Vertebral Column and Spinal Cord Flashcards
Click on Answer for diagrams on tracts of the spinal cord.
Name the various curvatures of the spine.
- Cervical curve (C2 - T2): convex anteriorly [cervical lordotic curve]
- Thoracic curve (T2 - T12): concave anteriorly [thoracic kyphotic curve]
- Lumbar curve (T12 - sacrovertebral angle): convex anteriorly [lumbar lordotic curve]
- Sacral curve (sacrovertebral articulation - coccyx): concave anteriorly [sacral kyphotic curve]
Extra Notes:
☛ The thoracic and sacral (pelvic) curvatures are concave anteriorly and are referred to as kyphoses (singular: kyphosis). They appear during the fetal period of embryonic development, hence they are also termed primary or developmental curvatures. It is important to note that the sacral curvature differs in males and females; the latter is less pronounced so that the coccyx protrudes less into the pelvic outlet, making it suitable for childbirth.
☛ The cervical and lumbar curvatures are concave posteriorly and convex anteriorly, being referred to as lordoses (singular: lordosis). These curvatures arise as a consequence of extension from the flexed fetal position. Although they begin to appear before birth, they are not apparent until later in infancy when they are accentuated by support of the head and by the adoption of an upright or erect human posture. As a result, they are termed secondary or acquired curvatures.
State three functions of the spinal cord.
The spinal cord has three major functions:
1. It acts as a pathway for motor information, which travels down the spinal cord.
2. It serves as a passage for sensory information in the reverse direction.
3. It is a centre for coordinating simple reflexes.
Describe the external features of the spinal cord.
☛ The length of the cord is about 45 cm.
☛ It resembles a flattened cylinder, though not uniform in cross section. The spinal segments that contribute to the nerves of the upper limbs (C5 to T1) are enlarged to form the cervical enlargement. Similarly, the segments innervating the lower limbs (L1 to S3) form the lumbar enlargement. [The cervical enlargement gives rise to the brachial plexus, whereas the lumbar enlargement gives rise to the lumbosacral plexus.
☛ The distal end of the spinal cord presents a bundle of spinal nerves that arise from the lumbar enlargement and conus medullaris, known as the cauda equina.
☛ The anterior surface of the spinal cord is marked by a deep anterior median fissure, which contains anterior spinal artery.
☛ The posterior surface is marked by a shallow posterior median sulcus from which a posterior median septum of neuroglial tissue extends into the substance of the cord to a variable extent.
Further Notes:
Why does the cauda equina exist? Remember a spinal nerve exits under its corresponding vertebra (save for cervical nerves). Spinal cord terminated at L1/L2 junction, but segments are still maintained so what do they do? For the remaining lumbar and sacral nerves to exit, they have to move downwards before exiting…hence the cauda equina.
State the location and extents of the spinal cord.
LOCATION: Within the vertebral canal
EXTENTS:
The spinal cord begins as a downward extension of medulla oblongata at the level of the foramen magnum/upper border of the first cervical vertebra and ends as conus medullaris at:
a) L1/2 junction in adults
b) L2 at puberty
c) L3 at birth
d) S1 at 6 months of fetal life
e) Coccyx at 3 months of fetal life (remember here, the spinal cord and vertebral column are of equal length)
NB: Vertebral column grows faster than the spinal cord.
Outline the arterial blood supply of the spinal cord.
-
Anterior spinal artery: it is formed in the posterior cranial fossa by the union of the right and left anterior spinal arteries which are the branches of the fourth part of the vertebral artery. It runs caudally in the anterior median fissure of the spinal cord and terminates along the filum terminale. It supplies the anterior 2/3 of the spinal cord, covering the following areas:
i) The anterior horn
ii)The lateral horn
iii) The central gray
iv) The basal part of the posterior horn
v) Anterior and lateral funiculi - Posterior spinal arteries: There are two posterior spinal arteries each arising as a small branch from either the vertebral or posterior inferior cerebellar artery. Each posterior spinal artery runs down on the posterolateral aspect of the cord in the posterolateral sulcus. It supplies the posterior 1/3 of the spinal cord, covering the posterior horns and posterior funiculi.
- Radicular arteries - The main source of blood to the spinal arteries is from the vertebral arteries (from which the anterior and posterior spinal arteries take origin). However, the blood from the vertebral arteries reaches only up to the cervical segments of the cord. Lower down, the spinal arteries receive blood through radicular arteries that reach the cord along the roots of spinal nerves. These radicular arteries arise from spinal branches of the vertebral, intercostal, lumbar and sacral arteries. These provide the principal blood supply to thoracic, lumbar, sacral and coccygeal spinal segments.
- [Diagram]
What is striking about the spinal meninges?
(1) The spinal dura is a single layer.
