The Dorsal Column-Medial Lemniscal System

"I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to

forgo their use." - Galileo Galilei

Introduction

• The dorsal column-medial lemniscus system conveys somatic discriminative sensory information from touch, vibration, and joint position receptors

• Throughout the system, the fibers are arranged somatitopically in relation to their entry into the CNS

• The cell bodies reside in the dorsal root and trigeminal ganglia

Synapsing in the cord

The fibers from the lower

limbs synapse on the

Gracile Nucleus.

Those from the upper limbs synpase on theCuneate Nucleus.

Gracile

Cuneate

From below the belt (and above it)

The fibers from the leg, trunk, andarm ascendipsilaterally as the dorsal

columns

L5

C8

C1

The great cross over

Axons leaving the

dorsal columnnuclei cross asarcuate fibers

andAscend as thecontralateral medial

lemniscus.

Medulla

What about the face?

At the level of thebrainstem,

primarysensory axons

fromthe face synapsein the principle trigeminal nucleusand cross to join the contralateral medial lemniscus.

Midbrain

Pons

Up, up , and away!

The medial lemniscus ascends to the

ventralposterior thalamic nucleus

• Lateral Division (VPL) - Leg, Trunk, and Arm

• Medial Division (VPM) - Face

Top Floor - Cortex

From the VPL and the

VPM of the thalamus,

the fibers extend to the primary

sensory cortex

Primary Sensory Cortex

Sensory information from the dorsal column-lemniscal

system eventually terminates on the postcentral gyrus

of the brain.

The Homunculus!The arrangement of fibers correlates totheir entry into the spinal cord.

Legs, feet,ankles

Shoulder,arms, abdomen

Hand(large thumb)

Face

Tongue

And now for the movie….

QuickTime™ and aSorenson Video decompressorare needed to see this picture.