13 - Vertebral Column and Musculature Flashcards
What do I need to know?
- recognise different vertebrae and related their characteristics to function
- how the spinal cord is positioned and protected in the vertebral canal
- how the muscles of the lower back are arranged to provide support and movement
- stability/rigidity vs flexibility
- curvatures
- lumbar vertebra
- Linkages (discs and ligaments)
- Muscles and movements
- Nerves and vessels
How does the spine share an analogy to a yacht mast and rigging?
- a (jointed) mast (vertebral column)
- spars (ribs and transverse processes)
- rigging (muscles > NOT ligaments/tendons)
- attached to the hull (pelvis)
Is the spine stable or flexible?
It is BOTH stable and flexible
What is the benefit of having muscle as ‘rigging/support the mast’ rather than tendons and ligaments?
- having muscle means you can adjust the amount of tone so the spine has some inbuilt flexibility
- without this the spine would be quite rigid
How does stiffness change as you move towards the base (pelvis) of the spine?
> stiffness of the spine increases towards the base/pelvis
this means the lumbar region is more stiff than the cervical regions
this is because there is less material up the top
our ‘mast’ is relatively flexible but with increasing stability towards the base to support weight resulting in less lateral flexion and rotation permitted
What is the biological principle?
> high stability = low manoeuvrability
> low stability = high manoeuvrability/change direction quickly
How does flexion and extension change in the cerv/thor/lumbar regions?
Same degree of flexion and extension movement in all 3 vertebrae (40 degrees)
How does lateral flexion change in the cerv/thor/lumbar regions?
cervical - 40
thoracic and lumbar - 20
How does rotation change in the cerv/thor/lumbar regions?
Cervical and thoracic both 40 degrees
In the lumbar region this dramatically drops to 5 degrees (this is less than 1 degree per vertebra, meaning the lumbar region is very stable)
What are the 4 curvatures of the spine?
- Cervical: anterior
- Thoracic: reverses and is convex towards the posterior
- Lumbar: Anterior
- Sacral: Posterior
> is 9 vertebrae but is compressed and fused (variability among people)
> sacrum is 5 bones coccyx is 4
Lateral curvature?
Scoliosis
Increases Thoracic curvature?
Kyphosis / Kyphotic Spine
Increased Lumbar curvature?
Lordosis
> occurs in pregnant women to balance over the vertebral bodies
How do the curvatures of the spine arise?
We are NOT born with them. They occur by us standing up and by 10 years a child has an adult spine.
The bone remodels and changes shape as depending on the mechanical forces
What is the consequence of the lumbar curvature?
- as the lumbar curvature is anterior, it places vulnerable internal soft organs at some danger
- means the AORTA, which sits in front of the vertebral body, is positioned more to the anterior surface than the posterior
Where is the centre of gravity relative to the vertebral bodies?
- spinous processes are posterior vertebral body is considerably anterior
- centre of gravity is more posterior through the vertebral body than dead centre
- in an upright position we are standing over and balance over the vertebral bodies
Consequence of putting our centre of gravity over the vertebral bodies?
- means we can stand upright without excessive pressure on toes or heel
- it also minimises energy expenditure
- when we lean forwards and move away from the vertebral column THEN we expend energy to stay upright
What are the 7 parts of a typical vertebra?
- Vertebral body
- Arch
- Superior and Inferior Articular Processes
- Transverse Processes
- Spinous processes
- Pedicles
- Laminae
Vertebral Body?
- mostly spongy bone
- has a posterior depression for spinal cord
- has a smoother edge but a rough central region as there was a cartilage plate here to begin with and the fibres went from the bone into the cartilage. When the cartilage was taken out/dried out it leaves a rough dry surface
Superior and Inferior Articular Processes
- Where the lamina and pedicles meet
- on the inferior and superior surfaces are facets (part of the synovial joint between 2 adjacent vertebrae)
Transverse Processes
Where the lamina, pedicles and inf/sup articular processes meet. Project laterally
Spinous Process
Project posteriorly from the top of the arch
> in the lumbar region are flat and wide
> in the thoracic region they face inferiorly and overlap each other
Pedicles
The 2 pillars of arising from the vertebral body that make up the start of the arch
Laminae
Top bit of the arch
Where does the spinal cord run?
In the vertebral foramen (and cauda equina after L1)
How is our weight transferred down the spine?
The stacking of the vertebral bodies as well as the 2 posterior bony columns (articular processes) means there is 3 units/columns contributing to transfer the load
Describe the intervertebral discs
- the intervertebral discs are tightly adhered to the vertebral bodies
- mostly consist of a tough fibrous tissue (AF)
Describe the arrangement of collagen in the intervertebral disc/annulus fibrosus
The collagen is arranged in bands of concentric collagen, especially in the outer layers
What makes up the intervertebral discs?
Annulus fibrosus and nucleus pulposus
Describe the Annulus Fibrosus
- the collagen of these discs gets inserted into the bone of the vertebral body and effectively extends as ligaments
- The collagen is arranged in bands of concentric collagen, especially in the outer layers
- few bands of collagen run straight up/down (outer layers), most are on angles in orthogonal arrays
Where is the annulus fibrosus most prominent?
Lumbar region. Prevents movement especially rotation
What is the soft centre of the intervertebral disc?
