B and SC 1.3 Flashcards
How many pairs of spinal nerves are there?
Thirty-one pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal) course from the spinal cord
What is the the spinal cord surrounded by?
- 3 meningeal layers
1. The innermost layer is the pia mater, which is closely applied to the spinal cord
2. The middle layer is the arachnoid mater
3. The tough, outer fibrous meningeal layer is the dura mater
What forms the cauda equina?
Posterior and anterior roots of the lumbar and sacral spinal nerves form the cauda equina (horse’s tail).
What is the terminal filum?
- The terminal filum is an extension of pia mater from the tip (conus medullaris) of the spinal cord
- It blends with dura at the apex of the dural sac and attaches to the dorsum of the coccyx. It helps anchor the distal spinal cord
Where would you insert a needle into the back?
- A spinal needle may be used to sample the cerebrospinal fluid in the subarachnoid space, 2. This procedure is done in the lower lumbar region where the needle will not penetrate the spinal cord (the cord ends at about the L1 vertebral level in adults)
- The roots of the cauda equina, bathed and floating in cerebrospinal fluid, will part and allow the needle to enter the subarachnoid space without puncturing a root.
What forms the posterior and anterior roots of the spinal nerve?
Posterior (dorsal) and anterior (ventral) nerve filaments combine in the intervertebral foramen to form the posterior and anterior roots of the spinal nerve
What is the spinal ganglion?
The spinal ganglion contains the sensory nerve cell bodies
What does each spinal nerve divide into?
Each spinal nerve divides into a very large anterior ramus and a much smaller posterior ramus
What anchors the spinal cord to the dura?
About 20 pairs of denticulate ligaments
What are denticulate ligaments?
are pial extensions that pass laterally between the posterior and anterior roots of spinal nerves to attach to the dura
Where is CSF found?
Subarachnoid space
What does subarachnoid space contain?
- The subarachnoid space (brain and spinal cord) contains about 150 mL of cerebrospinal fluid.
- The pressure of this fluid can be measured or sampled for laboratory analysis to determine if an infection is present somewhere in the central nervous system.
How does the spinal cord connect to the sympathetic chain ganglia?
By rami communicantes
Where are white and gray rami communcicantes found?
- White and gray rami communicantes are found between the T1 and L2 spinal cord levels
- but only gray rami communicantes are found at the other spinal cord levels.
Where do anterior and posterior roots join to form the spinal nerve?
In the interverbral foramen
What does the spinal nerve immediately divide into?
small posterior ramus, which supplies the skin and underlying intrinsic back muscles, and a much larger anterior ramus
What is the epidural space filled with?
The epidural space (between the dura mater and the bony vertebral canal) is filled with fat and a rich vertebral venous plexus
What could narrow the size of the intervertebral foramen and what could this cause?
Any pathology that narrows the size of the intervertebral foramen (excessive growth of adjacent bone, a tumor, an abscess) can impinge on the posterior or anterior roots or the spinal nerve and cause symptoms related to the nerve fibers carried in those roots or the nerve
How do afferent nerve fibres return to the spinal cord?
- Afferent (sensory) nerve fibers return to the spinal cord via the splanchnic nerve (pain sensation from viscera) and via the spinal nerve
- The cell bodies of these sensory nerve fibers reside in the spinal (dorsal root) ganglion
Where do the Preganglionic sympathetic efferent (motor) nerve fibers originate from?
originate from neurons in the intermediolateral cell column of the thoracic spinal cord
Where do the Preganglionic sympathetic efferent (motor) nerve fibers leave the cord by?
leave the cord via the anterior root
How do Preganglionic sympathetic efferent (motor) nerve fibers enter the sympathetic chain?
enter the sympathetic chain via a white ramus communicans
What happens after the Preganglionic sympathetic efferent (motor) nerve fibers enter the sympathetic chain?
- the nerve may continue via a splanchnic nerve to the celiac ganglion to synapse
- pass up or down the sympathetic chain to synapse at a higher-level or lower-level chain ganglion
- or synapse in the chain ganglion at the spinal cord level where it exited the cord
What happens when the preganglionic fiber has synapsed on the postganglionic neuron?
When the preganglionic fiber has synapsed on the postganglionic neuron (in a chain ganglion or the celiac ganglion), postganglionic fibers course to innervate viscera, smooth muscle, glands, or arrector pili muscles of the skin (attached to hair follicles)
How is the vagus nerve involved?
- Parasympathetic efferent fibers course to the viscera via the vagus nerve
- Reflex afferents from the viscera return to the brainstem also via the vagus nerve
- Visceral afferents also convey pain from distention, inflammation, or ischemia and return to the spinal cord via the splanchnic nerve and posterior root (cell bodies in the spinal ganglion)
Where are arteries supplying the spinal cord derived from?
branches of the vertebral, ascending cervical, posterior intercostal, lateral sacral, and lumbar arteries
What generally courses the length of the spinal cord?
- a single longitudinal anterior spinal artery
- and 2 longitudinal posterior spinal arteries
What accompanies the posterior and anterior roots of the spinal cord?
Segmental radicular arteries
What do anastomoses between the anterior and posterior spinal arteries and the segmental medullary branches form?
a pial arterial plexus
What provides the main blood supply to the spinal cord? What is it supplemented by?
- The anterior spinal artery and paired dorsal spinal arteries
- supplemented by radicular arteries from the aorta
What happens if blood flow through the radicular arteries is impaired?
(e.g., during surgery or if a fracture, dislocation, or other injury has occurred), the spinal cord may become ischemic and a spinal infarct can result.
What are the spinal veins?
Usually, there are 3 anterior and 3 posterior spinal veins (although veins are often variable)
How do these 6 veins communiste and drain?
- These veins communicate freely with one another
- drain into segmental radicular veins
What do the veins of the spinal cord and vertebrae form?
an internal vertebral plexus of veins
What do the veins of the spinal cord snd vertebrae communicate with?
an external vertebral venous plexus surrounding the bony vertebrae
Where does the vertebral venous plexus drain?
This vertebral venous plexus ultimately drains into intervertebral veins and then into the vertebral veins, ascending lumbar veins, azygos venous system, and inferior vena cava.
Do viens in the vertebral venous plexus possess valves?
- Most of the veins of the vertebral venous plexus do not possess valves
- but recent evidence suggests that some do; because of the large region that they drain (entire spine), they provide a conduit for the spread of cancer cells (metastasis) from one region (e.g., the pelvic region) to distant sites (e.g., the lungs, brain).
What do veins in the vertebral venous plexus provide a route for?
- The vertebral venous plexus (of Batson) is a network of veins that course along the spine 2. provide a route for venous metastases of cancer cells from distal locations (e.g., the pelvis) to seed the spine and other organs located more proximally (e.g., the lungs, brain)
