1. Copyright © 2010 Pearson Education, Inc. Spinal Cord Location Begins at foramen magnum Ends as conus medullaris at L 1 vertebra Functions Provides two-way communication Contains spinal reflex centers

2. Copyright © 2010 Pearson Education, Inc. Spinal Cord: Protection Bone, meninges, and CSF Denticulate ligaments: extensions of pia mater that secure cord to dura mater Filum terminale: fibrous extension from conus medullaris; anchors the spinal cord to the coccyx

3. Copyright © 2010 Pearson Education, Inc. Figure 12.30 Ligamentum flavum Supra- spinous ligament Lumbar puncture needle entering subarachnoid space Filum terminale Inter- vertebral disc T 12 L5L5 Cauda equina in subarachnoid space Dura mater L5L5 L4L4 S1S1 Arachnoid matter

4. Copyright © 2010 Pearson Education, Inc. Figure 12.29a Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum terminale Cervical spinal nerves Lumbar spinal nerves Sacral spinal nerves Thoracic spinal nerves (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.

5. Copyright © 2010 Pearson Education, Inc. Spinal Cord Spinal nerves 31 pairs Cervical and lumbar enlargements Nerves serving upper and lower limbs emerge here Cauda equina Collection of nerve roots at inferior end of vertebral canal

6. Copyright © 2010 Pearson Education, Inc. Cross-Sectional Anatomy Two lengthwise grooves divide cord into right and left halves Ventral (anterior) median fissure Dorsal (posterior) median sulcus Gray commissure—connects masses of gray matter; encloses central canal

7. Copyright © 2010 Pearson Education, Inc. Figure 12.31a (a) Cross section of spinal cord and vertebra Epidural space (contains fat) Pia mater Spinal meninges Arachnoid mater Dura mater Bone of vertebra Subdural space Subarachnoid space (contains CSF) Dorsal root ganglion Body of vertebra

8. Copyright © 2010 Pearson Education, Inc. Figure 12.31b (b) The spinal cord and its meningeal coverings Dorsal funiculus Dorsal median sulcus Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater Gray commissure Dorsal horn Gray matter Lateral horn Ventral horn Ventral funiculus Lateral funiculus White columns Dorsal root ganglion Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Spinal nerve

9. Copyright © 2010 Pearson Education, Inc. Gray Matter Dorsal horns—interneurons that receive somatic and visceral sensory input Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons Dorsal root (spinal) gangia—contain cell bodies of sensory neurons

10. Copyright © 2010 Pearson Education, Inc. Figure 12.32 Somatic sensory neuron Dorsal root (sensory) Dorsal root ganglion Visceral sensory neuron Somatic motor neuron Spinal nerve Ventral root (motor) Ventral horn (motor neurons) Dorsal horn (interneurons) Visceral motor neuron Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons

11. Copyright © 2010 Pearson Education, Inc. White Matter Consists mostly of ascending (sensory) and descending (motor) tracts Transverse tracts (commissural fibers) cross from one side to the other Tracts are located in three white columns (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior) Each spinal tract is composed of axons with similar functions

12. Copyright © 2010 Pearson Education, Inc. Pathway Generalizations Pathways decussate (cross over) Most consist of two or three neurons (a relay) Most exhibit somatotopy (precise spatial relationships) Pathways are paired symmetrically (one on each side of the spinal cord or brain)

13. Copyright © 2010 Pearson Education, Inc. Figure 12.33 Ascending tractsDescending tracts Fasciculus gracilis Dorsal white column Fasciculus cuneatus Dorsal spinocerebellar tract Lateral spinothalamic tract Ventral spinothalamic tract Ventral white commissure Lateral corticospinal tract Lateral reticulospinal tract Ventral corticospinal tract Medial reticulospinal tract Rubrospinal tract Vestibulospinal tract Tectospinal tract Ventral spinocerebellar tract

14. Copyright © 2010 Pearson Education, Inc. Ascending Pathways Consist of three neurons First-order neuron Conducts impulses from cutaneous receptors and proprioceptors Branches as it enters spinal cord Synapses with second-order

