The Vertebral Column, Spinal Cord And Spinal Tracts Flashcards
Function of vertebral column
Protecting the spinal cord
Supporting the head and torso
Providing attachments for muscles and ribs
Site of haematopoesis
Number of vertebra in vertebral column
33
Number of cervical vertebrae
7
Number of thoracic vertebrae
12
Number of lumbar vertebrae
5
Number of sacral vertebrae
5- fused to form sacrum
Number of coccygeal vertebrae
4 - fused to form coccyx
Lordosis
Inwards curvature of the vertebral colimn
Kyphosis
Outwards curvature of the vertebral column
Where is lordosis of the vertebral column
Cervical lordosis of neck
Lumbar lordosis of lower back
Where is kyphosis in the vertebral column
Thoracic kyphosis of upper back
Scoliosis
Spine curves laterally
Body of vertebrae structure
Large, often cylindrical, structure located most anteriorly
Body of vertebrae function
Supports weight of vertebral column above it
What separates neighbouring vertebral bodies
Intervertebral discs
Pedicle
Stems posteriorly from vertebral body
Forms lateral wall of the spinal canal
Lamina
Posterior wall of spinal canal
Spinous process stems from the lamina
Spinal canal
Hole formed by the body, pedicle and Lamina
Spinal cord travels within the spinal canal
Transverse processes structure
Lateral protrusions from the vertebrae at the junction between the pedicle and Lamina
Transverse processes function
Provide an attachment for muscles
Cervical transverse processes
Form a canal for the vertebral arteries
Thoracic transverse processes
Form the primary site of articulation for the ribs
Articular processes structure
Vertical protrusions from the vertebrae
Articular processes function
Provide attachment site to the vertebrae above and below
Facet joints
Synovial articulations between vertebrae via Articular processes
Intervertebral foramina
Holes at the side of each vertebra formed by the spaces between the bodies and pedicles of neighbouring vertebra
Spinal nerves leave the cord via these foramina
Name of C1 vertebrae
Atlas
Atlas C1 articulates with
Articulates directly with the occipital bone of the skull- allows us to nod our heads
Atlas C1 structure
Shaped like a ring
The atlas bone has a space where the vertebral body should be
No spinous process
Name of C2 vertebra
Axis
Axis C2 structure
Body that protrudes vertically upwards = odontoid process- which takes the place of the body of the atlas above it so the atlas can spin around the axis
Allows us to then our heads = atlanto-axial joint (pivot joint)
Odontoid process
Body of axis C2 which protrudes vertically up into the body of the atlas
Name of pivot joint between atlas and axis
Atlanto-axial joint
C7 vertebrae
More prominent spinous process
Vertebra prominens = most superior spinous process that you can palpate through skin
No bifid spinous process
No transverse foramina
Distinctive Features of cervical vertebrae
Smaller body- support less weight
Transverse foramina to transmit vertebral arteries
Bifid spinous process
Distinctive features of thoracic vertebra
Additional Articular surface for rib
Long, sharp and downwards pointing spinous process - protect spinal canal
Increasingly large as must support more weight
Heart-shaped vertebral body
Distinctive features of lumbar vertebrae
Very large vertebral bodies
Transverse processes project laterally- provide attachment for additional muscles
Large, short and rectangular spinous processes
Joint between sacrum and pelvis
Sacroiliac joints
Sacral promontory
Anterior prominence at top of sacrum
Primary movements of C3-C7
Flexion, extension and lateral flexion
Primary movements of T1-T12
Rotation
Primary movements of L1-L5
Flexion, extension and lateral flexion
Function of intervertebral discs
Strong fibrocartilaginous structures able to withstand compression forces whilst also allowing flexibility and movement between each vertebrae
Nucleus pulposus
Central gelatinous core of intervertebral disc
Annulus fibrosus
Concentric rings of collagen surrounding the nucleus pulposus of the intervertebral discs
Secondary cartilaginous joint
Joint between vertebral bodies
Bone - hyaline cartilage - fibrocartilage - hyaline cartilage - bone
Function of spinal ligaments
Maintain upright position
