Contents of the Vertebral Canal SDL Flashcards
The spinal cord, spinal nerve roots and their meningeal coverings are the primary contents of the canal. However, because of differential growth between the spinal cord and the vertebral column, they do not maintain the same relationship throughout life.
In adulthood, why is the spinal cord is much shorter than the length of the vertebral column?
Due to the differential growth between the spinal cord and the vertebral column
A which vertebral level does the spinal cord end in the newborn?
Approx L3
A which vertebral level does the spinal cord end in adults?
Between L1-L2
Due to the spinal cord ending around L1-L2 in adults, what does this mean for the lower spinal nerve roots?
At the end of the spinal cord, it tapers to form a cone called the conus medullaris. At the bottom of the spinal cord (conus medullaris) is the cauda equina. The cauda equina is a bundle of spinal nerves and spinal nerve rootlets, consisting of the second through fifth lumbar nerve pairs, the first through fifth sacral nerve pairs, and the coccygeal nerve, all of which arise from the lumbar enlargement and the conus medullaris of the spinal cord.
What is the conus medullaris?
The tapered end of the spinal cord from which a thin pial thread the filum terminale, continues downwards to attach to the coccyx
What is the filum terminale?
A delicate strand of fibrous tissue, about 20 cm in length, proceeding downward from the apex of the conus medullaris. It is one of the modifications of pia mater.
What is the cauda equina? What is it made up of?
A bundle of spinal nerves and spinal nerve rootlets, made up of lower lumbar, sacral and coccygeal nerve roots descending through the lumbar cistern
What is the lumbar cistern?
The region of subarachnoid space between the level of termination of the cord and the level at which the dura and arachnoid coverings terminate (about S2).
Complete the labelling in the diagrams below:
The spaces between the dura and arachnoid, and the arachnoid and pia, are called the subdural and subarachnoid spaces, respectively.
- What does the subdural space contain?
- What does the subarachnoid space contain?
- Subdural: potential space
- Subarachnoid: CSF
There is also a space between the dura and vertebra called the epidural (or extradural) space. What does this contain?
Fat
Vertebral level of:
- Termination of cord in adult?
- Termination of cord in neonate?
- Termination of subarachnoid space?
- Termination of epidural space:
- inferiorly?
- superiorly?
- L1-L2
- Around L3
- S2
- …
- S2
- Base of skull (C1)
What does the spinal cord receive its arterial supply from?
3 small longitudinally running arteries: one anterior and two posterior spinal arteries.
Where do the anterior and posterior spinal arteries originate? Describe the areas of the spinal cord supplied by these arteries.
- The anterior spinal artery is formed rostrally from paired branches of the intracranial vertebral arteries that descend from the level of the medulla. These two arteries fuse to form a single anterior spinal artery that overlies the anterior longitudinal fissure of the spinal cord.
- Supplies the anterior side of the spinal cord
- The posterior spinal arteries arise from the vertebral artery in 25% of humans or the posterior inferior cerebellar artery (PICA) in 75% of humans, adjacent to the medulla oblongata.
- It supplies the grey and white posterior columns of the spinal cord.
The anterior and posterior spinal arteries are small. What are they reinforced by?
Are reinforced by radicular branches of the intercostal and lumbar arteries which enter the vertebral canal through the intervertebral foramina.
How are the veins that drain the spinal cord orientated?
Longitudinally
What fissure/sulcus in the spinal cord does the:
- Anterior spinal vein parallel?
- Posterior spinal vein parallel?
- The anterior spinal vein parallels the anterior median fissure
- The posterior spinal vein parallels the posterior median sulcus
What do the posterior and anterior spinal veins drain into?
These veins drain into the internal vertebral plexus embedded in the extradural/epidural fat of the vertebral canal.
On the following diagram label the:
- Anterior spinal vein
- Posterior spinal vein
- Internal vertebral plexus
- Epidural/extradural fat
- Dura mater
At each vertebral level, what does the internal vertebral plexus drain into?
There is drainage from the internal vertebral plexus into segmental thoracic, abdominal and intercostal veins and the external vertebral venous plexus to eventually connect with the major systemic veins.
Do spinal veins have any valves?
No - blood passes directly into the systemic venous system
Which aspect of spinal veins plays a role in metastasisation?
No internal valves allows the blood to flow in both directions, facilitating the spread of malignant tumours that invade blood vessels. The continuity of the vertebral venous plexuses with the prostatic plexus is probably the path along which prostatic neoplastic cells metastasise to the central nervous system.
What is the prostatic plexus continuous with?
The vertebral venous plexuses
What is the functional difference between the dorsal and ventral nerve roots?
