Difference between revisions of "Spinal Column - Anatomy & Physiology"
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==Cervical Vertebrae== | ==Cervical Vertebrae== | ||
*The first two cervical vertebrae are known as the '''atlas''' and the '''axis''' respectively, and are modified to allow movement of the head | *The first two cervical vertebrae are known as the '''atlas''' and the '''axis''' respectively, and are modified to allow movement of the head | ||
− | **The atlas has no conventional body: instead it is | + | **The atlas has no conventional body: instead it is composed of two lateral masses joined by dorsal and ventral arches |
**The atlas and axis are fused in embryonic life | **The atlas and axis are fused in embryonic life | ||
**The '''wing of the atlas''' is the transverse process of this vertebra and allows the spinal column to articulate with the skull by providing a resting place for the occipital condyles | **The '''wing of the atlas''' is the transverse process of this vertebra and allows the spinal column to articulate with the skull by providing a resting place for the occipital condyles |
Revision as of 12:15, 3 September 2008
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Divisions and Landmarks
The common pattern of canine landmarks, according to Dyce, Sack, et al, can be quantified as such:
Vertebrae and Joints
- Vertebrae consist of a body which encloses the vertebral foramen (through which the spinal cord and meninges run), a spinous process, and a transverse process, as well as articular processes by which they join together
- The form of the spinous process varies with respect to species and region
Cervical Vertebrae
- The first two cervical vertebrae are known as the atlas and the axis respectively, and are modified to allow movement of the head
- The atlas has no conventional body: instead it is composed of two lateral masses joined by dorsal and ventral arches
- The atlas and axis are fused in embryonic life
- The wing of the atlas is the transverse process of this vertebra and allows the spinal column to articulate with the skull by providing a resting place for the occipital condyles
- The axis is the longest vertebra
- The nuchal ligament connects the spinous process of the axis to the spinous process of the first thoracic vertebra (T1)
- The last (C7) cervical vertebra has a taller spinous process than those proceeding it, and articulates with the first pair of ribs
Thoracic Vertebrae
- Thoracic vertebrae articulate with the ribs
- They are distingushed by short bodies with flattened extremities, costal facets, short transverse processes, and prominent spinous processes
- They reach a maximum height a few vertebrae behind the cervicothoracic junction (constituting the withers of the horse) and then decline
- The orientation of spinous processes shifts from caudo- to craniodorsal
Lumbar Vertebrae
- Longer and more uniform in shape than thoracic vertebrae
- Shorter in height, with long, flattened transverse processes that project laterally
Sacral Vertebrae
- Sacrum: a single bone formed by the fusion of several vertebrae that articulates with the pelvic girdle
- Allows the thrust of the hindlimbs to be transmitted to the trunk
- Narrows caudally and is curved to present a concave surface to the pelvic cavity
Caudal Vertebrae
- Number varies greatly even within species
- Progressive simplification of form
Joints of the Spinal Column
- Two types of joints:
- Cartilaginous: direct connections between vertebral bodies
- Bodies of adjacent vertebrae connected by thick, flexible intervertebral discs, consisting of two parts:
- Nucleus pulposus: slightly eccentric, notochord derivative, contained under pressure and prone to escape
- Annulus fibrosis: encircling bundles of fibrous tissue that pass obliquely from one vertebra to another, with changing orientation
- Bodies of adjacent vertebrae connected by thick, flexible intervertebral discs, consisting of two parts:
- Synovial: between facets on vertebral arches
- Cartilaginous: direct connections between vertebral bodies
- Modified in the regions of the head and pelvis
- Joints of the atlas:
- Atlanto-occipital joint: between condyles of the skull and corresponding cavities of the atlas
- Functions as a ginglymus: movement is restricted to flexion/extension in the sagittal plane (eg nodding)
- Atlantoaxial joint: ventral arch of atlas and the body of the axis face into a single synovial cavity with limited areas of contact
- Movement is rotational about a longitudinal axis (eg. head shaking)
- Atlanto-occipital joint: between condyles of the skull and corresponding cavities of the atlas
- Joints of the atlas:
Spinal Cord
Hypaxial and Epaxial Muscles
- Epaxial muscles: extensors of the vertebral column
- Dorsal to the line of the transverse processes of the vertebrae
- Innervation comes from the dorsal branches of the spinal nerves
- Rarely of clinical importance
- Arranged in three parallel columns
- Lateral column: Iliocostalis arises from the ilium and transverse processes of the lumbar vertebrae to insert on cranial lumbar vertebrae and ribs, spanning about 4 vertebrae
- Middle column: Longissimus; strongest, extending from the ilium and sacrum to the head and neck
- Medial column: Transversospinalis; most complex, lying between medial vertebral arches and spinous processes
- Hypaxial Muscles: flexors of the neck and tail
- Longus colli: from cranial thoracic region to the atlas, covering ventral vertebral bodies
- Rectus capitis ventralis: atlas to ventral skull
- Longus capitis: midcervical vertebrae to skull
- Scalenus muscles: caudal cervica vertebrae to first few ribs, which they stabilize on inspiration