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
Ventral
root
Dorsal
root
Cauda
equina
Conus
medullari
s
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
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
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


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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
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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