Prevent hyperflexion and hyper extension injuries
5 spinal ligaments
Anterior longitudinal ligament
Posterior longitudinal ligament
Ligamentum flavum
Interspinous ligament
Supraspinous ligament
Location of anterior longitudinal ligament
Along the anterior surfaces of the vertebral bodies
Location of posterior longitudinal ligament
Along the posterior surfaces of the vertebral bodies
Anterior to spinal canal
Location of ligamentum flavum
Along the inside of the laminae
Why does the Ligamentum flavum appear yellow
Amount of elastin protein within it
What colour does the Ligamentum flavum appear
Yellow
Location of interspinous ligament
Between the spinous processes
Location of supraspinous ligament
Along the very tips of the spinous processes
Erector spinae structrue
A group of paraspinal muscles which form a column either side of the spinous processes
Erector spinae function
Maintain an upright posture
Where can the erector spinae muscles be palpated
Either side of the lumbar spine when standing
Disc herniation
Repetitive compression of the intervertebral discs can lead to weakening of the annulus fibrosus and posterior herniation of the nucleus pulposus which can narrow the intervertebral foramina or spinal canal. If an intervertebral foramen is narrowed and the transiting spinal nerve is compressed, this can cause weakness in muscles supplied by that nerve or altered sensation in the dermatome. If the spinal cord or cauda equina is compressed by the herniated disc, this can cause significant neurological deficit below that level and is a surgical emergency.
Lumbar puncture
This procedure involves sampling some CSF from the subarachnoid space in the lower vertebral canal. As the spinal cord terminates at L1/L2, a lumbar puncture (LP) must be performed lower than L2 to avoid damaging the cord. Below this level, the nerves of the cauda equina are simply pushed out of the way of the needle rather than being damaged by it.
To find an appropriate space between the vertebrae, the patient is positioned either sitting on the edge of a bed, or in the foetal position, and asked to push out their lower back to widen the space between the vertebrae. The L4/L5 space is in line with the intercristal plane (top of the iliac crests) so this is an appropriate space to aim for. As the needle reaches the subarachnoid space, the clinician can usually feel several gentle ‘pops’ when the needle pushes through the ligamentum flavum and dura mater. When CSF starts flowing out, the needle is in far enough.
Anaesthetic drugs may also be injected into the subarachnoid space through the same approach to give anaesthesia for surgery of the lower pelvis or lower limbs. This is known as spinal anaesthesia. A similar method involves injecting anaesthetic into the extradural space in the lower back and this is known as an ‘epidural’ anaesthetic.
Between which vertebra is a lumbar puncture conducted
L4/L5
What do spinal nerves leave the spinal cord through
Intervertebral foramina
Where do the cervical spinal nerves leave the spine
Directly above their corresponding vertebra (as far as C7)
C8 spinal nerves
Additional pair of spinal nerves that leave the vertebral column below the C7 vertebra
Where do all spinal nerves after C8 spinal nerves leave the vertebral column
Directly below their corresponding vertebra
Number of spinal nerve pairs
31
Conus medullaris
At level of L1-L2 junction
Spinal cord tapers off into a cone shape and terminates
At what level does the spinal cord terminate
L1/L2
Filum terminale structure
Dura and arachnoid meninges continue down to the sacrum
Pia mater thickens after the cord terminates to form a thin strand of fibrous tissue which continues down to the coccyx
Filum terminale function
Helps tether spinal cord in position
Which spinal nerves are given off just before the spinal cord terminates
L3-L5, S1-S5, Co1
Cauda equina
The mass of spinal nerves dangling within the spinal canal of L3-L5, S1-S5 and Co1 that descend so that can exit the canal at the correct level
What forms the spinal nerves
2 roots- dorsal and ventral roots
Dorsal root
Carries sensory fibres into the spinal cord
Contains dorsal root gangliom
Ventral root
Carries motor fibres out of spinal cord
No ganglion
