Explain each and everything about Spinal Cord and Ascending, Descending, and lntersegmental Tracts. I want even the minor details about the topic. Also explain all the clinicals along the content

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Here is a complete, detailed reference on the Spinal Cord and all its tracts, drawn from Gray's Anatomy for Students, Neuroanatomy through Clinical Cases, Localization in Clinical Neurology, Medical Physiology (Guyton & Hall), Harrison's Principles, Campbell's Operative Orthopaedics, and Goldman-Cecil Medicine.

The Spinal Cord: Complete Reference

1. OVERVIEW AND BASIC STRUCTURE

The spinal cord is a thin, tubular extension of the central nervous system (CNS) contained within the bony spinal canal. It originates at the medulla oblongata (level of the foramen magnum) and continues caudally, terminating as the conus medullaris at approximately the L1-L2 vertebral level in adults (L3 in neonates). From the conus, a fibrous cord called the filum terminale connects the spinal cord to the dorsum of the first coccygeal segment. The adult spinal cord is approximately 46 cm long.

The spinal cord is enclosed in three protective membranes - the pia, arachnoid, and dura mater - which are continuous with the cranial meninges:

Pia mater: innermost, highly vascular, adherent directly to cord surface. Forms the denticulate ligament midway between anterior and posterior roots, which anchors the cord within the subarachnoid space.
Arachnoid mater: middle layer; creates the subarachnoid space (filled with CSF) between itself and the pia. This space extends to S2 level, below the cord - the basis for safe lumbar puncture.
Dura mater: outermost tough fibrous layer.

31 pairs of spinal nerves emerge from the cord. There are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pairs. Key point: there are 8 cervical segments but only 7 cervical vertebrae, so C1-C7 nerves exit above their corresponding vertebra; C8 exits below C7. All subsequent nerves exit below their corresponding vertebra.

Gray's Anatomy for Students
Harrison's Principles of Internal Medicine 22E

2. EXTERNAL FEATURES

The spinal cord has several longitudinal fissures and sulci on its surface:

Anterior median fissure: deep midline groove on the anterior surface. The anterior spinal artery runs here.
Posterior median sulcus: shallower midline groove on the posterior surface.
Posterolateral sulci (bilateral): where posterior (dorsal) root fibers enter.
Anterior rootlets emerge in a line lateral to the anterior median fissure.

Two enlargements accommodate neurons for the limbs:

Cervical enlargement (C5-T1): for brachial plexus / upper extremities
Lumbar (lumbosacral) enlargement (L2-S3): for lumbar plexus / lower extremities

Below the lumbosacral enlargement, the cord tapers as the conus medullaris. Below that, the remaining lumbar and sacral nerve roots form the cauda equina ("horse's tail"), which floats freely within the subarachnoid space before exiting at their respective foramina.

Gray's Anatomy for Students

3. INTERNAL FEATURES - CROSS-SECTIONAL ANATOMY

3A. Gray Matter

A cross-section of the spinal cord reveals centrally-placed gray matter surrounded by white matter. The gray matter is butterfly-shaped (or H-shaped), with two lateral columns joined by a transverse gray commissure. It is divided into:

Dorsal (posterior) horn: involved mainly in sensory processing. Intermediate zone: contains interneurons and autonomic nuclei. Ventral (anterior) horn: contains motor neurons (alpha and gamma).

There is also an intermediolateral gray column from T1-L2 - the source of preganglionic sympathetic fibers. Sacral segments S2-S4 contain a similar column for parasympathetic outflow.

