Gross and cross-sectional anatomy of the spinal cord Flashcards
What is the function of the spinal cord?
1) Conduction:
- Provides tracts that conduct upwards (afferent, sensory, to the brain) and downwards (efferent, motor, to the muscles), connecting different levels of the trunk with each other and with the brain
2) Reflexes: Serves as the reflex center for all spinal reflexes that are involuntary of the brain
- Axon bundles in the CNS are known as tracts
Where is the location of the spinal cord?
Inside the spinal vertebrae canal, extending from the upper border of the atlas (as a continuation of the medulla oblongata) till the L1 & L2 in adults and the upper border of L3 in children
- The first vertebrae is called the atlas
- Conus medullaris is located where the spinal cord ends (L1-L2)
What is the filum terminale? and what is its function?
It is a strand of connective tissue that attaches the conus medullaris to the first coccygeal vertebrae
- It adheres to the bone stabilizing the spinal cord in place
Describe the spinal cord
- 45cm long
- elongated and cylindrical in shape, having 2 enlargements: (cervical enlargements = muscles of the U.L. “C5-T1” & lumbar enlargement, for muscles of the L.L. “L2-S3”)
- It tapers inferiorly forming the conus medullaris
- Filum terminal extends downwards attaching to the back of the coccyx
What is cauda equina?
It is the bundle of spinal nerves coming from L1-L2 till the coccygeal 1
What is the content of the spinal cord below L1 & L2?
- CSF that also surrounds the whole spinal cord
- Roots of spinal nerve arising from the lower lumbar and sacral segments (cauda equina), as they did not exit through the foramen yet
What is the level of the conus medullaris in regard to the vertebral level?
L1 & L2 IN ADULTS WHILE L3 IN CHILDREN
What are the different segments of the spinal cord?
- It comprises 31 segments
- 31 segments of spinal nerves (each segment is attached by two roots “ventral & dorsal”)
- The dorsal root has a ganglion “collection of nerves/cell bodies”
1) 8 cervical
2) 12 thoracic
3) 5 lumbar
4) 5 sacral
6) 1 coccygeal
- Lumbar + sacral + coccygeal = cauda equina below the conus medullaris
At which location does the spinal nerve exit the vertebrae?
All of the nerves exit below the vertebrae except the cervical nerves they exit from above, giving 8 cervical nerves although there are only 7 vertebrae
Describe the composition of the spinal nerve
- The spinal nerve is made when the dorsal and ventral roots join together, a mix of motor and sensory fibers
- The spinal nerve splits into 2: one that goes to the back of the neck known as dorsal rami and the other one moves to the anterio lateral surface known as ventral rami, communicating rami is connected to the ganglia and to the spinal cord
- Dorsal has sensory fibers “afferent”, while ventral has the motor fibers “efferent”
What is the relative position of the spinal cord segment and vertebral body segment?
1) For the cervical nerves the spinal nerve exits above the vertebrae so you add one for each vertebral segment
2) For the thoracic vertebrae 1-6, you add two
3) For the thoracic vertebrae from 7-9, we add 3 to get the corresponding spinal cord segment
4) For the thoracic vertebrae 10, the spinal cord segment associated with it is L1 and L2
5) For the thoracic vertebrae 11, the spinal cord segment associated with it is L3 and L4
6) For the thoracic vertebrae 12, the spinal cord segment associated with it is L5
7) For the lumbar vertebrae 1, the spinal cord segment associated with it are all sacral and coccygeal segments
What is meant by disc herniation?
a condition during which a nucleus pulposus is displaced from intervertebral space
What are the most common sites for disc herniation?
Cervical and lumbosacral region
What is cauda equina syndrome?
It is a central lumbosacral disc herniation, which is a dysfunction of one or more of the sacral nerve roots S2 and below
What is meant by a disc prolapse?
It is a bulging/protrusion of the disk compressing the spinal nerve at a specific level
What is the difference between a tumor and disc herniation in regards to the nerve root affected?
between L4 and L5 is L5 so in herniated disc nerve L5 is affected but in the case of a tumor to the L4 vertebra the L4 spinal nerve will be affected.
- On the other hand in the thoracic region if a disc herniation occurs the above nerve is affected (if the disk between T4 and T5 is enlarged it compresses on the T4 nerve)
What is the importance of the spinal nerves?
- Diagnosing neurological disorders
- Lesion of one or more nerve roots results in neurological defects (muscle weakness, loss of sensation), this will allow us to localize the causing lesion
What is a dermatome?
An area of the skin innervated by sensory axons (cutaneous branches) of a single spinal nerve
C2 The top part of the head
C3 the top part of the neck anteriorly and posteriorly
C4 middle part of the neck anteriorly and posteriorly
C5 from the clavicle to the lateral part of the upper limb (shoulder)
C6 Lateral part of the forearm (UL) and thumb
C7middle of the hand, second third, and half of fourth finger
C8 half of fourth, fifth finger, and medial part of the forearm
T1 Medial part of the arm
T2 Axilla
T2-12 thorax till the umbilical (below it)
L1-5 anterior and inner surface of lower limbs and part of the lower back
L4 median side of the great toe
L4, 5, S1 foot
S1, 2 L5 posterior and outer surface of lower limbs
S1 Lateral margin of the foot and little toe
S2, 3, 4 perineum
What is a myotome?
All the muscles innervated by the motor neuron of a single spinal nerve
for example, biceps are innervated by C5 & 6
If there’s a lesion in the C5 segment, Which region of the skin will be affected? Which muscles will be affected? Which movements will be affected?
Shoulder, biceps, flexion
What happens to the foramen when the disc degenerates?
It narrows
What are the examples of disc problems?
