The spinal cord is a crucial component of the central nervous system (CNS) and plays a vital role

in transmitting information between the brain and the rest of the body, as well as generating
reflexes. Its delicate nature is protected by the vertebral column, meninges, and cerebrospinal
fluid (CSF).
Embryological Development of the Spinal Cord
The entire nervous system, including the spinal cord, is primarily derived from the ectoderm,
with the exception of its blood vessels and some neuroglial elements.
 Neural Plate and Tube Formation:
o Around the 16th day of embryonic life, the ectoderm overlying
the notochord thickens to form the neural plate.
o The margins of the neural plate elevate into neural folds, and
the center sinks to create the neural groove.
o The neural folds gradually fuse in the midline, beginning in the
middle (around the fourth somite on the 20th day), to form a
cylindrical neural tube. This process is called neurulation.
o The neural tube temporarily communicates with the amniotic
cavity through anterior and posterior neuropores, which close by
the end of the fourth week of embryonic development.
 Histogenesis and Differentiation:
o The spinal cord develops from the caudal elongated part of the
neural tube through its histogenesis, involving repeated mitosis
of its epithelial lining.
o By the middle of the fifth week, the neural tube's transverse
section shows three distinct layers:
 Matrix (ependymal) zone: The innermost layer, lining
the enclosed cavity (neurocele), produces neuroblasts
(which develop into neurons) and spongioblasts (which
develop into neuroglial cells).
 Mantle zone: Neuroblasts migrate here, forming the
future spinal grey matter.
 Marginal zone: Axons from neuroblasts enter this
outermost layer, which becomes the future white matter
upon myelination.
o The neural tube's dorsal and ventral walls remain thin, forming
the roof and floor plates, respectively.
o A longitudinal groove, the sulcus limitans, demarcates the wall
of the neural tube into dorsal and ventral regions.
 Cells of the dorsal region, or alar lamina, are functionally
afferent/sensory. These arrange into general somatic
afferent (receiving impulses from skin, bones, muscles,
joints) and general visceral afferent (receiving impulses
from viscera and blood vessels in thoracolumbar and sacral
regions) columns.
  Cells of the ventral region, or basal lamina, are
efferent/motor. These form general visceral efferent
(providing preganglionic fibers to viscera, glands, blood
vessels in thoracolumbar and sacral regions) and general
somatic efferent (innervating skeletal muscles) columns.
 Meninges Development: The membranes surrounding the brain and
spinal cord (pia mater, arachnoid mater, and dura mater) are derived
from mesenchyme, though some suggest pia and arachnoid mater
(leptomeninges) are from the neural crest.
 Postnatal Growth: Mitotic activity within neural tissue largely
completes prenatally, meaning a person is born with their destined
number of neurons. However, nervous tissue continues to grow and
specialize after birth, particularly in the initial years.
Structure of the Spinal Cord
The spinal cord is a long, cylindrical structure, slightly flattened anteroposteriorly, measuring
about 45 cm in adult males and 42 cm in adult females, and weighing approximately 30g. It
extends as a continuation of the medulla oblongata from the upper border of the first cervical
vertebra (C1) to the lower border of the first lumbar vertebra (L1), terminating as the conus
medullaris.
 External Features:
o Enlargements: The spinal cord has two fusiform swellings to
accommodate innervation of the limbs:
 Cervical enlargement: Extends from spinal segments C5
to T1, corresponding to vertebral levels C3 to T1. It
supplies the musculature of the upper limbs and associated
girdles.
 Lumbosacral enlargement: Extends from spinal
segments L2 to S3, corresponding to vertebral levels T9 to
L1. It supplies the musculature of the lower limbs and
associated girdles.
o Fissures and Sulci: The anterior aspect features a deep
anterior median fissure and two anterolateral sulci. The
posterior aspect has a posteromedian sulcus, and two
posterolateral and posterointermediate sulci.
 Spinal Nerves:
o There are 31 pairs of spinal nerves that arise from the spinal
cord, named after the vertebral column regions: 8 cervical, 12
thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
o Each spinal nerve arises from the cord by two roots: an anterior
(motor/efferent) root and a posterior (sensory/afferent)
root. The cell bodies of motor neurons are in the anterior and
lateral horns, while sensory neuron cell bodies are in the
posterior root ganglion.
 o After emerging from the intervertebral foramen, each spinal
nerve divides into a larger anterior ramus and a smaller
posterior ramus, both containing motor and sensory fibers. The
anterior rami often form major somatic plexuses (cervical,
brachial, lumbar, sacral).