Basic Spinal Cord Anatomy: gray matter, white matter, dorsal and ventral roots

Spinal cord - gray matter, white matter, dorsal and ventral root organization. - Neuroanatomy through Clinical Cases 3rd Ed

3B. Rexed's Laminae (Cytoarchitecture)

The Swedish anatomist Bror Rexed described 10 cell layers within the gray matter:

Lamina	Region	Key Nuclei/Function
I	Dorsal horn (tip)	Nucleus posteromarginalis (posterior marginal nucleus) - pain/temperature
II	Dorsal horn	Substantia gelatinosa of Rolando - pain modulation
III & IV	Dorsal horn	Nucleus proprius dorsalis - sensory processing
V	Dorsal horn (neck)	Nucleus reticularis - receives spinoreticular input
VI	Base of dorsal horn	Proprioception from muscle spindles
VII	Intermediate zone	Nucleus dorsalis of Clarke (C8-L3) - spinocerebellar relay; autonomic neurons
VIII	Ventral horn (medial)	Interneurons, commissural neurons
IX	Ventral horn	Alpha and gamma motor neurons (extrafusal and intrafusal muscle fibers)
X	Central canal zone	Gray commissure (dorsal and ventral)

Alpha motor neurons (large): innervate extrafusal skeletal muscle fibers. Gamma motor neurons (small): innervate intrafusal muscle fibers of muscle spindles, regulating spindle sensitivity. Renshaw cells: inhibitory interneurons in the anterior horn; receive collaterals from alpha motor neuron axons and provide lateral inhibition to adjacent motor neurons, sharpening motor output.

Neuroanatomy through Clinical Cases 3rd Ed
Localization in Clinical Neurology 8e

3C. White Matter - Funiculi

Each half of the spinal cord white matter is divided into three funiculi (columns):

Dorsal (posterior) funiculus: between dorsomedian and dorsolateral sulci - contains dorsal column tracts
Lateral funiculus: between dorsolateral and ventrolateral sulci - contains spinocerebellar tracts, spinothalamic tract, corticospinal tract
Ventral (anterior) funiculus: between ventrolateral sulcus and anterior median fissure - contains anterior corticospinal tract, vestibulospinal, reticulospinal tracts

Dorsal and ventral white commissures run alongside the corresponding gray commissures and allow decussation of fibers between sides.

The white matter is thickest at cervical levels (where most ascending fibers have entered and most descending fibers have not yet terminated) and thinnest at sacral levels (mostly gray matter).

Localization in Clinical Neurology 8e
Neuroanatomy through Clinical Cases 3rd Ed

4. ASCENDING TRACTS (Sensory Pathways)

All ascending tracts transmit sensory information from the periphery to higher centers. They are classic 3-neuron pathways for conscious perception.

Spinal Cord Cross Section - Ascending and Descending Tracts with Lamination

Cross-sectional anatomy showing tract lamination: S=sacral, L=lumbar, Th=thoracic, C=cervical. - Localization in Clinical Neurology 8e

Complete Tract Diagram - Ascending Left, Descending Right

All ascending tracts (left) and descending tracts (right) in a spinal cord cross-section. - Gray's Anatomy for Students

4A. ANTEROLATERAL SYSTEM (Spinothalamic + Related Tracts)

This system carries pain, temperature, and crude/light touch. It is composed of three tracts:

4A-1. Lateral Spinothalamic Tract (Neospinothalamic Tract)

Modalities: Sharp, localized pain; temperature Pathway (3 neurons):

1st-order neuron: Cell body in the dorsal root ganglion (DRG). Axon enters the spinal cord via the posterior root, splits into the zone of Lissauer (posterolateral tract of Lissauer) - ascending or descending 1-2 segments before synapsing.
Synapse: On 2nd-order neurons in laminae I and V of the dorsal horn.
2nd-order neuron: Axons cross obliquely within the anterior commissure, traveling over 2-3 segments before joining the anterolateral tract on the contralateral side. They then ascend to the ventral posterolateral (VPL) nucleus of the thalamus.
3rd-order neuron: From VPL, fibers pass through the posterior limb of the internal capsule to reach the primary somatosensory cortex (postcentral gyrus, areas 3, 1, 2).

Laminar arrangement (somatotopy): In the lateral spinothalamic tract, fibers from cervical segments are situated dorsomedially, and sacral fibers are ventrolaterally (C-Th-L-S from inside out). There is also a segregation between pain and temperature fibers within the tract.

