Lecture 9 - Vertebrate Skeletal System Part I

Question 1

Describe the two subdivisions of the vertebrate skeletal system

Answer 1

Vertebrates are characterized by an internal skeleton made of cartilage and/or bone. This internal framework can be divided into subdivisions as follows:

• Axial skeleton:
• Chondrocranium: Braincase and capsules for organs of special sense
• Viscerocranium: Gill arches and jaws
• Vertebral column
• Appendicular skeleton:
• Limb girdles (pectoral and pelvic)
• Limbs (forelimbs and hindlimbs, including fins)

Question 2

What is the vertebral column indicative of in vertebrates

Answer 2

• Segmentation
• The vertebral column consists of a series of segments called vertebrae as well as additional related structures.
• The vertebrae and related structures may be composed entirely of cartilage or bone or both.

Question 3

Describe the vertebral centrum in fish

Answer 3

• The centrum is typically a cylindrical structure that is connected to similar cylindrical centra both cranially and caudally.
• This chain of centra replaces the notochord of the protochordates, such as amphioxus, as the principal axial support structure.
• This chain of centra is flexible, but may not be as flexible as a notochord.
• A flexible chain of centra would be useful for swimming, but would not be as useful for supporting a terrestrial life-style.
• In many vertebrates (including humans) parts of the notochord may persist within and/or between adjacent vertebrae.
• Note: More commonly known as discs. Discs consist of an outer tough layer, and inside is a pulpy component called the nucleus pulposis. That used to be our notochord.
• Other Note: Discs don’t “slip”. Someone tells you they have a slipped disc, tell them they’re wrong and stupid.
  What they have is a “herniated disc”.

Question 4

Describe the neural arch of a fish vertebra

Answer 4

• Sits on top of the centrum (dorsal surface) and provides a protective passageway for the spinal cord.
• A neural spine often projects from the dorsum of the neural arch.
• • Provides lever arm for muscle attachment.
• • In Latimeria the neural spines are hollow and filled with cartilage –“coelacanth” means hollow spine.
• A corresponding hemal arch is present on the ventral surface of the centrum of each of the caudal (tail) vertebrae.
• • A caudal artery and vein pass through the hemal arch.

Question 5

• What does the intercalary plate of a shark vertebra do?

- What does amphicelous mean?

Answer 5

• Fill in gaps between adjacent neural arches and protect the spinal cord.
• The cranial surface of the centrum is concave. In sharks, both ends of each centra are concave. This type of centrum is referred to as amphicelous.

Question 6

Review Anatomy Lecture 9 Deck in Chegg

Answer 6

Do it

Question 7

Describe the regional variations within the vertebral column of fish

Answer 7

The vertebral columns of most vertebrates consist of several kinds of vertebrae. In fish, the kinds of vertebrae are limited:

• Precaudal vertebrae: Include all the more cranial vertebrae that lack a hemal arch
• Caudal vertebrae: Include all the vertebrae caudal to the precaudal vertebrae. They possess hemal arches

Question 8

Describe the vertebral column in fish

Answer 8

• Centra tend to be more ossified.
• Each neural arch is topped by a long, slender neural spine.
• Prominent notochord instead of ossified centra are still retained in more primitive bony fishes such as the sturgeon.
• Pelvic and pectoral girdles are not tied into fish vertebral column.
• Incomplete Resume Later

Question 9

Review slide 13

Answer 9

Memorize it yet?

Question 10

How is the vertebrate body compartmentalized

Answer 10

• The vertebrate body plan is tied together by sheets of connective tissue referred to as myosepta. The myosepta tie into the vertebral column. Collectively, the myosepta form compartments in which are enclosed masses of skeletal muscle.
• Myosepta is visible in humans in the form of 6-pack abs.

