Module 5: Axial Musculoskeletal Structures and Body Wall PDF

Module 5: Axial Musculoskeletal Structures and Body Wall Module 5: Axial Musculoskeletal Structures and Body Wall Topics: Bones and Joints of the Axial Skeleton, Epaxial and Hypaxial Musculature, Cervical visceral space and cervical nerv...

Module 5: Axial Musculoskeletal Structures and Body Wall Module 5: Axial Musculoskeletal Structures and Body Wall Topics: Bones and Joints of the Axial Skeleton, Epaxial and Hypaxial Musculature, Cervical visceral space and cervical nerves Resources: TVA: Ch. 2 (pp. 31-39, 42-49, 62-64), Ch. 12, Ch. 14 (pp. 418-420), Ch. 19, Ch. 26 Reprised in week 13: Ch. 21 (pp. 535-540), Ch. 28 (pp. 664-667) GDD: Ch. 2 (pp. 20-23, 77-95), Ch. 3 (pp. 97-98) Course Materials: available on Canvas under the module of the same chapter name Lab Review Videos (Canvas) - Please watch them before coming to lab! Laboratory Specimens: Bone Boxes; Canine Cadavers; Canine Trunk Prosections Objectives: 1. Describe the vertebral formulas for the dog and cat, horse, and cow/bull. 2. Identify and discuss the common features of all vertebrae. 3. Identify and discuss the unique characteristics of each canine vertebral group and distinguish a given vertebra as cervical, cranial thoracic, caudal thoracic, lumbar, or sacral. 4. Discuss the unique features of vertebrae C1, C2, C6, C7, and T11. 5. Discuss the anatomy of the sternum and ribs. 6. Discuss the atlanto-occipital and atlantoaxial joints, and their particular ligaments and movements. 7. Discuss the vertebral joints and the ligaments supporting the vertebral column. 8. Discuss the articulations between the thoracic vertebrae and the ribs. 9. Identify and describe the orientation and location of the three epaxial muscle systems and the action of the epaxial muscles on the vertebral column (flex vs. extend). 10. Discuss the hypaxial musculature. Compare the size, location, and actions of the epaxial muscles to the hypaxial muscles that lie directly ventral to the vertebral bodies and vertebral transverse processes. 11. Identify the dorsal and ventral muscular boundaries of the cervical visceral space. 12. Identify and describe the major visceral structures within the cervical visceral space. 13. Locate by dissection and discuss the branches of the ventral branch of cervical spinal nerve 2; describe its position in relation to the wing of the atlas. 14. Describe the accessory nerve (Cranial Nerve XI) and cervical spinal nerve 2 by discussing their origin (brain vs. spinal cord) and distribution. 15. Locate by dissection and discuss the ventral branches of cervical spinal nerves 3 to 5 and their position in relation to the hypaxial muscles of the neck. 16. Distinguish between inspiratory and expiratory muscles. 17. Discuss the pressure/volume relationship of the thorax relative to respiration. 18. Discuss the origin, insertion, and muscle fiber orientation of each abdominal muscle. 56  Module 5: Axial Musculoskeletal Structures and Body Wall 19. Discuss the layers of the abdominal wall, as well as the superficial inguinal ring, deep inguinal ring, inguinal canal, vaginal process, vaginal tunic, prepubic tendon, and rectus sheath. 20. Discuss the function of the abdominal muscles (abdominal press) and effects on breathing and defecation. 21. Discuss the abdominal and inguinal topographic regions. Note: Large animal structures will be studied in lab weeks 13 and 14. 22. Describe and discuss the tunica flava abdominis of the large animal abdominal wall. What is the clinical relevance of this layer of the abdominal wall? 23. Discuss the prepubic tendon and its significance in the horse. 24. Discuss the significance of the accessory ligament of the femoral head in the horse. 25. Describe and discuss the boundaries and importance of the paralumbar fossae in both the horse and the bovine. Laboratory Guidelines and Dissection Goals: 1. Your goals for the first session are to study the bones (GDD pp. 77-84) and joints (GDD pp. 94-95) of the axial skeleton and to dissect the epaxial musculature (GDD pp. 90-93). The majority of the ligaments of the vertebral column will not be dissected and will be studied via prosections. You will be expected to identify the locations and relevance of these ligaments. Reflect the latissimus dorsi m. dorsally (cut origin on ribs) and transect through both parts of the serratus dorsalis musculature to visualize the three epaxial muscles. You do not need to identify the specific origins and insertions of epaxial muscles. You do not need to learn the individual muscles within the three epaxial systems, with the exception of the splenius and the two components of the semispinalis capitis m. (biventer cervicis and complexus mm.) of the transversospinalis system. You will identify the regions of these systems and where each group is located relative to the other two groups (medial, intermediate, lateral). 