Clinical significance: Lesions of the anterior commissure (e.g., syringomyelia) interrupt crossing fibers, producing a cape-like bilateral loss of pain and temperature at the affected segments while sparing touch and proprioception (dissociated sensory loss).

4A-2. Spinoreticular Tract (Paleospinothalamic System)

Modalities: Poorly localized, burning, chronic pain; emotional/arousal aspects of pain Pathway: Similar 1st-order neuron. 2nd-order axons project to the reticular formation of the brainstem instead of the thalamus. From the reticular formation, signals go to the intralaminar nuclei of the thalamus, then diffusely to the cortex. Key point: This system is responsible for the suffering and autonomic component of pain. It projects to the limbic system, explaining why pain has emotional dimensions.

4A-3. Spinomesencephalic Tract

Pathway: 2nd-order axons project to the periaqueductal gray (PAG) and superior colliculi in the midbrain. Function: Central modulation/inhibition of pain. The PAG is the main center for endogenous opioid-mediated pain suppression. Stimulation here causes profound analgesia.

4A-4. Anterior (Ventral) Spinothalamic Tract

Modality: Light touch (crude touch) Pathway: Similar to lateral spinothalamic - 2nd-order axons cross through the ventral white commissure and ascend as the ventral spinothalamic tract to the VPL thalamus. Note: Light touch is also carried by the dorsal column-medial lemniscal pathway, so isolated damage to the ventral spinothalamic tract does not completely abolish light touch.

4B. POSTERIOR COLUMN - MEDIAL LEMNISCAL PATHWAY (Dorsal Column System)

Modalities: Fine/discriminative touch, two-point discrimination, vibration sense, conscious proprioception (joint position sense), stereognosis, graphesthesia.

Pathway (3 neurons):

1st-order neuron: Cell body in the DRG. Heavily myelinated axons (fast conduction) enter through the medial bundle of the dorsal root. They pass ipsilaterally into the dorsal funiculus and ascend without synapsing all the way to the caudal medulla.
- Fibers from the lower body (sacral, lumbar, lower 6 thoracic levels) enter medially and form the fasciculus gracilis (Goll's column) - carries lower limb and trunk sensation
- Fibers from the upper body (upper 6 thoracic + all cervical levels) add laterally to form the fasciculus cuneatus (Burdach's column) - carries upper limb and neck sensation
Synapse: In the caudal medulla at the nucleus gracilis (for gracilis) and nucleus cuneatus (for cuneatus)
2nd-order neuron: Axons from these nuclei cross the midline as internal arcuate fibers (medial lemniscal decussation), forming the medial lemniscus, which ascends through the brainstem to the VPL nucleus of the thalamus.
3rd-order neuron: VPL nucleus projects via the posterior limb of the internal capsule to the primary somatosensory cortex.

Somatotopy in dorsal columns: As fibers accumulate from below, sacral fibers are most medial, then lumbar, then thoracic, and cervical fibers are most lateral. This is the opposite of the spinothalamic tract arrangement.

Clinical significance: Damage to dorsal columns causes:

Loss of vibration and proprioception ipsilaterally below the lesion
Positive Romberg sign (patient falls when eyes closed due to loss of proprioceptive input)
Sensory ataxia: unsteady gait, worse in the dark
Subacute combined degeneration (Vitamin B12 deficiency) causes demyelination of dorsal columns + lateral corticospinal tracts
Tabes dorsalis (tertiary syphilis): selective degeneration of dorsal columns and dorsal roots

4C. SPINOCEREBELLAR TRACTS (Subconscious Proprioception)

These carry proprioceptive and kinesthetic information to the cerebellum for subconscious coordination - not for conscious perception.

