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Vertebral Column and Thoracic Anatomy – Study Notes

  • Vertebral column overview

    • Sections (from cranial to caudal): cervical, thoracic, lumbar, sacral, coccygeal.

    • Common abbreviations mentioned (for vertebra groups): cervical (C), thoracic (T), lumbar (L), sacral (S), coccygeal (Cy or Co). In lecture notes, they sometimes abbreviated together as CTLSCY.

    • Six species discussed: dog, cat, horse, cattle (cow), sheep, and pigs.

    • All mammals have seven cervical vertebrae (C1–C7). Size varies, but count stays 7.

    • The first two cervical vertebrae are special: C1 is the atlas; C2 is the axis. C3–C7 look similar to each other.

    • For vertebra identification, focus on type (cervical vs thoracic vs lumbar, etc.) and key structures, not on exact position among C3–C7.

    • The quiz date is September 3; topics from today’s discussion are fair game; topics from Wednesday are not on the quiz.

  • Cervical vertebrae (C1–C7)

    • Seven cervical vertebrae in all mammals; C1 (atlas) and C2 (axis) are unique in shape/name; C3–C7 are similar to one another.

    • Atlas (C1): broad and flat (some say butterfly-like); sits directly below the skull; has two indentations that articulate with the occipital condyles of the skull.

    • Axis (C2): clearly different from C1; identified as the second cervical vertebra.

    • C3–C7: identical in appearance; you should identify them by being cervical-type vertebrae rather than by exact numbered rank.

    • Key cervical structures to know on any cervical vertebra: spinous process, body, and transverse process; vertebral foramen (central hole) is present in all vertebrae.

    • Lateral foramina: unique to the cervical vertebrae; there are two lateral foramina on either side of the vertebral foramen, present in C1–C7 (including C1 and C2).

    • Vertebral foramen: the large central hole through which the spinal cord runs.

    • Spinous process: the ridge running down the back of the vertebra.

    • Transverse process: the two projections on the sides.

    • Body: the main, ventral part of the vertebra; the large portion you hold/observe.

  • Thoracic vertebrae (T1–T13 in dog, etc.)

    • Species variations in the number of thoracic vertebrae: dog ≈ 13; horse ≈ 18; cow and sheep ≈ 13; pig ≈ 15 ext{–}16 (breed-dependent).

    • Each thoracic vertebra has the same basic structures as other regions: spinous process, transverse process, body, and vertebral foramen.

    • Thoracic vertebrae differ in appearance from cervical: thoracic spinous processes are taller and more pronounced; thoracic transverse processes are relatively small; vertebral foramen is still the central opening.

    • The vertebral foramen is the opening in the center through which the spinal cord passes.

    • The body forms the ventral aspect of the vertebral canal.

  • Lumbar vertebrae

    • Similar structural components as thoracic vertebrae (spinous process, vertebral foramen, body, transverse process).

    • Transverse processes in the lumbar region are very prominent (large, elongated wings to the sides).

    • The body is the large, ventral portion; the vertebral foramen sits just above it.

    • The spinous process in lumbar vertebrae tends to be broader and fatter than in thoracic vertebrae.

  • Sacrum

    • Located between the wings of the pelvis; not counted as part of the pelvis itself, but part of the vertebral column.

    • In dogs, the sacrum is composed of three fused sacral vertebrae; in horses and cows, it’s five; in sheep and pigs, it’s four.

    • Features similar to other vertebrae: spinous process along the top, vertebral body, vertebral foramen; the sacrum also has wings/transverse elements, though they’re smaller.

    • Function: helps with pelvic stability and serves as a landmark for certain surgical procedures.

  • Coccygeal vertebrae (tail)

    • The coccygeal vertebrae compose the tail; the number varies by species and breed (e.g., boxers have many coccygeal bones; tail docking practices vary).

    • Notable feature: coccygeal vertebrae do not have a vertebral foramen; they are solid bone.

    • Nerves between coccygeal vertebrae run along the outside rather than through a central vertebral foramen.

    • Spinal cord termination varies by species:

    • In dogs, the spinal cord ends at L5; in cats, ends at L4.

    • Beyond the end of the spinal cord, the cauda equina forms a frayed bundle of nervous tissue.

    • Epidural considerations:

    • In dogs, epidurals are performed between L7 and S1; this location is well caudal to the actual termination of the spinal cord, reducing risk of injuring the cord.

    • In large animals (horses, cows), epidurals are performed between the sacrum and coccygeal vertebrae.

    • In humans, the spinal cord runs the length of the column, so spinal anesthesia/epidurals can risk damaging exposed neural tissue if not performed correctly; this is noted as part of broader clinical considerations.