 Spinal Segments: The part of the spinal cord to which a pair of spinal
nerves is attached is called a spinal segment. Due to the vertebral
column growing faster than the spinal cord, spinal segments are
generally located above their numerically corresponding
vertebral spines, especially in the lower cord.
 Cauda Equina: Since the spinal cord is shorter than the vertebral
column, the nerve roots of lumbar, sacral, and coccygeal nerves (L2 to
Cx1) descend vertically from the conus medullaris, forming a "horse's
tail" bundle called the cauda equina.
 Meninges: The spinal cord is enveloped by three protective
membranes:
o Dura mater: The thickest, outermost layer, extending from the
foramen magnum to the lower border of the second sacral
vertebra (S2). The epidural space lies between the dura and
the vertebral canal, containing loose connective tissue, fat, and
the internal vertebral venous plexus.
o Arachnoid mater: A thin, delicate, avascular membrane that
loosely invests the spinal cord, continuous with the brain's
arachnoid mater. The subdural space is a potential space
between the dura and arachnoid.
o Pia mater: A thin, highly vascular membrane that closely
invests the spinal cord. The subarachnoid space lies between
the arachnoid and pia mater and is filled with cerebrospinal
fluid (CSF).
o Filum Terminale: A thin, non-nervous fibrous prolongation of
the pia mater that extends from the conus medullaris to the first
coccygeal vertebra, helping to anchor the spinal cord.
o Ligamenta Denticulata: Ribbon-like bands of pia mater with 21
tooth-like processes on each side that pierce the arachnoid and
attach to the dura, anchoring the spinal cord in the middle of the
subarachnoid space.
 Internal Structure: The spinal cord's cross-section reveals an inner
core of grey matter and a peripheral zone of white matter.
o Grey Matter: Appears H-shaped, with a central canal and
anterior, posterior, and lateral horns (columns). The amount of
grey matter is largest in the cervical and lumbar enlargements,
correlating with the mass of tissue they supply. Neurons are
multipolar, including Golgi type I (long axons forming tracts or
anterior nerve roots) and Golgi type II (short axons/interneurons).
Specific cell groups within the horns include:
  Anterior Horn: Contains motor neurons that innervate
axial musculature (medial group), limb muscles (lateral
group), and specific nuclei like the phrenic nucleus (C3-C5,
diaphragm) and spinal accessory nucleus (C1-C5, spinal
root of accessory nerve).
 Posterior Horn: Contains sensory relay nuclei such as the
substantia gelatinosa (pain and temperature), nucleus
proprius (proprioception, two-point discrimination,
vibration), nucleus dorsalis/Clarke's column (proprioceptive
and exteroceptive afferents), and visceral afferent nucleus
(visceral afferents).
 Lateral Horn: Present in thoracolumbar (T1-L2) and sacral
(S2-S4) regions, containing the intermediolateral nucleus
(sympathetic preganglionic fibers) and intermediomedial
nucleus (parasympathetic preganglionic fibers).
o White Matter: Surrounds the grey matter and consists mainly of
myelinated nerve fibers, giving it a white appearance. The
amount of white matter progressively increases from below
upwards, as more ascending fibers are added and descending
fibers terminate. It is divided into three parts: posterior, lateral,
and anterior white columns (funiculi).
 Fibers: Functionally, fibers are sensory (ascending to
higher centers), motor (descending from higher centers or
to motor roots), or association (interconnecting neurons
within the spinal cord).
 Tracts: Collections of nerve fibers with common origin,
course, and termination.
 Descending (Motor) Tracts: Conduct impulses
from the brain to the spinal cord. Key examples
include the corticospinal tracts (pyramidal tracts,
responsible for voluntary movement, dividing into
lateral and anterior parts after decussation in the
medulla), rubrospinal tract, tectospinal tract,
vestibulospinal tracts, and reticulospinal tracts.
The medial brain stem pathways (reticulospinal,
vestibulospinal, tectospinal) primarily control axial
and proximal muscles, while lateral pathways
(corticospinal, rubrospinal) control distal limb
muscles for fine motor control.