4C-1. Dorsal (Posterior) Spinocerebellar Tract

Origin: Clarke's nucleus (nucleus dorsalis, lamina VII), present only at C8-L3 Course: Axons enter the lateral funiculus ipsilaterally and ascend to enter the cerebellum via the inferior cerebellar peduncle Function: Carries proprioceptive signals from muscle spindles and Golgi tendon organs of the ipsilateral lower limb and trunk

4C-2. Ventral (Anterior) Spinocerebellar Tract

Origin: Laminae V-VII (border cells), thoracolumbar cord Course: Axons cross to the contralateral lateral funiculus and ascend to enter the cerebellum via the superior cerebellar peduncle. Many fibers then recross within the cerebellum, so the final information is largely ipsilateral. Function: Monitors spinal cord interneuron activity and provides the cerebellum with information about the state of motor activity (efference copy/internal feedback)

4C-3. Cuneocerebellar Tract

Origin: Accessory (external) cuneate nucleus in medulla Function: Carries proprioception from upper limb to cerebellum (analogous to dorsal spinocerebellar tract for lower limb). Since Clarke's nucleus only extends to C8, upper limb proprioception cannot use the dorsal spinocerebellar tract directly.

5. DESCENDING TRACTS (Motor Pathways)

Descending tracts are involved in voluntary movements, postural control, and coordination of head, neck, and eye movements. They originate in the cerebral cortex and brainstem and are organized into lateral and medial motor systems.

Each descending pathway has two neurons:

Upper motor neuron (UMN): cell body in cortex or brainstem
Lower motor neuron (LMN): cell body in anterior horn of spinal cord

All Descending Tracts - Schematic Cross Section (Campbell's)

Schematic cross section of the cervical spinal cord showing numbered ascending and descending tracts with somatotopic lamination. - Campbell's Operative Orthopaedics 15th Ed

5A. LATERAL MOTOR SYSTEM

Controls distal limb muscles (fine, skilled movements). Tracts are located in the lateral column and synapse on lateral anterior horn cells.

5A-1. Lateral Corticospinal Tract (Pyramidal Tract)

This is the most clinically important motor tract.

Origin: Primary motor cortex (precentral gyrus, Brodmann area 4), supplementary motor area, premotor cortex. Course:

Axons converge in the corona radiata → descend through the posterior limb of the internal capsule
→ form the crus cerebri in the midbrain
→ pass through the anterior pons as small bundles (scattered by transverse pontocerebellar fibers)
→ regroup at the medulla to form the pyramids (the large swellings on the anterior medullary surface - hence "pyramidal tract")
→ at the caudal medulla: ~85-90% of fibers decussate at the pyramidal decussation (cervicomedullary junction) to form the lateral corticospinal tract in the contralateral lateral column
→ descend through the entire spinal cord, synapsing on lower motor neurons in the lateral anterior horn at all levels

Somatotopy: Cervical (arm) fibers are central (medial); thoracic, lumbar, sacral fibers are progressively peripheral (lateral). This explains central cord syndrome.

Function: Voluntary, skilled, fractionated movements of the contralateral limbs (especially fine finger movements).

Termination: Primarily at cervical and lumbosacral enlargements, on LMN cell bodies and interneurons.

5A-2. Rubrospinal Tract

Origin: Red nucleus (magnocellular division), midbrain tegmentum Decussation: Ventral tegmental decussation in the midbrain (immediately after leaving the nucleus) Course: Descends in the lateral column of the spinal cord, parallel and anterior to the lateral corticospinal tract Termination: Only to cervical cord levels, on interneurons in the lateral anterior horn Function: Facilitates flexor muscle activity and inhibits extensor activity of the upper limb. In humans, its function is considered uncertain / largely redundant with the lateral corticospinal tract.

5B. MEDIAL MOTOR SYSTEM

Controls axial and proximal muscles (posture, balance, automatic gait). Tracts are in the anterior and medial columns and project bilaterally on interneurons, making individual tract testing difficult clinically.

5B-1. Anterior (Ventral) Corticospinal Tract

Origin: Primary motor cortex + supplementary motor area (the ~10-15% of fibers that did NOT decussate at the pyramidal decussation) Course: Descends ipsilaterally in the medial aspect of the anterior column Termination: Cervical and upper thoracic cord. Most fibers eventually cross at the segmental level via the anterior white commissure before terminating on LMNs in the medial anterior horn. Function: Control of bilateral axial and girdle muscles (trunk, neck). This bilateral control explains why axial movements (trunk, neck) are much less affected by unilateral cortical lesions.

