Enhance your knowledge with our comprehensive guide and curated study materials.
The vertebral canal is the bony canal formed by vertebral foramina of all the vertebrae.
It extends from the foramen magnum above to the sacral hiatus below.
It transmits and protects the spinal cord, its meninges, and related neurovascular structures.
In the cervical region, the canal is triangular and spacious to accommodate the cervical enlargement of the spinal cord.
The main contents of the vertebral canal include:
Spinal cord
Spinal meninges
Cerebrospinal fluid (CSF)
Spinal nerve roots (dorsal and ventral)
Blood vessels of spinal cord and meninges
Epidural fat and venous plexuses (in epidural space)
Spinal Cord – the central nervous structure.
Pia Mater – thin vascular membrane adhering to the cord.
Subarachnoid Space – contains cerebrospinal fluid.
Arachnoid Mater – delicate, transparent membrane.
Subdural Space – potential space.
Dura Mater – thick fibrous membrane forming dural sheath.
Epidural Space – between dura mater and vertebral canal; contains fat and internal vertebral venous plexus.
Extends from foramen magnum to the lower border of L1 vertebra in adults.
In children, it extends up to L3 vertebra.
Enlarged in cervical (C4–T1) and lumbosacral (L1–S2) regions due to limb innervation.
Tapers below into the conus medullaris, continued as filum terminale.
From conus, cauda equina (bundle of nerve roots) descends within lumbar cistern.
Pia Mater
Closely invests the spinal cord.
Sends denticulate ligaments to dura mater for anchorage.
Continues downward as filum terminale internum (up to S2) and externum (to coccyx).
Arachnoid Mater
Thin, avascular membrane enclosing subarachnoid space.
CSF circulates in this space and cushions the cord.
Dura Mater
Tough outer sheath extending from foramen magnum to S2.
Fuses with filum terminale externum below.
Surrounds spinal nerves as dural sleeves.
Lies between the dura mater and vertebral canal.
Contains loose areolar tissue, fat, and internal vertebral venous plexus.
Clinically important for epidural anesthesia.
Arteries:
One anterior spinal artery and two posterior spinal arteries (from vertebral arteries).
Reinforced by radicular arteries from intercostal and lumbar arteries.
Veins:
Internal vertebral venous plexus in epidural space → communicates with cranial venous sinuses and external vertebral plexus.
Remove the posterior elements (laminae and spinous processes) of vertebrae.
Expose the dura mater enclosing the cord.
Open dura longitudinally to display arachnoid, CSF, and spinal cord.
Identify nerve roots, denticulate ligaments, and conus medullaris.
Note cauda equina and filum terminale in the lumbar region.
Lumbar Puncture:
Performed in the L3–L4 or L4–L5 interspace, below termination of spinal cord.
Needle passes through skin → ligaments → dura → arachnoid to reach subarachnoid space.
Used for CSF withdrawal or spinal anesthesia.
Epidural Anesthesia:
Injection into epidural space to block spinal nerves.
Common in obstetrics and lower limb surgeries.
Spinal Shock:
Loss of motor and sensory function below lesion due to cord injury.
Reflexes are initially absent, later become exaggerated.
Cauda Equina Syndrome:
Compression of cauda equina roots (e.g., herniated disc, tumor).
Causes saddle anesthesia, loss of bladder and bowel control, and leg weakness.
Meningitis:
Inflammation of meninges; diagnosed by CSF analysis via lumbar puncture.
Epidural Abscess:
Infection in epidural space → compression of spinal cord → neurological deficits.
CSF Leak:
Can occur after trauma or puncture → post-dural puncture headache due to CSF pressure loss.
Each spinal nerve is formed by the union of anterior (motor) and posterior (sensory) roots of the spinal cord.
The union occurs within the intervertebral foramen.
After emerging from the intervertebral foramen, each spinal nerve divides into:
Dorsal (posterior) ramus – supplies muscles and skin of the back.
Ventral (anterior) ramus – supplies muscles and skin of limbs and anterior part of trunk.
In cervical, brachial, lumbar, and sacral regions, these rami form plexuses.
Meningeal branch – re-enters the vertebral canal to supply meninges, vertebrae, and blood vessels.
Ramus communicans – connects to the sympathetic ganglion.
Each spinal nerve carries four functional types of fibres:
Somatic efferent (motor) – to skeletal muscles.
Somatic afferent (sensory) – from skin and joints.
Visceral efferent – to smooth muscle and glands (via sympathetic fibres).
Visceral afferent – from viscera.
Total: 31 pairs.