 Ascending (Sensory) Tracts: Convey sensory
modalities to higher centers. These include:
 Lateral Spinothalamic Tract: Carries pain
and temperature sensations from the
contralateral side of the body, relaying in the
posterior horn and terminating in the thalamus.
  Anterior Spinothalamic Tract: Carries light
touch, pressure, tickle, and itch sensations
from the contralateral side, also relaying in the
posterior horn and terminating in the thalamus.
 Dorsal Column System (Fasciculus Gracilis
and Fasciculus Cuneatus): Carries conscious
proprioception, two-point tactile discrimination,
and vibration from the ipsilateral side of the
body. These fibers ascend to the medulla,
synapse in the gracilis and cuneate nuclei, and
then cross the midline (forming the medial
lemniscus) to ascend to the contralateral
thalamus.
 Spinocerebellar Tracts (Posterior and
Anterior): Carry unconscious proprioceptive
sensations to the cerebellum for muscular
coordination.
 Blood Supply:
o The spinal cord receives its main arterial supply from a single
anterior spinal artery (supplying the anterior two-thirds of the
cord) and two posterior spinal arteries (supplying the
posterior one-third).
o These longitudinal arteries are reinforced by segmental
arteries (spinal branches of vertebral, deep cervical, posterior
intercostal, lumbar, and lateral sacral arteries), which give off
anterior and posterior radicular arteries. Some larger radicular
arteries become segmental medullary arteries that anastomose
with the longitudinal vessels.
o Venous drainage occurs via a single anterior spinal vein and a
single posterior spinal vein, which drain into the internal
vertebral plexus, then the external vertebral plexus, and finally
into systemic veins.
Function of the Spinal Cord
The spinal cord serves several critical functions:
 Communication Link: It forms the primary communication pathway
between the brain and the peripheral nervous system below the head.
It transmits sensory information (afferent impulses) from the periphery
to the brain via ascending pathways, and motor commands (efferent
impulses) from the brain to effector organs (muscles, glands) via
descending pathways.
 Reflex Generation: The spinal cord can integrate incoming
information and produce rapid, automatic responses known as spinal
reflexes, without conscious thought. Examples include:
 o Stretch reflex (monosynaptic, e.g., knee jerk): A muscle stretch
stimulates sensory fibers in muscle spindles, which directly
stimulate alpha motor neurons in the spinal cord, causing the
muscle to contract.
o Golgi tendon reflex (polysynaptic): Detects muscle contraction
(shortening) and causes relaxation of the muscle.
o Flexor-withdrawal reflex (polysynaptic): Initiated by painful
stimuli, it causes withdrawal of a limb from the source of the
stimulus through excitatory interneurons stimulating flexor
muscles.
 Integration: It integrates incoming sensory information and
coordinates appropriate motor responses.
Different Injuries to the Spinal Cord
Spinal cord injuries (SCI) can have varied deficits depending on the level and extent of damage.
 General Effects of SCI: Transection of the spinal cord is followed by a
period of spinal shock, characterized by profound depression of all
spinal reflex responses, which can last for a minimum of 2 weeks in
humans. Subsequently, reflexes often return and become hyperactive.
 Traumatic Brain Injury (TBI): While primarily brain injury, TBI can be
associated with spinal injuries. It can lead to permanent or temporary
impairment of cognitive, physical, emotional, and behavioral functions,
and altered consciousness. Primary injuries are caused by mechanical
force (e.g., skull fracture, surface contusions, diffuse axonal injury,
intracranial hematoma), while secondary injuries are delayed
responses due to impaired cerebral blood flow leading to cell death.
 Cervical Spine Injury: Injuries in the cervical region, such as a
wedge compression fracture of C4/C5 vertebra, can damage
structures responsible for motor, coordination, and sensation. Injuries
above the level of the third cervical spinal segment (C3) can be fatal
due to damage to vital centers that control respiration and
cardiovascular function in the medulla.
 Regional Susceptibility: Spinal cord injuries are more common in the
thoracic region due to the relatively smaller diameter of the vertebral
canal and the resistance provided by the rib cage, which can lead to
considerable displacement of fractured vertebral segments.
 Intervertebral Disc Herniation (Slipped Disc): Most commonly
occurs in the lower cervical (e.g., C5/C6, C6/C7) and lumbar (e.g.,
L3/L4, L4/L5) regions, where mobile parts of the vertebral column join
relatively immobile parts. A ruptured annulus fibrosus can lead to
central prolapse (compressing the spinal cord) or posterolateral
prolapse (compressing spinal nerve roots), causing pain and muscle
wasting.
