Anatomy of the
Spinal Cord
(Lecture 2)
LECTURER
PROF. DR. ALI K. AL-SHALCHY
MBCHB/ FIBMS/ MRCS/ FRCS
2017
Gross Anatomy of the Spinal Cord
DORSAL
ROOT:
THE
DORSAL
ROOT
CARRIES
BOTH
MYELINATED
AND
UNMYELINATED AFFERENT FIBERS TO THE SPINAL CORD.
POSTERIOR GRAY COLUMN: LONG AND NARROW COLUMN OF GRAY MATTER
REACHES ALMOST TO THE SURFACE OF THE SPINAL CORD. PRIMARILY CONCERNED
WITH SENSORY INPUT.
ANTERIOR GRAY COLUMN: SHORT AND BROAD COLUMN OF GRAY MATTER.
CONCERNED WITH MOTOR FUNCTION. BOTH POSTERIOR AND ANTERIOR GRAY
COLUMNS ARE SITES WHERE SENSORY AND MOTOR CELL BODIES, RESPECTIVELY, ARE
FOUND.
VENTRAL ROOT: BUNDLE OF SOMATIC MOTOR FIBERS. CONSTITUTE THE EFFERENT
OUTFLOW OF THE SPINAL CORD.
ANTERIOR MEDIAN FISSURE: ABOUT 3 MM DEEP. CONTAINS BLOOD VESSELS
(ANTERIOR SPINAL ARTERY) SUPPLYING THE ANTERIOR TWO THIRDS OF THE CORD.
ANTERIOR
FUNICULUS:
BETWEEN THE ANTERIOR
MEDIAN
FISSURE AND
ANTEROLATERAL SULCUS (VENTRAL ROOT). MERGES WITH THE LATERAL FUNICULUS.
CONTAINS ASCENDING AND DESCENDING TRACTS.
LATERAL FUNICULUS: BETWEEN THE DORSAL AND VENTRAL ROOTS. MERGES WITH
THE ANTERIOR FUNICULUS. CONTAINS ASCENDING AND DESCENDING TRACTS.
POSTERIOR LATERAL SULCUS: SITE OF ENTRY OF DORSAL ROOT.
POSTERIOR FUNICULUS: BETWEEN POSTERIOR MEDIAN SULCUS AND DORSAL ROOT.
CONTAINS ASCENDING TRACTS.
Spinal Cord Tracts
THE SPINAL CORD TRACTS CAN BE DIVIDED INTO ASCENDING (SENSORY OR
AFFERENT) AND DESCENDING (MOTOR OR EFFERENT) TRACTS.
THE SENSORY TRACTS INCLUDE DORSAL COLUMN/MEDIAL LEMNISCUS
SYSTEM, ANTEROLATERAL SYSTEM, AND SPINOCEREBELLAR TRACTS ; WHILE
THE MOTOR TRACTS INCLUDE THE
PYRAMIDAL AND EXTRAPYRAMIDAL
TRACTS.
Dorsal column/medial lemniscus system
IN THE DORSAL COLUMN-MEDIAL
LEMNISCUS
TRACT,
A
PRIMARY
NEURON'S AXON ENTERS THE SPINAL
CORD AND THEN ENTERS THE DORSAL
COLUMN.
IF
THE
PRIMARY AXON
ENTERS BELOW SPINAL LEVEL T6, THE
AXON TRAVELS IN THE FASCICULUS
GRACILIS, THE MEDIAL PART OF THE
COLUMN. IF THE AXON ENTERS ABOVE
LEVEL T6, THEN IT TRAVELS IN THE
FASCICULUS
CUNEATUS,
WHICH
IS
LATERAL TO THE FASCICULUS GRACILIS.
EITHER WAY, THE PRIMARY AXON
ASCENDS TO THE LOWER MEDULLA,
WHERE IT LEAVES ITS FASCICULUS AND
SYNAPSES WITH A SECONDARY NEURON
IN ONE OF THE DORSAL COLUMN
NUCLEI:
EITHER
THE
NUCLEUS
GRACILIS OR THE NUCLEUS CUNEATUS.
AT THIS POINT, THE SECONDARY AXON
LEAVES
ITS
NUCLEUS AND
PASSES
ANTERIORLY
AND
MEDIALLY.
THE
COLLECTION OF SECONDARY AXONS
THAT DO THIS ARE KNOWN AS INTERNAL
ARCUATE
FIBERS.
THE
INTERNAL
ARCUATE
FIBERS
DECUSSATE
AND
CONTINUE
ASCENDING
AS
THE
CONTRALATERAL MEDIAL LEMNISCUS.
SECONDARY AXONS FROM THE MEDIAL
LEMNISCUS FINALLY TERMINATE IN THE
VENTRAL POSTEROLATERAL NUCLEUS
(VPL) OF THE THALAMUS, WHERE THEY
SYNAPSE WITH TERTIARY
NEURONS.
FROM
THERE,
TERTIARY
NEURONS
ASCEND VIA THE POSTERIOR LIMB OF THE
INTERNAL CAPSULE AND END IN THE
PRIMARY SENSORY CORTEX.
THIS
SYSTEM TRANSMITS TOUCH,
PROPRIOCEPTION
AND
VIBRATION
MODALITIES OF SENSATIONS.
The Anterolateral System
THE ANTEROLATERAL SYSTEM WORKS SOMEWHAT DIFFERENTLY. ITS PRIMARY
NEURONS AXONS ENTER THE SPINAL CORD AND THEN ASCEND ONE TO TWO
LEVELS BEFORE SYNAPSING IN THE SUBSTANTIA GELATINOSA. THE TRACT THAT
ASCENDS BEFORE SYNAPSING IS KNOWN AS LISSAUER'S TRACT. AFTER
SYNAPSING, SECONDARY AXONS DECUSSATE AND ASCEND IN THE ANTERIOR
LATERAL PORTION OF THE SPINAL CORD AS THE SPINOTHALAMIC TRACT. THIS
TRACT ASCENDS ALL THE WAY TO THE VPL, WHERE IT SYNAPSES ON TERTIARY
NEURONS. TERTIARY NEURONAL AXONS THEN TRAVEL TO THE PRIMARY SENSORY
CORTEX VIA THE POSTERIOR LIMB OF THE INTERNAL CAPSULE.
THIS SYSTEM TRANSMITS PAIN AND TEMPERATURE MODALITIES OF
SENSATIONS.