Spinal Cord and Meninges Flashcards
Describe the spinal cord
Part of the central nervous system
Within the vertebral canal
Covered with 3 layers of meninges
List the boundaries of the vertebral canal
Body of vertebra
Pedicle
Lamina
Spinous process
Transverse process
Vertebral foramen
Describe the development of the spinal cord
The vertebral column grows faster than the spinal cord.
In the embryo (8 weeks), the spinal cord and vertebral canal are equivalent lengths. [spinal segments = vertebrae]
In neonates, the spinal cord ends at the L3 vertebra.
In adults, the spinal cord extends from the foramen magnum to the disc between L1/L2
Define the extent of the spinal cord within the vertebral canal
Begins at the foramen magnum of the skull, as a continuation of medulla oblongata.
Ends at L1/L2 vertebrae in adults.
Inferior end of the cord is called the conus medullaris which narrows as filum terminale.
External features of the spinal cord
Cervical enlargement between C4-T1 vertebrae
(brachial plexus)
Lumbosacral enlargement between T11-S1 vertebrae
(lumbosacral plexus)
Internal features of the spinal cord
Contains gray matter and white matter
Gray matter - inside : looks like a butterfly
White matter - outside : covers the gray matter
Describe the gray matter of the spinal cord
Contains neuronal cell bodies within its ‘horns’
Has a central canal
Anterior and posterior grey commissures.
Describe the horns of the gray matter in the spinal cord
TOP
MIDDLE
STUBBY BOTTOM
- Dorsal (posterior) horns : inter-neurons
- Lateral horns : visceral (autonomic) motor neurons
- Ventral (anterior) horns : somatic motor neurons
Describe the white matter of the spinal cord
Columns containing a number of ascending and descending tracts.
All tracts are paired and most decussate.
Anterior and posterior white commissures.
Describe the 3 parts of white matter
Ventral (anterior) columns
Lateral columns
Dorsal (posterior) columns
Describe the structure of the spinal cord
The spinal cord is ‘divided’ into segments that are associated with one pair of spinal nerves.
Cervical - 8 segments and nerves
Thoracic - 12
Lumbar - 5
Sacral - 5
Coccygeal - 1
Spinal nerve terminology
Rootlets converge to become roots
Ventral (motor, efferent) and dorsal (sensory, afferent) roots converge to become a spinal nerve (mixed motor and sensory)
Spinal nerves divide into ventral and dorsal rami (mixed motor and sensory nerve fibres)
Spinal nerve
Mixed motor and sensory nerves
Formed by the converging of ventral and dorsal roots.
Rami
Mixed, motor and sensory nerve fibres.
Formed by the division of spinal nerves
C1 nerve
Passes between the occipital bone and the atlas.
C8 nerve
Passes between C7 and T1
Describe the relationship between the number of vertebrae and spinal nerves.
Seven cervical vertebrae – Eight cervical spinal nerves
1-4 coccygeal vertebrae – One coccygeal spinal nerve
Number of vertebrae and spinal nerves are equal in other regions.
31 pairs of spinal nerves emerge from the intervertebral foramina, each nerve through its own foramen (except C1).
Describe the spinal nerves of the cervical region
In the cervical region, spinal nerves are numbered according to the vertebra below.
e.g. C3 nerve passes out between C2 and C3
Describe the spinal nerves of the thoracic region
Below T1, spinal nerves are numbered according to the vertebra above.
e.g. T3 nerve passes out between T3 and T4
Cauda equina
[aka horses tail]
It is the roots of the lower lumbar and sacral spinal nerves, within the lumbar cistern.
Describe the function of the meninges
Three membranes which surround, protect and suspend the brain, spinal cord and spinal nerves.
Contains cerebrospinal fluid (CSF) in the subarachnoid space.
Describe the arrangement of the meninges
INSIDE
Pia matter
Subarachnoid space
Arachnoid matter
Dura matter
Epidural fat
Vertebral canal
OUTSIDE
What is dura mater ?
Outermost, thick layer (in the skull it has 2 layers : outer periostea layer, inner meningeal layer)
Function of the dura mater
It covers the roots of spinal nerves as they pass through the intervertebral foramina.
Within the vertebral canal, dura mater is called the dural sac, and is not attached to bone.
Where does the dura mater end ?
The dura mater narrows extensively at the lower border of the S2 vertebra where it fuses with film terminale.
What is arachnoid mater ?
It is the middle layer of meninges.
It lies deep to and in contact with dura in the living. There is no space between the Dura and Arachnoid mater.
What is between arachnoid and Pia mater ?
Subarachnoid space containing CSF and blood vessels.
Features of the arachnoid mater
Continuous with subarachnoid space around the brain.
Ends at lower border of the S2 vertebra.
Between L1/2 and S2 forms the lumbar cistern.
Define the extent of the subarachnoid space
Between the arachnoid and pia mater.
What does the lumbar cistern contain ?
Contains CSF, Cauda Equina and some blood vessels
Outside Pia mater
What is Pia mater ?
Innermost layer of meninges
A thin vascular layer, closed adhered to the surface of the spinal cord.
Covers the surface of spinal cords
Describe what Pia mater becomes
Becomes filum terminale at the tip of the conus medullaris, attached to the coccyx.
Condenses and forms denticulate ligaments between the roots of the spinal nerves.
What is epidural space ?
Between the periosteum and dura.
Extends between the foramen magnum and sacral hiatus.
Contains internal vertebral venous plexus within fatty tissue.
Describe arterial supply to the spinal cord
2 sources of supply :
- Longitudinal arteries
- Segmental arteries
Longitudinal arteries
x3
Branches of (branches of) the subclavian artery.
Lie on the surface of the cord.
What are the 3 longitudinal arteries ?
2 posterior spinal arteries
- branches of vertebral and posterior inferior cerebellar arteries
1 anterior spinal artery
- branch of vertebral artery
Segmental arteries
Numerous
Branches of the aorta
Enter vertebral canal via intervertebral formaina
Describe segmental arteries
Reinforcement of supply via Segmental / Radicular branches
Arteries enter via the intervertebral foramina
- Cervical (arise from vertebral arteries)
- Thoracic (arise from intercostal arteries)
- Lumbar (arise from lumbar arteries)
Describe the blood supply and venous drainage of the spinal cord
Longitudinal channels on surface of cord
Internal vertebral venous plexus
External vertebral venous plexus
Longitudinal channels on surface of cord
No valves, blood flows in either direction
Internal vertebral venous plexus
Lies in extradural fat of epidural space
Lies within vertebral canal
External vertebral venous plexus
Drains medullary cavity of the vertebral bodies and connects to segmental veins (lumbar and azygous)
Surrounds vertebrae
Clinical relevance of venous connections
Venous connections can result in metastasis of tumours to vertebral bodies.
List the structures through which the needle must pass when performing a lumbar puncture.
Skin
Superficial fascia
Supraspinous ligament
Interspinous ligament
Ligamentum flavus
Extradural (EPIDURAL) space
Dura mater
Arachnoid mater
Subarachnoid space
