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
Afferent
Spinal Cord Cross Section
Dorsal root
sensory
afferent
Ventral root
motor
efferent
Cross Section of Spinal Cord
White matter
peripheralGray matter
central
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
Interneurons
Glial cells
Motor neuron = lower motor neuron
= anterior horn cell
= second order motor neuron
Organization of Gray Matter
Pain
Temperature
Organization of Gray Matter
Position sense
Vibration
Pressure
Touch
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
(preganglionic)
Intermediolateral Horn
Sympathetic Innervation
Organization of Gray Matter
.
At S2, S3, and S4
Parasympathetic neurons
(preganglionic)
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
Breathing
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
movement
feedback
Unconscious position sense
Ascending & Descending Tracts
• ↑ 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
• ↓ Motor– 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 Tracts
SensoryPosition Vibration
SensoryPain Temperature
Spinal Cord Injury
Position
Pain
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
Monday
Brainstem
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