Cervical: 8 pairs
Thoracic: 12 pairs
Lumbar: 5 pairs
Sacral: 5 pairs
Coccygeal: 1 pair
The first cervical nerve (C1) emerges above the atlas, while the eighth cervical nerve (C8) emerges below C7.
Each posterior root has a spinal ganglion that contains sensory neuron cell bodies (unipolar type).
Located in the intervertebral foramen, outside the dura mater.
The anterior root has no ganglion.
As they emerge, spinal nerves are covered by:
Pia mater (inner vascular covering)
Arachnoid mater (delicate membrane)
Dura mater (fibrous sheath forming dural sleeve)
Intervertebral disc prolapse or osteophyte formation can compress spinal nerve roots.
Symptoms depend on level affected:
Cervical: Pain radiates to upper limb.
Lumbar: Sciatica due to L5 or S1 nerve compression.
Cervical myelopathy may occur if cord itself is compressed.
Trauma or surgical injury can cause loss of motor and sensory function in the corresponding dermatome and myotome.
C5–T1 form brachial plexus → injury leads to limb weakness.
Compression of lumbosacral nerve roots in lumbar cistern (L2–S2).
Causes urinary retention, saddle anesthesia, and paralysis of lower limbs.
Emergency surgical decompression required.
Reactivation of varicella-zoster virus in spinal ganglion.
Painful vesicular eruption appears in the dermatomal distribution of affected nerve.
Spinal cord ends at L1 (adult); puncture done at L3–L4 or L4–L5 to avoid injury.
Allows safe access to CSF in subarachnoid space.
Injection into epidural space (outside dura mater).
Used in labor analgesia or pelvic surgery.
Anterior root lesion: motor paralysis.
Posterior root lesion: sensory loss.
Complete nerve lesion: both motor and sensory loss in affected dermatome and myotome.
The vertebral venous plexus is of high clinical relevance because it provides a pathway for the spread of infection and metastasis between the pelvis, vertebral column, and cranial cavity.
Common examples:
Carcinoma of the prostate → spreads to vertebral column and skull via this system.
Chronic empyema → may lead to brain abscess through septic emboli.
The vertebral venous system is a valveless, extensive network of veins arranged longitudinally, parallel to the vertebral column.
It communicates freely with the superior and inferior venae cavae.
It consists of three intercommunicating subdivisions:
Located within the vertebral canal, outside the dura mater.
Divided into:
Postcentral plexus (behind vertebral bodies).
Prelaminar plexus (in front of the laminae).
Drains spinal structures and empties into segmental veins — vertebral, posterior intercostal, lumbar, and lateral sacral veins.
Lies within the vertebral bodies.
Drains backwards into the epidural plexus and anterolaterally into the external vertebral plexus.
Lies outside the vertebral column.
Divided into:
Anterior external plexus — in front of vertebral bodies.
Posterior external plexus — on the posterior arches and adjacent muscles.
Drains into segmental veins.
Part of the external plexus, situated in the suboccipital triangle.
Receives occipital veins of the scalp.
Communicates with the transverse sinus via emissary veins.
Ultimately drains into the subclavian veins.
The valveless vertebral venous system communicates:
Superiorly – with intracranial venous sinuses.
Inferiorly – with pelvic veins and portal venous system.
These communications explain the bidirectional flow of blood, facilitating both normal venous return and pathological spread of infection or tumor.
Metastasis pathway: Tumors (e.g., from prostate or breast) may spread to the brain and vertebrae via this plexus.
Raised intra-abdominal pressure (coughing, straining) → reverses venous flow → allows retrograde spread.
Absence of valves allows free communication between cranial and pelvic cavities.
The vertebral canal extends from foramen magnum to sacral hiatus, enclosing and protecting the spinal cord, meninges, and neurovascular structures.
The spinal cord ends at the lower border of L1 in adults and L3 in children.
Below the cord lies the lumbar cistern, containing cauda equina and CSF.
Meninges of spinal cord:
Pia mater → forms filum terminale and denticulate ligaments.
Arachnoid mater → encloses CSF in subarachnoid space.
Dura mater → extends up to S2, continuous with cranial dura.
CSF is formed in choroid plexuses and circulates in the subarachnoid space around the brain and cord.
Epidural space (between dura and vertebral canal) contains fat and internal vertebral venous plexus.
Blood supply of spinal cord:
One anterior spinal artery and two posterior spinal arteries, supported by radicular arteries.
31 pairs of spinal nerves:
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.
