Spinal Cord and Nerves Flashcards
Subdivisions of the nervous system
What is gray matter? What is it called in the CNS/PNS?
A collection of nerve cell bodies.
CNS: Cortex and nucleus
PNS: Ganglion
What is white matter? What is it called in the CNS/PNS?
Axons with glial sheath (myelin).
CNS: pathway e.g. tract/fascicle
PNS: nerve
How many spinal nerves are there?
31 pairs:
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
Where do the spinal nerves emerge from the spinal cord?
Intervertebral formaina (space between each vertebrae)
how many spinal vertebrae are there?
- 7 cervical
- 12 thoracic
- 5 lumbar
- Sacrum (5 fused)
- Coccyx (3-4 fused)
- Where does the spinal cord extend from/to?
- How does it terminate?
- What is it continuous with superiorly?
- Extends from: foramen magnum
- Continuous with medulla oblongata superiorly
- Extends to: vertebral levels L1-L2
- Terminates as conus medullaris
What is the conus medullaris?
The tapered, lower end of the spinal cord. It occurs near lumbar vertebral levels 1 (L1) and 2 (L2), occasionally lower.
Cross section of spinal cord
- Spinous process posteriorly
- Vertebral body anteriorly
Dorsal view of spinal cord. What is cauda equina?
The long collection of nerves that leave the spinal cord at the lower end of the spinal cord (i.e. below the conus medullaris)
View of termination of spinal cord as the conus medullaris as well as cauda equina
What is the filum terminale?
- A delicate strand of fibrous tissue proceeding downward from the conus medullaris to insert into the coccyx
- Provides an inferior attachment for spinal cord –> secures it into the coccyx to prevent excessive movement
Describe the meningeal arrangement surrounding the spinal cord
- Dura mater –> only one layer: the meningeal layer
- Dural sac:
- Membranous sheath of dura mater that surrounds the spinal cord and caudal equina
- Contains CSF
- Extends lower than termination of spinal cord –> encompasses cauda equina nerves
- Under dura mater is the arachnoid layer
- Under the arachnoid layer is the subarachnoid space, filled with CSF
What are the cauda equina nerves suspended in?
CSF
What 2 enlargements are found along the spinal cord?
- Cervical enlargement
- Lumbar enlargement
What are the regions of the spinal cord?
Based on spinal nerves: each spinal nerve segment gives rise to 1 pair of segmental spinal nerves.
- 8 Cervical segments (C1-C8)
- 12 Thoracic segments (T1-T12)
- 5 Lumbar segments (L1-L5)
- 5 Sacral segments (S1-S5)
- 1 Coccygeal segment (Co1)
- Conus medullaris
- Cauda equina
- Filum terminale
Are the pairs of spinal nerves part of the CNS or PNS?
PNS
Where does the dural sac extend to?
S1/S2
What is the lumbar cistern? What does it contain?
- Refers to the subarachnoid space in the lower lumbar spinal canal.
- The cistern is an enlargement of the subarachnoid space in the dural sac, distal to the conus medullaris.
- It contains CSF and the nerve roots of the cauda equina.
Why is the cervical spinal region thicker (cervical enlargement)?
- Cervical region is where you find all the motor cell bodies (gray matter) that innervate the upper limbs
- Including collections of nerves that form the brachial plexus (C1-C8)
What is the lumbosacral enlargement?
- A widened area of the spinal cord that gives attachment to the nerves which supply the lower limbs
- Lumbosacral plexus (L1-S4)
- It commences about the level of T11 and ends at L2
What roots does the cauda equina contain?
Dorsal and ventral roots of lower lumbar, sacral and coccygeal spinal nerves
Why is there 7 cervical vertebrae (C1-C7) but 8 cervical nerves (C1-C8)?
C1–C7 emerge above their corresponding vertebrae, while C8 emerges below the C7 vertebra (and just above T1 vertebrae)
how do the cervical spinal nerves emerge in relation to their corresponding cervical vertebrae?
