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![Page 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.](https://reader035.fdocuments.in/reader035/viewer/2022062308/56649e305503460f94b205a7/html5/thumbnails/1.jpg)
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
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Dorsal roots
Dorsal rootVentral
root
Conus medullaris
Filum terminale
Cauda equina
Spinal Cord
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Embryonic Development of the Spinal Cord
Figure 12.27
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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
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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)
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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
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White Matter: Major Columns
Spinocerebellar – from spine to cerebellum Reticulospinal – from reticular nuclei to spine Etc…
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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
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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
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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
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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
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Spinocerebellar Tracts
Muscle stretch stimuli to cerebellum Spinocerebellar tracts 1st & 2nd order neurons Don’t decussate Don’t provide conscious
awareness of stimulusbecause they do not conduct to cerebrum
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White Matter: Major Columns
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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
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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
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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