Vertebral venous plexus is valveless, connecting pelvic veins, vertebral veins, and cranial venous sinuses, forming an important route for spread of infection or cancer.
Causes: Tumors (meningioma, neurofibroma, glioma, metastasis).
Effect: Depending on the level, produces paraplegia or quadriplegia.
Diagnostic clue: Low CSF pressure below the block (Froin’s syndrome).
Cause: Compression of cauda equina roots (herniated disc, tumor).
Symptoms:
Flaccid paralysis of lower limbs.
Saddle anesthesia (loss of sensation in perineum).
Loss of bladder and bowel control.
Emergency: Requires urgent decompression.
Mechanism: Nucleus pulposus herniates through annulus fibrosus.
Common levels: L4–L5, L5–S1.
Effect: Compression of nerve roots → sciatica (shooting pain along leg).
Inflammation of meninges (bacterial or viral).
Symptoms: Headache, neck stiffness, fever, vomiting.
Diagnosis: Lumbar puncture and CSF examination.
Done in L3–L4 or L4–L5 level (below spinal cord).
Used for CSF sampling, drug administration, or spinal block.
Due to valveless vertebral venous plexus, cancers of prostate, breast, or thyroid can metastasize to vertebral column or skull.
Infection in epidural space → compresses spinal cord → neurological deficits.
Requires prompt drainage and antibiotics.
Explains spread of infection from pelvic organs or abdomen to brain or vertebrae, bypassing systemic circulation.
The vertebral canal contains:
Spinal cord
Meninges (dura mater, arachnoid mater, pia mater)
Cerebrospinal fluid (CSF)
Spinal nerves and roots
Epidural fat and venous plexus
Blood vessels of spinal cord
In adults: From foramen magnum to the lower border of L1 vertebra.
In children: Extends down to the L3 vertebra.
The conical lower end of the spinal cord, situated opposite L1 vertebra.
It gives rise to the filum terminale and cauda equina.
A bundle of descending lumbar, sacral, and coccygeal nerve roots that continue below the conus medullaris within the lumbar cistern.
The portion of the subarachnoid space below the termination of the spinal cord (L1–S2).
It contains CSF, cauda equina, and filum terminale.
Common site for lumbar puncture.
The dural sac extends from the foramen magnum down to the S2 vertebra.
The space between the dura mater and vertebral canal.
Contains fat and internal vertebral venous plexus.
Site for epidural anesthesia.
Lateral extensions of pia mater that attach to dura mater between nerve roots.
They anchor the spinal cord centrally within the vertebral canal.
Fibrous prolongation of pia mater from the conus medullaris.
Extends to S2 (filum terminale internum), then attaches to coccyx (filum terminale externum).
By lumbar puncture at L3–L4 or L4–L5 interspace, below the end of the spinal cord.
Protects and cushions the spinal cord.
Maintains constant intracranial pressure.
Provides nutrition and removes waste products.
A valveless network of veins surrounding the spinal cord and vertebral column.
Provides bidirectional flow, allowing spread of infection or metastasis between the pelvis, vertebrae, and brain.
They can become engorged in pregnancy or portal hypertension, making epidural anesthesia technically difficult or risky.
Subdural space: Potential space between dura and arachnoid mater.
Epidural space: Actual space outside the dura, containing fat and veins.
L4–L5 and L5–S1 intervertebral discs are most commonly affected, compressing corresponding spinal roots.