C1–C7 emerge above their corresponding vertebrae, while C8 emerges below the C7 vertebra (and above T1)
how do the thoracic spinal nerves emerge in relation to their corresponding thoracic vertebrae?
Emerge below their corresponding vertebrae
View of cervical and thoracic spinal nerves leaving in relation to their corresponding vertebrae
Meninges of spinal cord view.
- is the subdural space real or potential?
- is the subarachnoid space real or potential?
- subdural: potential
- subarachnoid: real
What are denticulate ligaments?
- Lateral extensions of pia mater that secure the spinal cord each side
- Found interspersed between spinal nerve roots
- Pass from the pia mater, through the arachnoid mater and into the dura mater
- Function: prevent excessive movement
As the spinal nerve roots leave the spinal cord, what do they take with them?
A layer of meninges
As the spinal nerve roots leave the spinal cord, they take with them a layer of meninges. What do these go on to form?
The epineurium: a protective outer sheath of connective tissue for each spinal nerve.
How does the dura mater in the cranium differ from that of the spinal cord?
- Cranium: dura mater has 2 layers (meningeal and periosteal)
- Space between these 2 layers is potential
- Spinal cord: dura mater has 1 layer (meningeal only)
- Space between vertebrae and dura mater is real –> filled with fat
What is the epidural space (between vertebrae and meningeal dura mater) filled with?
Fat
Why does the spinal cord end before the vertebral column ends? Describe changes from foetus, to birth, to adult
- Differential growth of vertebral column:
- During development, the dural sac grows along the vertebrae but not the spinal cord
- Vertebral column grows faster (so spinal cord ascends)
In foetus (2-3 months):
- Spinal cord extends all the way along length of vertebrae
- S1 spinal nerve root exits near level or origin
- Spinal cord and dura terminate near end of vertebral canal
At birth:
- Vertebral column grows faster compared to spinal cord
- Spinal cord regresses and ascends upwards
- Filum terminale remains attached to coccyx
- Spinal cord (conus medullaris) ends around L3 vertebral level
- S1 spinal nerve root now originates near lumbar region but still extends down to exit below S1
- Spinal cord regresses and ascends upwards
Adult:
- Vertebral column keeps growing faster than spinal cord (cord keeps ascending)
- Spinal cord now terminates between L1 and L2
- S1 now originates around L1
- Lumbar and sacral nerves extend down as the cauda equina to reach their corresponding vertebral level exits
- Lumbar cistern: filled with CSF
- Filum terminale continues to attach to coccyx and secure spinal cord
Describe the changes in disparity between the vertebral level of the emergence of spinal roots from the spinal cord and their level of exit via intervertebral foramina
Spinal nerve roots show disparity between their segmental attachment to the cord and the corresponding vertebral levels:
- Cervical spinal nerves emerge and then exit close to cervical segment
- BUT as you continue down the spinal cord, spinal nerves start to emerge and then descend before exiting the spinal cord below their corresponding vertebrae
- This is due to differential growth
View of cauda equina
Travel through the lumbar cistern in order to reach their corresponding vertebrae
What is a lumbar puncture? What is the function? Where must the needle be inserted?
- The CSF within the lumbar cistern is the target of a lumbar puncture
- Cistern is an enlargement of the subarachnoid space in the dural sac, distal to the conus medullaris.
- It contains cerebrospinal fluid and the nerve roots of the cauda equina
- Cistern is an enlargement of the subarachnoid space in the dural sac, distal to the conus medullaris.
- Purpose:
- Take a sample of CSF from your spinal cord
- Measure the pressure of the CSF – to help diagnose a condition
- Inject medications – such as painkillers, antibiotics or chemotherapy.
- Needle must be inserted below L3 (to be safe, as conus medullaris may extend further in anatomical variations)
- Spinal cord normally ends between L1-L2