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Lecturer
Prof. Dr. Ali K. Al-Shalchy
MBChB/ FIBMS/ MRCS/ FRCS
2014
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.
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.
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 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.
Proprioceptive information in the body travels up the spinal cord via three
tracts. Below L2, the proprioceptive information travels up the spinal cord in the
ventral spinocerebellar tract. Also known as the anterior spinocerebellar tract,
sensory receptors take in the information and travel into the spinal cord. The cell
bodies of these primary neurons are located in the dorsal root ganglia. In the
spinal cord, the axons synapse and the secondary neuronal axons decussates and
then travel up to the superior cerebellar peduncle where they decussate again.
From here, the information is brought to deep nuclei of the cerebellum including
the fastigial and interposed nuclei.
From the levels of L2 to T1,
proprioceptive information enters the
spinal cord and ascends ipsilaterally,
where it synapses in Clarke's nucleus.
The secondary neuronal axons continue to
ascend ipsilaterally and then pass into the
cerebellum via the inferior cerebellar
peduncle. This tract is known as the
posterior spinocerebellar tract.
From above T1, proprioceptive primary
axons enter the spinal cord and ascend
ipsilaterally until reaching the accessory
cuneate nucleus, where they synapse. The
secondary axons pass into the cerebellum
via the inferior cerebellar peduncle where
again, these axons synapse on cerebellar
deep nuclei. This tract is known as the
cuneocerebellar tract.
The corticospinal tract serves as the
motor pathway for upper motor neuronal
signals coming from the cerebral cortex
and from primitive brainstem motor
nuclei.
Cortical upper motor neurons originate
from Brodmann areas 1, 2, 3, 4, and 6 and
then descend in the posterior limb of the
internal capsule, through the crus cerebri,
down through the pons, and to the
medullary pyramids, where about 90% of
the axons cross to the contralateral side at
the decussation of the pyramids.
They then descend as the lateral
corticospinal tract. These axons
synapse with lower motor neurons in
the ventral horns of all levels of the
spinal cord.
The remaining 10% of axons
descend on the ipsilateral side as the
ventral corticospinal tract. These axons
also synapse with lower motor neurons
in the ventral horns. Most of them will
cross to the contralateral side of the
cord (via the anterior white
commissure) right before synapsing.
They are called so because they don’t reach their targets by traveling through the
"pyramids of medulla". Pyramidal tracts go through the pyramids of medulla.
Extrapyramidal tracts indirectly control the anterior horn cells (for modulation and
regulation).
Extrapyramidal system is responsible for gross, synergic movements which require
the activity of large groups of muscles
Radiculopathy
Nerve root impingement with typical pain
radiation and/or motor or sensory impairment
leading to nerve root dysfunction.
Typical Findings: weakness of the index
muscle mainly innervated by that nerve,
diminished reflexes of the same muscle and
dermatomal sensory disturbance.
The most common distribution of
radiculopathy is the lumbar spine followed
by the cervical spine. Radiculopathy is less
common in the thoracic spine.
Pain usually exacerbated with coughing,
sneezing or during defecation.
Myelopathy
Compression or stretching of the spinal cord
can cause myelopathy, which is more common
in the cervical rather than the thoracic spine.
Hyperreflexia and positive Babinski sign are
common.
Sensory deficits include impaired sensory
level, dermatomal sensory disturbance in the
arms, glove-distribution sensory loss in the
hands and posterior column dysfunction.
Motor deficits with arm weakness and
wasting of hand muscles are encountered and
paraparesis can occur . However, hemi- or
tetraparesis are less frequent. Spasticity and
sphincter distubances occur also.
Localized demyelination of the spinal
cord.
Is caused by an immune process
resulting in small vessel vasculopathy,
ischemia, and demyelination.
Symptoms: Clinical picture is identical
to cord transection occurring over hours to
a few days. Most common in the thoracic
cord. Band-like chest pain mimicking
acute myocardial infarction may occur
before the onset of flaccid paralysis,
sensory level, and urinary retention.
Progressive rise in the sensory level may
occur.
Treatment: High-dose intravenous
steroids
Definition: The procedure of taking CSF from the spine in the lower back
through a hollow needle, usually done for diagnostic purposes (e.g.
meningitis).
The patient should lie flat on his
side with the back at the edge of the
bed.
Flexion of hips and knees is
done.
Introduction of 20- to 22-gauge
needle in between 2 spinous
processes (either ,commonly L3-L4,
or L4-L5) exactly in the midline.
By pushing the needle pointing
slightly towards the patient’s head,
piercing the dura is performed at 5-6
cm.
Collect the CSF and send it to
analysis.