Also carries sympathetic firbes
Grey matter
In centre of spinal cord
H shaped
Forms 2 dorsal horns and 2 ventral horns
Shortly after spinal nerve formation
Divides into 2 rami- dorsal ramus and ventral ramus
Dorsal ramus
Contains both sensory and motor fibres supplying dorsal structures eg skin over the back and paraspinal msucles
ventral ramus
Carries both sensory and motor fibres to ventral structrues
Which spinal rami is larger
Ventral
Thoracic ventral rami=
Intercostal nerves
Number of neurones in sensory pathways
3
First order sensory neurones
Receptor to CNS
Where are the cell bodies of first order sensory neurones
Dorsal root ganglion
Second order sensory neurones
Spinal cord or brainstem —> thalamus
Third order sensory neurones
Thalamus —> somatosensory cortex
Number of neurones in descending motor pathways
2
First order motor neurones (UMN)
Motor cortex —> ventral horn of spinal cord
Second order motor neurones (LMN)
Spinal cord —> target muscle
Spinal tracts
Bundles of axons within the peripheral white matter of the spinal cord
Function of dorsal column-medial lemniscus
Sensory
Fine touch, two-point discrimination, vibration and proprioception
dorsal column-medial lemniscus first order neurones
Enter spinal cord via the dorsal root and enter the ipsilateral dorsal columns
2 distinct tracts of dorsal columns
Fasciculus gracilis (medial)
Fasciculus cuneatus (lateral)
Function of Fasciculus gracilis
Sensory information from lower limbs
Function of Fasciculus cuneatus
Sensory information from upper limbs
Where do the dorsal column-medial lemniscus first order neurones synapse
Medulla
Gracile / cuneate nuclei
dorsal column-medial lemniscus second order neurones
Decussate in medulla
Continue to thalamus on contralateral side= medial lemniscus
Medial lemniscus
Second order neurones of dorsal column-medial lemniscus decussate in medulla and travel to contralateral thalamus
Where does the dorsal column-medial lemniscus decussate
Medulla
dorsal column-medial lemniscus third order neurones
Thalamus to primary somatosensory cortex in parietal lobe via internal capsule
Location of spinothalamic tracts
Antero-laterally in spinal cord
Function of spinothalamic tracts
Sensory
Crude touch, pain and temperature
Spinothalamic tract first order neurones
Enter spinal cord via dorsal root and synapse within dorsal horn
Spinothalamic tract second order neurones
Decussate in spinal cord after travelling up one or two vertebrae
Continues to thalamus on contralateral side
Where do the Spinothalamic tract decussate
Spinal cord - usually 1/2 levels above entry
Spinothalamic tract third order neurones
Thalamus —> primary somatosensory cortex in parietal lobe via internal capsule
What do third order neurones travel via from thalamus to primary somatosensory cortex
Internal capsule
Function of lateral corticospinal tract
Motor imoulses
Lateral corticospinal tract first order neurones
Leave motor cortex and pass through internal capsule
Decussate within medulla at level of medullary pyramids
Continue contralaterally in spinal cord
Synapse in ventral horn at desired spinal cord level
Where do Lateral corticospinal tract first order neurones decussate
Medulla at level of medullary pyramids
Where do Lateral corticospinal tract first order neurones synapse
Ventral horn of spinal cord
Lateral corticospinal tract second order neurones
Leave the cord via the ventral root towards target muscles
Anterior and posterior Spinocerebellar tracts location
Most laterally in cord
Anterior and posterior Spinocerebellar tracts function
Carry unconscious proprioceptive information to cerebellum
Anterior Spinocerebellar tracts
Decussates twice - once at level of entry to spinal cord and once as soon as it enter the cerebellum through the superior peduncle
Terminates ipsilaterally
Where does the Anterior spinocerebellar tracts decussate
Level of entry to spinal cord
As soon as it enters the cerebellum
Posterior Spinocerebellar tracts
Does not decussate
Ipsilateral cerebellum
Brown-sequard syndrome
This syndrome is caused by damage to one side of the cord only (hemisection of the cord). In clinical practice, it is quite a rare injury but causes characteristic findings on examination that explain the decussations of the tracts.
