Download Vertebral column and back Bony framework of the vertebral

ANAT20006 Lecture 13: Vertebral column and back Bony framework of the vertebral column The vertebral column: • Axial skeleton – forms the axis from which our upper and lower limbs hang off • Regionally distinct vertebrae (33) • Intervertebral joints (and discs) – between adjacent vertebral are joints => movement • Vertebral canal and intervertebral foramen Function: • Support/supporting axis – be able to move lower and upper limbs • Movement – joints • Protection of nervous system – spinal cord housed within vertebral column From diagram: • 7 cervical vertebrae (C1-­‐C7) = neck • 12 thoracic vertebrae (T1-­‐12) = back (unique: ribs) • 5 lumbar vertebrae (L1-­‐L5) = lower back • Sacrum (5 fused sacral vertebrae 1-­‐5): they develop embryologically as individual vertebrae, but later fuse in post-­‐natal development to become 1 structure • Coccyx (3-­‐4 coccygeal vertebrae 1-­‐4): residual tail Structure of vertebral column • When we develop (embryologically), our back develops with single, anteriorly, concaved primary/foetal “C” shaped curvature • Secondary “lordotic” curves develop in cervical and lumbar regions o Cervical: following normal development (a few months of age) as nervous system matures (neck becomes stronger, eyes function better), baby takes interest in surroundings § It starts lifting its head § Reversal of primary curve – occurs in neck o Lumbar: when pelvic musculature occurs, become stronger in lower limbs (~ 1 year old), toddlers can pull themselves up § Secondary curve develops in lumbar regions (lumbar lordosis) § Gets our lower limbs underneath us, instead of in front of us (dogs, cats) • Abnormal curvatures may occur: o Lordosis (sway back): particularly in overweight men/pregnant women due to anterior weight they carry o Kyphosis (hunchback): increased primary curvature of thoracic region o Scoliosis (sideways curvature): vertebral column does not run straight up and down Structure of a typical lumbar vertebra Vertebrae are irregular bones Pedicles Once you start stacking vertebrae on top of each other Comes off the back of vertebral body 1. Transverse process 2. Spinous process 3. Articular process (2 superior, 2 inferior) Lamina – arches around posteriorly Body itself is reasonably large structure – pedicle that comes off back of the body is relatively small => notch Muscles move Vertebrae takes the vertebrae weight from head (back + neck) down until transferred to pelvis => vertebral body bears weight Vertebrae are regionally distinct Differences in size between the vertebrae reflect the amount of weight each vertebra are taking • Cervical vertebra – weight of head • Lumbar vertebrae – weight of head, both arms, trunk => larger than cervical vertebra • Sacrum – 5 individual vertebrae that fuses -­‐-­‐> forms triangular shape singular bone When lumbar vertebrae articulate with sacral vertebrae – weight gets dissipated down through the pelvis -­‐-­‐> down to the lower limbs. • The more distal sacral vertebrae don’t have to be large because they don’t take much weight => sacral vertebrae tapering down The vertebral canal and spinal cord The spinal cord • Does not pass entire length of vertebral column o Body grows taller than nervous system elongates • Terminates at L1/2 o Nervous system extends more distally (nerves emanate from vertebral column) • Cauda equina – long filaments of our dorsal rootlets and ventral rootlets that emerge down the vertebral column • Surrounded by meninges (protective layering) = dura mater, arachnoid mater, pia mater Intervertebral foramen • Stacking up vertebrae -­‐-­‐> see new structures emerging between adjacent vertebrae • Once you have 2 adjacent vertebrae articulating anteriorly with the bodies and posteriorly with articular processes, foramen forms o Bilateral – if bounded superiorly by inferior notch and inferiorly by superior notch • Contents: o DRG o Mixed spinal nerve (yellow) o Vessels • Intervertebral disk – makes up joint between 2 adjacent bodies Spinal nerves • Spinal nerves that emerge from intervertebral foramen are named according to where they come out of the spinal cord (e.g. 1st cervical nerve, 2nd cervical nerve etc.) • Thoracic vertebra – nerves are named for the vertebrae that come out below Spinal nerves: • Rootlets emerge bilaterally from the spinal cord • Contain ventral (motor) and dorsal (sensory) roots • Note location of cell bodies: o Motor neurons in the spinal cord ventral horn o Sensory neurons in the dorsal root ganglion • Mixed spinal nerves gives off anterior and posterior rami in the intervertebral foramen o As it emerges, it divides into anterior and posterior ramus Vertebral column itself is subdivided into anterior ventral regions/horn and dorsal horn • Ventral horn = motor neurons • Dorsal horn = sensory • They combine at intervertebral foramen – where they combine is where the cell bodies of sensory neurons are Joints of the vertebral bodies Intervertebral joints – secondary cartilaginous joints • Joints appear between adjacent vertebrae bodies • Anulus: o Attaches to the epiphyseal ring above and below o Consists of concentric lamellae (layers -­‐-­‐> form rings) o Functions to keep vertebra together – to attach from 1 body to the body adjacent (stops vertebra from being pulled apart) o Anulus fibrosus: heavily fibrous and multi-­‐layered • Nucleus: o Encapsulated within the anulus fibrosis o Consists almost entirely of water – very hydrated o Functions to keep vertebra apart Over time, our ability to reabsorb water decreases (in our 70’s/80’s) = shorter – lose height due to compressive forces occurring constantly in our backs Aged person (nucleus is dried out – normal process of aging) Young child – disk is well hydrated (normal) Functions of intervertebral disc • Anulus: o Concentric fibrous rings orientated at right angles (obliquely) – because they are orientated concentrically, if you twist, it tightens up 1 set but loosens up another o Enables movement in all directions without tearing o Resists excessive movement • Nucleus: o Deformable but not compressible o ‘Shock absorber’ Joints of the vertebral arches Zygapophyseal (facet) joints – between articular processes of adjacent vertebrae • Plane synovial joint o Synovial joint = synovial membrane, joint capsule, hyaline cartilage on articular surfaces Articular processs: • Plane synovial joints – permit gliding along only 1 axis • Movements available are determined by the shape and depth of the articular surfaces • Orientation of the articular processes differ regionally o E.g. thoracic articular processes – facets orientated in the coronal plane and permit rotation o E.g. lumbar articular processes – orientated in the sagittal plane and permit flexion/extension • Facets guide direction of the movement Joints of vertebral bodies Ligaments of the vertebral column: • Anterior and posterior longitudinal ligaments: o Posterior runs down the back of the vertebral bodies – runs within the vertebral canal § Over the body, it’s a straight band but as it gets to intervertebral disk, it gets wider over disks -­‐-­‐> comes back narrower over body (and so on) o Anterior runs down the front of vertebral bodies • Interspinous and supraspinous ligaments o Interspinous = between the spines o Supraspinous = runs on top of the spines With power lifting techniques, can get injury occurring to intervertebral disk where nucleus can push its way through the anulus. • In posterior longitudinal ligament, it gives extra protection posteriorly to intervertebral disk • Don’t want disk bulge to push back directly posteriorly because it will put pressure/push against the spinal cord • Widening of posterior longitudinal ligament gives extra protection to posterior aspect of intervertebral disk => if a disk does tend to bulge, it cannot push back posteriorly -­‐-­‐> ends up pushing more laterally Ligamenta flava – runs down the back of the vertebral column – attached to adjacent lamina • Very high in elastic – can be stretched and then returned to normal state • Great degree of flexion occurring around the back – need ligamenta flava to stretch a little to allow flexion to occur • When we straighten up, stretch has to come back to stable position/shorter length Muscles of the back Superficial/extrinsic muscles of back – have 1 attachment to the back but their 2nd attachment is to structures of upper limb • Trapezius – broad attachment to spine and scapula • Latissimus dorsi – large attachment to thoracic and lumbar vertebrae o Emerges and attaches to humorus • Levator scapulae – elevates the scapula • Rhomboid major + rhomboid minor – attach to the back and scapula Not true back muscles – they move the upper limbs