spinal_cord by liwenting


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


               Ventral     root


Embryonic Development of the Spinal Cord

                                           Figure 12.27
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
    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
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)
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
White Matter: Major Columns
§ Spinocerebellar – from spine to cerebellum
§ Reticulospinal – from reticular nuclei to spine
§ Etc…
Neuronal Composition of Ascending Pathways
               § 1st order neurons
                  § Soma in ganglion of dorsal root
                    or cranial nerve
                  § Synapse with 2nd order neuron
               § 2nd order neurons
                  § Soma in dorsal horn or
                    medullary nuclei
                  § Extend axons to thalamus or
               § 3rd order neurons
                  § Soma in thalamus and extend
                    axons to cerebrum
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
  Nonspecific Ascending Pathway
§ Pain, temperature, & crude
§ Lateral spinothalamic tract
§ 1st, 2nd & 3rd order neurons
§ Decussation at level of
  spinal nerve

                                  2nd order neuron axons

                                  Axons of 1st order
  Specific Ascending Pathways
§ Stretch & fine touch impulses
§ 1st order bundled in posterior
   § Pelvic level in gracilis
   § Pectoral level in cuneatus
§ Decussate in medulla into
  medial lemniscal tract
§ Allows discriminative touch
  and proprioception
§ Uses 1st, 2nd, & 3rd order
§ 1st order neurons synapse with
  interneruons at level of spine
  entry creating reflex arcs
Spinocerebellar Tracts
§   Muscle stretch stimuli to cerebellum
§   Spinocerebellar tracts
§   1st & 2nd order neurons
§   Don’t decussate
§   Don’t provide conscious
    awareness of stimulus
    because they do not
    conduct to cerebrum
White Matter: Major Columns
  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
  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
  Indirect (Extrapyramidal) Tract
§ Brain stem motor nuclei
  § rubrospinal, vestibulospinal,
    reticulospinal, & tectospinal
  § motor components of cranial
§ Regulate
  § Axial muscles maintaining
    balance and posture
  § Muscles controlling coarse
    movements of proximal limbs
  § Head, neck, and eye

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