If a patient suffers damage to the left-hand side of their spinal cord, for example, then descending lateral corticospinal tract fibres are interrupted on the left side. Ascending dorsal column fibres on the left side are also interrupted. However, the ascending spinothalamic fibres that are interrupted on the left side had already decussated, therefore they were providing sensory information about the right side.
In this example, clinical examination below the level of the lesion would reveal loss of motor control of muscles on the left, loss of two-point discriminative touch, vibration and proprioception sensation on the left, but loss of pain and temperature sensation on the right from one or two levels below the lesion.
- What is the name of the joints that connect individual vertebrae together and allow movements between them?
Facet joints- intervertebral discs between them
- The ligamentum flavum connects which parts of the vertebrae together?
Laminae
- From where do sympathetic nerve fibres leave the spinal cord grey matter? Which root do they take to leave the cord? Where do they go after this?
T1 – L2 spinal cord, lateral horn. They leave via the ventral root alongside motor fibres and then travel with the spinal nerve towards the sympathetic trunk, where they join the sympathetic trunk and either synapse at that level, travel up or down the sympathetic chain to synapse at another level, or pass through it as a splanchnic nerve.
- What type of joint is the atlanto-axial joint?
Synovial pivot joint
- Where in the cervical spine does the majority of movement during nodding and turning the head take place?
C0-C1 = nodding (atlanto-occipital junction)
C1-C2 = turning head (atlanto-axial joint)
- Which arteries supply the spinal cord?
Anterior and posterior spinal arteries
- Describe the sensory and motor deficit (and which side is affected) by a lesion in the following locations:
a. Right side of the spinal cord only.
a. Loss of right sided motor function below the affected level, loss of right-sided fine-touch, vibration and proprioception sensation below the affected level, loss of left-sided pain and temperature sensation below the affected level.
- Describe the sensory and motor deficit (and which side is affected) by a lesion in the following locations:
b. Posterior third of the cord bilaterally.
b. Loss of fine-touch, vibration, and proprioception sensation bilaterally below the affected level.
- Describe the sensory and motor deficit (and which side is affected) by a lesion in the following locations:
c. Left sided dorsal root.
c. Loss of all sensory modalities in the affected left-sided dermatome.
- What layers of tissue must be penetrated to reach the CSF in a lumbar puncture?
Skin, subcutaneous fat, supraspinous ligament, interspinous ligament, ligamentum flavum, dura mater, arachnoid mater.
- Why are lumbar punctures performed as low as possible in the lumbar region? What might be the consequence of a ‘lumbar’ puncture in the thoracic region?
The spinal cord terminates at around L1/L2 and the cauda equina hangs in the spinal canal below this level. When a needle in inserted into the subarachnoid space below L1/L2, the needle can push the cauda equina nerves out of the way. If a lumbar puncture is performed higher than this level, the needle cannot push the spinal cord out of the way, and instead will penetrate it, which could cause neurological injury. The lower the lumbar puncture is performed, the less likely it is to damage the spinal cord.
- Explain why there are 33 vertebrae but only 31 spinal nerves.
There are 8 cervical nerves, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. In the cervical region, nerves leave above the corresponding vertebrae, except for the C8 nerves which leave below the C7 vertebrae. From that point onwards, all nerves leave the intervertebral foramina below their corresponding vertebrae. Finally, there is only one coccygeal nerve, but 4 fused coccygeal vertebrae.
Most lateral tracts
Spinocerebellar
Most posterior tracts
Dorsal columns
Tracts posterior to anterior
Dorsal columns
Lateral corticospinal
Spinothalamic
Spinocerebellar (lateral)
Most medial tract
Fasciculus gracilis
Posterior circulation of spinal cord supplies
Dorsal column-medial lemniscus
Anterior circulation of spinal cord supplies
Lateral corticospinal tracts
Spinothalamic tracts
Spinocerebellar tracts
Where do the ascending tract first order neurones synapse
Grey matter of dorsal horn
