3- Axial Structures.docx

- **Vertebral Formulae** - Dogs: C7, T13, L7, S3 - Cats: C7, 713, L7, S3 - Ox (cows): C7, T13, L6, S5 - Horses (and donkeys): C7, T18, L6, S5 - C= cervical; T= thoracic; L= lumbar; S= sacrum - Essentially: All (above) animals will have C7 and T 13, except...

- **Vertebral Formulae** - Dogs: C7, T13, L7, S3 - Cats: C7, 713, L7, S3 - Ox (cows): C7, T13, L6, S5 - Horses (and donkeys): C7, T18, L6, S5 - C= cervical; T= thoracic; L= lumbar; S= sacrum - Essentially: All (above) animals will have C7 and T 13, except horses with T18. - Small animals (dogs and cats) will have L7 and S3. - Large animals (Ox and horses) will have L6 and S5. - **Common vertebral features** - Vertebral body - Intervertebral discs are located between the bodies of each vertebra - Vertebral arch - This consists of paired pedicles (sides) and paired laminae (roof). - Vertebral foramen (plural- foramina) are surrounded by the arch and dorsal surface of the body. - Processes - (dorsal) spinous process - Transverse process: bilateral - Articular process: cranial and caudal pairs - Synovial joint - **Vertebral canal and intervertebral foramina** - Vertebral canal - Formed by the vertebral foramina and houses the spine - Intervertebral foramina - This is located laterally between adjacent vertebrae, and is formed by vertebral notches. - Spinal nerves and blood vessels course through this. - **Cervical Vertebrae: General Info** - Transverse foramina are present in C1-C6 vertebrae. - The **atlanto-occipital joint** is located between the atlas and the occipital condyles of the skull. - This joint allows for extension and flexion ONLY, and is referred to as the "yes" joint. - This joint can also be used for CSF (cerebral spinal fluid) sampling. - The **atlantoaxial joint** is located between C1 and C2, where it allows for rotational movement. - This joint can be referred to as the "no" joint. - The **transverse ligament of the atlas** courses across the vertebral arch of C1 and holds the dens against the atlas. - The **apical ligament of the dens** runs from the dens of the axis to the (occipital bone of the) skull. - The **alar ligament** runs from the dens of the axis to the (occipital bone of the) skull. - C1-C6 have transverse foramina for vertebral veins, arteries, and nerves. - C6 has an expanded ventral transverse process (that is very fat). - C7 lacks a transverse foramina and caudal costal foveae, which are typically used for articulation with the heads of the first ribs. - **Cervical Vertebrae: Atlas** - The Atlas is the C1 vertebrae, and has the following abnormal features, in comparison to the other cervical vertebrae: - No spinous process - Articulates with the occipital condyles of the skull - Has transverse foramina, which vertebral artery, vein, and nerve course through. - This also allows the vertebral artery to enter the vertebral canal - **Cervical Vertebrae: Axis** - The axis is the C2 vertebrae, and has the following abnormal features, in comparison to the other cervical vertebrae: - Large elongated spinous process - Dens: a peg like eminence which articulates with the atlas. - The dens of the Axis lies inside the vertebral canal, ventral to the spinal cord. - The dens can indicate the cranial aspect of the bone. - Like other cervical vertebrae, the axis has a caudal articular process. - However, unlike other cervical vertebrae, this process articulates with C3. - **Thoracic Vertebrae** - Cranial thoracic vertebrae have tall spinous processes, and short transverse processes. - T11 (anticlinal vertebra) has a spinous process which is perpendicular to the body. - This would be T16 in horses with this feature. - Thoracic vertebrae have a costal fovea present on vertebral bodies and transverse processes for rib articulation. - They also have extra processes for muscle attachment. - T10 has a spinous process that leans caudally towards T11. - T12 and T13 have a spinous process that leans cranially towards T11. - **Rib Articulation** - All 13 ribs have the following characteristics: - The tubercle of the rib articulates with the transverse process of the same numbered vertebra. - For example, the tubercle of Rib 5 will touch the transverse process of T5 (the 5^th^ thoracic vertebra). - The head of the rib articulates with the body of the same numbered vertebra. - For example, the head of Rib 5 will touch the body of T5. - For only ribs 1-20, they have the following characteristics: - The head of the rib articulates with the body of the preceding vertebrae, too. - For