1. Spinal Cord  Enclosed within the vertebral column  Contiguous with and extends from the medulla oblongata at the foramen magnum to 1 st lumbar vertebra  Provides two-way communication to and from the brain  Protected by vertebrae, meninges, and CSF  Epidural space between vertebrae and dura mater filled with fat and blood vessels

2. Dorsal roots Dorsal root Ventral root Conus medullari s Filum terminale Cauda equina Spinal Cord

3. Embryonic Development of the Spinal Cord Figure 12.27

4. Cross-Sectional Anatomy of the Spinal Cord  Gray matter located centrally, white matter peripherally  Dorsal roots – entry point of sensory neuron axons  Ventral roots – exit point of motor neuron axons

5. Gray Matter and Spinal Roots  Gray commissure connecting gray matter horns  Posterior horns – interneurons  Anterior horns – interneurons & somatic motor neurons  Lateral horns – sympathetic nerve fibers

6. Gray Matter: Organization  Dorsal half – sensory roots and ganglia  Ventral half – motor roots  Dorsal and ventral roots fuse laterally to form spinal nerves  Four zones are evident within the gray matter – somatic sensory (SS), visceral sensory (VS), visceral motor (VM), and somatic motor (SM)

7. White Matter in the Spinal Cord  Axonal tract directionalities  Ascending, descending, and transverse fibers  Pathways decussate (cross midline)  Tract positions  Posterior, lateral, and anterior columns  exhibit somatotopy  are paired  Composition  Each column contains several tracts composed of axons with similar destinations & functions  consist of two or three neurons

8. White Matter: Major Columns  Spinocerebellar – from spine to cerebellum  Reticulospinal – from reticular nuclei to spine  Etc…

9. Neuronal Composition of Ascending Pathways  1 st order neurons  Soma in ganglion of dorsal root or cranial nerve  Synapse with 2 nd order neuron  2 nd order neurons  Soma in dorsal horn or medullary nuclei  Extend axons to thalamus or cerebellum  3 rd order neurons  Soma in thalamus and extend axons to cerebrum

10. Three Ascending Pathways  Nonspecific (anterolateral)  Conducts pain, temperature & course touch stimuli  Specific (medial lemniscal)  conducts stretch & fine touch impulses to the sensory cortex  Spinocerebellar  conducts impulses to the cerebellum

11. Nonspecific Ascending Pathway  Pain, temperature, & crude touch  Lateral spinothalamic tract  1 st, 2 nd & 3 rd order neurons  Decussation at level of spinal nerve 2 nd order neuron axons Axons of 1 st order neurons

12. Specific Ascending Pathways  Stretch & fine touch impulses  1 st order bundled in posterior tracts  Pelvic level in gracilis  Pectoral level in cuneatus  Decussate in medulla into medial lemniscal tract  Allows discriminative touch and proprioception  Uses 1 st, 2 nd, & 3 rd order neurons  1 st order neurons synapse with interneruons at level of spine entry creating reflex arcs

13. Spinocerebellar Tracts  Muscle stretch stimuli to cerebellum  Spinocerebellar tracts  1 st & 2 nd order neurons  Don’t decussate  Don’t provide conscious awareness of stimulus because they do not conduct to cerebrum

14. White Matter: Major Columns

15. Descending (Motor) Pathways  Efferent impulses from brain to the spinal neurons  Two pathways  Direct or pyramidal tract  Indirect tract  Involve 2 or 3 neurons  Upper –cerebral cortex or midbrain to spinal nerve  Lower – soma in spine where motor nerve exits  Interneurons – in gray matter of at level of spinal nerve

16. The Direct (Pyramidal) Tract  Pyramidal neuron soma in precentral gyri (motor cortex)  Synapse with interneurons in anterior horn at level of exit  Corticobulbar tracts innervate cranial nerves  Regulates fast and fine movements

17. Indirect (Extrapyramidal) Tract  Brain stem motor nuclei  rubrospinal, vestibulospinal, reticulospinal, & tectospinal tracts  motor components of cranial nerves  Regulate  Axial muscles maintaining balance and posture  Muscles controlling coarse movements of proximal limbs  Head, neck, and eye movement