Question 11

Describe the vertebral column of early tetrapods

Answer 11

• Early tetrapod centrum developed from two parts:
• • Intercentrum.
• • Pleurocentrum.
• One or the other or both contributed to the formation of the centrum in early tetrapods.
• Vertebral column replaced notochord as the main axial support.
• Precaudal vertebrae became specialized (correlated with terrestriality):
• Cervical: articulated with skull
• Trunk: processes for rib attachment
• Sacral: articulated with pelvic girdle
• Pelvic girdle tied into vertebral column via ilia.

Question 12

Describe the vertebral column of crossopterygians

Answer 12

Reminder: these were not tetrapods. Just close

• Each centrum consisted of:
• • Single, larger intercentrum: “U”-shaped and cranial
• • Paired, smaller pleurocentra: Caudal and dorsal to intercentrum

Question 13

Describe the vertebral column of labyrinthodonts

Answer 13

• Stereospondylous labyrinthodonts:
• Centrum entirely derived from intercentrum
• Embolomerouslabyrinthodonts:
• Intercentrum and pleurocentrum equal in size.

Question 14

Describe the vertebral column in modern amphibians

Answer 14

• Tendency in later tetrapods was to reduce:
• • The intercentrum to a small, cranial, ventral element to which attached the capitulum (head) of the rib.
• • Considerably increase the size of the pleurocentrum.
• In later tetrapods, notochord was either completely eliminated in the adult or persisted as a slender rod passing through the pleurocentrum or confined to spaces between intercentra.
• Uncertain in modern amphibians whether centrum is derived from pleurocentrum or intercentrum.

Question 15

Describe the vertebral column in salamanders

Answer 15

• Regional variations within the vertebral column seem to be correlated with terrestriality.
• Specializations of precaudal vertebrae (First seen in primitive tetrapods):
• • First precaudal vertebra = cervical vertebra: Only one in amphibians
• • Last precaudal vertebra = sacral vertebra: Only one in amphibians
• Vertebrae between cervical and sacral are trunk vertebrae
• • Numerous in salamanders
• • Reduced to about six or seven in anurans
• • Transverse processes have attachment sites for ribs.
• In Necturus, ribs are bicipital:
• • The tuberculum attaches to the dorsal part of the transverse process (diapophysis).
• • The capitulum attaches to the ventral part of the transverse process (parapophysis).
• Neural arches with short, blunt neural spines are located on the dorsal surfaces of the centra.
• Caudal vertebrae in salamanders also have hemal arches.
• Centraarticulate with each other via two pairs of zygapophyses:
• • The cranial (anterior) zygapophyses have articular facets that face dorsally.
• • The caudal (posterior) zygapophyses have articular facets that face ventrally

Question 16

Describe the vertebral column in anurans

Answer 16

• Regional variation in anuran vertebral column:
• Cervical vertebra*
• Trunk vertebrae*
• Sacral vertebra*
• Caudal vertebrae (1) (variable) (1) (1)
• • Urostyle = single caudal vertebra in anurans.
• • Modified adaptation for saltatory locomotion:
• • Attachment site for muscles involved in jumping.
• • Iliatie pelvic girdle into vertebral column through sacral vertebra.
• See Slide 20
• = Collectively comprise the precaudal vertebrae

Question 17

What are the sections of the amniote vertebra?

Answer 17

• Parts of an amniote vertebra are similar to those of the Necturus vertebra.
• They consist of:
• Centrum
• Neural and hemal arches (with spines)
• Transverse processes
• Zygapophyses
• See Slide 23 for diagram

Question 18

Describe the amniote vertebra centrum

Answer 18

• The centrum functionally replaces the notochord.
• Classification of centrum based on shape of cranial and caudal ends:
• Amphicoelous: both ends are concave (Some reptiles)
• Procoelous: only cranial end is concave (Most reptiles)
• Opisthocoelous: only caudal end is concave
• Acoelous: both ends are flat (Mammals)
• In the tails of reptiles and some mammals small pieces of bone may be found between the ventral edges of centra:
• Intercentra (or hypocentra)
• Form hemalarches (chevron bones)
• In primitive reptiles the bulk of the centrum is formed from the pleurocentrum.
• In modern reptiles and mammals the intercentrum has disappeared and the centrum is formed entirely from the pleurocentrum
• Intercentrum persists in Sphenodon

