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Spinal Cord Organization. January 9, 2008. Spinal Cord 31 segments terminates at L1-L2 special components - conus medularis - cauda equina no input from the face. Spinal Cord, Roots & Nerves. Dorsal root. Ventral root. Spinal nerve. Dorsal Root Ganglion.

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Spinal Cord Organization

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Spinal cord organization l.jpg

Spinal Cord Organization

January 9, 2008

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Spinal Cord 31 segments terminates at L1-L2 special components - conus medularis - cauda equina no input from the face

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Spinal Cord, Roots & Nerves

Dorsal root

Ventral root

Spinal nerve

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Dorsal Root Ganglion

Cell bodies of 1st order sensory neurons


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Spinal Cord Cross Section

Dorsal root





Ventral root

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Cross Section of Spinal Cord

White matter


Gray matter


Central canal

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Volume of Gray & White Matter

Gray matter enlarges at cervical and lumbar regions.

White matter increases at higher levels of the cord.

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Central Gray Matter

Motor neurons

2nd order sensory neurons


Glial cells

Motor neuron = lower motor neuron

= anterior horn cell

= second order motor neuron

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Organization of Gray Matter



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Organization of Gray Matter

Position sense




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Organization of Gray Matter

Position sense

from legs

Between T1 and L2 enlarged

Dorsal nucleus of Clarke

2nd order sensory neuron going to cerebellum

Neck & base of Posterior Horn

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Organization of Gray Matter

Interomedio-lateral horn

Between T1 and L2 enlarged

Sympathetic neurons


Intermediolateral Horn

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Sympathetic Innervation

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Organization of Gray Matter


At S2, S3, and S4

Parasympathetic neurons


Intermediolateral Horn

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Parasympathetic Innervation

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Organization of Gray Matter

Modulates motor activity via gamma motor neurons

Adjusts briskness of deep tendon reflexes

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Organization of Gray Matter

Nuclei of alpha and gamma motor neurons

Innervates muscle spindles and muscles

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Lower Motor Neurons

Alpha motor neurons

originate from Rexed lamina IX

ventral – dorsal organization

ventral  extensor muscles

dorsal  flexor muscles

medial – lateral organization

medial  proximal muscles

lateral  distal muscles

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Somatotopic Organization

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Coordinating Role of Interneurons

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Nuclei of alpha and gamma motor neurons

LMNs from spinal levels C3, C4 & C5 innervate the phrenic nerve

Controls diaphragm

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Control Functions

Nuclei of alpha and gamma motor neurons

At levels S1 - S4 LMNs form Onuf’s nucleus

Innervates anal and urethral spincters; needed for sexual function

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Sacral cord

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Configuration of Gray Matter

Abundant white matter high in the spinal cord

Enlargement of gray matter at the cervical level

Innervates arm muscles

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Configuration of Gray Matter

Enlargement in thoracic region for sympathetic neurons

Enlargement in lumbar region for motor neurons to the legs

Minimal white matter at the lower cord

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Descending Motor Pathway

Upper motor neuron

1st order neuron

synapses on LMN

Crossed pathway

Lateral corticospinal

Uncrossed pathway

Anterior corticospinal

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Somatotopic Organization

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Spinal Cord Tracts

Unconscious position sense



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↑ Sensory

Gracile tract

Leg position & vibration

Cuneate tract

Arm position & vibration

Dorsal spinocerebellar tract

Strength & muscle speed

Ventral spinocerebellar tract

Modulation; interneurons

Lateral spinothalamic tract

Pain & temperature

Anterior spinothalamic tract

Light touch

Spinocervical thalamic tract

Kinesthetic movement & discriminative touch


Corticospinal tract

Speed & agility

Reticulospinal tract

Differential facilitation of motor neurons

Rubrospinal tract

Fix movement errors

Lateral vestibulospinal tract

Extensor & posture

Medial vestibulospinal tract

Flexor & head position

Tectospinal tract

Head turning

Ascending & Descending Tracts

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Ascending Tracts


Position Vibration


Pain Temperature

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Spinal Cord Injury



Brown – Sequard Syndrome

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Transverse vs Hemi Cord Syndrome

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Anterior vs Posterior Cord Syndromes

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Blood Supply to Spinal Cord

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Traumatic Spinal Cord Injury

DUI: $100 addt’l fine

South Carolina

Spinal Cord Injury

Research Board

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