example, the head of Rib 5 will touch both the body of T5 and the body of T4. - **Costovertebral Ligaments** - **Intercapital ligaments** - These ligaments extend across the dorsal surface of the intervertebral disk and hod the heads of ribs in place. - They also reinforce the dorsal walls of intervertebral discs, making them less likely to herniate. - During herniation, intervertebral discs slip dorsally (up) and can hit the spinal cord. - **Costotransverse ligaments** - These ligaments course between the ribs and transverse process of the vertebra. - **Ribs and Sternum** - **Ribs** - Ribs have a bony and cartilaginous part, called the costochondral junction. - Dogs and cats have 13 pairs of ribs. - Ribs 1-9 are "true ribs" that connect to the sternum - Ribs 10-12 articulate with the cartilage of cranial rib to form the costal arch, where the ribs touch each other, rather than the sternum. - Rib 13 is the "floating rib" - **Sternum** - There at 8 sternebrae. - The manubrium is the 1^st^ sternebra. - The xiphoid process is the last sternebra. - **Lumbar Vertebrae** - The lumbar vertebrae have large bodies, and a large transverse process that points cranially. - They have a prominent spinous process, mammillary processes (on either side of spinous process), and accessory processes which point caudally. - **Sacrum** - The sacrum is composed of fused S1, S2, and S3 vertebrae. - The median sacral crest is formed by the fused spinous processes. - They have fused transverse processes. - The sacrum articulates with the ilium. - Rather than using the intervertebral foramina for spinal nerves, the sacrum uses these foramina: - Dorsal sacral foramen - Pelvic sacral foramen (sometimes called the "ventral sacral foramen") - The **sacral promontory** is a reference point for obstetrics, and is the cranioventral part of the sacrum. - This us useful as a reference point for bovine palpation. - **Caudal/Coccygeal Vertebrae** - The caudal/coccygeal vertebrae can be abbreviated to "Cd" or "Ca", while "C" is strictly used for cervical vertebrae. - The first few caudal vertebrae look like typical vertebrae, and then they become more rod-shaped. - The **Hemal Arch** is located on Cd4-Cd6, and works to protect tail vessels. - **Intervertebral Disc** - The intervertebral disc are located between the vertebral bodies, except for C1-C2 and at the sacrum. - The intervertebral disc is composed of a fibrocartilaginous structure with 2 parts: - **Anulus fibrosus** - The anulus fibrosus is the outer circumferential collagenous fibers that are thicker ventrally than dorsally. - **Nucleus pulposus** - The nucleus pulposus is the inner gelatinous core. - The intervertebral discs work as a shock absorber, spreading the load evenly between the bones. - **Vertebral ligaments** - **Supraspinous Ligament** - The supraspinous ligament courses dorsally along the spinous processes of the T1-Cd3 vertebrae. - **Nuchal Ligament** - The nuchal ligament is a cranial extension of the supraspinous ligament. - In dogs, this ligament courses between the spinous processes of the axis (C2) and T1. - In large animals, this ligament attaches to the skull, rather than C2. - Cats and pigs lack nuchal ligaments. - The nuchal ligament **in horses** has the following features: - It attaches to the nuchal crest of the skull. - The cranial and caudal nuchal bursae are located above the atlas and axis. - The supraspinous bursa is located over the most prominent processes of the withers. - The **withers** is a bump located between the shoulder blades of horses. - When there is inflammation of the bursae, it is referred to as "**poll evil**" and "**fistulous withers**". - The **poll** is a bump located between the ears of horses. - Bursae inflammation happens when the bursa bursts and the fluid leaks out, resulting in "poll evil". - **Dorsal Longitudinal Ligament** - The dorsal longitudinal ligament is located on the dorsal surface of the vertebral bodies, ventral to the spinal cord, and it courses from C2 to the sacrum. - NOTE: The dorsal longitudinal ligament is located dorsal to the body, but ventral to the spinal cord!! - **Ventral Longitudinal Ligament** - The ventral longitudinal ligament is located on the ventral surface of the vertebral bodies, and it courses from C2 to the sacrum. - **Interarcuate Ligament (AKA: Yellow Ligament or Ligamentum Flava)** - The yellow ligament courses between the vertebral arches dorsally and fills the interarcuate space. - Often, epidural injections are inserted through this ligament.