How many cervical vertebrae are in most mammals and which processes do they have? What type of joints do they have between them?
Most mammals except for manatees and sloths have seven cervical vertebrae (the manatee has six and depending on the sloth species they have either six or nine cervical vertebrae).
Cervical vertebrae are distinguished by having large spinous and transverse processes except for the atlas and the axis.
Their joints are Intervertebral symphyses with fibrocartilaginous discs like the rest of the vertebrae except for the rib articulations with the vertebrae.
How many thoracic vertebrae are in most mammals and which processes do they have? What type of joints do they have between them?
Most mammals have 13 thoracic vertebrae except for horses, which have 18. The Arabian horse has 17 thoracic vertebrae.
The vertebrae themselves are joined together by intervertebral symphyses with fibrocartilagenous discs, while the ribs articulate via costavertebral synovial joints.
How many lumbar vertebrae do most mammals have and what are their processes? What types of joints do they form?
Most mammals have seven lumbar vertebrae. They are characterised by much wider transverse processes and short spinous processes.
L3 & L4 are the widest transverse processes in the horse; L5 & L6 arch cranially on horse.
They have the usual intervertebral symphyses with fibrocartilagenous discs inbetween.
How many sacral vertebrae do most mammals have? What are their characteristic processes and their joints?
Dogs and cats have three.
Sheep and pigs have four.
Horses have five.
The can have large dorsal processes that pitch caudally against grain of lumbar & thoracic spinous processes, & shallow or no transverse processes.
They are all fused so they don't from any joints.
How many coccygeal vertebrae do most mammals have, what are their characteristic processes and what type of joints do they have?
There is a lot of species and even breed variation in the number of coccygeal vertebrae. They range from 15 to 23.
Horses have 15-21.
Sheep have 16-18.
Cattle have 18-20.
Cats have 18-21.
Dogs and pigs have 20-23.
Cranial-most coccygeal vertebrae have have spinous, mammary & articular processes but more-caudal vertebrae are simple rods with tiny vertebral arches.
Their joints are intervertebral symphyses with fibrocartilagenous discs.
What are the main ligaments associated with the vertebral column and was it its role?
The nuchal ligament originates from the external occipital protuberance, extends down the length of the neck to insert on C7 spinous process.
In the horse, the nuchal ligament goes down to T3 where it is continuous with the supraspinous ligament that runs along the length of the spine along the dorsal processes.
The nuchal ligament IN THE HORSE & OX ONLY is comprised of BOTH the double, parallel funicular part that runs down the length of the neck, and the lamellar portion that connects to the spinous processes of T3.
It is made of very elastic tissue that enables the animal to hold its head up normally without muscle fatigue.
NB The nuchal ligement is absent in cats and very reduced in the pig.
Describe the epaxial and hypaxial musculature in relation to the spine.
Explain how these muscles contribute to the "bow and string" theory of the spine.
Epaxial muscles (thoracolumbar & pelvic regions) are located above and lateral to the spine.
Hypaxial (abdominal muscles) are located below the spine.
In quadripeds, the epaxial muscles EXTEND the spine and hypaxial FLEX the spine:
Imagine the spine as a bow, with the hypaxial muscles like the string of the bow pulling the ends closer together, flexing the bow. The epaxial muscles along the dorsolateral aspects of the spine extend the bow when they contract, pulling apart the ends of the bow.
The opposite bow & string theory works in the cervical spine, where the hypaxial muscles are the upside-down bow (the ends curved upward) and the epaxial muscles and nuchal ligament are the string. The contraction of the epaxial muscles and nuchal ligament flex the bow, ie., bring the ends closer together, while the hypaxial muscles and the lowering of the head to eat extend the bow.
Describe the intervertebral, fibrocartilagenous disc.
Discs have two parts"
1. soft, cushion-like nucleus pulposus
2. a fibrocartilagenous ring, annulus fibrosus, that surrounds the nucleus pulposus. The annulus fibrosus keeps the nucleus pulposus under pressure between the vertebrae.
What are some pathologies that can occur due to problems with the intervertebral disc.
The entire disc structure can slip or bulge out of the intervertebral space.
The nucleus pulposus, under pressure, can also slip out to touch/compress the spinal cord in prolapse.
Degeneration - loss of water in nucleus pulposus partly due to decrease in proteoglycan concentration (PG+water=hydrostatic cushion, sponge)
- less able to act as hydrostatic cushion - becomes less spongy
Chondrodystrophic Prolapse - chondrodystrophic dogs like Corgis or Dachshunds: their fibrocartilage disks turn into hyaline cartilage, which can mineralise, then prolapse. Ie., dogs with shortened legs relative to size; their limbs articificially shortened by introducing cartilage & bone disorders to limbs don't develop properly
Non-chondrodystrophic Prolapse - nucleus pulposus replaced with fibrous tissue (Collagen Type I), which is similar to the surrounding Annulus fibrosus
- Type I - NP extrusion - centre pops out
- Type II - AP protrusion - entire disc pops
What is the clinical relevance of the following disorders involving the spine?
Wobbler Syndrome (cervical spondylomyelopathy)
Kissing spines - spinous processes are too close together and impinge on each other. The most common location of these lesions is the vertebral segment between T10 and T18, although kissing spines are not rare between L1 and L6.
Wobbler Syndrome - also called cervical vertebral malformation-malarticulation and cervical spondylomyelopathy, is compression of the spinal cord caused by abnormal development of the cervical vertebrae. Genetic factors and possibly nutrition may be involved.
In dogs, middle-aged Doberman Pinschers and young Great Danes are most commonly affected, but the condition occurs in many large breeds. In horses, cervical spondylomyelopathy is the most common noninfectious disease of the spinal cord and occurs in many breeds.
What is the clinical relevance of:
Animals use their tails for balance, as rudders and for expression. Tail-docking can reduce animals' balance itself, to change position quickly, like a cheetah running after prey, and to express itself. Surgery and infections can also occur with the procedure.
What is the thoracolumbar fascia? In what animal is it very well-devleoped?
It is a deep investing membrane that covers the deep muscles of the back of the trunk. It is well-developed in the horse and is continuous with the nuchal fascia.
What are the three main groups of epaxial muscles from lateral to medial?
Iliocostalis - Lateral column; arises from the ilium and transverse processes of the lumbar vertebrae to insert on cranial lumbar vertebrae and ribs, spanning about 4 vertebrae.
Longissimus - Middle column; the strongest, extending from the ilium and sacrum to the head and neck
Transversospinalis - Medial column; the most complex, lying between the medial vertebral arches and the spinous processes.