Axial Skeleton

What two structures fall under the axial skeleton?

vertebral column and notochord

What are the functions of the vertebral column and notochord?

• defines long axis of organisms

• provides support of organisms

• prevents compression

• support/position of head

• locomotion

What are the functions of the ribs?

• protection of viscera

• contributes to respiration

Describe the notochord

• rod of fibrous connective tissue surrounding a core of fluid cells

• dorsal to the coelom (gut)

• only present in the embryos of higher vertebrates, not when they’re adults

What is an example of an animal where you might fight the notochord?

in primitive fishes like the lamprey, the notochord is the primary component of the axial skeleton

What is a chordoma?

A slow growing tumor due to a persistent notochord. The example we looked at in class was a human case.

What are the regions of the vertebral column in many animals?

• cervical

• thoracic

• lumbar

• sacrum

• caudal/coccyx

How many vertebrae are there per region generally?

• cervical - 7

• thoracic - 13

• lumbar - 7

• sacrum - fused

• caudal/coccyx - variable

What is the general structure of a vertebra?

a centrum complemented by various processes and/or foramen

What is a process and what is their function in relation to the vertebrae?

a process is a bony projection that serves as a site for muscle or tendon insertion

What are vertebral processes called?

apophyses

What direction do spinous processes point?

dorsally

What are the function of zygapophses?

prevents twisting and connects to other vertebrae

the pre-zygapophyses points ventrally and is in the anterior margin

the post-zygapophyses points dorsally and is in the posterior margin

Where do the basapophyses/hypophyses project?

ventral sides

Where in the function of the diapophyses and parapophyses?

rib articulation

Where do transverse processes project?

laterally

What are superior articular processes another name for?

pre-zygapophyses

What are inferior articular processes another name for?

post-zygapophyses

What are cervical vertebrae characterized by? What landmark distinguishes them?

the presence of transverse foramen

What are distinguishing features of thoracic vertebrae?

costal facets, aka the diapophyses and parapophyses, as well as prominent spinous processes

Which region of the vertebrae do the ribs articulate?

thoracic

What is the function of the lumbar vertebrae?

support abdominal organs

Describe the shape of an acoelous centrum.

flat ends (in mammals)

Describe the shape of an amphicoelus centrum.

both ends are concave, limiting motion

Describe the procoelous and opisthocoelous centrum.

ball and socket ends (in reptiles and amphibia)

Describe the heterocoelous centrum.

saddle joint to allow lateral or vertical flexion (in birds)

What are intervertebral disks?

The structures between adjacent vertebrae that form a “vertebral joint”

What are the components of the intervertebral disks?

• annulus fibrosus

• nucleus pulposus

What is the annulus fibrosus?

the fibrocartilage outer ring of the intervertebral disks

What is the nucleus pulposus?

the central gel-like core of the intervertebral disks, it is a remnant of the notochord

How can you distinguish the annulus fibrosus when examining cytology/histology?

it is avascular, distinct lack of blood cells

What is IVDD?

intervertebral disk disease, a degeneration of this structure between the vertebrae that results in vertebrae compressing into each other

What are the functions of the ribs?

• support body

• resist longitudinal compression

• muscle insertion

• viscera protection

• respiration aid

Describe true ribs

ribs 1-8, the vertebralsternal ribs; they meet at the sternum

Describe false ribs

vetebralchondral ribs, connect with the costal cartilage; articulate with ribs, not the sternum

Describe floating ribs

no articulation ventrally; the vertebral ribs

Describe the sternum.

• a mid-ventral skeletal structure

• endochronal in origin, ossifies to bone

• muscle origin for chest muscles

Is the sternum present in fish?

no

Is the sternum present in amphibians?

yes, as part of the shoulder girdle

Is the sternum present in birds?

Yes, birds have a prominent sternum called the keel that serves as an attachment point for flight muscles

Is the sternum present in mammals?

Yes, as a series of ossified elements

What are gastralia?

• abdominal ribs that are dermal in origin

• present in lizards and crocodiles

• makes up the ventral floor of the turtle - fused ventral dermal elements

What are some vertebral adaptations relating to the cervical vertebrae?

In amniotes, the first and second cervical vertebrae have become modified over time for increased movement

• skull-atlas: nodding, tilting

• atlas-axis: twisting

How has evolutionary adaptation altered the pectoral girdle?

It separated from the skull after fish in response to increased need for rotation

Describe the sacrum in terms of evolutionary adaptation.

It developed for pelvic girdle attachment in response to an increased need for support

What is the cisterna magna?

the space between the skull and the atlas; often used as a site to tap for spinal fluid