- Dorsal root: sensory fibres enter spinal cord
- Ventral root: motor fibres leave spinal cord
Where do the dorsal and ventral roots unite to form the spinal nerves?
join just lateral to the dural sheath to form the spinal nerve
In the upper part of the vertebral canal, how does each spinal nerve exit the vertebral vana? What do they emerge as?
Via the intervertebral foramen –> emerge as the anterior primary ramus and posterior primary ramus
What do the ventral and dorsal rami consist of?
both sensory and motor fibres
What does the dorsal rami innervate?
Innervate the:
- skin of the back
- intrinsic muscles of the back
- sympathetics to the skin
What does the ventral rami innervate?
Innervate all other muscles and cutaneous regions of the body. Visceral pain.
The spinal nerves are named according to the region of the vertebral column from which they emerge. How many spinal nerves are associated with each region:
- Cervical
- Thoracic
- Lumbar
- Sacral
- Coccygeal
- Cervical: 8 pairs of spinal nerves
- Thoracic: 12 pairs of spinal nerves
- Lumbar: 5 pairs of spinal nerves
- Sacral: 5 pairs of spinal nerves
- Coccygeal: 1 pair of spinal nerves
If the diagram above represents the third and fourth vertebrae in each of the cervical, thoracic and lumbar regions, which spinal nerve emerges through the intervening intervertebral foramen?
- C4
- T3
- L3
Name 3 conditions in which the composition of CSF is altered
- Meningitis
- Autoimmune disorders, such as Guillain-Barré Syndrome and multiple sclerosis (MS)
- Bleeding in the brain
In adults, where is is the most common site from which CSF is sampled?
Lumbar cistern using a procedure called a lumbar puncture
Describe the position of the patient during a lumbar puncture. Between which vertebrae is the needle usually inserted?
The patient is positioned on one side, perpendicular to the bed and curled up as much as possible. A needle is then inserted in the mid-line, usually between the L3/L4 vertebrae or L4/L5 vertebrae.
What surface landmarks would you use to determine the point at which to insert the needle during a lumbar puncture?
The anatomical landmark which is used to identify the correct level for lumbar puncture is the line connecting both iliac crests. This crosses the vertebra column at the level of the L4-L5 intervertebral space or L4 vertebra.
Why are patients asked to curl up during lumbar punctures?
In these positions, the patient bends their back and stretches the ligaments between the vertebrae (specifically the ligamentum flavum) so their is more room to insert the needle
Starting with the skin, list the layers pierced by the lumbar puncture needle.
- Skin
- Subcutaneous tissue
- Supraspinous ligament
- Interspinous ligament
- Ligamentum flavum
- Epidural space
- Dura
- Arachnoid
- Finally into the subarachnoid space
Oten, clinicians describe feeling a ‘pop’ or ‘give’ when the lumbar cistern is reached. Moving the needle through which ligament causes this?
Ligamentum flavum
Complete the labelling of the diagram (note: the meninges have been omitted in order to avoid making the diagram too complex).
From the diagram, which segmental spinal nerve would be compressed by herniation of the disc indicated by stippling? What signs and symptoms would the patient show?
The cauda equina
- Severe low back pain.
- Motor weakness, sensory loss, or pain in one, or more commonly both legs.
- Saddle anesthesia (unable to feel anything in the body areas that sit on a saddle)
- Recent onset of bladder dysfunction (such as urinary retention or incontinence)
- Recent onset of bowel incontinence.
In what way is bladder function affected by compression of the cauda equina, eg. by a tumour?
The cauda equina nerves supply muscle sensation to the bladder –> compression can lead to loss of bladder control
Examine the following photographs taken from four levels of the spinal cord: cervical, thoracic, lumbar and sacral. These sections were stained so that the white matter appears blue-black. In descending order; cervical, thoracic, lumbar and sacral.
Which sections contain:
- Dorsal, ventral and lateral grey horns
- Dorsal, ventral and lateral white matter (white columns)
- Central canal
- Dorsal and ventral rootlets (if present)
- Cervical:
- ???
Which cross section has the most white matter? Why?
Cervical region - this pattern is caused by the many axons going up to the brain from all levels of the spinal cord AND there are many axons traveling from the brain down to different segments of the spinal cord.
In which section(s) is the dorsal white matter subdivided into two columns on each side? What type of information runs in these columns?
Is located laterally in the upper thoracic and cervical (C1 to T6) spinal cord segments - it contains afferents from the upper trunk and extremities.
In which spinal cord segments is the ventral grey horn enlarged due to the accumulation of motor neurons for innervation of the limbs?
Cervical and lumbar enlargements
