Spinal Gray and White Matter

White Matter: Tracts= Ascending and Descending Axons 

Gray Matter:  Nerve cell bodies,

Dendrites,  Axon Terminals,

Synapses.

Spinal Gray Matter Zones

PH =Posterior Horn

            (Sensory)

IZ = Intermediate  Zone

(Autonomics& Motor Interneurons) 

AH = Anterior Horn

 (Lower Motor Neurons- GSE)

Embryology of Gray Matter

Alar Plate = SENSORY

Basal Plate = MOTOR

Spinal Cord  Surface Anatomy 

-Posterior Median Sulcus (ABOVE LEVEL T6)

IDENTIFICATION  OF  SPINAL  LEVELS

- Wider Gray Commissure and more white matter at rostral levels

- Large anterior and posterior horns at  cervical & lumbosacral enlargements

- Lateral horn  (sympathetic)  visible at thoracic levels

- Posterior Intermediate Sulcus (septum) above T6

Radicular Arteries

 Radicular arteries supply roots

at every level. Some radicular arteries,

interspersed at irregular intervals, supply

either the anterior or posterior spinal

arteries; these are  called MEDULLARY

ARTERIES.

Medullary Artery  of Adamkiewicz

-Major anterior Medullary artery usually

 from lower thoracic or upper lumbar

 artery on LEFT side.

RESULT of Ischemia :

Total  paralysis and Incontinence below level of

Lesion

PERIPHERAL  NERVE  FIBERS (AXONS)

Sensory Fibers:

 I : Heavily Myelinated, VERY FAST

II & III: Myelinated, FAST

IV: Unmyelinated, SLOW

Motor Fibers: 

A: Heavily Myelinated, FAST, GSE

B: Myelinated, FAST, Preganglionics, GVE

C: Unmyelinated, SLOW, Postganglionic, GVE

Spinal Reflexes

VISCERAL (Autonomic)--> VERY SLOW

SKELETAL MUSCLE

SLOW----> FLEXOR WITHDRAWAL REFLEX

FAST---->MUSCLE RECEPTOR REFLEXEES

1) - Myotatic

  ( Stretch,  Deep Tendon Reflex – DTR )

2)- Golgi Tendon Reflex

RECIPROCAL INNERVATION

- ALL Motor activity exhibits Reciprocal Innervation via interneurons in the  IZ

Excitatory Interneuron

(Glutamate)

(Glycine)

Golgi Tendon Reflex

- Protects  muscle & redistributes load

by inhibiting with GLYCINE

Myotatic (Stretch) Reflex

(DTR)

-Monosynaptic Reflex

 ( No interneurons)

- Very Fast 

-Note: Gamma Motor

Neuron is not involved

in the reflex

What stimulates the Gamma Motor Neuron ?

UPPER MOTOR NEURONS

&

 Coactivation of Alpha and

Gamma LOWER MOTOR NEURONS