2. Your goals for the consecutive sessions are to: Review and complete the dissection of the hypaxial mm. of the neck (GDD pp.20-23, p.84). Dissect and study the hypaxial mm. of the thorax (GDD pp. 84-86) and of the abdominal wall, including the inguinal canal (GDD pp. 86-90). On the undissected (right) side of your cadaver, dissect and discuss the main nerves of the neck. Use both sides to study the content of the cervical visceral space (GDD pp. 97-98). By the end of the chapter, you should have a clear understanding of the axial skeleton and its joints, the three epaxial muscle systems along their entire length, and should have observed the nuchal ligament. You should have identified the hypaxial muscles. You should have transected at least one external intercostal muscle to observe the internal intercostal m. located deep to it. 57  Module 5: Axial Musculoskeletal Structures and Body Wall You should have: observed the muscular boundaries and visceral contents of the cervical visceral space; observed the fiber orientation and aponeuroses of the abdominal musculature and transected through the muscular components of the external and internal abdominal oblique mm.; observed the superficial inguinal ring, the borders of the deep inguinal ring, the inguinal canal, the vaginal tunic (male), the vaginal process (female), and the cremaster muscle (male). You should have dissected the accessory nerve, cervical spinal nerve 2 and cervical spinal nerves 3 to 5. List of Terms: Axial Skeleton: Defined as the skeletal elements that are located along the axis of the body. Components of the axial skeleton include the bones of the skull, vertebral column, and thorax (sternum and ribs). Vertebrae: (“vertebra” is singular, the term “vertebrae” is plural) Vertebral formula of the dog and cat C7 T13 L7 S3 Cd ~20 Vertebral formula of the horse C7 T18 L6 S5 Cd ~20 Vertebral formula of the ox C7 T13 L6 S5 Cd ~20 Typical Features of Vertebrae: Vertebral body o Cranial articular surface is convex o Caudal articular surface is concave o Adjacent vertebral bodies, with the exception of C1 and C2, are connected via intervertebral discs Vertebral arch o Arches dorsally from the vertebral body to cover the spinal cord and create the vertebral foramen o Each vertebral arch consists of right and left pedicles (think of these as the posts forming the lateral walls of the vertebral foramen) and left and right laminae (these form the roof of the vertebral foramen); the dorsal aspect of the vertebral body forms the floor of the vertebral foramen o When the vertebrae are articulated, the resultant alignment of the vertebral foramina forms the vertebral canal which contains the spinal cord. Cranial and caudal vertebral notches o When the vertebrae are articulated, the notches of adjacent vertebrae form the bilateral intervertebral foramina for passage of spinal nerves. The caudal vertebral notch of the more cranial vertebra aligns with the cranial vertebral notch of the more caudal vertebra to form one intervertebral foramen. 58  Module 5: Axial Musculoskeletal Structures and Body Wall Spinous process (the first cervical vertebra does not have a spinous process but does possesses a dorsal tubercle) o Midline prominence dorsal to the laminae Transverse processes o Bilateral (left and right) processes that extend laterally Articular processes o Cranial pair o Caudal pair o The caudal articular processes of the more cranial vertebra articulate with the cranial articular processes of the more caudal vertebra. Unique Features Cervical vertebrae All cervical vertebrae (except C7) have bilateral transverse foramina. When articulated, adjacent transverse foramina form a canal that accommodates the vertebral artery, vein and nerve. Atlas (cervical vertebra 1) Reduced body o Fovea dentis (which articulates with the dens of the axis) is located on the floor of the vertebral foramen. o Lacks a true spinous process, but has a dorsal tubercle Transverse processes are often referred to as the wings of the atlas Lateral vertebral foramina perforate the cranial part of the (dorsal) vertebral arch for passage of the first cervical spinal nerves. Axis (cervical vertebra 2) Spinous process is elongated o Observe a flattened area at the caudal aspect of the spinous process where the nuchal ligament attaches Vertebral body o Dens – tooth-like extension of the cranial vertebral body; articulates within the fovea dentis of the atlas Cervical Vertebra 6 (C6) Expanded laminae (bilateral) of the transverse processes – this is obvious on a radiograph and is an excellent point of reference. Cervical Vertebra 7 (C7) Lacks transverse foramina Has caudal costal foveae (bilateral) on the vertebral body for articulation with the heads of the first pair of ribs 59  Module 5: Axial Musculoskeletal Structures and Body Wall Thoracic vertebrae Spinous processes are prominent cranially and become progressively shorter in the caudal thoracic vertebrae. T11 is designated the anticlinal vertebra (spinous process points straight up) o Cranial to T11, the spines incline caudally o Caudal to T11, the spines incline cranially Cranial and caudal costal foveae on the vertebral bodies (T1 – T10; bilateral) o A fovea is a small cuplike depression. The costal foveae articulate with the head of the ribs. The foveae of two adjacent vertebrae form the articular surface for the head of one rib, with the exception of T11-T13. o The head of a rib articulates with the