Question 19

Describe the neural arch of the amniote vertebra

Answer 19

• Neural arch consists of a neural spine and diapophyses.
• Diapophyses are for rib attachment.
• Neural arch is composed of lateral and dorsal plates which form the neural canal.
• Dorsal plates are the laminae and meet in the midline to fuse with the neural spine.
• Lateral plates are the pediceles which fuse to the centrum ventrally and to the laminae dorsally to form the transverse processes.
• The posterior edge of each pedicele is typically notched so that when vertebrae are articulated, holes are formed between them to allow the passage of spinal nerves.

Question 20

Describe the development of the vertebral column in amniotes.

Answer 20

• The vertebral column develops from the sclerotome portion of the embryonic somites.
• Somitesare paired blocks of mesodermal tissue that form along the notochord during embryonic development.
• Each somite consists of three major components:
• Dermatome:
• Forms dermis of integument.
• Myotome:
• Forms axial muscles.
• Sclerotome:
• Forms parts of vertebrae.

Question 21

Describe the chick embryo after 24 hours

Answer 21

• Neural folds are no longer approximated.
• Notochord well formed but somewhat flattened.
• Somites, intermediate mesoderm, and lateral plate mesoderm present
• Lateral Plate Mesoderm has split (delaminated) into parietal and visceral mesoderm.
• See Flashcards

Question 22

Describe Sclerotomal breakup

Answer 22

• Sclerotomal portion of each somite breaks up into an anterior and a posterior portion.
• Posterior portion of one somite joins the anterior portion of an adjacent somite, etc.
• This creates gaps that allow nerves to grow out from the neural tube into the epaxial segmental musculature derived from the myotomes.
• See Slide 30

Question 23

Compare vertebral column regions between amniote types (Reptiles vs. Birds)

Answer 23

• Reptiles:
• Cervical vertebrae: Atlas-axis complex first appears in reptiles. Atlas #1: Centrum becomes odontoid process of axis. Axis (#2) 8 in most reptiles, 9 in alligator.
• Trunk: Typically with ribs.
• Sacral vertebrae: 2+
• Caudal vertebrae: Variable with hemal arches.
• Birds:
• Cervical vertebrae: With transverse foramina. Hetereocoelous • Had between 8-25.
• Anterior thoracic (extensively fused groups of vertebrae): Wing brace.
• Synsacrum (also extensively fused groups of vertebrae): Posterior thoracic, Lumbar, Sacral (2+), and Proximal caudal.
• Pygostyle: Fused caudal vertebrae

Question 24

How many vertebrae do humans have in each region? Which of these is common with all (most) other mammals?

Answer 24

• Humans: 7 in Cervical, 12 in thoracic, 5 in lumbar, 5 in sacral, & 3-4 in caudal.
• All mammals have seven cervical vertebrae except: sloths (6 or 9) and sirens (6)

Question 25

Describe the centrum and atlas of the mammalian vertebral column

Answer 25

* Centrum: - Generally acoelous. (Except cervical vertebrae of ungulates (opisthocoelous) ) - Centrum derived from pleurocentrum (Intercentrum lost) * Atlas (C1): - Articulates with two occipital condyles - Lacks a centrum: Has become associated with C2 intercentrum as the odontoid process (dens). Serves as axis for lateral rotation

Question 26

Describe the cervical section of the mammalian vertrebra.

Answer 26

Cervical: - 3-7: - Possess short fused bicipital ribs that create transverse foraminae: - Pathway for vertebral arteries to brain

Question 27

Describe the thoracic section of the mammalian vertebral column

Answer 27

- Have articulation facets for ribs (costal facets) - Costal facets on transverse processes articulate with tubercles of ribs. - Costal facets on centra articulate with heads (capitula) of ribs. - Most heads of ribs in upper part of thoracic region articulate between two adjacent centra, resulting in the formation of costal demifacets.

