Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out

spinal_cord

VIEWS: 0 PAGES: 17

									Spinal Cord
§ Enclosed within the vertebral column
§ Contiguous with and extends from the medulla
  oblongata at the foramen magnum to 1st 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
Spinal Cord

                Dorsal
                 roots




                           Dorsal
               Ventral     root
                 root


                           Cauda
                           equina
                 Conus
              medullaris


                           Filum
                           terminale
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
                    cerebellum
               § 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
  touch
§ Lateral spinothalamic tract
§ 1st, 2nd & 3rd order neurons
§ Decussation at level of
  spinal nerve

                                  2nd order neuron axons




                                  Axons of 1st order
                                  neurons
  Specific Ascending Pathways
§ Stretch & fine touch impulses
§ 1st 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 1st, 2nd, & 3rd order
  neurons
§ 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
  movements
  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

								
To top