cranial costal fovea of the same numbered thoracic vertebra and the caudal costal fovea of the preceding vertebra. Example: the head of rib number 7 articulates with the cranial costal fovea of T7 and the caudal costal fovea of T6. The head of rib number 1 articulates with the cranial costal fovea of T1 and the costal fovea of C7. Note: T11-T13 have only cranial costal fovea (bilateral) and therefore the heads of ribs 11- 13 articulate only with the cranial costal foveae of the same numbered thoracic vertebra Transverse costal fovea (bilateral) o Located on the transverse processes of the thoracic vertebrae o Articulates with the tubercle of the same numbered rib E.g., the transverse costal fovea of T1 articulates with the tubercle of the first rib. Mamillary processes (bilateral) o Project dorsally from the transverse process (on vertebrae cranial to T11) or from the cranial articular process (on vertebrae caudal to T11) Accessory processes (bilateral) o Project caudally from the pedicles of the vertebral arches, ventral to the caudal articular process and dorsal to the caudal vertebral notch Mamillary and accessory process are attachment sites for the epaxial muscles. Lumbar vertebrae Transverse processes (bilateral) are long, oriented laterally, cranially and ventrally. The cranial costal foveae are no longer present (no more articulations with the heads of ribs). Mamillary and accessory processes (bilateral) are very well developed. Sacrum (fusion of 3 sacral vertebrae in the dog and cat, and 5 sacral vertebrae in the horse and ox) Wing of the sacrum o Auricular face (surface that articulates with the ilium making the “S-I” sacroiliac joint) The promontory of the sacrum is the transverse ridge on the cranioventral portion of the body. This is the dorsal boundary of the pelvic inlet. Median sacral crest (fusion of spinous processes) 60  Module 5: Axial Musculoskeletal Structures and Body Wall Dorsal sacral foramina (two pairs; transmit the dorsal brs. of first two sacral spinal nerves) Pelvic sacral foramina (two pairs; transmit the ventral brs. of first two sacral spinal nerves) Caudal (coccygeal) vertebrae progressively lose their distinctive features. Ribs Dogs, cats, and the ox have 13 pairs of ribs; horses have 18 pairs of ribs. Have both bony and cartilaginous parts, where the junction between these two parts is the costochondral junction o The bony part of a typical rib has a head, neck, tubercle, and body. o The cartilaginous parts, called costal cartilages, extend ventrally from the osseous body of the rib and articulate with the sternum. The first nine pairs of ribs articulate directly with the sternum. The costal cartilages of ribs 10-12 unite to form the costal arch. The thirteenth rib does not have a sternal attachment (a true “floating” rib). The intercostal spaces are the spaces between ribs. Sternum Comprised of eight sternebrae which are joined by cartilages o Manubrium (first sternebra) o Xiphoid process (last sternebra) is continued by the xiphoid cartilage and is an easily palpable landmark. Joints and Ligaments of the Vertebral Column: Atlanto-occipital joint Between the occipital bone of the skull and the atlas Action at this joint is responsible for “Yes” head movement. Atlantoaxial joint Between the atlas and axis. Note the fovea dentis of the atlas and the dens of the axis. Transverse ligament of the atlas o Attaches to the internal wall of the vertebral foramen of the atlas on both sides; passes dorsal to the dens o Stabilizes the dens within the fovea dentis; prevents the dens from projecting dorsally (and potentially into the spinal cord) Apical and alar ligaments of the dens 61  Module 5: Axial Musculoskeletal Structures and Body Wall The remaining vertebrae articulate by synovial joints between articular processes and by fibrous joints between the bodies (intervertebral discs). Intervertebral discs o Between bodies of the adjacent vertebrae o Two parts: Annulus fibrosus – outer circumferential collagenous fibers Nucleus pulposus – inner gelatinous core Ligaments of the Vertebral Column and Ribs: Supraspinous ligament o Fibrous connective tissue that connects the apices of all spinous processes o From T1 to the caudal vertebrae Nuchal ligament o The cranial continuation of the supraspinous ligament o Extends from the spinous process of thoracic vertebra 1 (T1) to the caudal aspect of the spine of the axis (C2) in the dog o In the large animal, the nuchal ligament extends to the nuchal crest of the occipital bone of the skull. Dorsal longitudinal ligament o Located on the dorsal surface of vertebral bodies, ventral to the spinal cord Ventral longitudinal ligament o Located on ventral surface of vertebral bodies Note: You will not observe these in lab: Interspinous ligaments Intertransverse ligaments Interarcuate ligaments Ligaments of the Ribs Intercapital ligaments o Connect left and right rib heads o Dorsal to the intervertebral discs and ventral to the dorsal longitudinal ligament Some clinically important locations: - Lumbosacral space (epidural anesthesia) - Sacrococcygeal space (sacrocaudal) (epidural anesthesia) - Atlanto-occipital joint (aspiration of cerebrospinal fluid) 62