1. The spinal cord in adults terminates at the level of:
A. L3
B. L2
C. L1
D. L5
✅ Answer: C. L1
2. The subarachnoid space in the spinal canal ends at:
A. S2
B. L5
C. S1
D. L3
✅ Answer: A. S2
3. The cauda equina is formed by:
A. Cervical nerve roots
B. Lumbar, sacral, and coccygeal nerve roots
C. Thoracic nerve roots
D. Sympathetic trunks
✅ Answer: B. Lumbar, sacral, and coccygeal nerve roots
4. Lumbar puncture is performed at the level of:
A. L1–L2
B. L2–L3
C. L3–L4 or L4–L5
D. L5–S1
✅ Answer: C. L3–L4 or L4–L5
5. The filum terminale is derived from:
A. Dura mater
B. Pia mater
C. Arachnoid mater
D. Ligamentum flavum
✅ Answer: B. Pia mater
6. The epidural space contains:
A. CSF
B. Lymph
C. Fat and internal vertebral venous plexus
D. Gray matter
✅ Answer: C. Fat and internal vertebral venous plexus
7. The vertebral venous plexus is important because it is:
A. Lined by valves
B. Valveless, allowing retrograde spread of infection
C. Drains only cranial cavity
D. Drains only thorax
✅ Answer: B. Valveless, allowing retrograde spread of infection
8. The number of pairs of spinal nerves is:
A. 29
B. 30
C. 31
D. 32
✅ Answer: C. 31
9. The lowest part of the dural sac lies opposite:
A. L4
B. S1
C. S2
D. Coccyx
✅ Answer: C. S2
10. Which of the following is not a meningeal layer of the spinal cord?
A. Pia mater
B. Arachnoid mater
C. Endosteal layer
D. Dura mater
✅ Answer: C. Endosteal layer
11. The spinal cord ends at L3 in:
A. Adults
B. Children
C. Elderly
D. Fetuses only
✅ Answer: B. Children
12. The denticulate ligaments are:
A. Modifications of arachnoid mater
B. Modifications of dura mater
C. Modifications of pia mater
D. Collagen fibers in CSF
✅ Answer: C. Modifications of pia mater
13. Lumbar puncture needle passes through all except:
A. Skin
B. Supraspinous ligament
C. Dura mater
D. Body of vertebra
✅ Answer: D. Body of vertebra
14. The main arterial supply to the spinal cord is by:
A. Posterior cerebral arteries
B. Anterior and posterior spinal arteries
C. Vertebral venous plexus
D. Radicular veins
✅ Answer: B. Anterior and posterior spinal arteries
15. The clinical significance of the vertebral venous plexus is:
A. Causes meningitis
B. Allows spread of pelvic carcinoma to skull or brain
C. Collects CSF
D. Stores lymph
✅ Answer: B. Allows spread of pelvic carcinoma to skull or brain
Q1. What is the vertebral canal?
A continuous canal formed by the vertebral foramina of all vertebrae; it encloses the spinal cord, meninges, and related vessels.
Q2. What are the meninges of the spinal cord?
Dura mater – outer tough covering.
Arachnoid mater – thin, delicate middle layer.
Pia mater – inner vascular membrane closely adherent to the cord.
Q3. What is the extent of the spinal cord?
From the foramen magnum to the lower border of L1 in adults and L3 in children.
Q4. What is the lumbar cistern?
The subarachnoid space below L1 up to S2, containing CSF, cauda equina, and filum terminale.
Q5. What is the filum terminale?
A fibrous prolongation of pia mater extending from the conus medullaris to the coccyx.
Q6. What are denticulate ligaments?
Lateral tooth-like extensions of pia mater that attach to dura mater and anchor the spinal cord.
Q7. What is the cauda equina?
A bundle of descending lumbar, sacral, and coccygeal nerve roots within the lumbar cistern below the conus medullaris.
Q8. What is the extent of the dura mater in the vertebral canal?
From foramen magnum to the level of S2 vertebra.
Q9. What does the epidural space contain?
Loose areolar tissue, fat, and internal vertebral venous plexus.
Q10. What is the clinical importance of the epidural space?
Site for epidural anesthesia and possible location for epidural abscess.
Q11. What is the vertebral venous plexus?
A valveless network of veins around the vertebral column that connects the pelvic, vertebral, and cranial venous systems.
Q12. Why is the vertebral venous plexus clinically important?
Because its valveless nature allows retrograde spread of infection or carcinoma from pelvis or abdomen to brain and vertebrae.
Q13. What is the extent of the subarachnoid space?
From foramen magnum to S2, enclosing CSF.
Q14. What is the function of CSF?
Cushions and protects brain and spinal cord.
Maintains intracranial pressure and chemical balance.
Q15. What is the significance of the lumbar puncture site?
The needle is introduced below L2, usually at L3–L4 or L4–L5, to avoid injury to the spinal cord.
Q16. What are the coverings of spinal nerves as they leave the canal?
Each spinal nerve is covered by pia, arachnoid, and dura mater forming a dural sleeve.
Q17. What is Froin’s syndrome?
A sign of spinal block where CSF below the block becomes xanthochromic (yellow) and coagulated due to protein accumulation.
Q18. What are the common causes of spinal cord compression?
Tumors, disc prolapse, epidural abscess, or trauma.
Q19. What is the difference between epidural and subarachnoid anesthesia?
Epidural: Injection into epidural space; segmental block.
Subarachnoid (spinal): Injection into subarachnoid space; complete lower body block.
Q20. What is the conus medullaris and where is it located?
The tapered end of the spinal cord, opposite the L1 vertebra in adults.
Get the full PDF version of this chapter.
Continue with Google