(2) The pia mater and arachnoid mater are closer together unlike in the brain (relatively apart in the brain hence large sub-arachnoid spaces) hence forming pia-arachnoid membrane. (Remember: pia and arachnoid mater are called leptomeninges)
(3) The vertebral column grows faster than the spinal cord. The attachment of the pia mater to Cx1 is however retained, and hence forms an elongation that extends up to the conus medullaris, known as the filum terminale.
(4) Since the filum terminale is just a narrow filament, the sub-arachnoid space around it is quite enlarged. This sub-arachnoid space is called lumbar cistern and it contains the cauda equina.
(5) The pia mater has very fine extensions that go through the arachnoid and attach to the dura. These tooth like extensions go from cervical to lumbar region. They are called ligamentum denticulate (denticulate ligaments).
Notes:
The lumbar cistern has a lot of CSF hence a common site for lumbar puncture procedure. Lumbar puncture procedure may be done to collect a sample of CSF or to administer an anaesthetic.
Briefly discuss the artery of Adamkiewicz/arteria radicularis magna.
[Many of these radicular arteries are small and end by supplying the nerve roots. A few of them, which are larger, join the spinal arteries and contribute blood to them.] One of the radicular branches, usually from the right or left 11th intercostal artery is very large and is called the arteria radicularis magna (artery of Adamkiewicz). Its position is variable. This artery may be responsible for supplying blood to as much as the lower two-thirds of the spinal cord.
What is the arterial vasocorona?
This is the arterial plexus found in the spinal pia mater which sends branches into the substance of the spinal cord.
Outline the venous drainage of the spinal cord.
The veins draining the spinal cord are arranged in the form of six longitudinal channels. These are:
a) Two median longitudinal channels, one in the anterior median fissure called the anteromedian channel, and the other in the posteromedian sulcus called the posteromedian channel
b) The paired anterolateral channels, one on either side, posterior to the anterior nerve roots
c) The paired posterolateral channels, one on either side posterior to the posterior nerve roots
These channels are interconnected by a plexus of veins that form a venous vasocorona. The blood from these veins is drained into radicular veins that open into a venous plexus lying between the dura mater and the bony vertebral canal (internal vertebral venous plexus) and through it, into various segmental veins.
Discuss anterior spinal artery syndrome. (cause and symptoms)
Anterior spinal artery syndrome: It occurs due to occlusion (thrombosis or compression) of the anterior spinal artery. Since the anterior spinal artery supplies the anterior 2/3 of the spinal cord, the occlusion of this artery will result in:
a) Motor symptoms due to involvement of corticospinal tracts and anterior grey columns (motor paralysis due below level of occlusion or lesion)
b) Sensory symptoms; bilateral loss of pain and temperature sensations due to ischemia of spinothalamic tracts
c) Note that proprioception and vibratory sensation will be retained due to intact dorsal columns
Notes:
1. What are corticospinal tracts? These are the major neuronal pathways providing voluntary motor function. They connect the cortex to the spinal cord to enable movement of distal extremities.
What are watershed regions of the spinal cord?
These are areas particularly susceptible to ischemia or insufficient blood supply due to their location at the border of the supply areas of two arteries.
The specific regions: T1, T4, T7-T9, L1
Clinical relevance: this region is vulnerable to watershed infarcts
Notes:
Infarction is tissue death and necrosis due to inadequate blood supply to the affected area.
What is Cauda Equina Syndrome? (Hint: cause, symptoms)
This is a syndrome that results from the compression and disruption of the functions of the nerves comprising the cauda equina. The compression is usually as a result of a herniated disc in the lumbar region.
Symptoms:
1. severe back pain
2. pain, numbness or weakness in one or both legs
3. numbness around the anus, loss of bowel or bladder control
4. sexual dysfunction
What is Conus Medullaris Syndrome? (Hints: cause, symptoms)
This is a syndrome resulting from compressive damage to the conus medullaris. Symptoms:
1. severe back pain
2. strange or jarring sensations in the back
3. bowel and bladder dysfunction
4. sexual dysfunction
5. weakness, numbness or tingling in the lower limbs
What is herpes zoster?
Dorsal nerve root ganglia (and the sensory ganglia of cranial nerves) can be infected with a virus. Vesicles appear on the skin over the area of distribution of the nerve.
Notes:
“Herpes zoster, also known as shingles, is caused by reactivation of varicella-zoster virus (VZV), the same virus that causes varicella (chickenpox). Primary infection with VZV causes varicella. After a person has varicella, the virus remains latent in the dorsal root ganglia.”
What is lumbar puncture?
Lumbar puncture is a procedure performed to obtain samples of cerebrospinal fluid (CSF) for various diagnostic and therapeutic purposes. In this procedure, a needle is introduced into the subarachnoid space through the interval between the third and fourth lumbar vertebrae.
State the anatomical basis for performing a lumbar puncture.
- presence of the lumbar cistern
- it is done at L3/L4 interval since the spinal cord in adults terminates at L1/L2 junction