15. Copyright © 2010 Pearson Education, Inc. Ascending Pathways Second-order neuron Interneuron Cell body in dorsal horn of spinal cord Axons extend to thalamus or cerebellum

16. Copyright © 2010 Pearson Education, Inc. Ascending Pathways Third-order neuron Interneuron Cell body in thalamus Axon extends to somatosensory cortex

17. Copyright © 2010 Pearson Education, Inc. Ascending Pathways Pathways transmit somatosensory information to sensory cortex via the thalamus Spinothalamic pathways Spinocerebellar tracts terminate in the cerebellum

18. Copyright © 2010 Pearson Education, Inc. Figure 12.34a (2 of 2) Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Fasciculus gracilis (axon of first-order sensory neuron) Axon of first-order neuron Muscle spindle (proprioceptor) Joint stretch receptor (proprioceptor) Cervical spinal cord Touch receptor Medial lemniscus (tract) (axons of second-order neurons) Dorsal spinocerebellar tract (axons of second-order neurons) Nucleus gracilis Nucleus cuneatus Lumbar spinal cord (a)Spinocerebellar pathway Dorsal column–medial lemniscal pathway

19. Copyright © 2010 Pearson Education, Inc. Figure 12.34a (1 of 2) Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons (a)Spinocerebellar pathway Dorsal column–medial lemniscal pathway

20. Copyright © 2010 Pearson Education, Inc. Descending Pathways and Tracts Deliver efferent impulses from the brain to the spinal cord Direct pathways—pyramidal tracts Indirect pathways—all others

21. Copyright © 2010 Pearson Education, Inc. Descending Pathways and Tracts Involve two neurons: 1.Upper motor neurons Pyramidal cells in primary motor cortex 2.Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles

22. Copyright © 2010 Pearson Education, Inc. Figure 12.35a (1 of 2) Primary motor cortex Internal capsule Cerebral peduncle Midbrain Cerebellum Cerebrum Pons (a) Pyramidal cells (upper motor neurons) Pyramidal (lateral and ventral corticospinal) pathways

23. Copyright © 2010 Pearson Education, Inc. Figure 12.35a (2 of 2) Medulla oblongata Cervical spinal cord Skeletal muscle Pyramids Decussation of pyramid Lateral corticospinal tract Ventral corticospinal tract Lumbar spinal cord Somatic motor neurons (lower motor neurons) (a)Pyramidal (lateral and ventral corticospinal) pathways

24. Copyright © 2010 Pearson Education, Inc. Spinal Cord Trauma Functional losses Parasthesias Sensory loss Paralysis Loss of motor function

25. Copyright © 2010 Pearson Education, Inc. Spinal Cord Trauma Flaccid paralysis—severe damage to ventral root or ventral horn cells Impulses do not reach muscles; there is no voluntary or involuntary control of muscles Muscles atrophy

26. Copyright © 2010 Pearson Education, Inc. Spinal Cord Trauma Spastic paralysis—damage to upper motor neurons of the primary motor cortex Spinal neurons remain intact; muscles are stimulated by reflex activity No voluntary control of muscles

27. Copyright © 2010 Pearson Education, Inc. Spinal Cord Trauma Transection Cross sectioning of the spinal cord at any level Results in total motor and sensory loss in regions inferior to the cut Paraplegia—transection between T 1 and L 1 Quadriplegia—transection in the cervical region

28. Copyright © 2010 Pearson Education, Inc. Poliomyelitis Destruction of ventral horn motor neurons by the poliovirus Muscles atrophy Survivors often develop postpolio syndrome many years later, as neurons are lost Post-Polio Syndrome Fact Sheet http://www.ninds.nih.gov/disorders/post_polio/ detail_post_polio.htm http://www.ninds.nih.gov/disorders/post_polio/ detail_post_polio.htm

29. Copyright © 2010 Pearson Education, Inc. Amyotrophic Lateral Sclerosis (ALS) Lou Gehrig’s disease http://video.sbrforum.com/video-4844-lou- gehrig-speech.html http://video.sbrforum.com/video-4844-lou- gehrig-speech.html Involves progressive destruction of ventral horn motor neurons and fibers of the pyramidal tract Symptoms—loss of the ability to speak, swallow, and breathe Death typically occurs within five years