Nucleus Pulposus
Describe the Nucleus Pulposus
- soft fibrous tissue centre of the intervertebral disc due to being rich in proteoglycans and hyaluronan which attract and bind water
- acts as a gel/soft ball bearing in youth that the vertebral discs rock over the top of
- the ball centre usually doesn’t squeeze out as is wrapped in the annulus fibrosus
What does the combination of the AF and NP provide?
Strength and flexibility
What is a slipped disc?
- is where there is a crack in the AF and the NP leaks out
- more common in older as the collagen bands become more cross linked and stiffer so more prone to fracture
- when the NP exudes out it often does so POSTERIORLY as the NP is situated more posteriorly to support body weight, and often sits onto the nerve roots that supply the lower limb and this causes back pain
What are some changes in the intervertebral disc that occur with age?
- there is a loss of water from the NP
- there is an increases stiffness and cross linking of the collagen in the AF
- there is calcification of the cartilage endplates (blue > red)
- the NP loses its softness with age and becomes fibrotic and movement is reduced
How is the intervertebral disc structured?
Articulating bone > plate of cartilage > AF > NP > AF > cart > bone
> the cartilage, AF and NP makes up the intervertebral disc
What are the 5 ligaments of the spine?
- Anterior Longitudinal Ligament
- Posterior Longitudinal Ligament
- Ligamentum Flavum (paired)
- Interspinous Ligament
- Supraspinous Ligament
Which of the 2 longitudinal ligaments is stronger?
- the anterior longitudinal ligament at the front of the vertebral bodies if thick and strong
- the posterior one is thinner and faces the vertebral foramen
Describe the paired ligamentum flavum
- are short and run between the bodies
- they run down the posterior of the foramen/anterior spinous process, on either side of the midline, and run from one lamina to the next
- they are slightly yellow as they have more elastin than collagen
Describe the interspinous ligament
- runs posterior between adjacent spinous processes
- when you flex this ligament allows the spinous processes to move away from each other
- short
Describe the supraspinous ligament?
- is also a longitudinal/continuous ligament that runs the length of the column
- runs along the tips of the spinous processes
What are the longitudinal ligaments that run the length of the column and what are the short ligaments?
Longitudinal = ant/post longitudinal ligaments, supraspinous ligament Short = Ligamentum Flavum, Interspinous Ligaments
What are 7 back muscles?
Latissimus Dorsi Serratus Posterior Inferior Iliocostalis Longissimus Multifidus Interspinalis Spinalis
What are the intrinsic muscles of the back and what are they called??
There are 3 They are the erector spinae muscles and they hold the spine erect > iliocostalis > longissimus > spinalis
What are the intrinsic back muscles?
Multifidus Interspinalis Spinalis Longissimus Iliocostalis
What is the superficial extrinsic back muscle?
Latissimus Dorsi
> limb movement
What is the intermediate extrinisc back muscle?
Serratus Posterior Inferior
> deep ventilation
What does extrinsic mean?
The muscles are not associated with spine movement
Iliocostalis?
Runs ilum to lateral costals/ribs
> they stabilise you out wide and allow lateral flexion
Back muscles from lateral to medial in a cross section?
Iliocostalis, longissimus, multifidus, interspinalis, spinalis (more medial)
What does intrinsic mean?
Muscles are integral to the function or support of the back
Longissimus
Extends along the transverse processes
- runs from the ribs to the transverse processes. Especially the sacrum (mostly tendon)
Spinalis
Runs along spinous processes
Which deep muscles are not intrinsic?
Interspinalis and multifidus
Multifidus?
Short stays from transverse processes to spinous processes
Compare the thoracic vertebra to the lumbar vertebra
THORACIC
- the articular processes are flat and insert to the one above/below
- the axis of rotation is therefore around the CENTRE of the vertebral body so in the upper body you can rotate and the facets slide over each other
LUMBAR
- the superior articular processes have inwardly curved facets towards the spinous processes
- in order to rotate the axis of rotation has to be around the spinous processes and would mean you would have to slide the vertebral bodies which you can’t as there are discs attached
= loss of rotation due to change in facet alignment joining adjacent vertebra
Why is there a loss of rotation in the lumbar region?
- Annulus Fibrosus is most prominent in the lumbar region
2. Due to the change in facet alignment joining the adjacent vertebra
Describe the nerve supply to the intervertebral discs
- supplied by branches of segmental spinal nerves that come anteriorly and posteriorly but only come in/supply the outer 1/3 of the disc and ligaments
- also get branches from the sympathetic system on each side of the disc
Describe the physiological consequence of the intervertebral discs nerve supply
Means only the periphery of the disc has a nerve supply so damage to the internal AF or NP will give no sensation
Why may it be difficult to localise back pain?
- there may be up to 3 levels of overlap of segmental nerves (& sympathetic)
- this means it is hard to tell which disc is affected
How is back pain similar to visceral (abdominal pain)?
It is diffuse - difficult to localise
Describe the blood supply to the intervertebral discs
- follows in a neurovascular bundle
- the blood is supplied via segmental vessels incl. posterior intercostal, lumbar and medullary
- the outer region of the annulus fibrosus is supplied directly
- the nucleus pulposus gets its nutrient supply via diffusion which means it has a low metabolic rate and nutrients
- this means damage done in the NP and inner AF is hard to repair as you need a lot of energy but there is no direct blood supply
Why are there more chronic conditions associated with the intervertebral disc?
- as it doesn’t repair fast enough after initial injury due to no blood supply/dependence on diffusion and so further damage accumulates