 Syringomyelia: A clinical condition where a fluid cavity develops near
the central canal of the spinal cord, usually in the cervical segments.
 This leads to the destruction of the cord, particularly involving the
decussating spinothalamic fibers in the anterior white commissure,
resulting in a dissociated sensory loss (bilateral loss of pain and
temperature sensation below the lesion, while other sensations are
preserved).
 Hemisection of the Spinal Cord (Brown-Séquard Syndrome):
Results in a specific constellation of deficits:
o Ipsilateral upper motor neuron (spastic) paralysis below
the level of hemisection due to pyramidal tract involvement.
o Ipsilateral loss of proprioceptive sensations (position,
posture, passive movement, vibrations) and fine
touch/discrimination due to posterior column involvement.
o Contralateral loss of pain and temperature sensation
below the level of the lesion due to ventrolateral spinothalamic
pathway involvement (fibers cross the midline). Corticosteroids
may be used to reduce inflammation.
 Anterior Spinal Artery Syndrome: Caused by occlusion (thrombosis
or compression) of the anterior spinal artery. Since this artery supplies
the anterior two-thirds of the cord, it results in:
o Motor symptoms (weakness/paralysis) due to involvement of
corticospinal tracts and anterior grey columns.
o Bilateral loss of pain and temperature sensation due to
ischemia of spinothalamic tracts.
o Preservation of conscious proprioceptive sensations
because the posterior white column is supplied by the posterior
spinal arteries.
 Conus Medullaris Syndrome vs. Cauda Equina Syndrome:
o Conus Medullaris Syndrome: Occurs due to compression of
the conus medullaris (sacral and coccygeal spinal segments).
Characterized by sudden onset, perianal anesthesia, early
bladder and bowel involvement, severe low back pain, more
frequent sexual dysfunction, and both upper motor neuron (UMN)
and lower motor neuron (LMN) type paralysis.
o Cauda Equina Syndrome: Occurs due to compression of the
cauda equina (nerve roots of L2 to Cx1 spinal nerves).
Characterized by gradual onset, saddle anesthesia, late bladder
and bowel involvement, less severe low back pain, less frequent
sexual dysfunction, and only LMN type paralysis.
 Tabes Dorsalis: A syphilitic degenerative disease involving the
posterior white columns and posterior nerve roots. It leads to loss of
sense of position, tactile discrimination, vibration, and appreciation of
posture. Patients may exhibit Romberg's sign (staggering/falling
when standing with feet together and eyes closed).
 Decerebrate Rigidity: Caused by a complete transection of the brain
stem between the superior and inferior colliculi (midcollicular
decerebration). This interrupts input from the cortex and red nucleus,
 but leaves excitatory reticulospinal pathways (primarily to postural
extensor muscles) intact. It results in hyperactivity in extensor
muscles in all four extremities (spasticity due to facilitation of the
stretch reflex). This posture resembles that seen with uncal herniation
due to a supratentorial lesion.
 Decorticate Rigidity: Damage to the upper midbrain can cause
flexion of the upper extremities at the elbow and extensor
hyperactivity in the lower extremities. It occurs on the hemiplegic side
after hemorrhage or thrombosis in the internal capsule.
 Multiple Sclerosis: A debilitating, degenerative autoimmune disease
characterized by multifocal demyelination throughout the white
matter of the CNS. Demyelination affects the conduction of nerve
impulses.
 Peripheral Nerve Injuries: Include entrapment syndromes (e.g.,
median nerve in carpal tunnel) and radiculopathy (compression of
nerve roots). The ability of nerves to regenerate depends on the type
of injury; axonotmesis (axon damaged, connective tissue intact)
allows regeneration, while neurotmesis (complete nerve section,
axons and connective tissue damaged) typically results in failure of
regeneration.
Radiological Anatomy and Investigations of the Spinal Cord
Medical imaging techniques are crucial for diagnosing spinal cord conditions.
 X-ray: Used to visualize bone structures, such as a wedge
compression fracture of the C4/C5 cervical vertebra.