1) Degenerated disc
2) Bulging disc (compresses spinal nerves)
3) Herniated disc (huge buldge)
4) Thinning disc
5) Disc degenerating with osteophyte formation
What are the coverings of the spinal cord?
- Covered by three layers “meninges”
From out to in they are:
1) Spinal dura matter
2) Spinal arachnoid matter (the sub-arachnoid space contains the cerebrospinal fluid)
3) Spinal pia matter
Describe the dura mater
- It is a tough, fibrous outer layer
- The space between it and the bony wall of the canal is called the epidural space
- The space under it the subdural space
- Inferiorly the dura mater ends at the S2 level
What are the contents of the epidural space?
1) Loose connective tissue
2) Fatty tissue
3) Plexus of veins (it doesn’t have valves, meaning that blood can travel in any direction, increasing the chance of spreading malignant cancer)
What is the level of dural sac termination?
The dura and arachnoid end at the S2 segment, while the film terminale is attached to the coccyx (pia continuation)
At what level does the CSF terminate?
S2, hence below it there is no CSF to withdraw
Describe the arachnoid matter
- Under the dura mater
- It has a consistency similar to spider web
- Contains abundant spaces within and beneath it “subarachnoid space”, which contains the cerebrospinal fluid (CSF)
- Closely adherent to the dura mater with almost no space
- Supplies a water jacket for the spinal cord and brain for protection and shock absorbing
At what level does the arachnoid mater ends?
S2
Describe the pia mater
- Very thin vascular layer that tightly adheres to the surface of the brain and spinal cord
- Nourishes the spinal cord with blood supply
- Follows all contours and fissures “sulci” of the spinal cord
- Does not terminate with the spinal cord at L1-L2 level rather it continuous as a filament “filum terminale” which is a continuation of the pia mater without the spinal cord attaching to the coccyx, providing stability
- Forms denticulate ligaments at regular intervals which extend laterally anchoring the spinal cord to the dura mater
Describe the internal structure of the spinal cord
1) Posterior median sulcus
2) Anterior median sulcus
3) Gray matter (contains lots of nuclei, and no axons)
4) White matter (contains myelinated axons and no nucleus)
5) Tracts
Describe the structure and content of the grey mater
- Consists mainly of nerve cell body
- It consists of two equal halves that are connected by the grey commissure, which is transversed by the central canal
- In all Spinal cord levels each half consists of:
1) Dorsal grey horn (towards the back)
2) Ventral grey horn (towards the front)
3) Lateral grey horn (column), the lateral is only from the level T1 to L2
- As we go down from the cervical segments to the coccyx the grey matter increases in size
Describe the function and contents of the dorsal/posterior grey horn
- Consists of groups of sensory cell bodies (nerve cells)
1) substantial gelatinosa of Rolando/lamina II (first one to be encountered posteriorly, it has a sensory nucleus that senses pain & temperature)
2) lamina III & IV/ main sensory nucleus/ nucleus proprius (senses touch and pressure)
3) Lamina VII/ nucleus dorsalis/ Clarks nucleus (it serves as a proprioception)
Describe the content and function of the ventral/anterior grey horn
- Consists of multipolar motor cells called anterior horn cells (A.H.C)
- The axon of the motor nerve passes through the ventral root to innervate the skeletal muscles
FYI: The anterior horn cells are considered the lower motor neurons (LMN) as they are second-order neurons in the long descending tract from the brain
Describe the location & function of the lateral grey horn
- Present in two regions only, for autonomic involuntary functions
1) Thoracic region (T1-L2): sympathetic flow, containing the sympathetic nerve cell bodies
2) Sacral segments (S2, 3, 4): for the parasympathetic nerve cell bodies, these nerves are controlled by it and the brain stem (craniosacral)
Describe the white mater and state its divisions
- Consists of ascending “sensory” and descending “motor” tracts (myelinated nerve fibers that are grouped together)
- Every tract has the same cells of origin, termination & carries the same function
- It is divided into:
1) Posterior white column
2) Lateral white column
3) Anterior white column
- As we go down the spinal cord the white matter decreases in size
How to differentiate between different regions of the spinal cord?
Depending on the cross-section, ventral horns, lateral horns, dorsal horns, and white matter:
1) Cervical:
- Oval cross-section
- Thick and large ventral horns
- No lateral horns
- Slender, long and diverging dorsal horns
- Large white matter
2) Thoracic
- Contains lateral horn
3) Lumbar
- Oval to rounded cross-section
- No lateral horn
- Thick and parallel dorsal horns
- Little white mater
4) Sacral
- Rounded cross-section
- No lateral horns
- Very little white mater
How to do a lumbar puncture?
A needle is introduced just above or below the L4 till the subarachnoid space
Why do we do a lumbar puncture?
1) To measure the pressure of the C.S.F (normal is 60-150 mm water)
2) Sampling for analysis of C.S.F
3) Injecting local anesthesia or antibiotic
4) Removing C.S.F incase of increased intracranial pressure
What is poliomyelitis?
- A viral infection that affects the motor Anterior Horn Cells, causing lower motor neuron lesions, which can lead to the atrophy of the muscle and can later affect the respiratory muscles
FYI the vertebral column is a very common site for secondary metastasis (due to the vessels not having valves) and the lesions may be traumatic, infectious, tumors, degenerative, etc
What happens if the spinal cord is transected?
1) If above C5 = Death (due to the paralysis of the phrenic nerve)
2) If between C5-T1 = Quadriplegia (loss of sensation and movement in all four limbs and the trunk)
3) If below T1 (in the thoracic region) = Paraplegia (loss of sensation and movement in the legs and in part or all of the trunk
