The vertebral column part 3 Flashcards
How many sacral vertebrae are there
5 (FUSED)
How many coccygeal vertebrae are there?
1-4 (FUSED)
How many vertebrae are there in total
30-33 depending on how many coccygeal vertebrae there are
Where do the spinal nerves emerge relative to their verebra
C1-C7 - above vertebrae
C8-coccygeal - below vertebrae
Where does the spinal cord extend from
The spinal cord extends from the foramen magnum to approximately the level of the disc between vertebrae LI and LII in adults, although it can end as high as vertebra TXII or as low as the disc between vertebrae LII and LIII (Fig. 2.47). In neonates, the spinal cord extends approximately to vertebra LIII but can reach as low as vertebra LIV.
Describe the distal end of the spinal cord
The distal end of the cord (the conus medullaris) is cone shaped. A fine filament of connective tissue (the pial part of the filum terminale) continues inferiorly from the apex of the conus medullaris.
Is the spinal cord uniform in diameter?
The spinal cord is not uniform in diameter along its length. It has two major swellings or enlargements in regions associated with the origin of spinal nerves that innervate the upper and lower limbs. A cervical enlargement occurs in the region associated with the origins of spinal nerves C5 to T1, which innervate the upper limbs. A lumbosacral enlargement occurs in the region associated with the origins of spinal nerves L1 to S3, which innervate the lower limbs.
Describe the external features of the spinal cord
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The anterior median fissure extends the length of the anterior surface.
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The posterior median sulcus extends along the posterior surface.
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The posterolateral sulcus on each side of the posterior surface marks where the posterior rootlets of spinal nerves enter the cord.
Describe the internal features of the spinal cord
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The gray matter is rich in nerve cell bodies, which form longitudinal columns along the cord, and in cross section these columns form a characteristic H-shaped appearance in the central regions of the cord.
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The white matter surrounds the gray matter and is rich in nerve cell processes, which form large bundles or tracts that ascend and descend in the cord to other spinal cord levels or carry information to and from the brain.
Ultimately, what does the blood supply to the spinal cord consist of
The arterial supply to the spinal cord comes from two sources (Fig. 2.49). It consists of:
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longitudinally oriented vessels, arising superior to the cervical portion of the cord, which descend on the surface of the cord; and
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feeder arteries that enter the vertebral canal through the intervertebral foramina at every level; these feeder vessels, or segmental spinal arteries, arise predominantly from the vertebral and deep cervical arteries in the neck, the posterior intercostal arteries in the thorax, and the lumbar arteries in the abdomen.
What do the longituidnal vessels consist of
a single anterior spinal artery, which originates within the cranial cavity as the union of two vessels that arise from the vertebral arteries—the resulting single anterior spinal artery passes inferiorly, approximately parallel to the anterior median fissure, along the surface of the spinal cord; and
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two posterior spinal arteries, which also originate in the cranial cavity, usually arising directly from a terminal branch of each vertebral artery (the posterior inferior cerebellar artery)—the right and left posterior spinal arteries descend along the spinal cord, each as two branches that bracket the posterolateral sulcus and the connection of posterior roots with the spinal cord.
Describe the segmental spinal arteries
After entering an intervertebral foramen, the segmental spinal arteries give rise to anterior and posterior radicular arteries. This occurs at every vertebral level. The radicular arteries follow, and supply, the anterior and posterior roots. At various vertebral levels, the segmental spinal arteries also give off segmental medullary arteries. These vessels pass directly to the longitudinally oriented vessels, reinforcing these.
Describe how the longituidnal arteries can be reinforced by the medullary arteries
The anterior and posterior spinal arteries are reinforced along their length by eight to ten segmental medullary arteries. The largest of these is the arteria radicularis magna or the artery of Adamkiewicz. This vessel arises in the lower thoracic or upper lumbar region, usually on the left side, and reinforces the arterial supply to the lower portion of the spinal cord, including the lumbar enlargement.
Summarise the venous drainage of the spinal cord
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Two pairs of veins on each side bracket the connections of the posterior and anterior roots to the cord.
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One midline channel parallels the anterior median fissure. (anterior spinal vein)
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One midline channel passes along the posterior median sulcus. (posterior spinal vein)
Where do the veins of the spinal cord drain into
These longitudinal channels drain into an extensive internal vertebral plexus in the extradural (epidural) space of the vertebral canal, which then drains into segmentally arranged vessels that connect with major systemic veins, such as the azygos system in the thorax. The internal vertebral plexus also communicates with intracranial veins.
Describe the spinal dura mater
The spinal dura mater is the outermost meningeal membrane and is separated from the bones forming the vertebral canal by an extradural space. Superiorly, it is continuous with the inner meningeal layer of cranial dura mater at the foramen magnum of the skull. Inferiorly, the dural sac dramatically narrows at the level of the lower border of vertebra SII and forms an investing sheath for the pial part of the filum terminale of the spinal cord.
This terminal cord-like extension of dura mater (the dural part of the filum terminale) attaches to the posterior surface of the vertebral bodies of the coccyx.
How do the spinal nerves emerge through the meninges
As spinal nerves and their roots pass laterally, they are surrounded by tubular sleeves of dura mater, which merge with and become part of the outer covering (epineurium) of the nerves.
Describe the arachnoid mater of the spinal cord
The arachnoid mater is a thin delicate membrane against, but not adherent to, the deep surface of the dura mater (Fig. 2.51). It is separated from the pia mater by the subarachnoid space. The arachnoid mater ends at the level of vertebra SII. Hence the sub-arachnoid space ends at S2.
Describe the sub arachnoid space of the spinal cord
The subarachnoid space between the arachnoid and pia mater contains CSF (Fig. 2.51). The subarachnoid space around the spinal cord is continuous at the foramen magnum with the subarachnoid space surrounding the brain. Inferiorly, the subarachnoid space terminates at approximately the level of the lower border of vertebra SII
Describe the arachnoid trabeculae
Delicate strands of tissue (arachnoid trabeculae) are continuous with the arachnoid mater on one side and the pia mater on the other; they span the subarachnoid space and interconnect the two adjacent membranes. Large blood vessels are suspended in the subarachnoid space by similar strands of material, which expand over the vessels to form a continuous external coat.
