LCRS: Anatomy: Head, Neck & Spine - Vertebral Column & Spinal Cord
Vertebral Column & Spinal Cord Recognise and name the following parts of a typical vertebra in osteological specimens or in suitable imaging: body, pedicle, lamina, transverse process, spinous process, articular surfaces
Recognise the distinctive features of cervical, thoracic and lumbar vertebrae The vertebrae are different depending on whereabouts in the spinal cord they lie:
•
Cervical Vertebrae: there are 7 cervical vertebrae. They are characterised by: o the foramen transversarium in the transverse processes through which the vessels run, o very small vertebral bodies o a short and bifid spinous process
o • • • •
triangular vertebral foramen LCRS: Anatomy: Head, Neck & Spine - Vertebral Column & Spinal Cord
Thoracic vertebrae are characterised by facets used for articulations with the ribs (the transverse processes) and are at more of an angle with the vertebral body. They are smaller than the lumbar vertebrae. Their vertebral foramen is circular. Lumbar vertebrae are characterised by their large bodies and have rounded upper and lower facets to prevent rotation. Sacrum is one fused set of five vertebrae that articulate with the pelvic bone. Coccyx is usually a set of 4 fused bones inferior to the sacrum.
Explain the roles of intervertebral discs, ligaments and muscles in load bearing in the vertebral column Intervertebral Discs o o
o o
The intervertebral disc forms the cartilagous symphyses between vertebral bodies in the vertebral column. It consists of 2 layers, the Anulus fibrosus (outer ring of collagen surrounding fibrocartilage) and the Nucleus pulposus (gelatinous filling in the centre which absorbs compression between the vertebrae). As we get older, the anulus fibrosus can degenerate resulting in herniation of the nucleus pulposus. These can press on the sciatic nerve root ( L5 and S1) and so cause pain in the lower back radiating to the back of the thigh. •
•
the spine is rotating at the same time. •
•
The lumbar region is the most common site of back pain because it is subjected to stress during weight bearing. Trying to extend the spine from a fully flexed position (bending over) places a lot of stress of the intervertebral discs and so the joints can become inflamed. This is even more dangerous if
In order to prevent this, when lifting heavy loads, the load should be held close to the body and the knees should be extended rather than the spine so that the load can be lifted.
NB: there are no discs between the skull and CI or between CI and CII due to specialised movements that occur at these joints Each vertebra articulates with the one above and below via; The midline cartilaginous joint – the intevertebral disc Two lateral synovial joints between the transverse processes – facet joints The movements permitted are flexion, extension, and lateral flexion to both sides Ligaments
There are 2 main ligaments running up either side of the vertebral bodies: the anterior and posterior longitudinal ligaments. Whip-lash neck hyperextension damage to anterior longitudinal ligament Ligamenta flava: runs in between each lamina. (pierced during a lumbar puncture) Suproaspinous ligament: runs up posterior to the spinous processes (i.e. along the ends). Interspinous ligaments: pass between the adjacent vertebral spinous processes. Articular Ligaments: surrounds all facet joints. LCRS: Anatomy: Head, Neck & Spine - Vertebral Column & Spinal Cord Describe the relative extents of antero-posterior flexion, lateral flexion and axial rotation in the major regions of the vertebral column and explain this in terms of skeletal anatomy Back Movement 4 main movement of vertebral column: -
Extension Flexion Lateral Flexion Rotation
The amount of movement between two adjacent vertebrae is limited, the additive effect of them all moving allows posture change. There is more limited movement in the thoracic part of the column because of the articulation with the ribs. Flexion/extension
Lateral flexion
Rotation
C1-C7
++
++
++
T1-T6
0
+
+
T7-T12
+
++
++
L1-sacrum
++
+
0
Muscles Contraction of the muscles of the abdominal wall causes flexion and lateral flexion There are two main groups of muscle: Superficial extrinsic muscles including trapezius and latissimus dorsi Deep intrinsic muscles, particularly the erector spinae, which are important in controlling the movement of the vertebral column. The large muscle bulk posterior and lateral to the vertebral column
Atlas and Axis Atlas: is the top bone (CI) in the vertebral column that articulates with the head. It lacks a vertebral body and is located just posterior to the mouth. The skull sits on top of the lateral masses
Axis: the second bone in the vertebral column (CII) on which the atlas rests and contains the dens (allows head rotation) which slots nicely into the facet in the atlas and is held together by the transverse ligament of the atlas. It has no emerging spinal roots. The CI-CII atlanto-axial joint: • In the midline • A synovial joint between the dens and the back of the anterior arch of the atlas, and a synovial bursa between the dens and the cruciate ligament behind • Laterally the articular surfaces are flat to allow gliding • The cruciate ligament separates the dens from the spinal meninges Atlanto-occiptal joints – between CI and the occipital bone of the skull form synovial joints linked by apical ligaments to allow nodding of the head.
State the number of vertebrae in each region of the spine, and how the pairs of spinal nerves are related to them Spinal Nerves: Nerve C1 is between the skull and CI vertebra. Nerves C2 – C7 emerge superior to the vertebral peduncles Nerve C8 emerges inferior to the vertebral peduncle CVII Nerves T1 downward emerge inferior to their respective vertebrae. Number of vertebra e
Number of spinal nerves
Relationship of nerve to vertebra
Cervical
7
8
All above corresponding vertebra except for C8
Thoracic
12
12
All below corresponding vertebra
Lumbar
5
5
All below corresponding vertebra
Sacral
5
5
All below corresponding vertebra
Coccyx
1 fused (or up to 4 unfused)
1
Below (or between if unfused)
Total
30
31 LCRS: Anatomy: Head, Neck & Spine - Vertebral Column & Spinal Cord
Explain the arrangement of the meninges around the spinal cord and roots, and indicate any differences from the cranial meninges Meningeal Layers Dura Mater – thick, hard external covering. In the brain this is attached to the skull but in the spinal cord it is not attached to any bone. Arachnoid mater – against (but not adherent to) inner surface of dura mater Subarachnoid Space - the subarachnoid space is in between the pia and arachnoid mater and contains CSF. Continuous with foramen magnum Pia Mater – a vascular membrane that is adherent to the spinal cord although has denticulate ligaments that attach it to the arachnoid mater.
NB: the filum terminale is at the lower end of the spinal cord (L2) and is attached to the coccyx. It is formed when the spinal cord withdraws upward during development - the Pia mater surrounding the cord is prolonged. Together with the nerve roots, it forms the cauda equine (horse’s tail) below L2.
a. Identify
two
major reasons for carrying out lumbar puncture, and explain the basis for the puncture site b.
Explain the danger of carrying out lumbar puncture without excluding the presence of raised intracranial pressure Lumbar Puncture - Used for obtain a sample of CSF for examination - Used to inject anaesthetics for patients with operations on their legs. - Used to asses CSF pressure. - It is done between L4 and L5 because the spinal cord stops but the CSF is still in the meninges. NB: lumbar punctures should not be done in the presence of raised intra-cranial pressure. This is because herniation of the cerebellum through the foramen magnum may occur. Epidural anaesthesia – a liquid agent can be injected into the epidural space to anaesthetise the spinal nerve roots. The sacral hiatus allows administration of caudal epidural anaesthesia
Describe the most common abnormalities of spinal curvature Spinal Curvature Abnormalities Scoliosis – vertebral column is laterally deviated. Kyphosis – thoracic curvature is bigger than normal (hump-back) Lordosis – lumbar curvature is bigger than normal (e.g. obesity)