  • Ribs and the thoracic cavity

    • Each rib has a head that articulates with a thoracic vertebra; the number of ribs equals the number of thoracic vertebrae present in a given animal.

    • Counting ribs is done cranial to caudal; with 13 thoracic vertebrae, there are 13 ribs on each side, totaling 26 ribs in the animal.

    • Costochondral junction: the region where the rib bone meets cartilage; this junction allows the thoracic cavity to expand and contract during respiration.

    • Quadrupeds (like dogs and others) generally expand laterally and contract vertically; bipeds (humans) expand the chest up and out during inhalation and down and in during exhalation.

    • Ribs classification:

    • True ribs: ribs 1 ext{–}9; attach directly to the sternum via cartilage.

    • False ribs: ribs 10 ext{–}12; their cartilage attaches to the cartilage of rib 9 rather than directly to the sternum.

    • Floating ribs: rib 13; does not attach to the sternum or to another rib in front.

    • Sternum and its parts:

    • Manubrium: the uppermost part of the sternum, at the thoracic inlet; in deep-chested dogs with a triangular chest, the manubrium sits close to the surface; if there were no clavicles, the manubrium would be the top point like a traditional “sternal knot,” but clavicles in humans depress it slightly.

    • Body (sternal body): the middle portion of the sternum.

    • Xiphoid process: the bottom projection; can be palpated in a person/dog, but should not be pushed hard (risk of injury or snapping).

    • The entire sternum is formed by the manubrium, sternum body, and xiphoid process.

    • The first rib attaches to the sternum via its costal cartilage; ribs 1–9 attach to the sternum, while ribs 10–12 do so indirectly via cartilage of rib 9, and rib 13 is floating with no direct anterior attachment.

    • Practical palpation note: the xiphoid process is a landmark for CPR and other procedures; excessive pressure can cause injury, so gentle palpation is advised.

  • Practical and clinical implications (summary highlights)

    • Be able to identify the atlas (C1) and axis (C2) and distinguish them from C3–C7 by their distinctive morphology.

    • Recognize that only cervical vertebrae have lateral foramina (on both sides of the vertebral foramen).

    • Distinguish vertebral regions by their characteristic shapes: thoracic vertebrae with taller, longer spinous processes; lumbar vertebrae with very prominent transverse processes; sacrum as a fused block that stabilizes the pelvis; coccygeal vertebrae lacking vertebral foramina and forming the tail.

    • Understand spinal cord termination points and the clinical implication for epidurals in dogs vs large animals vs humans:

    • Dog: cord ends at L5; epidural approaches are performed caudally (between L7 and S1).

    • Cat: cord ends at L4; beyond that, nerves form the cauda equina.

    • Large animals: epidurals performed between the sacrum and coccygeal vertebrae.

    • Humans: spinal cord runs the length of the vertebral canal; spinal anesthesia/epidurals pose different risks, hence dedicated practice standards.

    • Real-world relevance: tail docking and coat color or breed variations reflect anatomical differences in coccygeal vertebrae; tail length can vary by breed (e.g., boxer tails; bobtail cats).

  • Quick recap of key numerical and structural references (LaTeX format)

    • Cervical vertebrae count: 7 per animal.

    • Thoracic vertebrae counts by species: dog ext{T} = 13, horse ext{T} = 18, cow/sheep ext{T} = 13, pig ext{T} = 15 ext{–}16 (breed dependent).

    • Ribs per side: 13 (total ribs in many quadrupeds: 26).

    • True ribs: 1 ext{–}9; False ribs: 10 ext{–}12; Floating rib: 13.

    • Spinal cord termination points: dog L5, cat L4.

    • Epidural landmarks in dogs: between L7 and S1; large animals: between the sacrum and coccygeal vertebra.

    • Sternum components: Manubrium, sternum body, xiphoid process.

  • Exam strategy reminders (context from transcript)

    • Focus on major concepts first (vertebral region, unique anatomy by region, notable species differences).

    • Be able to identify C1 and C2 and explain how C3–C7 differ in appearance from them.

    • Memorize which vertebrae have lateral foramina (only cervical) and what the vertebral foramen is.

    • Know the rib categories (true/false/floating) and how ribs articulate with the sternum via costochondral junctions.

    • Understand the clinical relevance of vertebral region anatomy for procedures like epidurals and CPR landmarking.

  • Notes on terminology and care

    • Use consistent naming: atlas (C1), axis (C2), vertebral foramen, spinous process, transverse process, body, lateral foramen, costochondral junction, xiphoid process, manubrium, sternum body.

    • Be mindful of species differences, especially in vertebral counts (thoracic, sacral, coccygeal) and tail anatomy.

    • When studying, visualize the skull sitting on atlas with occipital condyles articulating with atlas; recognize axis as the prominent second vertebra.