Question 28

Describe the lumbar, sacral, and caudal region of the mammalian vertebral column

Answer 28

* Lumbar: - Thicker centra - No costal facets or ribs * Sacral: - Fused into a single element called the synsacrum. - Articular facets for pelvis * Caudal: - Found in most mammals - May have indications of hemal arches - (chevron bones) - See Slide 35 (and 36 for sacral vertebral number between groups)

Question 29

Describe Ribs in Tetrapods, and Amphibians

Answer 29

* Tetrapods: Arise in skeletogenous septa - Dorsal ribs: Formed at intersections between myosepta and horizontal septum. * Amphibians: - Reduced

Question 30

Describe the ribs of reptiles and birds

Answer 30

* Reptiles: - Double-headed (bicipital): - - Capitulum to centrum - - Tubercle to transverse process - 8 pairs in turtle fused to carapace * Birds: Uncinate processes of one rib overlap next caudal rib to stabilize rib cage for flight.

Question 31

Describe cervical and thoracic ribs in mammals

Answer 31

* Cervical ribs: - Short and fused to vertebrae. - Transverse foramina for vertebral arteries. * Thoracic ribs: - Double-headed - True ribs articulate with sternum via costal cartilages. - Floating ribs do not articulate with sternum.

Question 32

Describe the 5 types of bones based on their shape and give examples of each.

Answer 32

1. Long bones: Femur, tibia, humerus, phalanges 2. Short bones: Carpals and tarsals 3. Flat bones: Bones of skull cap, dermal bones) 4. Irregular bones: Vertebrae, facial bones 5. Sesamoid bones: Knee Cap (Patella)

Question 33

Describe the two types of bone markings

Answer 33

* Depressions: - Foramen. - Groove (sulcus). - Fossa (-ae). * Processes: - Spine. - Tuberosity. - Condyle - Epicondyle.

Question 34

Give the definition of a joint and an articulation

Answer 34

Definition: * Joint = an area where two bones meet. * Articulation = where a movable joint is formed. - Classification is usually based on type of material that holds the two bone

Question 35

Describe Ampiarthrosis

Answer 35

``` Ampiarthrosis: * Slightly movable joint - Joining material = cartilage 2 types: * Synchondrosis type: Joining material = hyaline cartilage - Example: epiphyseal plate * Symphysis type: Joining material = fibrocartilage. - Example: pubic symphysis ```

Question 36

Describe the syntharthrosis joint

Answer 36

Slightly movable joint Joining material = fibrous connective tissue 3 types: - Suture type: Example: joints between bones of skull cap - Gomphosis type: Example: tooth in socket. - Syndesmosis type: Example: interosseous membrane. Note: Gomphosis doesn't seem like a joint, but it is. Just not a moving one.

Question 37

Describe the diarthrosis joint

Answer 37

- Very movable joint. - Joining material = cartilage - Components: Articular cartilage (AC) - Fibrous capsule (FC): Innervated - Synovial membrane (SM): Vascularized - Synovial cavity (SC)

Question 38

Describe uniaxial and biaxial joint movement and degrees of freedom

Answer 38

* Uniaxial: Movement in one plane around one axis: - Example: - Hinge joints (elbow, knee) - Pivot joints (atlantoaxial) * Biaxial: - Movement in two planes around two axes. - Example: - Ellipsoid (metacarpalphalangeal).

Question 39

Describe triaxial and monaxial joint movement and degrees of freedom

Answer 39

* Triaxial: Movement in three planes around three axes: - Example: - Glenohumeral (shoulder) - Acetabulofemoral (hip) * Nonaxial (sliding): No axis of rotation - Example: Joints between carpals and tarsals