5B-2. Vestibulospinal Tracts

Two separate tracts arise from different vestibular nuclei:

Lateral Vestibulospinal Tract:

Origin: Lateral (Deiters') vestibular nucleus in the pons/medulla (receives input from cerebellum and inner ear)
Course: Descends ipsilaterally through the entire length of the spinal cord in the anterior column
Function: Facilitates extensor/antigravity muscle tone (ipsilateral), inhibits flexors. Critical for maintaining balance and upright posture in response to vestibular signals.

Medial Vestibulospinal Tract:

Origin: Medial and inferior vestibular nuclei
Course: Descends bilaterally only to cervical and upper thoracic cord, within the medial longitudinal fasciculus (MLF)
Function: Positioning of the head and neck in response to vestibular input

Example: When you trip and your head jerks forward, vestibulospinal activation extends the upper limb to break the fall.

5B-3. Reticulospinal Tracts

Two components arise from the reticular formation:

Pontine (medial) Reticulospinal Tract:

Origin: Pontine reticular formation (nucleus reticularis pontis caudalis/oralis)
Course: Descends ipsilaterally in the anterior column
Function: Facilitates extensor motor neurons, facilitates voluntary movements

Medullary (lateral) Reticulospinal Tract:

Origin: Medullary reticular formation (nucleus reticularis gigantocellularis)
Course: Descends ipsilaterally (mostly) in the anterior/lateral column
Function: Inhibits extensor motor neurons; regulates voluntary movement, reflex activity, and autonomic outflow

Together, these tracts regulate automatic postural and gait-related movements and modulate spinal reflexes. They also carry descending autonomic commands to sympathetic and parasympathetic preganglionic neurons.

5B-4. Tectospinal Tract

Origin: Superior colliculus (dorsal midbrain) - a visual processing center Decussation: Dorsal tegmental decussation (immediately crosses in the midbrain) Course: Descends near the anterior median fissure through brainstem, then into cervical cord only Termination: Interneurons in the anterior horn of cervical cord, bilaterally Function: Reflex postural movements in response to visual stimuli (orienting movements of the head and eyes toward visual targets). Function in humans is considered uncertain.

6. SUMMARY TABLE OF ALL TRACTS

#	Tract	Column	Function	Decussation	Laterality at Cord
ASCENDING
1	Lateral spinothalamic	Lateral	Pain, temperature	Anterior commissure (2-3 segs above)	Contralateral
2	Anterior spinothalamic	Anterior	Light touch (crude)	Anterior commissure	Contralateral
3	Spinoreticular	Lateral	Arousal/affective pain	Anterior commissure	Bilateral
4	Spinomesencephalic	Lateral	Pain modulation (PAG)	Anterior commissure	Contralateral
5	Fasciculus gracilis	Posterior	Proprioception/vibration/fine touch (lower body)	Internal arcuate fibers (medulla)	Ipsilateral
6	Fasciculus cuneatus	Posterior	Proprioception/vibration/fine touch (upper body)	Internal arcuate fibers (medulla)	Ipsilateral
7	Dorsal spinocerebellar	Lateral	Subconscious proprioception (lower limb)	None (ipsilateral)	Ipsilateral
8	Ventral spinocerebellar	Lateral	Spinal cord motor state (recrosses in cerebellum)	Crosses twice	Ipsilateral net
DESCENDING
9	Lateral corticospinal	Lateral	Voluntary skilled movement (contralateral limbs)	Pyramidal decussation (medulla)	Contralateral
10	Anterior corticospinal	Anterior	Bilateral axial/girdle motor	Segmental (at termination)	Bilateral
11	Rubrospinal	Lateral	Flexor facilitation of upper limb	Ventral tegmental dec. (midbrain)	Contralateral
12	Lateral vestibulospinal	Anterior	Extensor tone, balance	None	Ipsilateral
13	Medial vestibulospinal	Anterior	Head/neck positioning	None (bilateral)	Bilateral
14	Pontine reticulospinal	Anterior	Extensor facilitation, posture	None	Ipsilateral
15	Medullary reticulospinal	Lateral/Anterior	Extensor inhibition, autonomic	None	Ipsilateral
16	Tectospinal	Anterior	Visual-motor reflex (head/eye orient.)	Dorsal tegmental dec. (midbrain)	Contralateral

