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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

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

Cell bodies of 1st order sensory neurons


Spinal Cord Cross Section

Dorsal root





Ventral root

Cross Section of Spinal Cord

White matter


Gray matter


Central canal

Volume of Gray & White Matter

Gray matter enlarges at cervical and lumbar regions.

White matter increases at higher levels of the cord.

Central Gray Matter

Motor neurons

2nd order sensory neurons


Glial cells

Motor neuron = lower motor neuron

= anterior horn cell

= second order motor neuron

Organization of Gray Matter



Organization of Gray Matter

Position sense




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

Organization of Gray Matter

Interomedio-lateral horn

Between T1 and L2 enlarged

Sympathetic neurons


Intermediolateral Horn

Sympathetic Innervation

Organization of Gray Matter


At S2, S3, and S4

Parasympathetic neurons


Intermediolateral Horn

Parasympathetic Innervation

Organization of Gray Matter

Modulates motor activity via gamma motor neurons

Adjusts briskness of deep tendon reflexes

Organization of Gray Matter

Nuclei of alpha and gamma motor neurons

Innervates muscle spindles and muscles

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

Somatotopic Organization

Coordinating Role of Interneurons


Nuclei of alpha and gamma motor neurons

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

Controls diaphragm

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

Sacral cord

Configuration of Gray Matter

Abundant white matter high in the spinal cord

Enlargement of gray matter at the cervical level

Innervates arm muscles

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

Descending Motor Pathway

Upper motor neuron

1st order neuron

synapses on LMN

Crossed pathway

Lateral corticospinal

Uncrossed pathway

Anterior corticospinal

Somatotopic Organization

Spinal Cord Tracts

Unconscious position sense



↑ 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

Ascending Tracts


Position Vibration


Pain Temperature

Spinal Cord Injury



Brown – Sequard Syndrome

Transverse vs Hemi Cord Syndrome

Anterior vs Posterior Cord Syndromes

Blood Supply to Spinal Cord

Traumatic Spinal Cord Injury

DUI: $100 addt’l fine

South Carolina

Spinal Cord Injury

Research Board



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