 Magnetic Resonance Imaging (MRI): A non-invasive modality that
can visualize anatomical connections within the CNS. It is valuable for
diagnosing various clinical conditions like cerebral stroke and brain
tumors, by showing local glucose metabolism and oxygenated blood
levels, which correlate with neural activity.
 Lumbar Puncture (Spinal Tap): Performed to withdraw
cerebrospinal fluid (CSF) for diagnostic and therapeutic purposes.
o It is crucial to perform the puncture well below the termination of
the spinal cord (which ends at L1/L2 in adults, L3 at birth) to
avoid injury.
o The L3-L4 interspinous space is the most preferred and safest
site for needle insertion, as this region of the subarachnoid space
is roomy and contains only the filum terminale and roots of the
cauda equina, which usually float clear of the needle.
o The patient should be in a fully flexed position (lying on side or
seated) to maximize interspinous space opening.
o The needle passes through supraspinous and interspinous
ligaments, and then penetrates the dura mater.
 Cisternal Puncture: An alternative method to withdraw CSF when a
lumbar puncture is not feasible. It accesses the cerebellomedullary
 cistern by introducing a needle anterosuperiorly through the posterior
atlanto-occipital membrane, between the posterior arch of the atlas
and the posterior margin of the foramen magnum.
 Cerebral Angiography: A radiological technique to visualize brain
vessels by injecting a radiopaque solution into major arteries (e.g.,
common carotid, internal carotid, vertebral artery). It helps identify
vascular malformations, aneurysms, occlusive vascular disease, and
space-occupying lesions.
Quick Review of the Vertebral Column and Possible Injuries
The vertebral column (spine) provides the bony enclosure for the spinal cord, extending from
the base of the skull to the first lumbar vertebra.
 Structure: It is composed of 33-35 vertebrae, of which 24 are
separated by intervertebral discs. The remaining vertebrae are
typically fused to form the sacrum and coccyx. The column is divided
into five regions: cervical (7 vertebrae), thoracic (12 vertebrae),
lumbar (5 vertebrae), sacrum (5 fused), and coccyx (3-5 fused).
o When viewed laterally, the vertebral column presents four
natural curvatures: two anterior concavities (thoracic and sacral
kyphoses) and two anterior convexities (cervical and lumbar
lordoses).
o A typical vertebra consists of a large cylindrical vertebral
body anteriorly and a vertebral arch posteriorly, which
together enclose the vertebral foramen. Processes like the
spinous process, transverse processes, and superior/inferior
articular processes extend from the arch.
o Atypical cervical vertebrae include the atlas (C1), a ring-
shaped vertebra without a body or spinous process, and the axis
(C2), which features the dens axis for articulation with C1. The
seventh cervical vertebra (C7) is known as the vertebra
prominens due to its elongated spinous process.
 Joints and Ligaments: Vertebrae articulate via intervertebral
symphyses (between vertebral bodies and intervertebral discs) and
zygapophyseal joints (facet joints, between articular processes). In
the cervical region, uncovertebral joints (of Luschka) are also
present (C3-C7). These joints are reinforced by numerous ligaments,
including the anterior and posterior longitudinal ligaments, ligamenta
flava, interspinous ligaments, supraspinous ligaments, and
intertransverse ligaments.
 Movements: The vertebral column allows for flexion, extension,
lateral flexion, and rotation (torsion).
 Vascular Supply: Each vertebra receives arterial supply from
segmental spinal, periosteal, pre/postcentral, and pre/postlaminar
vessels, which arise from larger parent arteries such as vertebral,
ascending cervical, posterior intercostal, lumbar, iliolumbar, and
 lateral/median sacral arteries. Venous drainage occurs via internal and
external vertebral venous plexuses and intervertebral veins, ultimately
emptying into systemic veins.
 Possible Injuries to the Vertebral Column:
o Vertebral Fractures: A wedge compression fracture of the
C4/C5 cervical vertebra is an example of a bony injury that
can affect the spinal cord.
o Intervertebral Disc Herniation: This is a common injury where
the annulus fibrosus ruptures and the nucleus pulposus
protrudes, most frequently in the lower cervical and lumbar
regions where mobile segments meet relatively immobile ones.
o Cervical Spondylitis: A degenerative condition involving
degeneration of intervertebral discs and the formation of
osteophytes (bone spurs) from uncovertebral joints, leading to
narrowing of intervertebral foramina and compression of nerve
roots.