Dorsal Dorsal columns Corticospinal tract Ventral Spinal Cord Rubrospinal tract anterolateral columns

  8. Peripheral N. S. • Cranial Nerves - 12 pair • Spinal Nerves - 31 pair • Somatic Division • Sensory info • Body Movement • Autonomic division - Homeostasis • regulation ~

  9. Cranial Nerves • From ventral surface • numbered anterior ---> posterior • Sensory, motor, or mixed • Mnemonic ~

  10. I II III IV V VI VII VIII IX X XI XII Oh Oh Oh To Touch And Feel Very Green Vegetables A H Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulococlear Glossopharangeal Vagus Accessory Hypoglossal

  11. Spinal Nerves • 1 pair for each vertebral segment • 8 pr. cervical (C1-C8) • 12 pr. thoracic (T1-T12) • 5 pr. lumbar (L1-L5) • 5 pr. sacral (S1-S5) • 1 pr coccygeal ~

  12. Spinal Nerves • Thoracic nerves relatively small • back & ribs • Cervical, lumbar, & sacral: large nerves • rest of the body • All Interconnect • after leaving vertebral canal • form 4 major plexuses ~

  13. Somatic Nervous System • Sensory input • sensory receptors ---> • dorsal root ganglion (DRG) ---> • dorsal horns • Motor output • ventral horns ---> muscles ~

  14. Dorsal column-medial lemniscal pathway • Dorsal Columns • Submodalities • Touch • vibration • 2 point discrimination • proprioception ~

  15. Medial lemniscus Dorsal Column R Touch S1 Dorsal column-medial lemniscal pathway Thalamus - VP Medulla DRG R Spinal Cord

  16. Spinothalamic Tract • Anterolateral Columns • Sensory neuron • NT = Substance P • gray matter • 2d order neuron crosses midline • at spinal cord ~

  17. Pain S1 Thalamus - VPL & intralaminar Spinoreticular Tract Spinothalamic Tract Reticular Formation DRG R Spinal Cord

  18. Dermatomes • Sensory innervation • each spinal nerve has segmental field • (receptive field) • Overlap at distal branches • redundancy • retain some sensation even if a complete spinal nerve destroyed ~

  19. Somatic N.S.: Motor Output The Lateral Pathway • Voluntary movement • distal limbs • 2 tracts • Corticospinal tract • about 1 million axons • Rubrospinal tract • small part of pathway ~

  20. Motor N.S. • Striate muscle • uninterrupted neuron • * nerve-dependent • Excitatory only at neuroeffector synapse • Cholinergic - ACh • Nicotine = direct AG • Curare = direct ANT ~

  21. Somatic Motor N. S. Effector Motor Neuron ACh Spinal Cord

  22. Autonomic N. S. • Homeostasis • Effectors • Smooth Muscle • Cardiac Muscle • Glands ~

  23. Autonomic Subdivisions • Not nerve-dependent • Sympathetic • Emergency, flight/fight • Parasympathetic • Conservation / vegetative ~

  24. Preganglionic neuron Postganglionic neuron Ganglion Autonomic N. S.: General Features Effector

  25. Autonomic N. S.: General Features Effector ACh • Nicotinic • different than neuromuscular • antagonist: hexamethonium ~

  26. Autonomic N. S.: General Features Effector ACh • Neuroeffector junction • Different NT for each division ~

  27. Pharmacology of Autonomic NS • Preganglionic neuron • releases ACh • Different NT at effectors • sympathetic division: NE • parasympathetic division: ACh ~

  28. Sympatheticvs. Parasympathetic • Sympathetic • ganglia near spinal cord • interconnected ---> active together • long-lasting effects • Parasympathetic • ganglia near effector • discrete ---> active independently • transient effects • Antagonistic regulation ~

  29. Pre- Post- Smooth muscle Glands NE Adrenal Glands Parasympathetic Sympathetic ACh

  30. Sympathetic Arousal Syndrome • Fight or flight situations • Diffuse sympathetic activation • Adrenal glands • releases NE into blood • maintains sympathetic arousal • Parasympathetic rebound • Emotional experience • depends on set & setting ~

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