7. INTERSEGMENTAL TRACTS (Propriospinal Fibers)

Fasciculus Proprius (Propriospinal System):

The intersegmental tracts - also called propriospinal fibers or the fasciculus proprius - are a collar of white matter that immediately surrounds the gray matter on all sides. They are one of the most important yet under-appreciated components of the spinal cord.

Key facts:

More than half of all the nerve fibers that ascend and descend in the spinal cord are propriospinal fibers (Guyton & Hall).
These fibers run from one segment of the cord to another - they do NOT project to the brain.
When sensory fibers enter the cord via the posterior roots, they bifurcate and send branches both up and down the cord - some travel only 1-2 segments, others many segments.
They are present in all three funiculi (posterior, lateral, and anterior) immediately adjacent to the gray matter.

Functions:

Multisegmental reflexes: Propriospinal fibers coordinate reflexes that involve multiple cord segments simultaneously - for example, coordinating simultaneous movements of the forelimbs and hindlimbs during locomotion.
Long propriospinal neurons (C3-C4): A specific group of propriospinal neurons at C3-C4 segments mediate part of the corticospinal command for upper limb movements. Corticospinal fibers synapse on C3-C4 propriospinal neurons, which then relay commands to cervical motor neurons.
Interlimb coordination: Coordinate bilateral limb movements (e.g., the stepping reflex involves intersegmental communication via propriospinal fibers).
Provide short-loop feedback within the cord for segmental reflexes.
Bidirectional pathways - the fasciculus proprius has both ascending and descending fibers.

Lissauer's Tract (Posterolateral Tract / Zone of Lissauer):

Located at the tip of the posterior horn, between the dorsal gray column and the cord surface
Contains both ascending and descending fibers
Carries finely myelinated (Aδ) and unmyelinated (C) fibers for pain and temperature
Allows 1st-order pain afferents to travel up or down 1-2 segments before synapsing, enabling a wider zone of input convergence
The zone of Lissauer separates the dorsal gray column from the cord surface
Guyton and Hall Textbook of Medical Physiology
Gray's Anatomy for Students
Eric Kandel - Principles of Neural Science 6th Ed

8. VASCULAR SUPPLY

Three main longitudinal vessels supply the spinal cord:

Anterior Spinal Artery (ASA):

Formed by union of two branches from the vertebral arteries within the cranial cavity
Runs in the anterior median fissure throughout the cord's length
Sulcal (central) branches supply the anterior horn, lateral horn, central gray, and anterior 2/3 of the cord (including the lateral corticospinal tract and spinothalamic tracts)
Reinforced at the lower thoracic/upper lumbar level by the Artery of Adamkiewicz (great radicular artery of Adamkiewicz) - usually on the left side, enters between T9-L2. Its occlusion can cause catastrophic anterior spinal cord infarction.

Posterior Spinal Arteries (PSA) (paired):

Branches of vertebral arteries or PICA
Run along posterolateral sulci
Supply dorsal horns and dorsal funiculi (posterior 1/3 of cord)

Segmental/Radiculomedullary Arteries: 6-10 reinforce the ASA; 10-23 reinforce the PSA. The largest is the Artery of Adamkiewicz.

Vulnerable Zone: The midthoracic region (T3-T8) is the most poorly vascularized area, making it most susceptible to ischemia.

