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