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

Dorsal roots

Dorsal rootVentral

root

Conus medullaris

Filum terminale

Cauda equina

Spinal Cord

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 stimulusbecause 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