Gray's Anatomy for Students
Localization in Clinical Neurology 8e

9. CLINICAL CORRELATES

9A. Upper Motor Neuron (UMN) vs. Lower Motor Neuron (LMN) Lesions

Feature	UMN Lesion (above anterior horn)	LMN Lesion (anterior horn or below)
Weakness	Spastic (increased tone)	Flaccid (decreased tone)
Reflexes	Hyperreflexia, Babinski sign (+)	Hyporeflexia / areflexia
Atrophy	Disuse atrophy (late, mild)	Rapid, severe muscle atrophy
Fasciculations	Absent	Present

9B. Spinal Cord Injury Syndromes

Complete Cord Transection

Loss of ALL motor, sensory, and autonomic function below the level of the lesion
Initially: Spinal shock - flaccid paralysis, absent reflexes, urinary retention, hypotension
After weeks: Spasticity, hyperreflexia, autonomic dysreflexia

Brown-Séquard Syndrome (Cord Hemisection)

Cause: Penetrating trauma (stab wound), tumor, demyelinating lesion affecting one lateral half
Ipsilateral below lesion: Loss of motor function (corticospinal tract), loss of proprioception and vibration (dorsal column)
Contralateral below lesion: Loss of pain and temperature (spinothalamic tract - crossed 2-3 segments above)
At the level of lesion: Ipsilateral LMN signs (segmental weakness, loss of all sensation)

Central Cord Syndrome

Most common incomplete SCI, typically from hyperextension injury in older patients with cervical spondylosis
Affects the central cord first: arm fibers (cervical) are most central in the lateral corticospinal tract; leg fibers are peripheral
Classic presentation: Arm weakness > Leg weakness (arms affected worse than legs - "man in a barrel" syndrome)
Bladder dysfunction (urinary retention) common
Pain and temperature reduced; proprioception often spared
Best prognosis for recovery among incomplete syndromes

Anterior Cord Syndrome

Cause: Anterior spinal artery occlusion (e.g., aortic surgery, hyperflexion injury)
Bilateral loss of motor function (corticospinal tract), pain, and temperature (spinothalamic) below the level
Preserved: Posterior column functions (vibration, proprioception, fine touch) - because PSA is intact
Worst prognosis for ambulation among incomplete syndromes

Posterior Cord Syndrome

Rare; due to posterior spinal artery occlusion or posterior column damage
Bilateral loss of vibration, proprioception, and fine touch below the lesion
Motor function and pain/temperature preserved
Patient has profound sensory ataxia

Conus Medullaris Syndrome

Lesion at L1-L2 (the conus)
Mix of UMN and LMN signs: UMN signs from sacral cord + LMN signs from anterior horn cells
Bowel and bladder dysfunction, saddle anesthesia (S3-S5 dermatomes), sexual dysfunction
Lower limb weakness may be present

Cauda Equina Syndrome

Lesion below the conus (L2 and below) - affects spinal nerve roots, not cord tissue
Pure LMN signs: Flaccid weakness, areflexia, atrophy
Saddle anesthesia, bowel/bladder/sexual dysfunction
Often from large central disc herniation, tumor, or epidural hematoma
Surgical emergency - early decompression is required

9C. Specific Tract Lesion Syndromes

Syringomyelia:

Fluid-filled cavity (syrinx) expands within the central cord, destroying crossing fibers of the anterior commissure
Bilaterally destroys spinothalamic fibers as they cross
Cape-like dissociated sensory loss: bilateral loss of pain and temperature over the shoulders, arms, and upper trunk - while dorsal columns (proprioception, vibration) are preserved
As the syrinx enlarges: anterior horn cells destroyed → LMN weakness and wasting of hands; then lateral columns → spastic paraparesis

Subacute Combined Degeneration (B12 deficiency):

Demyelination of dorsal columns + lateral corticospinal tracts (bilateral)
Dorsal column: loss of proprioception/vibration → sensory ataxia, positive Romberg
Corticospinal: UMN signs (spasticity, hyperreflexia, Babinski)
Combined picture: spastic ataxia, with sensory > motor deficits early

Tabes Dorsalis (3° syphilis):

Selective degeneration of dorsal roots and dorsal columns
Loss of proprioception/vibration, severe sensory ataxia (tabetic gait - high-stepping, stamping)
Charcot joints (neuropathic arthropathy) due to loss of joint position sense
Lightning pains (episodic lancinating pain)
Argyll Robertson pupils (accommodate but don't react to light)

Anterior Spinal Artery Syndrome:

Occlusion of ASA → infarction of anterior 2/3 of cord
Bilateral paralysis + pain/temperature loss below lesion
Preserved posterior column (vibration/proprioception)
Can follow aortic aneurysm repair, embolism

Amyotrophic Lateral Sclerosis (ALS):

Degeneration of both UMN (lateral corticospinal tracts) and LMN (anterior horn cells)
Combined UMN + LMN signs in the same patient/same region: fasciculations + hyperreflexia; wasting + spasticity
Sensory system spared - hallmark of ALS

Spinal Shock:

Occurs immediately after acute complete cord transection
Temporary loss of all spinal reflexes below the level of injury (bulbocavernosus, anal wink, muscle stretch reflexes)
Also: neurogenic hypotension, peripheral vasodilation, ileus, urinary retention
If lesion at T3 or above: sympathetic tone to heart is lost → bradycardia + hypotension = neurogenic shock triad (bradycardia + hypotension + peripheral vasodilation)

Autonomic Dysreflexia:

Occurs in chronic complete SCI at T6 or above
Noxious stimulus below lesion (full bladder, fecal impaction, pressure sore) → massive sympathetic discharge below lesion
Severe hypertension, pounding headache, flushing/sweating above lesion, bradycardia (baroreceptor-mediated)
Medical emergency - can cause stroke or myocardial infarction

9D. Causes of Spinal Cord Dysfunction (Harrison's Classification)

Category	Examples
Compressive	Epidural/intradural/intramedullary neoplasm, epidural abscess, epidural hemorrhage, cervical spondylosis, herniated disc, fracture-dislocation
Vascular	Anterior spinal artery infarct, AVM, dural fistula, antiphospholipid syndrome
Inflammatory/Demyelinating	Multiple sclerosis, neuromyelitis optica (Devic's), sarcoidosis, ADEM
Autoimmune	SLE, Sjögren's syndrome, Behcet's disease, anti-MOG, paraneoplastic
Infectious	VZV, HSV-1/2, CMV, HIV myelopathy, HTLV-1 (tropical spastic paraparesis)
Degenerative	ALS, hereditary spastic paraplegia
Metabolic/Nutritional	B12 deficiency (subacute combined degeneration), copper deficiency
Developmental/Congenital	Syringomyelia, tethered cord, Chiari malformation

Harrison's Principles of Internal Medicine 22E
Goldman-Cecil Medicine

10. QUICK LOCALIZATION GUIDE

Finding	Tract Affected	Location
Contralateral pain/temp loss	Lateral spinothalamic	Anterolateral quadrant, opposite side
Ipsilateral proprioception/vibration loss	Fasciculus gracilis/cuneatus	Posterior column, same side
Ipsilateral spastic paresis	Lateral corticospinal	Lateral column, same side
Bilateral pain/temp loss ("cape")	Crossing spinothalamic fibers	Anterior commissure
Bilateral motor + proprioception loss	LCS + dorsal column	Subacute combined degeneration
Arm weak > leg weak	LCS (central fibers)	Central cord
Loss of motor + pain/temp, preserved proprioception	ASA territory	Anterior 2/3 of cord
Loss of proprioception, preserved motor + pain	PSA territory	Posterior 1/3

Sources: Gray's Anatomy for Students (ISBN 9780323934237) | Neuroanatomy through Clinical Cases 3rd Ed (ISBN 9781605359625) | Localization in Clinical Neurology 8e (ISBN 9781975160241) | Guyton and Hall Medical Physiology (ISBN 9780443111013) | Harrison's Principles of Internal Medicine 22E (ISBN 9781265977061) | Campbell's Operative Orthopaedics 15th Ed 2026 (ISBN 9780443117633) | Goldman-Cecil Medicine (ISBN 9780323930345)

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